Name: non-invasive monitoring of microvascular oxygenation and reactive hyperemia using hybrid, near-infrared diffuse optical spectroscopy for critical care
Uploaded: 2024-05-10T13:40:00.000+00:00
Duration: 14 min 28 s
Description: Watch this Scientific Journal Video about Non-Invasive Monitoring of Microvascular Oxygenation and Reactive Hyperemia using Hybrid, Near-Infrared Diffuse Optical Spectroscopy for Critical Care at JoVE

This research was funded by Fundaci&#243; CELLEX Barcelona, Fundaci&#243; Mir-Puig, Ajuntament de Barcelona, Agencia Estatal de Investigaci&#243;n (PHOTOMETABO, PID2019-106481RB-C31/10.13039/501100011033), the &#34;Severo Ochoa&#34; Programme for Centres of Excellence in R&#38;D (CEX2019-000910-S), , Generalitat de Catalunya (CERCA, AGAUR-2017-SGR-1380, RIS3CAT-001-P-001682 CECH), FEDER EC, Fundacion Joan Ribas Araquistain, l&#39;FCRI (Convocat&#242;ria Joan Or&#243; 2023), European Commission Horizon 2020 (Grants nos. 101016087 (VASCOVID), 101017113(TinyBrains), 871124 (LASERLAB-EUROPE V), 101062306 (Marie Sk&#322;odowska-Curie)), the Fundaci&#243; La Marat&#243; de TV3 (2017,2020), and the LUX4MED/MEDLUX special programs.

The study was approved by the local ethics committee at Parc Tauli Hospital Universitari. Informed and signed consent was obtained from the patients or their next of kin. Absolute contraindications for entering the protocol were: clinical suspicion or echographic confirmation of venous thrombosis in the studied arm, other vascular or traumatic injuries in the studied arm, skin loss of integrity or lesions that could hinder the probe placement.
1. Device self-test
<ol>
	<li>Switch on the device. The device starts with in-house developed software.</li>
	<li>Turn the safety key to ON position, place the probe completely inside the instrument response function (IRF) box, and press the Reset button on the probe if it is glowing.</li>
	<li>Press the OK button on the popup dialog box and wait until the device is ready. 
	NOTE: The device performs self-tests to ensure stable working. The user is notified by a popup message when the device is ready.</li>
</ol>
2. Optional IRF and phantom measurement
<ol>
	<li>Press OK when the device is ready.</li>
	<li>Press Yes when it asks to measure an IRF. The device automatically adjusts the laser intensity to reach the desired count rate of 1 million.</li>
	<li>Press the Stop button when a stable count rate and DTOF are observed. This IRF is saved in files as well as loaded in the software to be utilized for real time calculations.</li>
	<li>Insert the probe in the Phantom box properly so that the probe attached indicator is on.</li>
	<li>Press the Phantom button to start the phantom protocol. 
	NOTE: The quality control test verifies that a sufficient number of photons are received by the DCS and TRS detectors and also checks if the dark counts are within the desired limits.</li>
	<li>Continue recording for at least 30 s after the quality control to have a sufficient amount of data saved for further offline analysis.</li>
</ol>
3. Bedside measurement preparation
<ol>
	<li>Attach the tourniquet on the upper arm above the elbow as done during a blood pressure measurement. Do not wrap the cuff loosely or very tightly around the arm. 
	NOTE: Loosely attaching the tourniquet requires more air to reach the desired pressure. Slow inflation allows the body to readjust its physiology.</li>
	<li>Attach the pulse oximeter to the index finger of the same arm. If it is not possible to attach to the index finger, attach it to any other finger.</li>
	<li>Locate the brachioradialis muscle to be probed, which is in the lateral forearm just below the elbow. Ask the patient to open and close a fist to feel the muscle by placing fingers on the forearm. In the case of sedated patients or if they cannot move, trace the muscle by slightly twisting the arm with one hand. Feel the muscle between the thumb and fingers of the other hand.</li>
	<li>Measure the arm circumference around the located muscle using a soft measuring tape, as shown in Figure 3.</li>
	<li>Measure the approximate adipose tissue thickness on the top of the muscle by using a digital body fat caliper, as shown in Figure 4.</li>
	<li>Attach the probe head to the muscle with the optical fibers and cables going toward the hand, as shown in Figure 5. 
	NOTE: Do not attach the probe tightly; it can affect tissue physiology. Make sure the fibers are not touching moving objects, and it can create artifacts in the data.</li>
	<li>Cover the probe with a black cloth to block the external light. 
	NOTE: If the patient is awake, inform him that the VOT can cause a tingling sensation and he should not move the arm.</li>
</ol>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/66062/66062fig03.jpg" /> 
Figure 3: Measuring the arm circumference around the brachioradialis muscle. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/66062/66062fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/66062/66062fig04.jpg" /> 
Figure 4: Measuring the adipose tissue thickness on top of the muscle using a body fat caliper. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/66062/66062fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/66062/66062fig05.jpg" /> 
Figure 5: Probe attached to the muscle with fibers and cables going toward the hand. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/66062/66062fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
4. Data acquisition
<ol>
	<li>Ensure that the probe-attached LED indicator on the device&#39;s front panel is shining and the touch icon in the software is green, showing that the probe is attached.</li>
	<li>Press the Protocol timed button. Ensure it opens a new dialogue box, as shown in Figure 6. Enter the subject ID, operator ID, and the target pressure of 50 mmHg higher than the systolic blood pressure.</li>
	<li>Press OK to start the automated protocol. Real-time data is displayed in the graphs. The protocol starts with quality control that automatically adjusts laser power and checks the photon counts and the interference between modalities. The quality check is completed within 2 min. Observe the circular icons labeled TRS and DCS, which must turn green at the end of the data quality check. 
	NOTE: The green icons show that the photon count rate is within the desired range, there is no external light entering the probe, and there is no crosstalk between modalities. Hence, the measurement can be continued. The graphs are reset at the end of the quality phase, and signals representing patient data are plotted in real time.</li>
	<li>Continue from step 2.6 if the TRS and DCS icons do not turn green and remain red at the end of the quality check. Press the Stop button to abort the protocol if the patient is unstable or requires sudden clinical intervention at any instant during the protocol.</li>
	<li>Press the Extend button to add 30 s of pre-occlusion duration if the patient moves the arm and does not have stable baseline signals. 
	NOTE: The operator can press the Extend button as many times and in any phase as required; each button press will add 30 s.</li>
	<li>Ensure that the tourniquet automatically inflates to the desired pressure to start the VOT. Press + or - buttons to increase or decrease the desired occlusion pressure in steps of 5 mmHg if the blood pressure of the patient changes after starting the protocol. The start and stop of the VOT are automatically marked with yellow vertical lines. 
	NOTE: The software is set to continuously acquire data and to automatically perform 3 min of VOT after 3 min of baseline. The pre-defined standard protocol lasts for six more minutes after the completion of VOT to evaluate the recovery after the patient&#39;s hyperemic response is over and a stable condition is obtained.</li>
	<li>Press OK when the operator is notified at the completion of the protocol through a popup notification, which marks the successful completion of the protocol.</li>
	<li>Remove the probes and the cuff from the patient and clean them using an alcohol swab or the equivalent.</li>
	<li>Write down the clinical and demographic information (according to the pre-defined study protocols) along with the circumference of the arm at the probe location and the thickness of the overlying adipose tissue in the patient data form manually.</li>
</ol>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/66062/66062fig06v2.jpg" /> 
Figure 6: Screenshot of protocol parameters used for automatically executing the whole protocol. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/66062/66062fig06large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
5. Data analysis
<ol>
	<li>Use a script/program written in one&#39;s favorite language (example Python or MATLAB) to open and visualize recorded binary data.</li>
	<li>Calculate the index of oxygen consumption that represents tissue metabolism and is defined as: 
	<img alt="Equation 1" src="/files/ftp_upload/66062/66062eq01.jpg" style="margin: auto;" /> 
	where Hb is the hematocrit, which is recorded from clinical charts of the patient in the patient data form.</li>
	<li>Compute the rate of DeO2 (slope of StO2 from the onset of VOT to 1 min), amplitude of DeO2 (baseline StO2- minimum StO2), rate of ReO2 (slope of StO2 from completion of VOT to reaching peak value), amplitude of hyperemic peak of StO2 and BFI (peak values), and area under the curve (AUC) of the reactive response after VOT for both StO2 and BFI. 
	NOTE: The computation of real-time absolute values of HbO, HbR, HbT, and StO2 is achieved by fitting algorithm using the distribution of time of flight (DTOF) curves from TRS of both wavelengths. The theoretical details can be found in Torricelli et al. and Contini et al.18,21. The calculation of BFI in real-time is achieved by the fitting algorithm using the autocorrelation curves from DCS. The theoretical details can be found in Durduran and Yodh16.</li>
</ol>

The role in the project of all the companies and their employees involved has been defined by the project objectives, tasks, and work packages and has been reviewed by the European Commission. MB, ML, DC, Alberto Tosi, and Alessandro Toricelli are co-founders of PIONIRS s.r.l., spin off company from Politecnico di Milano (Italy). ICFO has equity ownership in the spin-off company HemoPhotonics s.l.. Potential financial conflicts of interest and objectivity of research have been monitored by ICFO&#39;s Knowledge &#38; Technology Transfer Department. UMW is the CEO, has equity ownership in HemoPhotonics s.l., and is an employee along with SP in the company.

We have demonstrated a fully automated, robust, non-invasive device for the continuous measurement and monitoring of skeletal muscle using hybrid diffuse optics for evaluating microvascular oxygenation, blood perfusion, and reactive hyperemia. Using this protocol with VASCOVID device, we can simultaneously measure absolute hemodynamic parameters of HbO, HbR, and HbT; oxygen saturation from StO2 and SpO2; DeO2 and ReO2; and BFI. The displayed real-time StO2 and BFI are obtained from the raw data of the previous second from the TRS and DCS modules, respectively. The fitting procedure is not time-consuming since modern processors use standard models of a semi-infinite, homogeneous medium. The parameters acquired do not paint the complete picture of endothelial function. However, reactive hyperemia measured has demonstrated prognostic value in several acute conditions where the endothelial impairment plays a major role, such as septic shock or COVID-19.6,28 The protocol also incorporates an automated quality check that records the device parameters, which are useful for a research protocol in case an unexplained anomaly is detected later in any patient's data. 
The quantification of the overlaying adipose layer and the arm circumference is important while measuring the brachioradialis muscle in this protocol since the photons pass primarily through the overlaying tissues when injected and when detected. It is well known in diffuse optics that there is an associated partial volume effect. Therefore, the superficial information should be recorded and utilized when analyzing the data in order to account for the effect of variations in adipose tissue46,47. This is further amplified in these patient populations of interest since it is common in ICU patients to develop edema where the limbs are swollen as water is trapped due to immobilization and other reasons48. In such patients, the variation in circumference during ICU stay can provide information about the severity of edema. The pathway of the light source reaching the detectors has to pass through all the superficial layers. 
The cuff should be comfortably wrapped around the arm, ensuring a close fit. However, it is important to avoid excessive tightness that could exert excessive pressure on the arm solely through the act of wrapping the cuff49. The goal is to achieve a secure and comfortable fit without causing unnecessary compression, which can alter baseline hemodynamic parameters. If it compresses the arm, the data quality will be compromised for the whole protocol, and the exerted pressure will be effectively added to the target pressure of VOT. In case the cuff is loosely wrapped to the arm, more air will be required to reach the target pressure and hence more time will be taken. This can give time to tissue for adjusting physiology as oxygen supply is being reduced slowly, which should be avoided50.
It is important to attach the smart probe in a manner that maintains proper contact without exerting excessive pressure on the tissue. This allows for reliable measurements while avoiding the risk of local ischemia. Local ischemia occurs when blood flow to the area is restricted leading to compromised circulation and potentially corrupting the measurements51. 
The capacitive touch sensor on the probe is used by the laser safety system to ensure that the laser shines only when the probe is attached to the tissue. If the patient has high hair density on the arm, the sensitivity of the touch sensor can be compromised. The application of a thin transparent double tape on the sensor side of the probe can effectively mitigate the touch sensor issue. When the probe is attached to the hairy arm together with this tape, it provides a reliable and stable touch signal. Predefined cuts of this tape are available for the smart probe with separation between light sources and detectors. The separation is essential to prevent the formation of a direct light channel between source and detector windows, which can affect the quality of the measurements. The use of transparent double tape serves as a practical solution to enhance the reliability of touch sensing in these circumstances. If the touch sensing is lost during the protocol, it turns off the lasers and the measurement is lost. The probe also has a load sensor which could, in the future, be utilized as a back-up safety measure.
If the patient moves their arm or a small clinical intervention disrupts the stability of acquired signals during the baseline phase, resulting in sharp peaks, it is advisable to utilize the extend feature. This feature allows for the acquisition of a stable baseline for three minutes, ensuring consistent and reliable signal measurement. 
It is important to consider that the patient's blood pressure may undergo significant changes after initiating the protocol, which can impact the ability to reach the target pressure of 50 mmHg higher than the systolic blood pressure for the VOT. These fluctuations in blood pressure may be influenced by various factors, such as the patient's physiological response, medication effects, or other clinical conditions52. Therefore, the target pressure should be adjusted by pressing "+" or "-" buttons if necessary to ensure consistent administration of the VOT.
The typical execution of VOT has limitations due to operator variability, which is addressed in this protocol by having an automatic VOT. We are using the strategy to set the occlusion pressure of 50 mmHg above the systolic blood pressure level. This method stops the blood flow and has been reported in previous studies for performing the VOT53,54. The individualized target pressure for VOT in this protocol helps in avoiding vasoconstriction that can happen by fixing a general target pressure for VOT. Pain caused by an unnecessarily high pressure can affect the measurement causing vasoconstriction, e.g. in a patient with systolic pressure of 120 mmHg and target pressure of 200 mmHg or 250 mmHg29. We note that patients admitted to ICUs face an increased risk of thrombosis, primarily due to factors such as prolonged immobility, and sedation55. This implies that to avoid risks, this protocol cannot be used in patients suffering from thrombosis or thrombophlebitis. 
The application of this protocol can be useful in the ICU population where impaired reactive hyperemia is a common feature and can contribute to microvascular abnormalities3,56. The parameters acquired in this protocol, without operator interventions during the measurement, have been previously used in the literature singularly or in a small combination for sepsis, cancer, stroke etc. to distinguish pathological conditions1,11,15,31. Therefore, we believe that the combination of these relevant parameters are beneficial for several clinical applications. The data recorded by this protocol can help to select appropriate therapeutic strategies to improve vascular health57. The valuable insights on tissue oxygenation and blood flow dynamics during occlusion and reperfusion allow us to assess the adequacy of blood supply to vital organs. It can help in identifying tissue hypoxia and guiding interventions to optimize organ perfusion58. By using real-time information on microvascular oxygenation and reactive hyperemia, it assists as an additional tool in guiding hemodynamic management, fluid resuscitation, and vasopressor therapy59,60. This ensures that interventions are tailored to individual patient needs, optimizing tissue oxygenation and perfusion61,62. Furthermore, in mechanically ventilated patients, evolutive changes in microvascular oxygenation and blood flow within a spontaneous breathing trial can be of utmost importance when evaluating the cardiovascular tolerance to meet and overcome the increased metabolic burden derived from the work of breathing without assistance2. On that behalf, a daily critical and challenging decision for the ICU patients on mechanical ventilation is the weaning process, which ends when the patient is considered able to breathe by himself, and the endotracheal tube is removed. The longitudinal application of this protocol can be used to evaluate the effectiveness of interventions, track disease progression, and guide treatment strategies.

Critically ill patients, particularly those with sepsis and other similar conditions, often exhibit impaired reactive hyperemia and microvascular oxygenation1,2,3. During the first waves of COVID-19 pandemic, an unforeseen number of patients required intensive care management, during which the impact of the virus on the endothelium became evident but without a clear strategy to assess and manage4,5,6. As a result, there has been a growing recognition of the importance of detecting endothelial dysfunction, which can be indirectly evaluated by reactive hyperemia, in critical care, i.e., the intensive care unit (ICU) populations7. A practical, robust, and widely available assessment of oxygen delivery and consumption to the tissues is expected to be of utmost importance in optimizing resuscitation strategies and directly addressing microcirculatory issues. Studies have consistently demonstrated that persistent microcirculatory alterations and lack of coherence between macrocirculation and microcirculation are, to some extent, predictive of organ failure and unfavorable outcomes in patients affected by septic shock or hemorrhagic shock, among other critical conditions, even when systemic parameters are considered to be normal8,9,10. It has become evident that relying solely on macrocirculatory parameters is inadequate, as microcirculation plays a critical role in tissue oxygenation and organ function11,12,13. This paper describes a protocol that uses a new multi-modal device based on near-infrared diffuse optical technologies that has been developed within an international consortium that focuses on ICU patients. The project, VASCOVID (https://vascovid.eu), was motivated by the COVID-19 pandemic to evaluate microvascular health in peripheral muscles in intensive care. We have designed a protocol using the developed VASCOVID device that aims to enhance our understanding of these parameters and how these parameters can be useful in managing critically ill patients with a much broader scope than COVID-19 patients.
Near infrared spectroscopy (NIRS) has been utilized to assess microcirculation non-invasively for decades in a broad range of clinical applications including, the ICU patients14,15,16,17. It is important to note that the simplest application of NIRS, i.e., continuous wave NIRS (CW-NIRS), is implemented in widely used and clinically approved devices17,18, used for measuring the absolute concentrations of oxy- (HbO) and deoxy-hemoglobin (HbR) to calculate the blood/tissue oxygen saturation (StO2) of the microvasculature. While these devices have found niche uses in clinical management, such as during cardiac surgery, they have clear limitations due to the physics of photon propagation in tissues. This means that their accuracy, precision, and repeatability are questionable, hence, they are often utilized as trend monitors19,20. Furthermore, their results are heavily influenced by superficial tissues such as the overlaying adipose and skin layers.
Time-resolved NIRS (TRS) employs short laser pulses in the picosecond range at multiple wavelengths to assess their delay and broadening after traversing through a tissue21. This allows TRS to separate the effects of absorption from scattering to obtain robust, accurate, and precise estimates, also allowing it to calculate the total hemoglobin concentration (HbT). Since TRS also resolves pathlengths, it can be utilized to better separate superficial signals from the deep signals of interest18,21. This comes at the cost of complexity, price, and bulkiness. However, in recent years, TRS systems have come down in complexity and cost, resulting in more accessible and easier-to-use devices. This manuscript describes a device that uses a compact original equipment manufacturer (OEM) commercial TRS module22,23.
Diffuse correlation spectroscopy (DCS) is another near-infrared technology that utilizes the temporal statistics of diffuse speckles to quantify the movement of light-scattering particles, which are dominated by red blood cells in tissues16,24. This, in turn, is well known to be an indicator of microvascular blood flow, which we refer to as the blood flow index (BFI)25. The simultaneous use of TRS and DCS in a hybrid optical device offers insights into oxygen metabolism by utilizing common models to derive the local oxygen extraction fraction and multiplying by the blood flow15,26,27.
In order to assess the microcirculation at the ICU, NIRS is often utilized with a vascular occlusion test (VOT), which is an ischemic challenge that is performed by blocking the blood supply to the probed peripheral muscle for a certain duration (a few minutes)28,29,30,31,32. Most commonly, it is executed by inflating a tourniquet wrapped around the upper arm above the systolic pressure33. During the VOT, the clinicians assess the response of the microvascular blood oxygenation to changes in blood flow to derive oxygen metabolism at rest and reactive hyperemia34. The assumption is that during the VOT, with the cuff inflated well above the limb occlusion pressure, there is no inflow or outflow of blood. Therefore, the start of VOT shows a downward slope of StO2, i.e., deoxygenation (DeO2), as oxygen is consumed by the tissue, which allows an estimate of the metabolic rate of oxygen consumption. When the VOT ends and the cuff is deflated, blood rushes in to compensate for its depletion, leading to a hyperemic response. This rush generates a sharp upward slope in StO2, i.e., a reoxygenation (ReO2). The hyperemic response, which is an increase beyond the initial baseline with a slow recovery back to the baseline, estimates the reactive hyperemia. The combination of NIRS with a VOT has gained increasing interest in intensive care due to its ease of use and potential for predicting adverse outcomes and even mortality in critical conditions such as sepsis35,36,37.
During the COVID-19 pandemic, our groups have initiated a worldwide consortium and recently completed the so-called HEMOCOVID-19 trial, showing an association between peripheral microcirculatory alterations and severity of acute respiratory distress syndrome in COVID-19 patients6. This was supported by other works as well7,38. All these studies were done with the above-mentioned CW-NIRS systems, hence suffering from their shortcomings. Furthermore, the execution of VOT was not standardized across different studies and is affected by various parameters like occlusion duration, tourniquet pressure, and operator-based variations29,39,40. A literature review clearly shows that for VOT and NIRS to gain traction in the clinics, it is important to measure blood flow, have standardized protocols, and have a robust NIRS system11. Therefore, we have proposed that by utilizing a more advanced form of NIRS (TRS), measuring blood flow, and standardizing the cuff control during VOT, a better discrimination of pathological conditions from healthy ones could be achieved. To that end, we have developed this hybrid diffuse optical device that integrates multiple modules encompassing two near-infrared diffuse optical modules of TRS and DCS, pulse oximetry, and an automated tourniquet. The pulse oximetry module provides the heart rate (HR), perfusion index, and percentage of arterial oxygen saturation (SpO2). A fast tourniquet is used in the device, which is critical for performing VOT. The device comes with an optional accessory box that allows us to acquire additional information during the use for extended and continuous quality control, such as routine and practical measurement of the instrument response function (IRF) for TRS and the measurement on a tissue-mimicking phantom for evaluating longitudinal stability. The device is shown as being utilized in the ICU in Figure 1.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/66062/66062fig01v2.jpg" /> 
Figure 1: Bedside arrangement of the portable device in the ICU with the probes and cuff attached to the patient. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/66062/66062fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The multimodal smart probe incorporates source and detector optical fibers for both TRS and DCS with optical filters inside the device that prevent interference between DCS and TRS. The source-detector separation used in this system is 25 mm. Additionally, the probe incorporates a capacitive touch sensor, providing a valuable safety feature to prevent laser hazards according to the laser safety standard (IEC 60601-2-22:2019)41. The laser safety system within the device ensures that the laser emission occurs only when the probe is in contact with the tissue. If detachment of the probe is detected, the lasers are immediately switched off, ensuring the safety of both patients and operators. Moreover, the probe is integrated with an accelerometer, load sensor, and light sensor for additional functionality and data collection purposes.
This paper describes the automated protocol where we probe the brachioradialis muscle simultaneously with a VOT using the developed device. The protocol timeline is shown in Figure 2. The protocol is completely automated, and no operator interventions are needed throughout its execution. By leveraging the capabilities of this novel device, we aim to gain valuable insights that let the physicians understand the physiopathology of peripheral oxygen consumption better and also assess the ratio of oxygen consumption and delivery thereby helping them to improve patient care comprehensively and efficiently.
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/66062/66062fig02v2.jpg" /> 
Figure 2: Protocol timeline. The patient is at rest throughout the timeline with 0 mmHg pressure at initial baseline and recovery period. The VOT is performed with a tourniquet inflated to a pressure of 50 mmHg higher than the patient&#39;s systolic blood pressure. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/66062/66062fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<table><tbody><tr><td>Alcohol swabs</td><td>No specific</td><td>N/A</td><td>For cleaning the probes and cuff after measurement</td></tr><tr><td>Black cloth</td><td>No specific</td><td>N/A</td><td>For blocking ambient light&amp;nbsp;</td></tr><tr><td>Blood pressure monitor</td><td>OMRON</td><td>N/A</td><td>Hopital ICU equipment or off the shelf product</td></tr><tr><td>Body fat Calliper</td><td>Healifty</td><td>3257040-6108-1618385551</td><td>For measuring the fat layer</td></tr><tr><td>Examination gloves</td><td>No specific</td><td>N/A</td><td>To be used for interacting with patients</td></tr><tr><td>Kintex tape</td><td>No specific</td><td>N/A</td><td>For attaching the probe on arm</td></tr><tr><td>Koban wrap</td><td>No specific</td><td>N/A</td><td>For attaching the probe on arm</td></tr><tr><td>Measuring tape</td><td>YDM Industries</td><td>25-SB-30-150V3-19-1</td><td>For measuring the arm circumference</td></tr><tr><td>Scissors</td><td>No specific</td><td>N/A</td><td>for cutting tapes</td></tr><tr><td>VASCOVID precommercial prototype</td><td>VASCOVID consortium</td><td>N/A</td><td>Integrated at ICFO</td></tr></tbody></table>

non-invasive monitoring of microvascular oxygenation and reactive hyperemia using hybrid, near-infrared diffuse optical spectroscopy for critical care

The detection of levels of impairment in microvascular oxygen consumption and reactive hyperemia is vital in critical care. However, there are no practical means for a robust and quantitative evaluation. This paper describes a protocol to evaluate these impairments using a hybrid near-infrared diffuse optical device. The device contains modules for near-infrared time-resolved and diffuse correlation spectroscopies and pulse-oximetry. These modules allow the non-invasive, continuous, and real-time measurement of the absolute, microvascular blood/tissue oxygen saturation (StO2) and the blood flow index (BFI) along with the peripheral arterial oxygen saturation (SpO2). This device uses an integrated, computer-controlled tourniquet system to execute a standardized protocol with optical data acquisition from the brachioradialis muscle. The standardized vascular occlusion test (VOT) takes care of the variations in the occlusion duration and pressure reported in the literature, while the automation minimizes inter-operator differences. The protocol we describe focuses on a 3-min occlusion period but the details described in this paper can readily be adapted to other durations and cuff pressures, as well as other muscles. The inclusion of an extended baseline and post-occlusion recovery period measurement allows the quantification of the baseline values for all the parameters and the blood/tissue deoxygenation rate that corresponds to the metabolic rate of oxygen consumption. Once the cuff is released, we characterize the tissue reoxygenation rate, magnitude, and duration of the hyperemic response in BFI and StO2. These latter parameters correspond to the quantification of the reactive hyperemia, which provides information about the endothelial function. Furthermore, the above-mentioned measurements of the absolute concentration of oxygenated and deoxygenated hemoglobin, BFI, the derived metabolic rate of oxygen consumption, StO2, and SpO2 provide a yet-to-be-explored rich data set that can exhibit disease severity, personalized therapeutics, and management interventions.

The ongoing clinical studies have utilized the device for over 300 h by several trained users to perform measurements in ICU patients and healthy controls, derive clinically relevant results, and characterize the in vivo performance of the system in a real setting. Here, we demonstrate some example time traces of the data from a single subject that are visible to the user. The preliminary results of the protocol are measured and displayed in real-time, such as HbO, HbR, HbT, StO2, SpO2, and BFI. Different derived parameters, such as MRO2, DeO2, ReO2, and AUC, are described.
Figure 7 shows the device monitor during step 3.3, which shows the data quality, where laser powers are adjusted, photon counts, and crosstalk between modalities are tested automatically. The device monitor shows two intensity autocorrelation (g2) curves as the device has two DCS detector fibers coupled to single photon counting modules and the DTOF for both wavelengths of the TRS device. The wavelength of the laser utilized for DCS is 785 nm, while the OEM TRS module shines lasers at 685 nm and 830 nm. The autocorrelation curves in the top graph appear to be noisy at lower lag times. This can be partially due to low light intensity in this specific example. Increased light intensity and independent/parallel detection fibers have been recommended to increase the signal-to-noise ratio for DCS42,43. Therefore, an average of two DCS channels is being planned to reduce the effect of noise and subsequently compute a better BFI.
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/66062/66062fig07v2.jpg" /> 
Figure 7: Screenshot of device monitor mode of software during the data quality checking phase. The top plot shows the autocorrelation curves from two channels of DCS. The middle plot shows the DTOF for TRS wavelengths. The bottom plot shows the photon counts for both DCS and TRS. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/66062/66062fig07large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The initial baseline period with clinical monitor, shown in Figure 8, has green icons for DCS and TRS, indicating the success of quality tests. The displayed signals look very stable, and hence, the Extend feature, described in step 3.5, was not required in this case. If the initial baseline appears as depicted in Figure 9, it is necessary to utilize the Extend feature. This feature extends baseline acquisition to obtain 3 min of stable data, which can be used to calculate the accurate baseline values for all parameters.
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/66062/66062fig08v2.jpg" /> 
Figure 8: Screenshot of clinical monitor mode of software during the initial baseline phase showing stable baseline signals. The top plot shows the absolute value of hemodynamic parameters measured by TRS, middle plot shows the oxygen saturation signals and pulse value measured by TRS and pulse oximeter, and the bottom plot shows the BFI measured using DCS. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/66062/66062fig08large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/66062/66062fig09v2.jpg" /> 
Figure 9: Screenshot showing spikes in the signals due to movement of the probe. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/66062/66062fig09large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The start and end of the cuff occlusion part are marked with yellow vertical lines, as shown in Figure 10. The pulse shape and the SpO2 values have no clinical/physiological meaning in this phase since the finger from the same arm being occluded is used for pulse oximetry. This is indicated by the red OXY icon expressing unreliable data from the pulse oximeter. To circumvent this situation, we could attach the pulse oximeter to the patient&#39;s unaffected hand, which is not subjected to the tourniquet and remains unobstructed. However, we want to obtain the perfusion index of the probed arm using the pulse oximeter for the initial baseline and final recovery phases to analyze the effects of VOT. Therefore, we have opted to use the pulse oximeter on the same arm as the tourniquet.
<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/66062/66062fig10v2.jpg" /> 
Figure 10: Software screenshot showing yellow vertical lines marking the starting and ending instants of VOT. The SpO2 and pulse values are insignificant as blood flow is restricted. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/66062/66062fig10large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Figure 11 shows the complete protocol timeline as indicated in step 3.6, including the final recovery phase, illustrating the hyperemic response and the return of clinical parameters to the initial baseline values. The top graph of Figure 11 shows the absolute hemodynamics parameters. The start of VOT marks a declining trend in HbO and a rising trend in HbR as both the inflow and outflow of blood are blocked by the cuff occlusion. The trend reverses at the time of VOT completion, goes beyond the initial baseline values, and returns to the baseline values in the recovery phase. The middle and bottom graphs show that the BFI signal is slightly noisier than StO2. This is inherently due to the fact that the DCS tends to have a higher contrast-to-noise ratio, which is evident from the large hyperemic response in BFI42,44. Using the rich dataset from this novel device, the oscillations in BFI have been used as potential biomarkers to diagnose septic patients45.
<img alt="Figure 11" class="xfigimg" src="/files/ftp_upload/66062/66062fig11v2.jpg" /> 
Figure 11: Screenshot of the clinical monitor showing the signals throughout the protocol timeline. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/66062/66062fig11large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
With this protocol, the oxygen being utilized by the muscle can be monitored in isolation during the VOT. The slope of DeO2 during the ischemic challenge indicates how the tissue consumes oxygen. The early decrease of StO2 during the VOT reflects the oxygen consumption rate for the tissue. The hyperemic peak and subsequent decaying trends in the StO2 and BFI are directly associated with hyperemic and microvascular reactivity. Apart from these obvious results, we can use several potential biomarkers to classify a specific group of ICU patients. The existing biomarkers are rate of deoxygenation, minimum value of StO2 during the VOT, rate of reoxygenation, hyperemic peak value, and area under the curve of both StO2 and BFI. These biomarkers can be utilized to identify patient populations and the severity of their diseases. The results obtained from an example data set from a patient are shown in Figure 12. The term &#34;DATA QC&#34; denotes the initial quality check, which does not pertain to patient data. Therefore, it is not displayed in the representation. The average values of StO2, BFI, and MRO2 for the baseline period are computed for comparison with phases of VOT and post-VOT recovery. The results obtained during this protocol can be different from the data from this example. The baseline values of all parameters can be higher or lower, and the rate of DeO2 can be faster or slower. The hyperemic response can have a higher or lower rate of ReO2 and peak values, or there may be an absence of peak. The recovery phase can show a faster or slower normalization of values. These variations are representative of the patient&#39;s condition suffering from a specific or set of diseases.
<img alt="Figure 12" class="xfigimg" src="/files/ftp_upload/66062/66062fig12.jpg" /> 
Figure 12: Summary of results compiled offline.&#160;The black dashed line marks the start of three minutes of the baseline period, while the red dashed line marks the inflating and deflating events. The top graph shows the StO2 signal with marked regions for calculating DeO2 and ReO2. The middle plot shows the BFI while the bottom plot shows the tourniquet pressure. The baseline values and the AUC are shown in blue in their respective phases. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/66062/66062fig12large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Non-Invasive Monitoring of Microvascular Oxygenation and Reactive Hyperemia using Hybrid, Near-Infrared Diffuse Optical Spectroscopy for Critical Care at JoVE

Non-Invasive Monitoring of Microvascular Oxygenation and Reactive Hyperemia using Hybrid, Near-Infrared Diffuse Optical Spectroscopy for Critical Care

We describe a protocol to non-invasively and continuously measure absolute microvascular blood flow index and blood oxygen saturation using a multi-modal device based on near-infrared diffuse optics. We then evaluate the metabolic rate of oxygen consumption and reactive hyperemia utilizing a vascular occlusion test.

The detection of levels of impairment in microvascular oxygen consumption and reactive hyperemia is vital in critical care. However, there are no ...

non-invasive-monitoring-microvascular-oxygenation-reactive-hyperemia

Nanyang Technological University

Research

JoVE Journal

Medicine

1.4K Views.  ICFO - Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology. Het doel van dit protocol is het evalueren van microvasculaire oxygenatie en reactieve hyperemie in perifere spieren, vooral in de context van intensive care-behandeling van ernstig zieke patiënten. Samen met Diffuse Optische Technologieën en Vasculaire Occlusietesten kunnen we verschillende parameters beoordelen om inzicht te krijgen in microvasculaire oxygenatie en reactieve hyperemie. We gebruiken het vasculaire apparaat dat verschillende modules combineert, waaronder twee near infra dif...

Video: Non-Invasive Monitoring of Microvascular Oxygenation and Reactive Hyperemia using Hybrid, Near-Infrared Diffuse Optical Spectroscopy for Critical Care

Non-invasive Optical Measurement of Cerebral Metabolism and Hemodynamics in Infants

Perinatal brain injury remains a significant cause of infant mortality and morbidity, but there is not yet an effective bedside tool that can accurately screen for brain injury, monitor injury evolution, or assess response to therapy. The energy used by neurons is derived largely from tissue oxidative metabolism, and neural hyperactivity and cell death are reflected by corresponding changes in cerebral oxygen metabolism (CMRO2). Thus, measures of CMRO2 are reflective of neuronal viability and provide critical diagnostic information, making CMRO2 an ideal target for bedside measurement of brain health.
Brain-imaging techniques such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT) yield measures of cerebral glucose and oxygen metabolism, but these techniques require the administration of radionucleotides, so they are used in only the most acute cases.
Continuous-wave near-infrared spectroscopy (CWNIRS) provides non-invasive and non-ionizing radiation measures of hemoglobin oxygen saturation (SO2) as a surrogate for cerebral oxygen consumption. However, SO2 is less than ideal as a surrogate for cerebral oxygen metabolism as it is influenced by both oxygen delivery and consumption. Furthermore, measurements of SO2 are not sensitive enough to detect brain injury hours after the insult 1,2, because oxygen consumption and delivery reach equilibrium after acute transients 3. We investigated the possibility of using more sophisticated NIRS optical methods to quantify cerebral oxygen metabolism at the bedside in healthy and brain-injured newborns. More specifically, we combined the frequency-domain NIRS (FDNIRS) measure of SO2 with the diffuse correlation spectroscopy (DCS) measure of blood flow index (CBFi) to yield an index of CMRO2 (CMRO2i) 4,5.
With the combined FDNIRS/DCS system we are able to quantify cerebral metabolism and hemodynamics. This represents an improvement over CWNIRS for detecting brain health, brain development, and response to therapy in neonates. Moreover, this method adheres to all neonatal intensive care unit (NICU) policies on infection control and institutional policies on laser safety. Future work will seek to integrate the two instruments to reduce acquisition time at the bedside and to implement real-time feedback on data quality to reduce the rate of data rejection.

We combined frequency-domain near-infrared spectroscopy measures of cerebral hemoglobin oxygenation with diffuse correlation spectroscopy measures of cerebral blood flow index to estimate an index of oxygen metabolism. We tested the utility of this measure as a bedside screening tool to evaluate the health and development of the newborn brain.

Perinatal brain injury remains a significant cause of infant mortality  and morbidity, but there is not yet an effective bedside tool that can  accurately ...

Non-invasive Assessment of Microvascular and Endothelial Function

The authors have utilized capillaroscopy and forearm blood flow techniques to investigate the role of microvascular dysfunction in pathogenesis of cardiovascular disease. Capillaroscopy is a non-invasive, relatively inexpensive methodology for directly visualizing the microcirculation. Percent capillary recruitment is assessed by dividing the increase in capillary density induced by postocclusive reactive hyperemia (postocclusive reactive hyperemia capillary density minus baseline capillary density), by the maximal capillary density (observed during passive venous occlusion). Percent perfused capillaries represents the proportion of all capillaries present that are perfused (functionally active), and is calculated by dividing postocclusive reactive hyperemia capillary density by the maximal capillary density. Both percent capillary recruitment and percent perfused capillaries reflect the number of functional capillaries. The forearm blood flow (FBF) technique provides accepted non-invasive measures of endothelial function: The ratio FBFmax/FBFbase is computed as an estimate of vasodilation, by dividing the mean of the four FBFmax values by the mean of the four FBFbase values. Forearm vascular resistance at maximal vasodilation (FVRmax) is calculated as the mean arterial pressure (MAP) divided by FBFmax. Both the capillaroscopy and forearm techniques are readily acceptable to patients and can be learned quickly.
The microvascular and endothelial function measures obtained using the methodologies described in this paper may have future utility in clinical patient cardiovascular risk-reduction strategies. As we have published reports demonstrating that microvascular and endothelial dysfunction are found in initial stages of hypertension including prehypertension, microvascular and endothelial function measures may eventually aid in early identification, risk-stratification and prevention of end-stage vascular pathology, with its potentially fatal consequences.

Capillaroscopy is a non-invasive, relatively inexpensive methodology for directly visualizing the microcirculation. The forearm blood flow technique provides accepted non-invasive measures of endothelial function.

The authors have utilized capillaroscopy and forearm blood flow techniques to investigate the role of microvascular dysfunction in pathogenesis of ...

Near Infrared Optical Projection Tomography for Assessments of &beta;-cell Mass Distribution in Diabetes Research

By adapting OPT to include the capability of imaging in the near infrared (NIR) spectrum, we here illustrate the possibility to image larger bodies of pancreatic tissue, such as the rat pancreas, and to increase the number of channels (cell types) that may be studied in a single specimen. We further describe the implementation of a number of computational tools that provide: 1/ accurate positioning of a specimen's (in our case the pancreas) centre of mass (COM) at the axis of rotation (AR)2; 2/ improved algorithms for post-alignment tuning which prevents geometric distortions during the tomographic reconstruction2 and 3/ a protocol for intensity equalization to increase signal to noise ratios in OPT-based BCM determinations3. In addition, we describe a sample holder that minimizes the risk for unintentional movements of the specimen during image acquisition. Together, these protocols enable assessments of BCM distribution and other features, to be performed throughout the volume of intact pancreata or other organs (e.g. in studies of islet transplantation), with a resolution down to the level of individual islets of Langerhans.

Near Infrared Optical Projection Tomography for Assessments of &#946;-cell Mass Distribution in Diabetes Research

We describe the adaptation of optical projection tomography (OPT)1 to imaging in the near infrared spectrum, and the implementation of a number of computational tools. These protocols enable assessments of pancreatic &beta;-cell mass (BCM) in larger specimens, increase the multichannel capacity of the technique and increase the quality of OPT data.

By adapting OPT to include the capability of imaging in the near infrared (NIR) spectrum, we here illustrate the possibility to image larger bodies of ...

Diffuse Optical Spectroscopy for the Quantitative Assessment of Acute Ionizing Radiation Induced Skin Toxicity Using a Mouse Model

Acute skin toxicities from ionizing radiation (IR) are a common side effect from therapeutic courses of external beam radiation therapy (RT) and negatively impact patient quality of life and long term survival. Advances in the understanding of the biological pathways associated with normal tissue toxicities have allowed for the development of interventional drugs, however, current response studies are limited by a lack of quantitative metrics for assessing the severity of skin reactions. Here we present a diffuse optical spectroscopic (DOS) approach that provides quantitative optical biomarkers of skin response to radiation. We describe the instrumentation design of the DOS system as well as the inversion algorithm for extracting the optical parameters. Finally, to demonstrate clinical utility, we present representative data from a pre-clinical mouse model of radiation induced erythema and compare the results with a commonly employed visual scoring. The described DOS method offers an objective, high through-put evaluation of skin toxicity via functional response that is translatable to the clinical setting.

We present a diffuse optical spectroscopic (DOS) approach that provides quantitative optical biomarkers of skin response to radiation. We describe DOS instrumentation design, optical parameters extraction algorithms and the animal handling procedures required to yield representative data from a pre-clinical mouse model of radiation induced erythema.

Acute skin toxicities from ionizing radiation (IR) are a common side effect from therapeutic courses of external beam radiation therapy (RT) and ...

A Model to Simulate Clinically Relevant Hypoxia in Humans

In case of apnea, arterial partial pressure of oxygen (pO2) decreases, while partial pressure of carbon dioxide (pCO2) increases. To avoid damage to hypoxia sensitive organs such as the brain, compensatory circulatory mechanisms help to maintain an adequate oxygen supply. This is mainly achieved by increased cerebral blood flow. Intermittent hypoxia is a commonly seen phenomenon in patients with obstructive sleep apnea. Acute airway obstruction can also result in hypoxia and hypercapnia. Until now, no adequate model has been established to simulate these dynamics in humans. Previous investigations focusing on human hypoxia used inhaled hypoxic gas mixtures. However, the resulting hypoxia was combined with hyperventilation and is therefore more representative of high altitude environments than of apnea. Furthermore, the transferability of previously performed animal experiments to humans is limited and the pathophysiological background of apnea induced physiological changes is poorly understood. In this study, healthy human apneic divers were utilized to mimic clinically relevant hypoxia and hypercapnia during apnea. Additionally, pulse-oximetry and Near Infrared Spectroscopy (NIRS) were used to evaluate changes in cerebral and peripheral oxygen saturation before, during, and after apnea.

Hypoxia simulation in humans has usually been performed by inhaling hypoxic gas mixtures. For this study, apneic divers were used to simulate dynamic hypoxia in humans. Additionally, physiological changes in desaturation and re-saturation kinetics were evaluated with non-invasive tools such as Near-Infrared-Spectroscopy (NIRS) and peripheral oxygenation saturation (SpO2).

In case of apnea, arterial partial pressure of oxygen (pO2) decreases, while partial pressure of carbon dioxide (pCO2) increases. To avoid damage to ...

Skeletal Muscle Neurovascular Coupling, Oxidative Capacity, and Microvascular Function with 'One Stop Shop' Near-infrared Spectroscopy

Exercise represents a major hemodynamic stress that demands a highly coordinated neurovascular response in order to match oxygen delivery to metabolic demand. Reactive hyperemia (in response to a brief period of tissue ischemia) is an independent predictor of cardiovascular events and provides important insight into vascular health and vasodilatory capacity. Skeletal muscle oxidative capacity is equally important in health and disease, as it determines the energy supply for myocellular processes. Here, we describe a simple, non-invasive approach using near-infrared spectroscopy to assess each of these major clinical endpoints (reactive hyperemia, neurovascular coupling, and muscle oxidative capacity) during a single clinic or laboratory visit. Unlike Doppler ultrasound, magnetic resonance images/spectroscopy, or invasive catheter-based flow measurements or muscle biopsies, our approach is less operator-dependent, low-cost, and completely non-invasive. Representative data from our lab taken together with summary data from previously published literature illustrate the utility of each of these end-points. Once this technique is mastered, application to clinical populations will provide important mechanistic insight into exercise intolerance and cardiovascular dysfunction.

Here, we describe a simple, non-invasive approach using near-infrared spectroscopy to assess reactive hyperemia, neurovascular coupling and skeletal muscle oxidative capacity in a single clinic or laboratory visit.

Exercise represents a major hemodynamic stress that demands a highly coordinated neurovascular response in order to match oxygen delivery to metabolic ...

How to Administer Near-Infrared Spectroscopy in Critically ill Neonates, Infants, and Children

Near infrared spectroscopy (NIRS) calculates regional tissue oxygenation (rSO2) using the different absorption spectra of oxygenated and deoxygenated hemoglobin molecules. A probe placed on the skin emits light that is absorbed, scattered, and reflected by the underlying tissue. Detectors in the probe sense the amount of reflected light: this reflects the organ-specific ratio of oxygen supply and consumption - independent of pulsatile flow. Modern devices enable the simultaneous monitoring at different body sites. A rise or dip in the rSO2 curve visualizes changes in oxygen supply or demand before vital signs indicate them. The evolution of rSO2 values in relation to the starting point is more important for interpretation than are absolute values.
A routine clinical application of NIRS is the surveillance of somatic and cerebral oxygenation during and after cardiac surgery. It is also administered in preterm infants at risk for necrotizing enterocolitis, newborns with hypoxic ischemic encephalopathy and a potential risk of impaired tissue oxygenation. In the future, NIRS could be increasingly used in multimodal neuromonitoring, or applied to monitor patients with other conditions (e.g., after resuscitation or traumatic brain injury).

This protocol is designed to assist clinicians to measure regional tissue oxygenation at different body sites in infants and children. It can be used in situations where tissue oxygenation is potentially compromised, particularly during cardiopulmonary bypass, when using non-pulsatile cardiac-assist devices, and in critically ill neonates, infants and children.

Near infrared spectroscopy (NIRS) calculates regional tissue oxygenation (rSO2) using the different absorption spectra of oxygenated and deoxygenated ...

Real-Time Monitoring of Neurocritical Patients with Diffuse Optical Spectroscopies

Neurophysiological monitoring is an important goal in the treatment of neurocritical patients, as it may prevent secondary damage and directly impact morbidity and mortality rates. However, there is currently a lack of suitable non-invasive, real-time technologies for continuous monitoring of cerebral physiology at the bedside. Diffuse optical techniques have been proposed as a potential tool for bedside measurements of cerebral blood flow and cerebral oxygenation in case of neurocritical patients. Diffuse optical spectroscopies have been previously explored to monitor patients in several clinical scenarios ranging from neonatal monitoring to cerebrovascular interventions in adults. However, the feasibility of the technique to aid clinicians by providing real-time information at the bedside remains largely unaddressed. Here, we report the translation of a diffuse optical system for continuous real-time monitoring of cerebral blood flow, cerebral oxygenation, and cerebral oxygen metabolism during intensive care. The real-time feature of the instrument could enable treatment strategies based on patient-specific cerebral physiology rather than relying on surrogate metrics, such as arterial blood pressure. By providing real-time information on the cerebral circulation at different time scales with relatively cheap and portable instrumentation, this approach may be especially useful in low-budget hospitals, in remote areas and for&#160;monitoring in open fields (e.g., defense and sports).

Presented here is a protocol for non-invasively monitoring cerebral hemodynamics of neurocritical patients in real-time and at the bedside using diffuse optics. Specifically, the proposed protocol uses a hybrid diffuse optical systems to detect and display real-time information on cerebral oxygenation, cerebral blood flow and cerebral metabolism.

Neurophysiological monitoring is an important goal in the treatment of neurocritical patients, as it may prevent secondary damage and directly impact ...

Measurement of Tissue Oxygenation Using Near-Infrared Spectroscopy in Patients Undergoing Hemodialysis

Near-infrared spectroscopy (NIRS) has recently been applied as a tool to measure regional oxygen saturation (rSO2), a marker of tissue oxygenation, in clinical settings including cardiovascular and brain surgery, neonatal monitoring and prehospital medicine. The NIRS monitoring devices are real-time and noninvasive, and have mainly been used for evaluating cerebral oxygenation in critically ill patients during an operation or intensive care. Thus far, the use of NIRS monitoring in patients with chronic kidney disease (CKD) including hemodialysis (HD) has been limited; therefore, we investigated rSO2 values in some organs during HD. We monitored rSO2 values using a NIRS device transmitting near-infrared light at 2 wavelengths of attachment. The HD patients were placed in a supine position, with rSO2 measurement sensors attached to the foreheads, the right hypochondrium and the lower legs to evaluate rSO2 in the brain, liver and lower leg muscles, respectively. NIRS monitoring could be a new approach to clarify changes in organ oxygenation during HD or factors affecting tissue oxygenation in CKD patients. This article describes a protocol to measure tissue oxygenation represented by rSO2 as applied in HD patients.

We present a protocol to measure regional oxygen saturation (rSO2) in hemodialysis (HD) patients by using a near-infrared spectroscopy monitor. The rSO2 value is an index of tissue oxygenation. This noninvasive and real-time monitoring could be useful for confirming changes in organ oxygenation during HD.

Near-infrared spectroscopy (NIRS) has recently been applied as a tool to measure regional oxygen saturation (rSO2), a marker of tissue oxygenation, in ...

Optimizing NIRS for Assessing Lower Limb Vascular Function

Near-Infrared Spectroscopy During Reactive Hyperemia for the Assessment of Lower Limb Vascular Function

Vascular diseases of the lower limb contribute substantially to the&#160;global burden of cardiovascular disease and comorbidities such as diabetes. Importantly, microvascular dysfunction can occur prior to, or alongside, macrovascular pathology, and both potentially contribute to patient symptoms and disease burden. Here, we describe a non-invasive approach using near-infrared spectroscopy (NIRS) during reactive hyperemia, which provides a standardized assessment of lower limb vascular (dys)function and a potential method to evaluate the efficacy of therapeutic interventions. Unlike alternative methods, such as contrast-enhanced ultrasound, this approach does not require venous access or sophisticated image analysis, and it is inexpensive and less operator-dependent. This description of the NIRS method includes representative results and standard terminology alongside the discussion of measurement considerations, limitations, and alternative methods. Future application of this work will improve standardization of vascular research design, data collection procedures, and harmonized reporting, thereby enhancing translational research outcomes in the areas of lower limb vascular (dys)function, disease, and treatment.

Author Spotlight: Enhancing Vascular Function and Physical Capacity in Cardiovascular Disease Through Novel Interventions and NIRS Technology

Here, we describe a non-invasive approach using near-infrared spectroscopy to assess reactive hyperemia in the lower limb. This protocol provides a standardized assessment of vascular and microvascular responsiveness that may be used to determine the presence of vascular dysfunction as well as the efficacy of therapeutic interventions.

Vascular diseases of the lower limb contribute substantially to the&#160;global burden of cardiovascular disease and comorbidities such as diabetes. ...

Non-Invasive Monitoring of Microvascular Oxygenation and Reactive Hyperemia using Hybrid, Near-Infrared Diffuse Optical Spectroscopy for Critical Care

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