The overall goal of this procedure is to induce a state of acute stress through application of the cold presser arm wrap. This is accomplished by first removing the cold presser arm wrap from cold storage and covering it with a protective layer of plastic sheeting. The second step is to test the surface temperature of the cold presser arm wrap in order to ensure it is within a desired and safe range.
Next, the cold presser arm wrap is fastened to the participant's arm. The final step is to remove the cold presser arm wrap from the participant's arm after the desired amount of time has passed or at the participant's request. Ultimately, salivary cortisol and skin conductance data are used to show that cold presser arm wrap evokes activation of both the hypothalamic pituitary adrenal axis and sympathetic nervous system.
The main advantage of this technique over existing methods, such as the traditional cold pressor, is that it does not involve the use of actual water, which can pose a danger to sensitive equipment such as MRI. This method can provide researchers interested in studying stress with an effective, easy, and versatile means of inducing stress in the lab. Demonstrating the procedure will be Stephanie and Travis, both graduate students in my laboratory.
To make the cold presser arm wrap first use rubber cement to affix two to three pieces of Velcro to each of two six by 12 inch gel packs. Assure that the Velcro is equally spaced and allow 24 hours for the cement to dry. Next fold a piece of thick fabric approximately 12 by 16 inches in size in half lengthwise, and then place the gel packs lengthwise along each inner half of the folded fabric.
Now affix the complementary side of each Velcro piece to the inner sides of the fabric using rubber cement or needle and thread. The pieces should be spaced so that they will match placement of the Velcro on the gel packs. This will allow gel packs to be easily removed for cleaning and then reattached for storage.
Next, obtain two larger pieces of Velcro approximately two by 10 inches in size, and cut one piece to about a quarter of its original size while keeping the other at the original size, affix the small piece of Velcro to the front and back of the outer portion of the fabric on the same side. Finally, affix the longer part of the Velcro to the analogous locations on the outer portion of the opposite side of the fabric. This can be done using rubber cement or needle and thread after this is completed.
It should be possible to wrap the fabric around one's forearm and hand and faceted in place using the Velcro straps Once completed, store the cold presser arm wrap in a freezer with a carefully monitored temperature between zero and five degrees Celsius. If the freezer cannot be set to a specific temperature and is below zero degrees Celsius, allow time for the arm wrap to warm to a safe temperature after removing it from storage. Otherwise, the potential exists for a study participant to experience a cold burn.
Be sure to inform participants multiple times during consent and prior to the cold presser arm wrap administration that they are free to withdraw and end the procedure at any time. Three discreet withdrawal statements are recommended. Additionally, be prepared to end the procedure at any time if the participant becomes distressed.
The following is a suggested statement that can be given to the participant prior to the experiment. The arm wrap is designed to be stressful and will thus be highly uncomfortable, but it's important to understand that it is your right to end the procedure or the experiment at any time for any reason whether the arm wrap is on your arm or not. Do you understand?
Yeah, I understand. If performing MRI experiments with the cold presser arm wrap first screen for MRI safety and remind the participant that the imaging experiment can be discontinued at any time. Functional MRI will not be demonstrated here, but note that the arm wrap should not be left in place for more than a few minutes during a functional task.
Prior to employing the arm wrap, cover the gel packs with a layer of plastic sheeting to avoid direct contact between gel packs and the participant's skin. Then measure the surface temperature of each covered gel pack using an infrared thermometer in two to three locations along its length to ensure a safe temperature. If the temperature is too low, allow additional time to pass and measure.
Again, take any baseline measurements that are needed for the experiment such as a salivary cortisol sample. Then once the desired temperature is reached, wrap the arm wrap around the participant's forearm and hand affixing it in place With the Velcro straps, leave the arm wrap in place for the desired period of time. Approximately two minutes is recommended.
Be sure to remove it immediately upon the participant's request or after the specified time has elapsed. This step can also be done within the MRI bore, if applicable. Acquire additional salivary cortisol samples or skin conductance measurements as needed.
A post experimental questionnaire can also be administered to allow the participant to report subjective ratings of perceived stress. Then once the experiment is complete, remove the plastic sheeting and store the cold presser arm wrap for future use as previously described. Here we can see mean salivary cortisol levels at baseline as well as after two FMRI Task runs for both no stress control and cold presser arm wrap groups.
A one-tailed independent T-test between the no stress control and cold presser group area under the curve with respect to increase indicated a significant increase in salivary cortisol for the cold presser group. Negative area under the curve values, which indicate a net decrease in salivary cortisol were retained as an index of decrease. Finally, here we can see square root transformed mean skin conductance levels in microsiemens during cold presser arm wrap or no stress control arm wrap application cold presser arm wrap group skin conductance levels are significantly higher than those exhibited by the no stress control group.
While performing this procedure, be sure to carefully monitor the cold pressor arm wraps temperature. Make sure the participants understand that they're free to withdraw or end the procedure at any time. Finally, be prepared to remove the cold pressor arm wrap at the participant's request, or if they show signs of unusual distress.
This technique may be of use to researchers interested in studying stresses influence on behavior and function, but have found the traditional cold pressor to be unwieldy or not feasible. Further, it can be easily used in combination with other stress induction techniques.
