Dynamic Quantitative Sensory Testing to Characterize Central Pain Processing

The overall goal of this experimental protocol is to present and improve individualized method to measure thermal temporal summation and conditioned pain modulation. This method may advance the field of pain medicine because reliably measured temporal summation and conditioned pain modulation will facilitate the diagnoses and prognosis of many clinical pain syndromes. This technique increases the success rate in capturing temporal summation and conditioned pain modulation by individualizing the thermo-stimuli using these tests, thereby, minimizing floor and ceiling effects.

Though this methods measures only temporal summation and conditioned pain modulation, it may be combined with other QST modalities to fully characterize the sensory profile of the patient. Visual demonstration of this method is important because both temporal summation and conditioned pain modulation require extensive training and complex sensory stimuli which are best demonstrated on video. Begin by turning on the thermode in the computer.

Program the sequence of the single heat pulses for training trial one with the following parameters. Heat pulse duration equals 0.5 seconds. Inter-stimulus interval equal 10 seconds.

Ramp rate equals 40 degrees Celsius per second. Then, sequentially increase the baseline and peak temperature of each pulse according to the temperature settings table. Present the computerized visual analog scale, CoVAS, to the subject.

And define the anchor points such that zero means no pain and 10 means the worst pain imaginable. Allow the subject to practice moving the lever left and right until comfortable. For the first training trial, instruct the subject to rate only second pain from each single heat pulse, which is defined as a slow burning achy pain that takes place about one second after the heat pulse.

Begin training trial one by replacing the circular thermode with a diameter of 2.9 centimeters on the thenar eminence of the subject, and securing it with an elastic band. Deliver the heat pulses by hitting the start button on the computer. Once the subject rates the second pain of a single pulse as more than two out of 10, press the stop button in the software, and record the baseline and peak temperature of the single pulse that resulted in this rating.

Next, program the rapid pulse train for training trial two. Use the final baseline and peak temperatures determined from the step above. And keep the pulse width at 0.5 seconds.

Decrease the inter-stimulus interval to two seconds and repeat the same pulse 10 times. Inform the subject that they will receive a series of 10 rapid pulses and that they must ignore first pain and only rate second pain continuously. Explain to the subject that second pain may increase, decrease, or remain the same between each pulse.

Begin training trail two by securing the thermode on the thenar eminence of the opposite hand and hitting start on the computer screen. Repeat training trial two until the subject is comfortable rating second pain continuously in response to rapid heat pulses. Next, conduct optimization trials by delivering rapid pulse trains until the subject's second paint rating at P1 is less than 50 on the VAS and their estimated temporal summation or TSE is between 30 and 70 on the VAS.

Achieve optimization by systematically adjusting the baseline and peak temperature of the pulse trains according to the protocol. Take the parameters from the very last trial as the final parameters. Finally, rest for five minutes after the optimization trials.

Then, use the final parameters to deliver another heat pulse train. Have the subject rest for three minutes and then repeat again. Begin by securing the thermode with a diameter of 2.9 centimeters to the thenar eminence of the subject's non-dominant hand and slowly increase the thermode temperature from 32 degrees Celsius at a rate of 0.3 degrees Celsius per second.

Instruct the subject to continuously rate the pain during the heat ramp. Stop whenever the subject reaches thermo tolerance or at 51 degrees Celsius maximum. Then, compute the average temperature where the pain rating is six out of 10 to estimate the Heat-6.

Next, instruct the participant to rest for about five minutes. During this time, construct the cold water bath conditioning stimulus using a clear plastic box with a perforated dividing wall. And filling it with ice and water on one side and just water on the other.

Gently agitate the box. Then insert thermometer to water-only side to ensure temperature is stable at 10 degrees Celsius. Next, secure the thermode to the opposite hand from the previous heat ramp trial, and apply a 30-second stimulus of the initially determined Heat-6.

Instruct the subject to verbally rate the overall pain from the stimulus on a scale from zero to 10 at the end of the 30 seconds. If the rating is less than five or greater than seven, apply a series of 30-second thermal heat stimuli to the subject. Ranging from 44 degrees Celsius to 49 degrees Celsius.

And changing in increments of 0.5 to one degree Celsius until the rating is between five and seven, allowing a 30-second rest between each stimulus. Once the rating is between five and seven, record this pain rating from the final Heat-6 temperature for the computation of the conditional pain modulation. Secure the thermode to the same hand as previously tested and then instruct the subject to rate the pain from the cold water bath at zero, 30, 60, and 90 seconds after immersal.

Then, apply the conditioning stimulus by instructing the subject to submerge the contralateral foot in the cold water bath at 10 degrees Celsius for two minutes. Apply the final Heat-6 temperatures to the same hand again during the last 30 seconds of the cold water bath. At the end of this 30-second heat stimulus which is also the end of the 120-second cold bath, instruct the subject to rate only the pain from the heat stimulus and take his or her foot out of the bath immediately.

Finally, compute CPM by subtracting the pain rating of the final Heat-6 stimulus during the cold bath from that immediately before the cold bath. TS and CPM are shown side by side to reveal patterns of central pain processing changes in patients with lower back pain. The main TS was 2.7 on a scale of 10 while that for CPM was 3.1.

Several pioneer studies have shown that such different profiles of central pain processing may predict different rates of development of chronic pain after surgery, as well as different response rates to specific medications for treating pain. High TS may indicate abnormally augmented ascending facilitation while a low CPM suggest impaired descending inhibition of non-susceptive transmission. For example, subject 10 showed high TS of 7.7 while subject 18 demonstrated an absent CPM at negative 0.5.

After watching this video, you should have a good understanding of how to measure temporal summation and conditioned pain modulation via an individualized approach. Once mastered, this protocol can be completed in one hour if it is performed properly. While attempting this procedure, it's important to remember to train your participants adequately so that they can rate their second pain consistently and accurately throughout the process.

Also remember to switch hands in between each trial, so that way you can minimize any risks. The key component of this protocol is the individual optimization of the thermo-stimulus for both TS and CPM. To truly master this protocol, follow the optimization steps exactly as described.

One step during this procedure that might be modified is the final Heat-6 stimulus during the CPM test. The Heat-6 stimulus might be applied immediately after instead of during the cold water bath. Dissemination of this technique will help advance research and quantitative sensory testing by providing an effective, reliable method to capture TS and CPM in a broad range of individuals particularly in longitudinal studies.