This blog will be dedicated to Temporal Summation (Wind-up) protocols and how it can be produced with our systems. Allow me to start with some background information to familiarize you with the matter. Temporal Summation (TS) is phenomenon in which the patient experiences progressive increase in pain intensity during the repetition of identical nociceptive stimuli.
TS is thought to be a representative summation of C fiber mediated second pain, and can be used to disclose central pain processing abnormalities of many chronic pain disorders. 1, 2, 3 TS protocol can be performed using various painful stimuli, with heat pain being one of the most common ones. Several publications indicate that Temporal Summation can be done using either phasic or tonic heat stimuli.
What is a Phasic TS protocol?
The phasic protocol is the most common protocol used for TS. The noxious heat stimuli in this protocol are delivered at frequency 0.33Hz or higher. The protocol includes a large number of short (0.5-0.7 sec) Ramp & Hold stimuli, with destination temperature that can be fixed or individually set according to the subject’s pain threshold.
In order to minimize the effect the rise time of the temperature may have, it is preferable to select a relatively high baseline temperature that is still comfortable yet not painful (for example 39°C), and to use very rapid destination rate. Usually this protocol is applied using Pathway-CHEPS system, in this case maximum available rate (70°C/sec) is used.
During the application of the stimuli, the subjects are asked to rate their level of pain after some of the stimuli (for example 1st, 5th, 10th and 15th). Pain rating can be performed using CoVAS or pain rating option.
Below is an example of phasic TS test performed, using 20 stimuli raising from baseline temperature of 39°C to 47°C with destination rate of 70°C/sec. The interval between stimuli is 2 sec and the pain rating option is used to rate pain intensity of 1st, 5th, 10th, 15th and 20th stimuli.
What is a Tonic TS protocol?
A protocol implementing tonic heat stimuli includes one long heat stimulus at a constant temperature (for about 60 sec). The temperature can be fixed or individually tailored according to the subjects’ individual pain threshold, as in phasic protocol. The baseline temperature used is usually relatively high and the raise to the destination should be as high as the system allows.
This protocol can easily be applied using the TSA-II or Pathway systems and the Ramp & Hold method. During the administration of stimulus, the subjects are asked to rate their pain level. Use the pain rating option or the CoVAS to chart the subject’s pain sensation during the test.
Although the CoVAS has the advantage of providing continuous pain rating, using numerical pain rating at various points during the test may be easier to manage during post-test analysis and possibly easier for the subject to understand.
In our latest S/W version, you can use the pain rating option to chart the subject’s pain sensation multiple times for every trial. For example, the following heat stimulus was created using a baseline of 39°C, destination temperature of 47°C and duration of 60 sec.
Here I used the pain rating option and selected an interval of 10 sec between ratings.
I would like to leave you, readers, with this recent paper by Staud et al 3 , demonstrating an interesting use of phasic temporal summation on fibromyalgia patients and healthy ones: instead of using one fixed stimuli intensity, the researchers used three wind-up trains of different intensity, and integrated their pain rating into a combined wind-up response function.
When compared to a single wind-up response, the combined response appeared to be more useful in distinguishing between healthy subjects and patients suffering from fibromyalgia.
In this study wind-up function slope of fibromyalgia patients was steeper in comparison to normal controls, indicating abnormality of their central pain sensitivity.
You can find the detailed protocol in the paper referenced below.
I hope you enjoyed reading this blog and found it useful.
If you have any questions, inputs or other suggestions – please comment below or email me at masha@medoc-web.com
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