The overall goal of this data collection procedure is to measure pressure and heat pain thresholds as well as tactile sensation in humans. These sensory measures include both quantitative measures of sensation as well as qualitative measures that help asses individuals sensory and emotional experience during testing. This method can help answer key questions in the Study of Chronic Pain Conditions by providing concrete data points to evaluate the efficacy of various therapies in the context of pain.
The main advantages of these techniques are that they're easy to implement and offer reliability between experimentaters. The equipment is easily purchased, stored, and transported by most clinics and research laboratories around the world. Individuals will struggle with these methods because small changes in the time of stimulus application, placement of stimulus application, and/or application pressure can introduce significant variability in the data set.
Application procedures of these tests are seemingly subjective, which can lead to inconsistent results. Visual demonstration is therefore critical to ensure accuracy and precision across multiple tests, multiple technicians, and multiple patients. Escort the subject into the testing room and have them sit on an exam table that provides arm support.
Give the filament to the subject and let them gently bend it against the skin of their hand. During each trial, ask the subject to look away from their forearm. Start by applying the smallest filament at 0.078 millinewtons to the subject's forearm until it boes and ask if they feel the filament.
Complete four positive trials where the filament is applied to the forearm, and one randomized negative trial where the filament is not applied, but the subject is still asked if they feel the filament. Finally, score the trials on the data form, such that if a subject detects greater than three of the positive trials, and zero of the negative trials for a filament, record that filament as the subject's mechanical sensory threshold. For a single filament, if the subject detects less than two of the positive trials, and or greater than zero of the negative trials, then start another round of five trials with the next biggest filament until the sensory threshold is reached.
Begin by showing the radiant heat device to the subject and allowing them to feel the stimulus with their hand. Next, ask the subject to rest their forearm on the room temperature glass plate, which is covered with a rubber insulating sheet except for the small opening for stimulus presentation. Use a mirror to position the light source under a marked area on the subjects forearm.
Then, for each trial, ask the subject to depress the stop button when they feel the temperature change. To achieve the withdraw threshold, set the device to ramp up the temperature so that the stimulus temperature reaches 47 degrees Celsius at 10 seconds. Begin by showing the constant heat block to the subject and allowing them to feel the stimulus with their hand.
Next, apply the stimulus for three seconds to the marked location on the left forearm. Finally, immediately following the stimulus, ask the subject to evaluate the quality and unpleasantness of the pain using a standard zero to 10 visual analog scale. Before starting the experimental trial, allow the subject to handle the algometer, and apply the stimulus to themselves under careful supervision.
Complete a pain threshold trial by placing the probe on the subject's forearm and gradually applying pressure until the stimulus transitions from innocuous pressure to painful pressure. Ask the subject to say stop when they want the stimulus removed from their forearm. Complete two trials to the forearm in two distinct sights on the right and left arm to avoid damage to a single area.
Then, remove the algometer from the subject. Record the greatest applied pressure as the pressure pain threshold for the trial. Finally, to complete a constant pressure trial, apply a painful stimulus for three seconds and ask the subject to evaluate the quality and unpleasantness of the pain on two standard, zero to 10 visual analogue scales.
Inform the subject that on the quality scale, zero is represented as no pain, and 10 is represented as the worst pain imaginable. On the unpleasantness scale, zero is represented as not unpleasant, and 10 is represented as the most unpleasant sensation imaginable. This intra-class correlation coefficient analysis examines the reliability between two examiners, male and female.
Inter-experiment reliability was strong for mechanical, thermal, and pressure testing. Such that average inter-experiment reliability measures were all statistically significant except for the mechanical sensitivity test. In addition, all visual analogue scale results for constant heat and constant pressure, showed significant correlations between the male and female experimenters.
Once mastered, these techniques can be completed in 30 minutes if performed properly. While attempting these procedures, it's important to remember to remain as consistent as possible when applying stimuli to the subject's testing areas. This is especially important for application of the Von Frey filament for cutaneous mechanical sensitivity, and the algometer for pressure sensitivity.
Following these procedures, other methods that evaluate cold hypersensitivity and mechanical pain, can be performed in order to answer additional questions related to other sensory modalities that are altered in the context of pain. Quantitative sensory testing is regularly applied in pre-clinical, and clinical testing. When combined with traditional qualitative measures, the entire procedure provides a valuable snapshot of an individuals sensory and emotional experience to noxious stimuli.
After watching this video, you should have a good understanding of how to measure quantitative and qualitative sensation and pain in humans. This includes tactile sensation and pain threshold for pressure and heat, as well as VAS qualitative assessments. Don't forget that working with noxious stimuli in human subjects can be hazardous, and precautions should always be taken when performing this procedure.
