The authors acknowledge the following funding sources: the Duquesne University Faculty Development Fund grants awarded to Kimberly Szucs, PhD and Alex Kranjec, PhD and to Benedict Kolber, PhD and Matthew Kostek, PhD. We also acknowledge Rachel Sweetnich for experimental assistance and funding from the Duquesne University Pain Undergraduate Research Experience program awarded to Sweetnich (Mentors: Szucs and Kostek).

All tests with human subjects should be approved by the Institutional Review Board at the individual institution. All testing described for the current study was approved by the Duquesne University Institutional Review Board for human subject research. Training for and descriptions of each measure are as follows:
1. Cutaneous Mechanical Sensitivity Assay13
NOTE: Enrolled participants are asked to sit in a chair, with support provided for the extremity to be tested. The assay involves determining the sensitivity threshold for innocuous cutaneous stimulation. Stimulation is provided with standard sensory evaluator von Frey filaments (see the equipment section). These small nylon filaments each apply a single force (ranging from 0.078 mN (0.008 g) to 4.08 mN (1.0 g)).
<ol>
	<li>Before the start of the first experimental trial, allow the participant to feel and manipulate the filaments. Give the filament to the participant and let them gently bend it against the skin of their hand.</li>
	<li>During each trial, ask the subject to look away from their forearm or calf. Apply the filament to the subject&#39;s forearm or calf until it bows, and ask if they feel the filament.</li>
	<li>Starting with the smallest filament (0.078 mN; below the sensory threshold for human detection), conduct five trials on the subject&#39;s forearm or calf for each filament.
	<ol>
		<li>With each filament (e.g., the 0.078 mN filament), apply the filament four times in the &#34;positive&#34; trials.</li>
		<li>For the other trial, do not apply the filament, but still ask the subject if they feel the filament. 
		NOTE: This &#34;negative&#34; trial will be randomly inserted with the four &#34;positive&#34; trials and is designed to test for false responses (i.e., the subject thinks they feel something even though no stimulus is applied). This is necessary for sensory threshold testing, because random noise in the sensory system and/or other stimuli (e.g., a light breeze) can cause a false response.</li>
	</ol>
	</li>
	<li>If a subject detects &#8805;3 of the positive trials and 0 negative trials for a filament, then record that filament as the subject&#39;s &#34;mechanical sensory threshold&#34; on the data form.</li>
	<li>For a single filament, if the subject detects &#60;2 of the real trials and/or &#62;0 of the false trials, then start another round of 5 trials with the next-biggest filament until the sensory threshold is reached. 
	NOTE: Sensory thresholds vary for human participants, but in experience, they typically range from 1.57-9.81 mN (data not shown). This force is enough to feel light innocuous pressure. Typical testing time for each body part (forearm and calf) is about 5 min. It is also possible to measure needle-like pain with these filaments, but this usually entails using larger-diameter filaments.</li>
</ol>
2. Radiant Heat Sensitivity Assay35
NOTE: Enrolled participants are asked to sit in a chair, with support provided for the extremity to be tested. The assay involves determining the sensitivity threshold for non-painful heat change and for painful thermal stimulation. Stimulation is provided with a radiant heat device35. This device uses a focused light beam to slowly heat a subject&#39;s skin through a piece of 0.64-mm-thick safety glass (see below in the instrument section).
<ol>
	<li>Before the start of the training and experimental trials, show the device to the subject; allow them to feel the stimulus with their hand.</li>
	<li>Ask the subject to rest their forearm or calf on the room temperature glass plate, which should be covered with a rubber-insulating sheet except for the small window for stimulus presentation. 
	NOTE: The insulating sheet allows the subject to focus on the stimulus presentation without the cooling sensation associated with placing one&#39;s body against a room-temperature object.</li>
	<li>Using a mirror, position the light source under a marked area on the subject&#39;s forearm or calf (Figure 1). 
	NOTE: When the leg or arm is raised from the surface of the glass, the thermal stimulus automatically stops and the time since the beginning of the trial is then recorded as the &#34;latency to respond.&#34;</li>
	<li>Complete two trials for each test on each limb (innocuous temperature detection and pain threshold) in two distinct marked areas to avoid retesting at a single site.</li>
	<li>For the innocuous temperature detection trial, ask the subject to raise their leg or arm or depress the &#34;stop&#34; button when they feel the temperature change.
	<ol>
		<li>Set the device so that the typical withdrawal threshold occurs at approximately 10 sec into the trial and so that the device shuts off after 20 sec. To accomplish this withdrawal threshold, set the device to ramp the temperature such that the stimulus reaches 47 &#176;C at 10 sec. 
		NOTE: For innocuous temperature detection trials, the typical temperature on the glass at threshold is 37 &#176;C (99 &#176;F). In the pain threshold trial, subjects are told to raise their leg or arm or depress the &#34;stop&#34; button when they feel the stimulus transition from &#34;innocuous warmth or heat&#34; to &#34;painful heat.&#34; The typical temperature on the glass at threshold is ~47 &#176;C (121 &#176;F). The maximum temperature of the trial at the 20 sec cutoff time point is 50 &#176;C, which is well below the cumulative temperature that causes tissue damage in humans36.</li>
	</ol>
	</li>
	<li>Use the constant temperature assay28 (heat block) to evaluate both the quality and unpleasantness of thermal pain. Using the heat block, set the temperature to 45 &#176;C for the stimulus. 
	NOTE: 45 &#176;C is a standard temperature that is the typical minimal stimulus necessary to feel thermal pain and is known to activate TRPV1 nociceptive receptors29.
	<ol>
		<li>Before step 2.7.2, explain the standard 0-10 VAS and show a 10 cm line to the subject. Inform the subject that on the &#34;quality scale,&#34; &#34;0&#34; represents &#34;no pain&#34; and &#34;10&#34; represents &#34;the worst pain imaginable,&#34; and that on the &#34;unpleasantness scale,&#34; &#34;0&#34; represents &#34;not unpleasant&#34; and &#34;10&#34; represents &#34;the most unpleasant sensation imaginable&#34; (Figure 2).</li>
		<li>Apply the stimulus (3 cm x 5 cm heating block) for 3 sec to the marked location on the left forearm or calf (as shown in Figure 1 at the site marked &#34;T&#34;).</li>
		<li>Immediately following the stimulus, ask the subject to evaluate the quality and unpleasantness of the pain using a standard 0-10 VAS.</li>
	</ol>
	</li>
</ol>
3. Pressure Sensitivity Assay13,37
NOTE: Enrolled participants are asked to sit in a chair, with support provided for the extremity to be tested. The assay involves determining the sensitivity threshold for painful pressure stimulation and then determining the quality and unpleasantness of that same pressure in a separate trial. Stimulation is provided with a standard clinical pressure algometer (see below in the instrument section in the Materials and Equipment Table). This device consists of a 2 cm probe connected to a pressure meter.
<ol>
	<li>Before the first training and experimental trial, allow the subject to apply the stimulus to themselves under careful supervision.</li>
	<li>For the pain threshold trial, place the probe on the subject&#39;s forearm or calf and apply pressure gradually.
	<ol>
		<li>Complete two trials each to the forearm and calf at two distinct sites (on each limb) to avoid damage to a single area.</li>
		<li>During a trial, apply pressure gradually, until the stimulus transitions from &#34;innocuous pressure&#34; to &#34;painful pressure&#34;. Ask the subject to say &#34;stop&#34; at this point and remove the stimulus from the subject&#39;s forearm or calf.</li>
		<li>Remove the algometer from the subject. The device automatically records the greatest pressure applied. Record this as the &#34;pressure pain threshold&#34; for the trial.</li>
	</ol>
	</li>
	<li>Inform the subject that the constant pressure trials are next.
	<ol>
		<li>After determining the pressure threshold for the subject, apply an additional trial on the opposite limb to determine the subject&#39;s pain associated with a painful pressure stimulus (in a third testing site). Match the exact stimulus to the subject&#39;s pain threshold determined during the baseline trials (e.g., if baseline trials for the forearm indicated a pressure threshold of 50 N, then the subject will be asked to evaluate the pain of that stimulus).</li>
		<li>In this trial, ask the subject to evaluate the quality and unpleasantness of a pressure stimulus given for 3 sec.</li>
		<li>Use a standard 0-10 VAS. Inform the subject that on the &#34;quality scale,&#34; &#34;0&#34; represents &#34;no pain&#34; and &#34;10&#34; represents &#34;the worst pain imaginable.&#34; On the &#34;unpleasantness scale,&#34; &#34;0&#34; represents &#34;not unpleasant&#34; and &#34;10&#34; represents &#34;the most unpleasant sensation imaginable.&#34;</li>
		<li>During this trial, apply a painful stimulus, and then ask the subject to evaluate that pain (on the two VASs described above).</li>
	</ol>
	</li>
</ol>
4. Reliability Study
NOTE: To examine the reliability of the protocol, we conducted a small study to compare the ratings of subjects between one male and one female examiner.
<ol>
	<li>Recruit participants by posting flyers. Have the interested volunteers who meet the inclusion criteria (Supplemental 1) participate in an orientation session where the study is described and the testing techniques are demonstrated.</li>
	<li>Ask potential volunteers questions and have them read and sign the informed consent documents approved by the University IRB. 
	NOTE: The two examiners for this study were laboratory technicians (one male and one female) who were trained by study investigators who have experience from the clinic and laboratory in pain measurement and management and in neural sensation.</li>
	<li>Test all subjects with two different examiners, with the two examinations 30 min apart.</li>
	<li>To assess inter-rater reliability for this study, calculate intraclass correlation coefficients (model 3,2) [ICC(3,2)] using a two-way mixed analysis of variance (ANOVA) with absolute agreement for each dependent variable (eight total)38. A statistical software can be used for all statistical analyses.</li>
</ol>

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The authors have nothing to disclose.

We have demonstrated cost-effective and simple qualitative and quantitative sensory tests that can be used to assess mechanical sensation, thermal sensation and pain, and pressure pain in human subjects. The value of these assays is their ease of implementation and low amount of necessary training time. Each experimenter received a minimal amount of training (one trial observation and one trial implementation). Thus, multiple technicians could be trained in one day. The results suggest strong inter-experimenter and withi...

Chronic pain conditions are a worldwide clinical problem. More than 1.5 billion people worldwide suffer from chronic pain, and approximately 5% of the global population suffers from neuropathic pain, with incidence rates increasing with age1. In America, it is estimated that pain affects more people than diabetes, heart disease, and cancer, combined2. While awareness of this problem is increasing, treatments are not always successful, can be expensive, and may have serious side effects, including addiction. Research on treatments is ongoing, but as pain varies greatly between individuals, pain measurement for research or diagnosis can be problematic. In particular, the reliance on qualitative approaches, such as the Visual Analog Scale (VAS), for determining treatment efficacy has been problematic because of the subjective and personal nature of pain3. As more research laboratories and smaller clinics around the world answer questions about and treat pain, measures that are accurate, consistent, portable, quantitative, and affordable are in great demand.
A key distinction in pain measurement is acute versus chronic pain. Acute pain is a normal response to injury, infection, or another noxious stimulus. Acute pain normally resolves with treatment and time, and the pain location is usually site-specific. Chronic pain, however, can be related to an initial bout of acute pain, or it can be idiopathic. Chronic pain may relate to the site of injury, but it is often widespread throughout the body4. Chronic pain can last for weeks, months, and even years, causing substantial physical, psychological, and monetary burdens on patients and their families, employers, and societies. The ability to identify and quantify pain is critical for correct diagnosis, evaluation of ongoing treatment, and development of new analgesic treatments. Quantitative and qualitative sensory testing are thus critical for diagnosis and treatment.
Several methods can be used to examine peripheral sensation and pain: nerve conduction velocity (NCV), somatosensory evoked potentials (SEP), skin biopsies, and quantitative sensory testing (QST). Clinicians also routinely use bedside neurologic sensory testing, but this testing is not calibrated and does not use a standardized set of instructions5. Exams of NCV and SEP can be informative, but compared to QST, they require highly specialized equipment, typically only examine large nerve fibers, only measure loss of function, and do not test the entire somatosensory system6,7. Skin biopsies are used to assess nerve fiber density, but compared to QST, they are invasive and require tissue processing and microscopy time, which could take several days to accomplish8. Furthermore, the biopsy only examines a small, specific area of the somatosensory system and does not test nerve function. QST measurements overcome most of the limitations of other testing methods. Recently, standardized normative data for QSTs have been made available, which further add to their utility to assess pain and neural sensation9-11. We therefore focus the current protocol on QST measures for chronic pain.
New technologies have made the assessment of pain and physical sensation (e.g., pressure and heat) precise and reliable within well-equipped laboratories that have established internal protocols12. Many of these technologies, however, are not easily portable and are cost-prohibitive for new or small research laboratories and medical clinics. Additionally, protocols for technology use are not standardized across laboratories13, which can affect reliability. Therefore, the goal of this manuscript is to demonstrate effective and reliable pain and sensory measures that can be conducted with equipment that is available in most clinics or research laboratories. The rationale for the development of the current protocol is that while many people suffer from chronic pain conditions, and accurate assessment of pain is needed for diagnosis and treatment, there are no published protocols with visual demonstrations of assays.
An example of a nearly fully automated device for testing acute pain is the Neuro Sensory Analyzer, which can reliably assess thermal pain sensation, as demonstrated by Angst et al. following a cutaneous burn in human subjects14. The unit is modular, and additional sensory testing devices can be added. In their study, Angst et al. also demonstrate pressure sensory testing with the use of Punctuated Pressure Probes, which were custom built. While these probes should offer more consistent results, few laboratories or clinics have them.
The current protocol demonstrates QST measures for chronic pain: von Frey filaments for cutaneous sensory testing, a radiant (&#34;Hargreaves&#34; method) and contact heat technique, and pressure algometry for deep tissue pain. These QST measurements are not unique. Rather, they are the most common and generally accepted measurements for human sensory testing in medical clinics, hospitals, and research laboratories13,15,16. Mechanical and thermal stimulation are used to examine cutaneous and deep sensation. These measures, furthermore, include the evaluation of both small and large fiber sensitivity for normal sensation and pain. To assess deep tissue pain (muscle), pressure algometry is used, which is the most frequently applied technique for the quantification of pain in soft tissue such as muscles17,18. Both A-delta and C fibers mediate pain induced by pressure stimulation19. Stimulation of both fibers is an advantage and a disadvantage, in that it examines multiple pathways, making it a good overall measure, but it is also less specific. To examine touch sensitivity, mechanical stimulation of skin with von Frey filaments is used because they are one of the most commonly used sensory devices in pain and medical neural clinics. Von Frey filaments stimulate A-beta fibers,20 but are not specific as both low threshold mechanoreceptors and nociceptors can be activated21. The use of these filaments has been criticized, mainly because of potential variability of the application procedure (degree of filament indention or accidental movement of the hand) and concerns that the mechanical filament characteristics may change over time22,23. This protocol addresses these issues by providing detailed instructions with a script and calibration of filaments.
For thermal pain, radiant heat using the &#34;Hargreaves&#34; method (visible light and ramping temperature) and a heat block to examine contact heat are used. Contact and radiant heat activate thermal receptors differently and can even confound one another. It has been shown that dynamic contact can inhibit thermal nociception24. This is similar to the concept of thermal referral, in which touch contributes to normal temperature perception25-27. Therefore, one measure of thermal sensation and two measures of thermal pain are included. First, radiant heat is used to determine the threshold for temperature change detection (starting from room temperature). Second, the radiant heat source is used to determine the threshold for heat pain. The detection of warm thermal change (non-nociceptive) is mediated in part by transient receptor potential (TRP) channels on C fibers, while heat pain is mediated by TRPV1/V2 and other higher-threshold channels on C and A-delta fibers28-30. At threshold determination, rapid skin heating activates first A-delta fibers, corresponding to the &#34;first pain,&#34; followed by a C fiber-mediated &#34;second pain,&#34; described as &#34;throbbing, burning, or swelling&#34;31. Heating gives a preferential activation of C fibers and is the best evaluation of second pain32. In the contact heat assay, a constant nociceptive temperature is applied to determine the qualitative intensity and affective aspects of pain.
Another variable considered in developing the QST protocol is anatomical location. For acute or location-specific pain, the anatomical site of the pain is typically used for testing. Because the protocol was designed with chronic pain conditions in mind, we take a more global approach. The protocol assesses sensation on the forearm and leg instead of the hand, as it has been shown that heat pain thresholds are significantly higher on the hand than on the forearm33 and that thermal nociception can be perceived on the hand, although less frequently and less intensely than on the forearm24. While the protocol was designed for the majority of chronic pain conditions, we caution users that some chronic pain conditions affect specific anatomical regions, and this should be taken into account when modifying the protocol for a specific patient population.
While these QST measures are the most commonly used and are accepted as some of the most reliable, they are inexpensive and common enough that most clinics and research laboratories might already have access to them, can afford them, and can transport them. This QST protocol is useful to any laboratory or clinic where measures are needed for humans with chronic pain. To date, there are currently no published visual reports demonstrating a protocol for the use and reliability of these measures. Based upon this protocol demonstration and tips on improving reliability, a laboratory or clinic could easily examine their own test-retest reliability. Because many clinics will need to utilize several technicians to measure all patients, inter-rater reliability data would be useful in selecting a protocol. We include a small set of data that suggests that the protocol has good reliability, but each clinic and laboratory is strongly advised to use this as an example, as each clinic and each patient population with chronic pain is unique.
Notes on injury risk for sensory and pain testing:
Risk of injury related to cutaneous mechanical testing is extremely rare and unlikely. Mechanical testing is safe and widely used. Risks to the individual are minimal because 1) this is not a painful or noxious stimulus; 2) subjects are instructed that they may stop any procedure at any time, with no adverse consequences; and 3) the level of sensation experienced by subjects is well below their tolerance level and threshold for pain.
Risk of injury related to thermal pain testing is minimal. Thermal testing is safe and widely used. While thermal testing does produce pain, risks to the individual are minimal because 1) the pain is transient in nature and generally subsides immediately after the procedure; 2) subjects are instructed that they may stop any procedure at any time, with no adverse consequences; and 3) the level of pain experienced by subjects is below their tolerance level. With Hargreaves thermal stimulation, there is a very slight risk of receiving a burn, but this is minimized by the following: 1) the positive lockout of stimulus parameters above 50 &#176;C; 2) the built-in shutdown system in the stimulator that prevents the delivery of prolonged or high-intensity stimuli (20 sec); and 3) the electronic thermometer that measures the temperature at the glass surface before and during each use (see below in the instrument section). Pain threshold trials will proceed only if the temperature detected at the 20 sec cutoff is &#8804;50 &#176;C.
Risk of injury related to pressure pain testing is minimal. Pressure testing is safe and widely used. While pressure testing does produce pain, risks to the individual are minimal because 1) the pain is transient in nature and generally subsides immediately after the procedure; 2) subjects are instructed that they may stop any procedure at any time, with no adverse consequences; 3) the level of pain experienced by subjects is below their tolerance level; and 4) the pain applied is never more than that subject&#39;s pain threshold, which is well below any pressure that could cause damage. A rare side effect of pressure testing is bruising at the stimulus site. In this situation, a subject should not be retested at the bruised site. The chance for bruising can be minimized by study exclusion of individuals that bruise easily or are taking blood thinners.
During the enrollment period, participants are given a full description of all sensory and pain measures that will be used. With initial consent, all participants are allowed to experience all sensory and pain measures before full enrollment. All sensory and pain assays are based on well-established assays used in both healthy human participants and in chronic pain patients34. All assays involve either innocuous (non-painful stimuli) or acute noxious stimuli (painful stimuli) that do not damage tissue. The time between different tests is &#62;5 min, to allow the subject to rest and to reduce the potential for sensory fatigue or sensitization. The sequential order of tests is the same during each testing session. Specific sites of testing are limited to the T1 dermatome on the left and right forearms and L3/S2 dermatome on the left and right calves. All sites for testing are marked with a marker, and individual sites are spread out to avoid overlapping receptive field activation (Figure 1). See the Materials and Equipment Table for the full materials list. For retest reliability studies, individual subjects were tested by two experimenters in a single day.

<table><tbody><tr><td>Pressure Algometer/Force Dial</td><td>Wagner Instruments</td><td>FDK 20</td><td>The pressure algometer quantifies pressure pain threshold. It has a rubber tip attachment that is applied to the marked skin site by the investigator. The dial records the pressure and is reset after each measurement.</td></tr><tr><td>von Frey cutaneous stimulators</td><td>Touch Test</td><td>NC1275-01 through -08</td><td>These von Frey filaments are commonly used to examine sensitivity in research and clinical settings. Our set of 8 filaments covers a range of sensitivities. The individual filaments are 1.65 mN, 2.36 mN, 2.44 mN, 2.83 mN, 3.22 mN, 3.61 mN, 3.84 mN, 4.08 mN.</td></tr><tr><td>&quot;Hargreaves&quot; apparatus, testing platform</td><td>Custom</td><td>n/a</td><td>One complete base and four supporting columns are used to form a platform for a sheet of safety glass through which the heat source directs heat to the subjects arm or leg that is resting on the glass. The heat lamp is placed beneath the glass.</td></tr><tr><td>0.64 cm Pyrex safety glass</td><td>DuPont</td><td>n/a</td><td>Safety glass is important to avoid injury in the unlikely event of a fracture in the glass surface.</td></tr><tr><td>Electronic thermometer/thermocouple 53 IIB</td><td>Fluke</td><td>3821062</td><td>The thermocouple is used for thermal testing. The thermocouple is placed on the glass underneath the subject&#039;s arm or leg and measures the temperature at the glass level.</td></tr><tr><td>IITC Plantar Analgesia Meter&amp;nbsp;</td><td>Life Science Inc. Woodland Hills, CA</td><td>390</td><td>This is the heat source and timer for Hargreaves testing. The unit&#039;s heat source has an &amp;ldquo;idle state&amp;rdquo; that allows exact placement of the heat source. The heat source is radiant light and the light beam is focused to the top of the glass to creates a 4 mm x 6 mm intense spot on the arm or leg.</td></tr><tr><td>Examiner script</td><td>Custom</td><td>n/a</td><td>A written script for the examiner is used for every testing session. Because pain and sensitivity can be affected by environmental stresses, we attempt to maintain as much consistency as possible between subjects. The examiner reads directly from the script every time a measure is made to ensure verbal consistency.</td></tr><tr><td>Markers for testing site</td><td>Sharpie</td><td>n/a</td><td>Washable markers may be preferable for situations where multiple days of testing is not necessary</td></tr><tr><td>Constant heat stimulus block</td><td>Benchmark Scientific</td><td>BR10-00</td><td>This block is digitally controlled. The surface of the block is 2 cm x 3 cm.</td></tr></tbody></table>

a protocol of manual tests to measure sensation and pain in humans

Numerous qualitative and quantitative techniques can be used to test sensory nerves and pain in both research and clinical settings. The current study demonstrates a quantitative sensory testing protocol using techniques to measure tactile sensation and pain threshold for pressure and heat using portable and easily accessed equipment. These techniques and equipment are ideal for new laboratories and clinics where cost is a concern or a limiting factor. We demonstrate measurement techniques for the following: cutaneous mechanical sensitivity on the arms and legs (von-Frey filaments), radiant and contact heat sensitivity (with both threshold and qualitative assessments using the Visual Analog Scale (VAS)), and mechanical pressure sensitivity (algometer, with both threshold and the VAS). The techniques and equipment described and demonstrated here can be easily purchased, stored, and transported by most clinics and research laboratories around the world. A limitation of this approach is a lack of automation or computer control. Thus, these processes can be more labor intensive in terms of personnel training and data recording than the more sophisticated equipment. We provide a set of reliability data for the demonstrated techniques. From our description, a new laboratory should be able to set up and run these tests and to develop their own internal reliability data.

&#160;Here, we describe the implementation of cost-effective qualitative and quantitative assays to measure innocuous sensation and pain in human participants using the VAS (Figure 2). The visual representation is important, because accurate and precise results of these examinations are dependent upon correct and consistent protocol execution by the technician. Additionally, it is valuable to know if multiple technicians performing the technique as described can collect r...

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A Protocol of Manual Tests to Measure Sensation and Pain in Humans

The goal of this procedure is to demonstrate a battery of quantitative techniques for sensory and pain measurement in humans. The equipment and techniques described are commonly found in pain clinics or are easy to obtain.

Numerous qualitative and quantitative techniques can be used to test sensory nerves and pain in both research and clinical settings. The current study ...

a-protocol-of-manual-tests-to-measure-sensation-and-pain-in-humans

Universidad de Cartagena UDEC

Research

JoVE Journal

Behavior

20.8K Views.  Duquesne University. The goal of this procedure is to demonstrate a battery of quantitative techniques for sensory and pain measurement in humans. The equipment and techniques described are commonly found in pain clinics or are easy to obtain.

Video: A Protocol of Manual Tests to Measure Sensation and Pain in Humans

Determining Pain Detection and Tolerance Thresholds Using an Integrated, Multi-Modal Pain Task Battery

Human pain models are useful in the assessing the analgesic effect of drugs, providing information about a drug&#39;s pharmacology and identify potentially suitable therapeutic populations. The need to use a comprehensive battery of pain models is highlighted by studies whereby only a single pain model, thought to relate to the clinical situation, demonstrates lack of efficacy. No single experimental model can mimic the complex nature of clinical pain. The integrated, multi-modal pain task&#160;battery presented here encompasses the electrical stimulation task, pressure stimulation task, cold pressor task, the UVB inflammatory model which includes a thermal task and a paradigm for inhibitory conditioned pain modulation. These human pain models have been tested for predicative validity and reliability both in their own right and in combination, and can be used repeatedly, quickly, in short succession, with minimum burden for the subject and with a modest quantity of equipment. This allows a drug to be fully characterized and profiled for analgesic effect which is especially useful for drugs with a novel or untested mechanism of action.

Human pain models are valuable tools used to assess the analgesic potential of novel compounds and predict their clinical efficacy, especially when used in an integrated manner. Although implementation of these models is complex, with proper execution, the pain models described in this protocol can provide predictive and reliable results.

Human pain models are useful in the assessing the analgesic effect of drugs, providing information about a drug&#39;s pharmacology and identify ...

Psychophysically-anchored, Robust Thresholding in Studying Pain-related Lateralization of Oscillatory Prestimulus Activity

In perceptual studies, it is often important to objectively assess the equality of delivered stimulation across participants or to quantify the intra-individual sensation magnitude that is evoked by stimulation over multiple trials. This requires a robust mapping of stimulus magnitude to perceived intensity and is commonly achieved by psychophysical estimation methods such as the staircase procedure. Newer, more efficient procedures like the QUEST algorithm fit a psychophysical function to the data in real time while at the same time maximizing the efficiency of data collection. A robust estimate of the threshold intensity between painful and nonpainful perceptions can then be used to reduce the influence of variations in sensory input in subsequent analyses of oscillatory brain activity. By stimulating at a constant threshold intensity determined by an adaptive estimation procedure, the variance in the ratings can be directly attributed to perceptual processes. Oscillatory activity can then be contrasted between &#34;pain&#34; and &#34;no-pain&#34; trials directly, yielding activity that closely relates to perceptual classification processes in nociception.

Psychophysical methods such as the QUEST estimation procedure can efficiently yield robust estimates of the stimulation intensity at which nonpainful sensations transition into painful sensations. By stimulating repeatedly at the threshold intensity, the variability in rating responses can directly be attributed to perceptual classifications in subsequent analyses.

In perceptual studies, it is often important to objectively assess the equality of delivered stimulation across participants or to quantify the ...

Determining heat and mechanical pain threshold in inflamed skin of human subjects

In a previous article in the Journal of Visualized Experiments we have demonstrated skin microdialysis techniques for the collection of tissue-specific nociceptive and inflammatory biochemicals in humans. In this article we will show pain-testing paradigms that are often used in tandem with microdialysis procedures. Combining pain tests with microdialysis provides the critical link between behavioral and biochemical data that allows identifying key biochemicals responsible for generating and propagating pain.
Two models of evoking pain in inflamed skin of human study participants are shown. The first model evokes pain with aid of heat stimuli. Heat evoked pain as described here is predominantly mediated by small, non-myelinated peripheral nociceptive nerve fibers (C-fibers). The second model evokes pain via punctuated pressure stimuli. Punctuated pressure evoked pain is predominantly mediated by small, myelinated peripheral nociceptive nerve fibers (A-delta fibers). The two models are mechanistically distinct and independently examine nociceptive processing by the two major peripheral nerve fiber populations involved in pain signaling.
Heat pain is evoked with aid of the TSA II, a commercially available thermo-sensory analyzer (Medoc Advanced Medical Systems, Durham, NC). Stimulus configuration and delivery is handled with aid of specific software. Thermodes vary in size and shape but in principle consist of a metal plate that can be heated or cooled at various rates and for different periods of time. Algorithms assessing heat-evoked pain are manifold. In the experiments shown here, study participants are asked to indicate at what point they start experiencing pain while the thermode in contact with skin is heated at a predetermined rate starting at a temperature that does not evoke pain. The thermode temperature at which a subject starts experiencing pain constitutes the heat pain threshold.
Mechanical pain is evoked with punctuated probes. Such probes are commercially available from several manufacturers (von Frey hairs). However, the accuracy of von Frey hairs has been criticized and many investigators use custom made punctuated pressure probes. In the experiments shown here eight custom-made punctuated probes of different weights are applied in consecutive order, a procedure called up-down algorithm, to identify perceptional deflection points, i.e., a change from feeling no pain to feeling pain or vice versa. The average weight causing a perceptional deflection constitutes the mechanical pain threshold.

Algorithms assessing heat and mechanical pain thresholds in experimentally inflamed skin of human study subjects are shown. The two pain testing paradigms independently examine nociceptive processing by the two major peripheral nerve fiber populations transmitting pain, i.e., non-myelinated C fibers and small myelinated A-delta fibers.

In a previous article in the Journal of Visualized Experiments we have demonstrated skin microdialysis techniques for the collection of tissue-specific ...

Biology

Multi-Modal Signals for Analyzing Pain Responses to Thermal and Electrical Stimuli

The assessment of pain relies mostly on methods that require a person to communicate. However, for people with cognitive and verbal impairments, existing methods are not sufficient as they lack reliability and validity. To approach this problem, recent research focuses on an objective pain assessment facilitated by parameters of responses derived from physiology, and video and audio signals. To develop reliable automated pain recognition systems, efforts have been made in creating multimodal databases in order to analyze pain and detect valid pain patterns. While the results are promising, they only focus on discriminating pain or pain intensities versus no pain. In order to advance this, research should also consider the quality and duration of pain as they provide additional valuable information for more advanced pain management. To complement existing databases and the analysis of pain regarding quality and length, this paper proposes a psychophysiological experiment to elicit, measure, and collect valid pain reactions. Participants are subjected to painful stimuli that differ in intensity (low, medium, and high), duration (5 s / 1 min), and modality (heat / electric pain) while audio, video (e.g., facial expressions, body gestures, facial skin temperature), and physiological signals (e.g., electrocardiogram [ECG], skin conductance level [SCL], facial electromyography [EMG], and EMG of M. trapezius) are being recorded. The study consists of a calibration phase to determine a subject&#8217;s individual pain range (from low to intolerable pain) and a stimulation phase in which pain stimuli, depending on the calibrated range, are applied. The obtained data may allow refining, improving, and evaluating automated recognition systems in terms of an objective pain assessment. For further development of such systems and to investigate pain reactions in more detail, additional pain modalities such as pressure, chemical, or cold pain should be included in future studies. Recorded data of this study will be released as the &#8220;X-ITE Pain Database&#8221;.

This article focuses on the experimental elicitation of pain through heat (thermal) and electrical stimulation while recording physiological, visual, and paralinguistic responses. It aims at collecting valid multimodal data for analyzing pain based on its intensity, quality, and duration.&#160;

The assessment of pain relies mostly on methods that require a person to communicate. However, for people with cognitive and verbal impairments, existing ...

Measuring Changes in Tactile Sensitivity in the Hind Paw of Mice Using an Electronic von Frey Apparatus

Measuring inflammation-induced changes in thresholds of hind paw withdrawal from mechanical pressure is a useful technique to assess changes in pain perception in rodents. Withdrawal thresholds can be measured first at baseline and then following drug, venom, injury, allergen,&#160;or otherwise evoked inflammation by applying an accurate force on very specific areas of the skin. An electronic von Frey apparatus allows precise assessment of mouse hind paw withdrawal thresholds that are not limited by the available filament sizes in contrast to classical von Frey measurements. The ease and rapidity of measurements allow for incorporation of assessment of tactile sensitivity outcomes in diverse models of rapid-onset inflammatory and neuropathic pain as multiple measurements can be taken within a short time period. Experimental measurements for individual rodent subjects can be internally controlled against individual baseline responses and exclusion criteria easily established to standardize baseline responses within and across experimental groups. Thus, measurements using an electronic von Frey apparatus represent a useful modification of the well-established classical von Frey filament-based assays for rodent mechanical allodynia that may also be applied to other nonhuman mammalian models.

Electronic von Frey measurements are an effective and improved alternative to classical von Frey filaments, as they allow rapid and precise measurement of changes in rodent mechanical withdrawal thresholds to continuously applied pressure stimuli before and after an inflammatory event.

Measuring inflammation-induced changes in thresholds of hind paw withdrawal from mechanical pressure is a useful technique to assess changes in pain ...

Neuroscience

Back Mechanical Sensitivity Assessment in the Rat for Mechanistic Investigation of Chronic Back Pain

Low back pain is the leading cause of disability worldwide, with dramatic personal, economic, and social consequences. To develop novel therapeutics, animal models are needed to examine the mechanisms and effectiveness of novel therapies from a translational perspective. Several rodent models of back pain are used in current investigations. Surprisingly, however, no standardized behavioral test was validated to assess mechanical sensitivity in back pain models. This is critical to confirm that animals with presumed back pain present local hypersensitivity to nociceptive stimuli, and to monitor sensitivity during interventions designed to relieve back pain. The objective of this study is to lay down a simple and accessible test to assess mechanical sensitivity in the back of rats. A test cage was fabricated specifically for this method; length x width x height: 50 x 20 x 7 cm, having a stainless-steel mesh on the top. This test cage allows the application of mechanical stimuli to the back. To perform the test, the back of the animal is shaved in the region of interest, and the test area is marked to repeat the test on different days, as needed. The mechanical threshold is determined with Von Frey filaments applied to the paraspinal muscles, utilizing the up-down method described previously. The positive responses include (1) muscle twitching, (2) arching (back extension), (3) rotation of the neck (4) scratching or licking the back, and (5) escaping. This behavioral test (Back Mechanical Sensitivity (BMS) test) is useful for mechanistic research with rodent models of back pain for the development of therapeutic interventions for the prevention and management of back pain.

To develop novel therapeutic interventions for the prevention and management of back pain, animal models are required to examine the mechanisms and effectiveness of these therapies from a translational perspective. The present protocol describes the BMS test, a standardized method to assess back mechanical sensitivity in the rat.

Low back pain is the leading cause of disability worldwide, with dramatic personal, economic, and social consequences. To develop novel therapeutics, ...

Assessment of Nerve Injury-Induced Mechanical Hypersensitivity in Rats Using an Orofacial Operant Pain Assay

Pain has sensory and affective components. Unlike traditional, reflex-based pain assays, operant pain assays can produce more clinically relevant results by addressing the cognitive and motivational aspects of pain in rodents. This paper presents a protocol for assessing mechanical hypersensitivity following chronic constriction injury of the infraorbital nerves (CCI-ION) in rats using an orofacial operant pain system. Before CCI-ION surgery, rats were trained in an orofacial pain assessment device (OPAD) to drink sweetened condensed milk while making facial contact with the metal spiked bars and lick-tube.
In this assay, rats can choose between receiving milk as a positive reinforcer or escaping an aversive mechanical stimulus that is produced by a vertical row of small pyramid-shaped spikes on each side of the reward access hole. Following 2 weeks of training in the OPAD and before the CCI-ION surgery, baseline mechanical sensitivity data were recorded for 5 days for each rat during a 10 min testing session. During a session, the operant system automatically records the number of reward bottle activations (licks) and facial contacts, contact duration, and latency to the first lick, among other measures.
Following baseline measurements, rats underwent either CCI-ION or sham surgery. In this protocol, mechanical hypersensitivity was quantified by measuring the number of licks, latency to the first lick, the number of contacts, and the ratio of licks to facial contacts (L/F). The data showed that CCI-ION resulted in a significant decrease in the number of licks and the L/F ratio and an increase in the latency to the first lick, indicating mechanical hypersensitivity. These data support the use of operant-based pain assays to assess mechanical pain sensitivity in preclinical pain research.

This protocol describes the assessment of mechanical hypersensitivity in a rat model of neuropathic orofacial pain using an operant-based orofacial pain assessment device.

Pain has sensory and affective components. Unlike traditional, reflex-based pain assays, operant pain assays can produce more clinically relevant results ...

Dynamic Quantitative Sensory Testing to Characterize Central Pain Processing

Central facilitation and modulation of incoming nociceptive signals play an important role in the perception of pain. Disruption in central pain processing is present in many chronic pain conditions and can influence responses to specific therapies. Thus, the ability to precisely describe the state of central pain processing has profound clinical significance in both prognosis and prediction. Because it is not practical to record neuronal firings directly in the human spinal cord, surrogate behavior tests become an important tool to assess the state of central pain processing. Dynamic QST is one such test, and can probe both the ascending facilitation and descending modulation of incoming nociceptive signals via TS and CPM, respectively. Due to the large between-individual variability in the sensitivity to noxious signals, standardized TS and CPM tests may not yield any meaningful data in up to 50% of the population due to floor or ceiling effects. We present methodologies to individualize TS and CPM so we can capture these measures in a broader range of individuals than previously possible. We have used these methods successfully in several studies at the lab, and data from one ongoing study will be presented to demonstrate feasibility and potential applications of the methods.

By assessing pain in response to repetitive or different types of standardized stimuli, dynamic quantitative sensory testing (QST) can reveal changes in the central processing of pain. We present methods to optimize and individualize two dynamic QST measures: temporal summation (TS) and conditioned pain modulation (CPM).

Central facilitation and modulation of incoming nociceptive signals play an important role in the perception of pain. Disruption in central pain ...

A Quantitative Sensory Testing Paradigm to Obtain Measures of Pain Processing in Patients Undergoing Breast Cancer Surgery

Chronic pain following surgery, persistent postsurgical pain, is an important highly prevalent condition contributing to significant symptom burden and lower quality of life. Persistent postsurgical pain is relatively refractory to treatment hence generating a high need for preventive strategies and treatments. Therefore, the identification of patients at risk of developing persistent pain is an area of active ongoing research. Recently it was demonstrated that peri-operative disruptions in central pain processing may be able to predict persistent postsurgical pain at long term follow-up in breast cancer patients. The aim of the current report is to present a short protocol to obtain pain thresholds to different stimuli at multiple sites and a measure of endogenous analgesia in breast cancer patients. We have used this method successfully in a clinical context and detail some representative results from a clinical study.

Persistent postsurgical pain may be related to changes in pain processing. By assessing pain in response to standardized stimuli, changes in pain processing can be elucidated. We present methods to obtain pain thresholds to different stimuli and a measure of endogenous analgesia in patients undergoing breast cancer surgery.

Chronic pain following surgery, persistent postsurgical pain, is an important highly prevalent condition contributing to significant symptom burden and ...

Medicine

Assessment of Sensory Thresholds in Dogs Using Mechanical and Hot Thermal Quantitative Sensory Testing

Quantitative sensory testing (QST) is used to evaluate the function of the somatosensory system in dogs by assessing the response to applied mechanical and thermal stimuli. QST is used to determine normal dogs&#39; sensory thresholds and evaluate alterations in peripheral and central sensory pathways caused by various disease states, including osteoarthritis, spinal cord injury, and cranial cruciate ligament rupture. Mechanical sensory thresholds are measured by electronic von Frey anesthesiometers and pressure algometers. They are determined as the force at which the dog exhibits a response indicating conscious stimulus perception. Hot thermal sensory thresholds are the latency to respond to a fixed or ramped temperature stimulus applied by a contact thermode.
Following a consistent protocol for performing QST and paying attention to details of the testing environment, procedure, and individual study subjects are critical for obtaining accurate QST results for dogs. Protocols for the standardized collection of QST data in dogs have not been described in detail. QST should be performed in a quiet, distraction-free environment that is comfortable for the dog, the QST operator, and the handler. Ensuring that the dog is calm, relaxed, and properly positioned for each measurement helps produce reliable, consistent responses to the stimuli and makes the testing process more manageable. The QST operator and handler should be familiar and comfortable with handling dogs and interpreting dogs&#39; behavioral responses to potentially painful stimuli to determine the endpoint of testing, reduce stress, and maintain safety during the testing process.

This work describes a standard protocol for mechanical and hot thermal quantitative sensory testing to evaluate the somatosensory system in dogs. Sensory thresholds are measured using an electronic von Frey anesthesiometer, pressure algometer, and hot contact thermode.

Quantitative sensory testing (QST) is used to evaluate the function of the somatosensory system in dogs by assessing the response to applied mechanical ...