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

This protocol for assessing sensory thresholds in dogs using quantitative sensory testing or QST will help standardize studies allowing for valuable comparisons across different studies. This technique provides a noninvasive method to measure sensory thresholds in dogs. Our protocol helps guide researchers on best practices to obtain accurate and consistent data.

This protocol can provide insight into mechanisms of pain sensation in dogs, including following surgeries and for diseases associated with chronic pain states. The most important aspect of this technique is being cognizant of canine behavior. To ensure safe, accurate testing, all involved must be mindful of the dog's behavior and anxiety levels.

Start with arranging the instrument setup by gently applying a rigid 0.9 millimeter Von Frey tip to the load cell, ensuring that the load cell is securely screwed into the handpiece. Then connect the cord from the handpiece to the recording device through the M0 channel. Next, turn on the recording device and press the max button to record and display the maximum force achieved when the dog responds to the applied stimulus.

Zero the instrument by pressing the CLR button. To collect the data and measure thresholds, instruct the dog to lay down and then help the dog to the lateral recumbency position. Apply minimal to moderate restraint to maintain the dog in the position and relatively still.

Provide gentle manual support to the limb of the dog being tested to keep the limb off the floor and provide a stable backing to apply force against while not preventing the dog from withdrawing the limb. Once the dog is calm and relaxed, with the limb being tested at 70%extension, apply the stimulus once. Place the Von Frey tip perpendicular to the skin of the area being tested.

If the dog exhibits reflex movements from the sensation of the Von Frey tip on the skin, allow the dog to relax the limb again before reapplying the Von Frey tip. When the skin does not cause reflex movements, take a measurement by applying the Von Frey tip. Apply steadily increasing force with the Von Frey tip at 20 grams per second until the dog withdraws the limb, vocalizes.

turns to look at the stimulus, or exhibits other movements or behavioral responses indicating the conscious perception of the stimulus. Remove the stimulus when the dog withdraws the limb or the maximum force is reached and record the maximum force applied that is displayed on the recording device. Repeat the measurements for five trials, allowing one minute between each measurement with the dog in lateral recumbency if they remain relatively calm and relaxed with no or minimal restraint.

Zero the instrument between each step by pressing the CLR button. Next, record a feasibility score of zero to five to indicate the ease of data collection. Give the dog a break of five minutes before starting measurements with the blunt probed pressure algometer.

While setting up the instrument, ensure the small blunt probe is securely screwed into the device. Then turn on the recording device and press the max button to continue when prompted on the screen. Press the unit button until the unit is displayed as grams at the top of the screen and push the zero button to zero the instrument.

Next, place and prepare the dog in lateral recumbency to measure the thresholds as mentioned before. Apply the blunt probe perpendicular to the skin of the area being tested to apply a steadily increasing force with the probe at 20 grams per second until the dog exhibits behavioral responses that indicate the conscious perception of the stimulus. Remove the stimulus when the dog withdraws the limb or the maximum force is reached.

After recording the maximum applied force from the recording device, repeat the measurements for a total of five trials. Allow the dog to remain in lateral recumbency to sit, stand, or move about the QST room to maintain comfort during the inter-trial interval. Then replace the dog in lateral recumbency before the subsequent measurement.

Record a feasibility score of zero to five to indicate the ease with which the data was collected. Give the dog a break of five minutes before starting measurements with the hot thermal probe. Before starting the experiment, prepare the dog as explained before.

Then apply the thermode to the skin of the area being tested and click on the start button in the lower left-hand corner of the test tab to start the test. When the dog exhibits movements or behavioral responses that indicate the conscious perception of the stimulus or when the maximum latency is reached, remove the thermode while simultaneously stopping the stopwatch. Record the latency to withdraw.

Repeat the measurements for a total of five trials by first clicking the stop button and then clicking the pre-test button in between each measurement to stop heating the thermode. This will allow the software to recalibrate the thermode to prepare for the next application. Record a feasibility score of zero to five to indicate the ease with which the data was collected.

The representative analysis summarizes the mechanical and hot thermal QST data from a group of healthy pain-free dogs. The data from the electronic Von Frey aesthesiometer sensory threshold measurements displayed no significant effect of body weights on the sensory thresholds. A similar impact of the body weights was noticed in the data from blunt probed pressure algometer sensory thresholds.

On the other hand, the data collected for the hot thermal probe sensory latency showed a significant effect of the body weight on the sensory latency. The overall average, standard deviation, and range of sensory thresholds for the mechanical and hot thermal QST were summarized in the same group of healthy pain-free dogs. This provides reference values for future researchers using these techniques It is most important to reliably identify the dog's behavioral response that indicates the conscious perception of the stimulus which may look different for different dogs.

In addition to quantitative sensory testing, collecting behavioral information through validated owner questionnaires and emotional reactivity tests can help provide a comprehensive assessment of the dog's affective state.