Monitoring core body temperature continuously with implantable telemetry is clearly the gold standard of thermoregulatory measurements. However it isn't the only parameter that should be considered. There are many other physiologic parameters that can assist researchers in understanding the health of an animal's thermoregulatory system and a few of them have been listed below.
Thermoregulation Indicators and Parameters
Core Body Temperature
This can be measured via telemetry by implanting a temperature telemetry device in the intraperitoneal space. Rectal probes have been used for this measurement in the past and are best used in acute monitoring of anesthetized animals. Core temperature may be averaged over time in most cases, but before averaging, ensure you understand the particular animal's circadian rhythm whether it be daily, weekly, or monthly so you can accurately subtract the normal rhythm to detect a true fever.
Infrared cameras can capture skin temperature gradients in some cases. Fur from the animal may impede the measurement. Peripheral temperature measurements can also be taken by placing a temperature telemetry device subcutaneously or via a hardwired thermistor probe in anesthetized models.
In some animal models, specific localized temperatures may be recorded such as Brown Adipose Tissue (BAT), brain, tail, or other specific organ temperatures. A thermistor at the end of a temperature probe may be required to enable this measurement. DSI offers telemetry products which have external thermistor probes for use in small animals. These are commonly used in neonatal, target organ and metabolic studies looking at quick temperature changes.
Heart rate can be measured to help understand an animal’s cardiac response to their environment. Changes in heart rate may indicate an animal’s thermoregulatory behaviors. Heart rate can be derived from an ECG or systemic blood pressure signal. DSI can accommodate these measurements in the conscious animal model via implantable telemetry, external telemetry, minimally invasive telemetry or acutely in an anesthetized model with hardwired electrodes and pressure catheters.
Physical Motor Activity
Animals exhibit certain behaviors when they are hot or cold in the same way that human beings do. They may burrow, groom, group together, shiver, sweat, and increase or decrease general activity. This can be observed manually by visual observation, but a camera can also be integrated into your software system via video. For nocturnal rodents or for animals that are easily excitable, manual observation may be impossible, so a camera solution may be worth investigating.
Monitoring and recording ambient temperature, pressure and humidity is important for thermoregulatory research. Each degree of variation can change heart rate by 15-20 BPM in mice. Humidity can also play a large factor in an animal's ability to regulate heat.
DSI’s implantable telemetry is typically calibrated over the normal core body temperatures of 33-41 degrees Celsius. If you are challenging an animal's ability to regulate temperature in a hypothermia or related study, several things must be considered including the calibration of the device you are using. Pressure is also temperature dependent and is calibrated at body temperature. If you want to use pressure in a temperature challenge environment ensure you understand the limitations before purchasing. DSI would be happy to answer your questions if you'd like more information on the limitations of products or if you'd like to request custom calibrations.
All measurement equipment needs to be regularly calibrated to be sure it doesn't drift over time. Check the accuracy, precision and resolution of your equipment before designing the study to see what changes you can realistically measure. To calibrate equipment yourself you should have a standard reference thermometer that is at least 10 times more sensitive as the signal you are calibrating. Take the time to understand how often your equipment needs to be calibrated and keep a schedule to ensure the best results.