Effect of heart rate and respiratory rate on thermal infrared-imaging of the horse’s head

Abstract

Summary: The aim of this study was to investigate the influence of heart rate, respiratory rate -which are used among other parameters for evaluating pain -and body core temperature on infrared-imaging of the horse's head. The results should be a base for future studies for dectecting signs of pain in lateral IR-images of the head. Furthermore, an evaluation method was proposed which does not strongly depend on the effects of the named circulatory parameters on infrared (IR)-imaging. For this, lamefree horses without any clinical signs (n = 9) were exercised in a controlled manner on a treadmill. Prior to exercising (measuring time point: MTP1) and after a 10 min walk (MTP2), 5 min slow trot (MTP3) and 5 min fast trot (MTP4) thermographic images of the lateral views of the horse's head were taken and the named physiological parameters recorded as well. The taken IR-images were evaluated, taking into account the anatomical structures of the horse's head so as to define the Regions of Interest (ROIs). Assessment of the change in surface temperature was carried out by calculating unilateral temperature differences (Dϑ) between the maximum temperature (ϑ max ) in the region of the medial angle of the eye (ROI1) or the region of the eye (ROI2) and the average temperatures (ϑ m ) of the remaining ROIs (ROI1, ROI3-6). The ROIs were defined above blood vessels. It was apparent in the course of exercise after MTP3 that some calculated temperature differences were significantly reduced (DϑROI6 and DϑROI5.3). ROI6, the region arteria angularis occuli, showed an instable course (DϑROI6) with a large relative percent range of variation of 36 %. This measuring area is located after the arteria dorsalis nasi has left the end artery of the arteria facialis. In contrast to this ROI4 positioned at the ventral edge of the horse's head rostrally from the muscle masseter (DϑROI4) showed the most stable course, a small relative percent range of variation with 8 % and insignificant (0.8 ≥ p ≥ 0.2) Wilcoxon signed rank (multiple comparison test) over the whole time span among all defined temperature differences during the entire examination period. Further studies for dectecting signs of pain in IR-images of the head seem to be reasonable. (ROIs) zu definieren. Die Beurteilung der Veränderung der Oberflächentemperaturverteilung erfolgte über die Berechnung von unilateralen Temperaturdifferenzen (Dϑ) zwischen der maximalen Temperatur (ϑ max ) im Bereich des medialen Augenwinkels (ROI1) bzw. der Augenregion (ROI2) und den Durchschnittstemperaturen (ϑ m ) der ROIs (ROI1, ROI3-6), die über definierte vaskuläre Bahnen positioniert wurden. Es zeigte sich, dass im Verlauf der Belastung nach MZP3 einige der berechneten Temperaturdifferenzen signifikant kleiner wurden (DϑROI6 und DϑROI5.3). ROI6, die Region arteria angularis occuli, zeigte einen instabilen Verlauf (DϑROI6) mit einer großen relativen Schwankungsbreite von 36 %. Dieser Messbereich befindet sich nach der Abzweigung der arteria dorsalis nasi aus der Endarterie arteria facialis. Di...