TESTE DE ESTRESSE AO FRIO EM CÃES

Abstract

Thermoregulation is directly related to the autonomic nervous system, thus, the verification of the integrity of this system can be carried out through the evaluation of cutaneous vasoconstriction and vasodilation. In humans, this is done through the cold stress test, in which a specific region of the body (hands or feet) is induced to vasoconstriction by immersion in a cold solution at a specific temperature and, after immersion, the time required for reheating to occur. In addition, the longitudinal thermal gradient allows the monitoring of improvement or worsening of diseases. So far, however, it is not known what the rewarming curve or the longitudinal thermal gradient is like after this test in healthy dogs, which makes it impossible to perform this test in dogs with suspected impairment of the autonomic nervous or vascular system. Thus, the aim of this study was to standardize the cold stress test in healthy dogs. For this, 34 healthy dogs were divided into two groups, males (n=17) and females (n=17). After acclimatization at 23±1ºC for 15 minutes, the pelvic limb was immersed in water (12±1ºC) up to the middle of the metatarsal, so that the entire plantar region was submerged. After 5 minutes, the region was immersed and carefully dried. Thermographic images were taken before immersion, immediately after immersion and every 3 minutes, totaling 30 minutes of evaluation. Heart rate, systolic blood pressure, and rectal and tympanic temperatures were also evaluated, which were collected before, immediately after, and every 10 minutes for 30 minutes. From the analysis of the results, it was verified that there was no statistical difference between males and females in the rewarming curve, longitudinal-distal difference and in the physiological parameters. There was no statistical difference between the tested (29.03.4°C) and control (29.1±3.4°C) limbs at the moment immediately before the test (p>0.9999). Immediately after the test, the tested paw showed a significantly lower temperature (19.9±3.1°C) compared to the contralateral paw (28.8±3.7°C) (p<0.0001), returning to being statistically equal only after the moment 27 minutes (test27min: 28.3±5.1°C; control27min: 31.3±3.8°C). When only the tested paw was analyzed, it was observed that it took 18 minutes for it to return to the temperature statistically equal to the moment before the test (testers: 29.0±4.3°C; test18min: 27.1±4.3°C; p-value = 0.1464) . During the evaluation period, it was verified that, from the moment 3 minutes onwards, the control paw showed a significant increase in temperature in relation to the moment “before” (controlbefore: 29.1±3.4°C; control3min: 31.2±3.3°C; p-value = 0.0002), with this difference remaining until the end of the evaluation period. The longitudinal-distal difference of each digit was constant between all moments, with the highest temperature found being 1.7±0.9°C. There was no statistical difference in the physiological parameters between the “before” moment and the other analyzed moments. The increase in temperature of the non-tested contralateral limb observed in this study also described in studies with humans submitted to the cold stress test, which can be attributed to a systemic reflex mechanism for the reestablishment of peripheral temperature. The non-change in the physiological parameters despite the increase in temperature of the untested extremity shows that the vascular system seems to be earlier to indicate involvement of the central nervous system. This is the first study that standardized the cold stress test in healthy dogs. Further studies with animals with autonomic or vascular alterations must be performed to demonstrate the clinical efficacy of this test in dogs.