Effect of Not-Spring Bathing on Equine Electrocardiographic Parameters

Abstract

Electrocardiographic studies were conducted on 6 horses subjected to partial immersion in a hot spring. These horses had been accustomed to entering the bath. They were held in a bath at 38-40°C for 30 minutes, at 40-43°C for 1 hour, and at 43-45°C for 30 minutes in experiments 1, 2, and 3, respectively. Bipolar electrocardiograms (from the apexbase lead) were recorded before bathing, immediately after, and 30 minutes after the end of bathing, as well as during bathing. In experiment 1, the heart rate remained unchanged or decreased slightly during bathing. It increased slightly immediately after bathing probably due to a slight exertion associated with getting out of the tub. In experiments 2 and 3, the heart rate increased progressively to sinus tachycardia over the period of bathing. It decreased immediately after the end of bathing. These results suggest that the bathing in hot water may be more effective in causing cardiac acceleration than the exertion associated with getting out of the tub. Before bathing, the T-wave had a diphasic (negative-positive) configuration. Immediately after bathing in experiment 1, the negative component decreased and the positive component increased slightly in amplitude. During the corresponding period in experiments 2 and 3, the T-wave became monophasic and positive, with an amplitude 2 to 3 times as high as that during the pre-bathing period. In experiment 1, a second-degree A-V block was observed in 2 horses during bathing . In experiments 2 and 3, the A-V block which had been observed before bathing, disappeared during bathing. From the presence of slight bradycardia and A-V block in experiment 1, it is suggested that the water temperature of 38-40°C may induce vagotonia. The occurrence of tachycardia and the disappearance of A-V block in experiments 2 and 3 may suggest that the water temperature of 40-45°C induces sympatheticotonia and reduction of vagal tone. The practice for race horses to bathe in water at 38-40°C for 2034 minutes at the hotspring sanitarium may cause vagotonia on account of its soothing effect on the horse. A water temperature of 40-45°C seemed to have no adverse effect on normal horses. Care should be teken, however, in bathing a horse in water at this temperature, if the horse is suspected to have an abnormality in the cardiac function.