Changes in heart rate variability in horses during immersion in warm springwater.
OBJECTIVE
To determine the effects of immersion in warm springwater (38 degrees to 40 degrees C) on autonomic nervous activity in horses.


METHODS
10 male Thoroughbreds.


METHODS
Electrocardiograms were recorded from horses for 15 minutes during a warm springwater bath after being recorded for 15 minutes during stall rest. Variations in heart rate (HR) were evaluated from the power spectrum in terms of low frequency (LF, 0.01 to 0.07 Hz) power and high frequency (HF, 0.07 to 0.6 Hz) power as indices of autonomic nervous activity.


RESULTS
Mean (+/- SE) HR during stall rest and immersion in warm springwater was 31.1 +/- 1.7 and 30.3 +/- 1.0 beat/min, respectively. No significant difference was found between the HR recorded during stall rest and that recorded during immersion in warm springwater. The HF power significantly increased from 1,361 +/- 466 milliseconds2 during stall rest to 2,344 +/- 720 milliseconds2 during immersion in warm springwater. The LF power during stall rest and immersion in warm springwater was 3,847 +/- 663 and 5,120 +/- 1,094 milliseconds2, respectively, and were not significantly different from each other. Similarly, the LF:HF ratio did not change during immersion in warm springwater. The frequency of second-degree atrioventricular block, which was observed in 2 horses, increased during immersion in warm springwater, compared with during stall rest.


CONCLUSIONS
Increases in HF power indicates that the parasympathetic nervous activity in horses increases during immersion in warm springwater. Thus, immersion in warm springwater may provide a means of relaxation for horses.
Kato
Tomohiro
T
Joban Branch, Equine Research Institute, Japan Racing Association, 71 Uenohara, Joban shiratori-machi, Iwaki-shi, Fukushima 972-8325, Japan.
Ohmura
Hajime
H
Hiraga
Atsushi
A
Wada
Shinya
S
Kuwahara
Masayoshi
M
Tsubone
Hirokazu
H
D000818:Animals; D001494:Baths / Q000662:veterinary*; D004562:Electrocardiography / Q000662:veterinary; D006339:Heart Rate / Q000502:physiology*; D006736:Horses / Q000502:physiology*; D045482:Hot Springs