Warm Springwater Immersion

Immersion of the body in natural springwater has been studied extensively in humans and dogs for its healing effects. The theory behind immersion is its ability to temporarily suppress the sympathetic nervous system (SNS, the part of the nervous system responsible for the "fight or flight" response) and enhance the parasympathetic nervous system (PNS, the part of the nervous system responsible for the "rest and restore" response), inducing relaxation.

The Joban Branch of the Equine Research Institute of the Japan Racing Association in Fukushima has been using springwater immersion to treat chronic bone and tendon injuries in racehorses for more than three decades. Thus, Hajime Ohmura, DVM, PhD, and colleagues conducted a study to evaluate the effects of springwater immersion on the autonomic nervous system of horses. SNS and PNS activity were quantitatively measured using power spectral analysis of heart rate variability.

Thoroughbred racehorses with chronic injuries were test subjects. Electrocardiogram (ECG) data were collected for 15 minutes with horses at rest, then for 15 minutes during springwater immersion. In other studies, prolonged periods of immersion were reported to cause respiratory tract disease thought to be related to increased external pressure of water on the chest cavity. Ohmura explains, "Increasing extrathoracic (outside the chest) pressure by immersing horses to the neck can result in changes in lung volumes and mechanics that may lead to pulmonary disease." Horses in this study were immersed only up to the elbow while warm springwater (38-40ºC) was showered over the back. Respiratory disease was unlikely following the short immersion period used in this study, Ohmura admits, "but increased extrathoracic pressure (during complete submersion) could still have restricted breathing and interfered with relaxation." After collection of ECG data, power spectral heart rate variability was analyzed. In simple terms, this method measures relative autonomic nervous system "tone." The high frequency power range (HF) primarily reflects PNS activity, while low frequency power range (LF) reflects both PNS and SNS activity.

The HF significantly increased from stall rest to springwater immersion. In contrast, there was no significant increase in LF. This suggests that PNS activity predominated during springwater immersion. "The increase in PNS activity and relaxation helps promote healing by improving circulation in peripheral tissue," explains Ohmura, "and the hydrostatic pressure of water around the horse reinforces this effect."

Ohmura is currently examining why cardiovascular function in horses changes so much with race training with little accompanying change in respiratory function.

Kato, T.; Ohmura, H.; Hiraga, A. American Journal of Veterinary Research, 64 (12): 1482-1485, 2003.

About the Author

Susan Piscopo, DVM, PhD

Susan Piscopo, DVM, PhD, is a free-lance writer in the biomedical sciences. She practiced veterinary medicine in North Carolina before accepting a fellowship to pursue a PhD in physiology at North Carolina State University. She lives in northern New Jersey with her husband and two sons.

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