OBJECTIVES: To investigate the cardiovascular autonomic responses to head-out water immersion in thermoneutral water. The effects of immersion levels (neck, chest, navel) and breathing frequencies (4, 6, 10, 15 times/min) were compared with in ambient air and spontaneous breathing as a control. METHODS: Spectral analysis of heart rate variability was recorded in 11 young (mean age 20 +/- 1 years) and 11 elderly (mean age 68 +/- 6 years) healthy male subjects during water immersion. Modeling was employed to estimate the time course of low-frequency (LF) and high-frequency (HF) power and the ratio of LF to HF power of heart rate variability. RESULTS: In the young group, stroke volume and cardiac output during navel level water immersion manifested a much greater increase than during chest and neck level water immersion. Systolic blood pressure and total peripheral resistance decreased significantly in response to water immersion. The elderly group, however, showed lesser attenuation of stroke volume and cardiac output. Ectopic arrhythmias occurred in only the elderly. The elderly group showed significantly lower and higher amplitudes of HF and LF/HF components of heart rate variability due to water immersion and breathing frequency changes. CONCLUSIONS: These findings suggest differential changes in cardiovascular autonomic responses between the young and elderly groups. These changes in integrative cardiovascular autonomic responses may account for the increased risk of ectopic arrhythmias in elderly people during water immersion. Water immersion model could be utilized to know circulatory regulation during bathing.
OBJECTIVES: To investigate the cardiovascular autonomic responses to head-out water immersion in thermoneutral water. The effects of immersion levels (neck, chest, navel) and breathing frequencies (4, 6, 10, 15 times/min) were compared with in ambient air and spontaneous breathing as a control. METHODS: Spectral analysis of heart rate variability was recorded in 11 young (mean age 20 +/- 1 years) and 11 elderly (mean age 68 +/- 6 years) healthy male subjects during water immersion. Modeling was employed to estimate the time course of low-frequency (LF) and high-frequency (HF) power and the ratio of LF to HF power of heart rate variability. RESULTS: In the young group, stroke volume and cardiac output during navel level water immersion manifested a much greater increase than during chest and neck level water immersion. Systolic blood pressure and total peripheral resistance decreased significantly in response to water immersion. The elderly group, however, showed lesser attenuation of stroke volume and cardiac output. Ectopic arrhythmias occurred in only the elderly. The elderly group showed significantly lower and higher amplitudes of HF and LF/HF components of heart rate variability due to water immersion and breathing frequency changes. CONCLUSIONS: These findings suggest differential changes in cardiovascular autonomic responses between the young and elderly groups. These changes in integrative cardiovascular autonomic responses may account for the increased risk of ectopic arrhythmias in elderly people during water immersion. Water immersion model could be utilized to know circulatory regulation during bathing.