Spectral characteristics of heart rate and blood pressure variabilities during head-out water immersion

Abstract

To elucidate the roles of the autonomic nervous system in cardiovascular adaptation to microgravity, spectral analysis of heart rate and blood pressure variabilities were conducted during thermoneutral head-out water immersion in eight healthy young subjects aged 23 to 31 years. In all subjects immersed up to the shoulder, the Low-Frequency (LF: 0.04 to 0.15 Hz) component in blood pressure variability and the ratio of LF power to High-Frequency power (LF/HF ratio) in heart rate variability decreased, while the high-frequency (HF: 0.15 to 0.5 Hz) component of heart rate variability increased. Concomitantly, a decrease in heart rate was observed without significant changes in blood pressure during immersion. These results suggest that cardiac and vasomotor sympathetic nerve activities are suppressed and cardiac parasympathetic (vagal) nerve activity is activated during head-out water immersion.

微少重力への心臓血管系の適応における自律神経系の役割を解明するために、23から31才の健康な青年8名に対して、頭を出してぬるま湯に入り心拍数と血圧の変化のスペクトル解析を行った。肩まで水浸した全員において、血圧変化の低周波数成分(LF:0.04-0.15Hz)と心拍数変化におけるLFパワーの高周波数パワーに対する比(LF/HF比)は減少し、心拍数変化の高周波数(HF:0.15-0.5Hz)成分は増加した。それに伴って、水浸中は血圧の大きな変化無しに心拍数の減少がみられた。これらの結果は、頭を出した水浸において心臓と血管運動自律神経活動が抑制され、心臓の副交換神経(迷走神経)活動が活性化されることを示唆する。