Effects of repeated long duration +2Gz load on man's cardiovascular function.
Usefulness of a short-arm human centrifuge is expected when it is used in space as a countermeasure against cardiovascular deconditioning, problem of bone-calcium metabolism, etc. However, nothing is solidly established regarding the most desirable program for artificial G application. Accordingly, this study was designed to analytically evaluate the effects of repeated long duration +Gz load on human cardiovascular function. Recently heart rate spectral analysis has been recognized as a powerful tool for quantitatively evaluating parasympathetic and sympathetic activity separately in human. It is reported that power of the high frequency component (HF-p) is mediated selectively by parasympathetic activity and the power ratio of low to high frequency components(LF/HF) is indicative of cardiac sympathetic activity or cardiac sympathovagal balance. Sequence method is developed to examine spontaneous baroreceptor reflex sensitivity (BRS). We studied cardiovascular control function by using these methods in 9 healthy men before and after 7 days of daily repeated 1hour +2Gz load. When compared with the data of pre-G load period, post-G load period, decrease of HR, increases of HF-p and BRS were statistically significant. SBP, DBP and LF/HF tended to decrease, however, these changes were not statistically significant. This results indicate that repeated +2Gz load increases parasympathetic activity and arterial baroreceptor-cardiac reflex sensitivity. In recent years, many investigators suggest that space flight and head-down bedrest leads to impaired baroreceptor-cardiac reflex responses and decrease of parasympathetic activity, which may contribute to orthostatic intolerance. So our results suggest that daily repeated 1hour +2Gz load would be useful in preventing post-flight orthostatic intolerance.
Iwasaki
K
K
Department of Hygiene and Space Medicine, Nihon University School of Medicine, Tokyo, Japan. kiwasaki@med.nihon-u.ac.jp
Hirayanagi
K I
KI
Sasaki
T
T
Kinoue
T
T
Ito
M
M
Miyamoto
A
A
Igarashi
M
M
Yajima
K
K
D000328:Adult; D000337:Aerospace Medicine; D001341:Autonomic Nervous System; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure; D018493:Cardiovascular Deconditioning / Q000502:physiology; D002346:Carotid Sinus / Q000502:physiology; D002498:Centrifugation; D018470:Gravity, Altered; D006339:Heart Rate; D006801:Humans; D018471:Hypergravity; D007024:Hypotension, Orthostatic / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control*; D008297:Male; D011311:Pressoreceptors / Q000502:physiology; D018544:Weightlessness Countermeasures