Heart Rate Variability Parameters to Evaluate Autonomic Functions in Healthy Young Subjects during Short-Term “Dry” Immersion

Abstract

There is a gap in the current knowledge on the immediate mechanisms of cardiovascular regulation in human subjects within short-term exposure to modeled microgravity using “dry” immersion. Aim. The purpose of the study was to evaluate cardiovascular responses in young healthy subjects during a 45 min session with the help of linear and nonlinear heart rate variability and hemodynamics parameters. The research voluntarily enrolled 33 subjects (18 men, 15 women) aged 19–23 years old. Results. The study showed that systolic and diastolic blood pressure was quite stable, some time-domain parameters of heart rate variability (SDNN, RMSSD, pNN50, etc.) and the frequency-domain (TP, HF, LF, but not VLF) have significantly increased within a 45 min “dry” immersion session. Of the non-linear parameters of heart rate variability, only ApEn significantly decreased during the “dry” immersion session. Conclusion. Our results suggest that a short-term 45 min DI session provokes in young healthy subjects neurogenic autonomic reaction based on the baroreceptor reflex. This provides stable hemodynamics in these subjects along the “dry” immersion session.

Cerebral Circulation and Brain Temperature during an Ultra-Short Session of Dry Immersion in Young Subjects

“…The study group was formed in accordance with previously published criteria for safe use under the conditions of DI [ 13 , 14 ]. Volunteers were invited to participate in the study, and the purpose of the study and the methods used were explained to them.…”

“…Volunteers were invited to participate in the study, and the purpose of the study and the methods used were explained to them. The subjects who accepted the invitation were then checked for the exclusion criteria (chronic diseases including, for example, arterial hyper- or hypotension, thrombophlebitis, acute inflammatory diseases, a history of traumatic brain injury, and cardiac arrhythmia) [ 13 , 14 , 15 ]. In addition, some basic examinations were conducted (body temperature and blood pressure (BP), heart rate (HR), body weight, height).…”

“…Prior the DI session, all subjects underwent an active orthostatic tolerance test [ 13 , 14 , 28 ]. The cardiovascular reactivity during this test indicates the baroreflex sensitivity [ 13 , 14 , 28 ].…”

“…Several studies are found in the field of the early (hours) effects of DI on the organism [ 11 , 12 ]. Only a few studies present data on the effect of an ultra-short DI session (less than one hour) on the cardiovascular [ 13 , 14 ] or neuromuscular systems [ 15 ].…”

“…It seems important to study cerebral circulation in such shorter DI sessions because shorter space flights (within one hour) are increasingly planned and even taking place due to space tourism industry development. In addition, ultra-short DI sessions are already applied for rehabilitation purposes in neurology and sport medicine [ 4 , 13 , 14 , 15 ].…”