title: Orthostatic Intolerance Is Independent of the Degree of Autonomic Cardiovascular Adaptation after 60 Days of Head-Down Bed Rest.
abstract: Spaceflight and head-down bed rest (HDBR) can induce the orthostatic intolerance (OI); the mechanisms remain to be clarified. The aim of this study was to determine whether or not OI after HDBR relates to the degree of autonomic cardiovascular adaptation. Fourteen volunteers were enrolled for 60 days of HDBR. A head-up tilt test (HUTT) was performed before and after HDBR. Our data revealed that, in all nonfainters, there was a progressive increase in heart rate over the course of HDBR, which remained higher until 12 days of recovery. The mean arterial pressure gradually increased until day 56 of HDBR and returned to baseline after 12 days of recovery. Respiratory sinus arrhythmia and baroreflex sensitivity decreased during HDBR and remained suppressed until 12 days of recovery. Low-frequency power of systolic arterial pressure increased during HDBR and remained elevated during recovery. Three subjects fainted during the HUTT after HDBR, in which systemic vascular resistance did not increase and remained lower until syncope. None of the circulatory patterns significantly differed between the fainters and the nonfainters at any time point. In conclusion, our data indicate that the impaired orthostatic tolerance after HDBR could not be distinguished by estimation of normal hemodynamic and/or neurocardiac data.
authors.affiliation: Department of Cardiology, Beijing Friendship Hospital, China Capital Medical University, Beijing 100050, China ; Department of Cardiology, University Hospital Gasthuisberg, KU Leuven, 3000 Leuven, Belgium.
authors.forename: Jiexin
authors.initials: J
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Space Medicine Fundamentals and Application, China Astronaut Research and Training Center, Beijing 100094, China.
authors.forename: Yongzhi
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Cardiology, University Hospital Gasthuisberg, KU Leuven, 3000 Leuven, Belgium.
authors.forename: Bart
authors.initials: B
authors.lastname: Verheyden
authors.affiliation: State Key Laboratory of Space Medicine Fundamentals and Application, China Astronaut Research and Training Center, Beijing 100094, China.
authors.forename: Zhanghuang
authors.initials: Z
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Space Medicine Fundamentals and Application, China Astronaut Research and Training Center, Beijing 100094, China.
authors.forename: Jingyu
authors.initials: J
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Space Medicine Fundamentals and Application, China Astronaut Research and Training Center, Beijing 100094, China.
authors.forename: Yinghui
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Cardiology, University Hospital Gasthuisberg, KU Leuven, 3000 Leuven, Belgium.
authors.forename: André E
authors.initials: AE
authors.lastname: Aubert
authors.affiliation: State Key Laboratory of Space Medicine Fundamentals and Application, China Astronaut Research and Training Center, Beijing 100094, China.
authors.forename: Ming
authors.initials: M
authors.lastname: Yuan
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D001341:Autonomic Nervous System / Q000503:physiopathology*; D017704:Baroreflex / Q000502:physiology; D001510:Bed Rest; D001794:Blood Pressure / Q000502:physiology; D002302:Cardiac Output; D002319:Cardiovascular System / Q000503:physiopathology*; D003971:Diastole / Q000502:physiology; D018475:Head-Down Tilt; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D054971:Orthostatic Intolerance / Q000503:physiopathology*; D065809:Respiratory Sinus Arrhythmia / Q000502:physiology; D013318:Stroke Volume; D013599:Systole / Q000502:physiology; D014655:Vascular Resistance / Q000502:physiology