Key result
Impaired orthostatic tolerance after 60 days of head-down bed rest could not be distinguished by normal hemodynamic or neurocardiac data, with no significant differences between fainters and nonfainters.
Why the study?
Does the degree of autonomic cardiovascular adaptation relate to orthostatic intolerance after 60 days of head-down bed rest in volunteers?
Observational (n=14)
Does the degree of autonomic cardiovascular adaptation relate to orthostatic intolerance after 60 days of head-down bed rest in volunteers?
Impaired orthostatic tolerance after prolonged head-down bed rest cannot be predicted by standard hemodynamic or neurocardiac adaptation patterns.
Progressive HR rise during HDBR in nonfainters may mark autonomic compensation; leaves open whether it predicts or prevents post-bed-rest orthostatic intolerance.
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.
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Liu et al. (2015) conducted an observational in Orthostatic intolerance (n=14). Head-down bed rest (HDBR) vs. Baseline was evaluated on Circulatory patterns and autonomic cardiovascular adaptation during head-up tilt test. Impaired orthostatic tolerance after 60 days of head-down bed rest could not be distinguished by normal hemodynamic or neurocardiac data, with no significant differences between fainters and nonfainters.
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