Key result
21-day head-down bed rest impairs baroreflex regulation, decreasing heart rate and blood pressure variability.
Why the study?
Impairments in baroreflex regulation during microgravity and simulated microgravity have shown contradictory autonomic mechanisms, necessitating further analysis of autonomic disturbances during simulated microgravity.
Does a 21-day head-down bed rest protocol impair baroreflex regulation and cardiorespiratory autonomic function in humans?
Does a 21-day head-down bed rest protocol impair baroreflex regulation and cardiorespiratory autonomic function in humans?
A 21-day head-down bed rest protocol induces an imbalance in baroreflex regulation, likely related to reduced parasympathetic influence and impaired sympathetic stimulation of vascular tone.
Suggests autonomic shifts during prolonged bedrest; hypothesis-generating for microgravity baroreflex effects, should not yet alter practice.
In response to changes in environmental conditions, particularly exposure to microgravity, the body adapts through changes in the function of its major vital systems, primarily the cardiovascular and respiratory systems. This adaptive reactivity is largely regulated by the autonomic nervous system (ANS) and by several reflex mechanisms that coordinate interactions between the cardiovascular and respiratory systems, including the baroreflex. Impairments in baroreflex regulation involved in maintaining the required level of systemic arterial pressure (AP) have been studied both after spaceflight and in models of microgravity; however, these studies have yielded a rather contradictory picture of the autonomic mechanisms involved in these processes. In the present study, we analyzed the mechanisms underlying disturbances in autonomic regulation of the cardiorespiratory system during simulated microgravity, with particular attention to the cardiochronotropic baroreflex. A 21-day head-down bed rest (HDBR) protocol was used as the model. The cardiovascular and respiratory systems were assessed by simultaneous continuous recording of the electrocardiogram, peripheral arterial pressure (AP), and respiration, which enabled automated analysis of the variability of these parameters and of baroreflex sensitivity (BRS). By the end of 21-day HDBR, several parameters associated with the high-frequency components of heart rate (HR), systolic AP, and respiratory-flow variabilities had decreased significantly; the low-frequency component of HR variability during controlled breathing also decreased. By day 21 of HDBR, among the hemodynamic parameters examined, only the minimum RR interval increased significantly, and only in tests with respiratory stimulation. HDBR abolished the correlation between the spectral index of systolic AP variability in the low-frequency band and BRS, indicating an imbalance in the baroreflex mechanism regulating HR and AP. Ultimately, this imbalance is likely related to both reduced parasympathetic influence and impaired effectiveness of sympathetic stimulation of vascular tone.
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Cherepov et al. (2026) studied Simulated microgravity. Head-down bed rest (HDBR) was evaluated on Autonomic regulation of the cardiorespiratory system and cardiochronotropic baroreflex. A 21-day head-down bed rest exposure significantly decreased high-frequency components of heart rate and systolic arterial pressure variability, indicating imbalanced baroreflex regulation.
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