Key result
Sixty days of head-down tilt bed rest reduced muscle-pump baroreflex causality and fraction time active in lower leg muscles during standing, mimicking the alterations observed with ageing.
Why the study?
Compromised muscle-pump baroreflex from ageing or prolonged inactivity may cause orthostatic hypotension, and understanding individual leg muscle contributions could aid muscle-specific prevention strategies.
Does 60 days of head-down tilt bed rest alter muscle-pump baroreflex during standing similarly to ageing in young adult males?
Observational
Does 60 days of head-down tilt bed rest alter muscle-pump baroreflex during standing similarly to ageing in young adult males?
Prolonged inactivity via 60 days of bed rest induces alterations in muscle-pump baroreflex control during standing that closely mimic those seen with ageing, potentially contributing to orthostatic hypotension.
May support muscle-specific exercises to counter orthostatic hypotension in older adults; leaves open need for interventional trials.
Introduction Baroreflex-mediated activation of lower leg muscles (i.e., muscle-pump baroreflex) has been suggested to play a significant role in blood pressure regulation during standing. Compromised muscle-pump baroreflex because of ageing or prolonged inactivity could contribute to orthostatic hypotension. Understanding the contribution of individual lower leg muscles to blood pressure regulation could lead to the development of muscle-specific strategies to prevent orthostatic hypotension associated with muscle-pump baroreflex dysfunctions. Methods In this study, individual muscle (tibialis anterior (TA), lateral soleus (SOL), medial gastrocnemius (MG), and lateral gastrocnemius (LG)) responses to blood pressure changes upon a supine-to-stand orthostatic challenge were examined in young adult male participants (35 ± 2 years) before and after 60 days of 6° head-down tilt bed rest (HDBR). By analyzing the interactions between systolic blood pressure (SBP) and heartbeat-by-heartbeat electromyogram impulse (EMG imp ) during standing, the interactions between SBP and EMGimp including muscle-pump baroreflex were characterized by fraction time active (FTA) and response gain from wavelet transform coherence analysis and the causality values using convergent cross mapping method for individual leg muscles. Since inactivity and ageing are common causes of orthostatic intolerance, the HDBR results were compared with those from young and older individuals in a previously published study to investigate the similarities in their effects on muscle-pump baroreflex. Results During standing, FTA reduced for all muscles except MG following HDBR and was lower in older compared to younger participants. Muscle-pump baroreflex causality (SBP→EMG imp ) reduced for all muscles following HDBR and was lower for LG and SOL muscles in older compared to younger adults. The mechanical muscle-pump causality (SBP→EMG imp ) was not affected by HDBR or by age. Increased TA muscle-pump baroreflex gain post-HDBR may point to a compensatory mechanism for decreased active control. Conclusions Our results showed striking similarities in the alteration of muscle-pump baroreflex induced via ageing and HDBR, suggesting strong commonalities between ageing and long-term inactivity in terms of the adverse effects on baroreflex mediated control of lower leg muscle activities in response to orthostatic challenge.
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Tremblay et al. (2025) conducted an observational in Orthostatic hypotension and muscle-pump baroreflex dysfunction. 60 days of 6° head-down tilt bed rest (HDBR) vs. Baseline (before HDBR) and previously published data from young and older individuals was evaluated on Interactions between systolic blood pressure and heartbeat-by-heartbeat electromyogram impulse (fraction time active, response gain, and causality values). Sixty days of head-down tilt bed rest reduced muscle-pump baroreflex causality and fraction time active in lower leg muscles during standing, mimicking the alterations observed with ageing.
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