Muscle sympathetic nerve activity (MSNA) after 120 days of 6 degrees head-down bed rest (HDBR).
The alterations in the sympathetic nervous system are commonly seen after spaceflight and its ground-based simulation model, 6 degrees head-down bed rest (HDBR). Several studies have examined the effect of HDBR for a few days or a weeks on the vasomotor sympathetic tone at rest. However, it remains unclear how a long-lasting (>50 days) HDBR affects resting vasomotor sympathetic nervous activity. Consequently, we measured muscle sympathetic nerve activity (MSNA) in six healthy male volunteers (range, 26-42 years) in a resting supine position before and after 60 and 120 days of HDBR. MSNA was measured directly from the tibial nerve using a microneurographic technique. Resting supine MSNA significantly increased after 60 (28.2 +/- 2.7 bursts/min) and 120 (29.4 +/- 4.2 bursts/min) days of HDBR compared with the pre-HDBR level (19.0 +/- 2.3 bursts/min). Heart rate was significantly higher after 60 (73 +/- 2 beats/min) and 120 (72 +/- 3 beats/min) days of HDBR than before (65 +/- 2 beats/min). In contrast, mean blood pressure remained unchanged during and after 120 days of HDBR. In conclusion, the resting vasomotor sympathetic tone increased after long-lasting simulated microgravity.
Kamiya
A
A
Department of Autonomic Neuroscience, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan.
Iwase
S
S
Kitazawa
H
H
Mano
T
T
D000328:Adult; D001510:Bed Rest; D001794:Blood Pressure / Q000502:physiology; D018475:Head-Down Tilt / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology*; D013979:Tibial Nerve / Q000502:physiology*; D013997:Time Factors; D014666:Vasomotor System / Q000502:physiology; D018474:Weightlessness Simulation