We have investigated the changes in muscle sympathetic nerve activity (MSNA) from the tibial nerve during brief periods of microgravity (μG) for ~20 s produced by parabolic flight. MSNA was recorded microneurographically from 13 quietly seated human subjects with their knee joints extended in a jet aircraft simultaneously with the electrocardiogram, the blood pressure wave (measured with a Finapres), the respiration curve, and the thoracic fluid volume (measured by impedance plethysmography). During quiet and seated parabolic flight, MSNA was activated in hypergravity and was suppressed in μG phasically. At the entry to hypergravity at 2 G just before μG, the thoracic fluid volume was reduced by 3.2 ± 3%, and the arterial blood pressure was lowered transiently and then gradually elevated from 89.5 ± 1.7 to 100.2 ± 1.7 mmHg, which caused the enhancement of MSNA by 91.4 ± 14.2%. At the entry to μG, the thoracic fluid volume was increased by 3.4%, which lowered the mean blood pressure to 77.9 ± 2.3 mmHg and suppressed the MSNA by 17.2%. However, this suppression lasted only ~10 s, followed by an enhancement of MSNA that continued for several seconds. We conclude that MSNA is suppressed and then enhanced during μG produced by parabolic flight. These changes in MSNA are in response not only to intrathoracic fluid volume changes but also to arterial blood pressure changes, both of which are caused by body fluid shifts induced by parabolic flight, and these changes are quite phasic and transient.
|Original language||English (US)|
|Journal||American Journal of Physiology - Regulatory Integrative and Comparative Physiology|
|Issue number||2 46-2|
|State||Published - Aug 1999|
All Science Journal Classification (ASJC) codes
- Physiology (medical)