The effect of 14 days of head down (-6°) bedrest (HDBR) on muscle sympathetic nerve activity (MSNA) during static handgrip (SHG) exercise was measured in healthy volunteers. Mean arterial pressure (MAP) (Finapres), heart rate (HR) and MSNA (peroneal nerve) burst frequency (Bf) were measured at rest and at fatigue (-20% MVC) before and following HDBR. The MAP and HR responses to SHG were similar in pre and post HDBR tests. MSNA Bf at rest (n=10) was reduced in the post (16.7±2.6 min-1), compared with the pre (23.0±2.0 min-1) tests (P<0.05). End exercise Bf (n=8) (34.3±3.8 min-1 vs. 23.3±3.7 min-1; pre vs. post HDBR, respectively) was reduced following HDBR (P<0.05). The reductions in MSNA persisted when Bf was normalized to heart rate, or to the increase above rest. In contrast, the increase in MSNA during a cold pressor test was not altered by HDBR (n=4). To examine if the reduction in exercise MSNA with HDBR was related to metabolic alterations in response to SHG exercise, deep venous lactate, pH and HbO2 saturation were measured during rhythmic handgrip exercise with +50 mmHg positive pressure about the forearm (n=5). End exercise lactate, pH and HbO2 saturation were not different after HDBR. Thus, HDBR resulted in a reduced MSNA Bf at rest and attenuated the ability to elevate MSNA during fatiguing exercise. The reductions in MSNA did not appear to be due to alterations in metabolite-sensitive afferent stimulation in the working muscle.
|Original language||English (US)|
|State||Published - Dec 1 1997|
All Science Journal Classification (ASJC) codes
- Molecular Biology