| Abstract: | Shoemaker, J. Kevin, Cynthia S. Hogeman, Urs A. Leuenberger,Michael D. Herr, Kristen Gray, David H. Silber, and Lawrence I. Sinoway. Sympathetic discharge and vascular resistance after bedrest. J. Appl. Physiol. 84(2):612-617, 1998. The effect of  6° head-down-tilt bedrest (HDBR) for 14 days on supine sympathetic discharge andcardiovascular hemodynamics at rest was assessed. Mean arterialpressure, heart rate (n = 25), musclesympathetic nerve activity (MSNA; n = 16) burst frequency, and forearm blood flow(n = 14) were measured, and forearmvascular resistance (FVR) was calculated. Stroke distance,our index of stroke volume, was derived from measurements of aorticmean blood velocity (Doppler) and R-R interval(n = 7). With these data, an index oftotal peripheral resistance was determined. Heart rate at rest wasgreater in the post (71 ± 2 beats/min)- compared with the pre-HDBRtest (66 ± 2 beats/min; P < 0.003), but mean arterial pressure was unchanged. Aortic strokedistance during post-HDBR (15.5 ± 1.1 cm/beat) was reduced frompre-HDBR levels (20.0 ± 1.5 cm/beat)(P < 0.03). Also, MSNA burstfrequency was reduced in the post (16.7 ± 2.8 beats/min)- comparedwith the pre (25.2 ± 2.6 beats/min)-HDBR condition(P < 0.01). Bed rest did not alterforearm blood flow, FVR, or total peripheral resistance. Thusreductions in MSNA with HDBR were not associated with a decrease inFVR. |
