TY - JOUR
T1 - Effects of lower body positive pressure on muscle sympathetic nerve activity response to head-up tilt
AU - Fu, Qi
AU - Iwase, Satoshi
AU - Niimi, Yuki
AU - Kamiya, Atsunori
AU - Kawanokuchi, Jun
AU - Cui, Jian
AU - Mano, Tadaaki
AU - Suzumura, Akio
PY - 2001
Y1 - 2001
N2 - The present study was performed to test the hypothesis that application of lower body positive pressure (LBPP) during orthostasis would reduce the baroreflex-mediated enhancement in sympathetic activity in humans. Eight healthy young men were exposed to a 70° head-up tilt (HUT) on application of 30 mmHg LBPP. Muscle sympathetic nerve activity (MSNA) was microneurographically recorded from the tibial nerve, along with hemodynamic variables. We found that in the supine position with LBPP, MSNA remained unchanged (13.4 ± 3.3 vs. 11.8 ± 2.3 bursts/min, without vs. with LBPP; P > 0.05), mean arterial pressure was elevated, but arterial pulse pressure and heart rate did not alter. At 70° HUT with LBPP, the enhanced MSNA response was reduced (33.8 ± 5.0 vs. 22.5 ± 2.2 bursts/min, without vs. with LBPP; P < 0.05), mean arterial pressure was higher, the decreased pulse pressure was restored, and the increased heart rate was attenuated. We conclude that the baroreflex-mediated enhancement in sympathetic activity during HUT was reduced by LBPP. Application of LBPP in HUT induced an obvious cephalad fluid shift as well as a restoration of arterial pulse pressure, which reduced the inhibition of the baroreceptors. However, the activation of the intramuscular mechanoreflexes produced by 30 mmHg LBPP might counteract the effects of baroreflexes.
AB - The present study was performed to test the hypothesis that application of lower body positive pressure (LBPP) during orthostasis would reduce the baroreflex-mediated enhancement in sympathetic activity in humans. Eight healthy young men were exposed to a 70° head-up tilt (HUT) on application of 30 mmHg LBPP. Muscle sympathetic nerve activity (MSNA) was microneurographically recorded from the tibial nerve, along with hemodynamic variables. We found that in the supine position with LBPP, MSNA remained unchanged (13.4 ± 3.3 vs. 11.8 ± 2.3 bursts/min, without vs. with LBPP; P > 0.05), mean arterial pressure was elevated, but arterial pulse pressure and heart rate did not alter. At 70° HUT with LBPP, the enhanced MSNA response was reduced (33.8 ± 5.0 vs. 22.5 ± 2.2 bursts/min, without vs. with LBPP; P < 0.05), mean arterial pressure was higher, the decreased pulse pressure was restored, and the increased heart rate was attenuated. We conclude that the baroreflex-mediated enhancement in sympathetic activity during HUT was reduced by LBPP. Application of LBPP in HUT induced an obvious cephalad fluid shift as well as a restoration of arterial pulse pressure, which reduced the inhibition of the baroreceptors. However, the activation of the intramuscular mechanoreflexes produced by 30 mmHg LBPP might counteract the effects of baroreflexes.
UR - http://www.scopus.com/inward/record.url?scp=0034818592&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0034818592&partnerID=8YFLogxK
U2 - 10.1152/ajpregu.2001.281.3.r778
DO - 10.1152/ajpregu.2001.281.3.r778
M3 - Article
C2 - 11506992
AN - SCOPUS:0034818592
SN - 0363-6119
VL - 281
SP - R778-R785
JO - American Journal of Physiology - Regulatory Integrative and Comparative Physiology
JF - American Journal of Physiology - Regulatory Integrative and Comparative Physiology
IS - 3 50-3
ER -