TY - JOUR
T1 - Cerebral vasoreactivity during hypercapnia is reset by augmented sympathetic influence
AU - Zhang, Peizhen
AU - Huang, Guoyuan
AU - Shi, Xiangrong
PY - 2011/2
Y1 - 2011/2
N2 - Sympathetic nerve activity influences cerebral blood flow, but it is unknown whether augmented sympathetic nerve activity resets cerebral vasoreactivity to hypercapnia. This study tested the hypothesis that cerebral vasodilation during hypercapnia is restrained by lower-body negative pressure (LBNP)-stimulated sympathoexcitation. Cerebral hemodynamic responses were assessed in nine healthy volunteers [age 25 yr (SD 3)] during rebreathing-induced increases in partial pressure of end-tidal CO2 (PETCO2) at rest and during LBNP. Cerebral hemodynamic responses were determined by changes in flow velocity of middle cerebral artery (MCAV) using transcranial Doppler sonography and in regional cerebral tissue oxygenation (ScO2) using near-infrared spectroscopy. PETCO2 values during rebreathing were similarly increased from 41.9 to 56.5 mmHg at rest and from 40.7 to 56.0 mmHg during LBNP of - 15 Torr. However, the rates of increases in MCAV and in ScO2 per unit increase in PETCO2 (i.e., the slopes of MCAV/PETCO2 and ScO2/PETCO2) were significantly (P ≤0.05) decreased from 2.62 ± 0.16 cm·s -1·mmHg-1 and 0.89 ± 0.10%/mmHg at rest to 1.68 ± 0.18 cm·s-1·mmHg-1 and 0.63 ± 0.07%/mmHg during LBNP. In conclusion, the sensitivity of cerebral vasoreactivity to hypercapnia, in terms of the rate of increases in MCAV and in ScO2, is diminished by LBNP-stimulated sympathoexcitation.
AB - Sympathetic nerve activity influences cerebral blood flow, but it is unknown whether augmented sympathetic nerve activity resets cerebral vasoreactivity to hypercapnia. This study tested the hypothesis that cerebral vasodilation during hypercapnia is restrained by lower-body negative pressure (LBNP)-stimulated sympathoexcitation. Cerebral hemodynamic responses were assessed in nine healthy volunteers [age 25 yr (SD 3)] during rebreathing-induced increases in partial pressure of end-tidal CO2 (PETCO2) at rest and during LBNP. Cerebral hemodynamic responses were determined by changes in flow velocity of middle cerebral artery (MCAV) using transcranial Doppler sonography and in regional cerebral tissue oxygenation (ScO2) using near-infrared spectroscopy. PETCO2 values during rebreathing were similarly increased from 41.9 to 56.5 mmHg at rest and from 40.7 to 56.0 mmHg during LBNP of - 15 Torr. However, the rates of increases in MCAV and in ScO2 per unit increase in PETCO2 (i.e., the slopes of MCAV/PETCO2 and ScO2/PETCO2) were significantly (P ≤0.05) decreased from 2.62 ± 0.16 cm·s -1·mmHg-1 and 0.89 ± 0.10%/mmHg at rest to 1.68 ± 0.18 cm·s-1·mmHg-1 and 0.63 ± 0.07%/mmHg during LBNP. In conclusion, the sensitivity of cerebral vasoreactivity to hypercapnia, in terms of the rate of increases in MCAV and in ScO2, is diminished by LBNP-stimulated sympathoexcitation.
UR - http://www.scopus.com/inward/record.url?scp=79851506846&partnerID=8YFLogxK
U2 - 10.1152/japplphysiol.00802.2010
DO - 10.1152/japplphysiol.00802.2010
M3 - Article
C2 - 21071587
AN - SCOPUS:79851506846
SN - 8750-7587
VL - 110
SP - 352
EP - 358
JO - Journal of Applied Physiology
JF - Journal of Applied Physiology
IS - 2
ER -