Abstract
At rest, respiratory-induced changes in the partial pressure of arterial carbon dioxide (PaCO2) play a major role in the regulation of cerebral blood flow (CBF). Changes in CBF affect stability of the ventilatory (VE) responsiveness to CO2 via alterations in the degree of washout in central chemoreceptor hydrogen [H+] . No data, however, is available on the comparison of the CBF and VE responsiveness to PaCO2 at rest and during exercise. To describe the CBF and VE reactivity to PaCO2, we measured the blood velocity in the middle cerebral artery (MCAV) in six males under various VE conditions by controlling ventilation for 12 min at rest (VE = 9 to 38 L/min) and during 40 W ergometer cycling (VE = 12 to 68 L/min). The MCAV and VE reactivity to PaCO2 at rest was similar to that during exercise (-0.9 ± 0.3 cm/s/mmHg vs. -1.0 ± 0.5 cm/s/mmHg, respectively, P>0.05; mean ± SEM). The intercept of MCAV with PaCO2 tended to be greater during exercise than at rest (83 ± 11 vs. 66 ± 9 cm/s when VE = 0 L/min: P=0.1); this finding indicates that the upward shift of MCAV reactivity to VE may have a role in washing out CO2 from the brain, potentially due to the greater amount of CO2 production during exercise. [J Physiol Sci. 2008;58 Suppl:S182]
