Nonlinear, multiple-input modeling of cerebral hemodynamics during baseline and hypercapnia in young and...

Normal aging is associated with changes in the cardiovascular system and more specifically in cerebral circulation. Sex-dependent changes in cerebrovascular CO2 reactivity, which may be related to hormonal levels, have been also reported. We therefore examined cerebral hemodynamics, i.e., dynamic pressure autoregulation and CO2 reactivity, by employing beat-to-beat values of mean arterial blood pressure and middle cerebral artery blood flow velocity, as well as breath-to-breath values of end-tidal CO2 tension during baseline and sustained, end-tidal forcing induced hypercapnia in pre- and post-menopausal women. For this purpose, we employed a recently proposed nonlinear, multiple-input model of cerebral hemodynamics. The results suggest that dynamic autoregulation and reactivity in response to spontaneous fluctuations are not affected in postmenopausal women and that CO2 reactivity to the larger, experimentally-induced hypercapnic stimuli are affected mildly. A significant decrease in CO2 reactivity to spontaneous fluctuations was also observed during hypercapnia in all three groups.