Demographic and Systemic Hemodynamic Influences in Mechanisms of Cerebrovascular Regulation in Healthy Adults

Abstract

A competent cerebrovascular regulation maintains an adequate cerebral blood flow by 3 major mechanisms: cerebral autoregulation (CA), vasomotor reactivity (VMR), namely to CO2, and neurovascular coupling (NVC). However, most studies generalize their results based on a response to a single parameter. Using a full battery of neurovascular stress tests, our study aims to evaluate the relationships among grades of CA, VMR, and NVC, and how their interplay is influenced by demographic and systemic hemodynamic factors. Fifty-eight healthy adults were recruited to fit each decade age stratum from 20 to 80 years old with similar sex ratio. Arterial blood pressure (Finometer), cerebral blood flow velocity in the middle cerebral arteries (transcranial Doppler), electrocardiogram, and end-tidal CO2 were monitored. We assessed CA by transfer function analysis, VMR at hypocapnia and hypercapnia (carbogen 5%), and NVC response during the N-Back Task. The Montreal Cognitive Assessment scores were recorded. Neurovascular stress tests were not affected by age or gender, and no correlation was found between their outputs (P > .05). Systemic hemodynamic parameters during tasks as well as cognitive scores had no correlation with cerebrovascular measurements (P > .05). Age and gender do not have major influence on the 3 major cerebrovascular regulation mechanisms. Our results also pinpoint the fact that neurovascular stress tests measure different aspects of cerebrovascular control, and that their outputs are uncorrelated and cannot be used interchangeability. Being independent of age and cognitive status, neurovascular stress tests seem adequate for studying several cerebrovascular conditions affecting the aging brain.