Interplay of cerebral autoregulation and neurovascular coupling evaluated by functional TCD in different orthostatic conditions

Adequate cerebral blood flow (CBF) is mainly governed by neurovascular coupling (NC) which adapts local CBF to underlying cortical activity, and cerebral autoregulation (CA) that tends to maintain constant CBF despite changes in arterial blood pressure (BP). Since it was suggested that resistance vessels play an important role in both mechanisms, we investigated their regulative interplay by performing a functional transcranial Doppler (f-TCD) test under different orthostatic conditions. Fifteen healthy volunteers performed a visual reading test stimulation task after stabilized in sitting, supine and upright position on a tilt table. Simultaneously, BP and heart rate (HR) were recorded by a photoplethysmographic method and CBF velocity was measured with TCD in left posterior cerebral artery, and, as a reference, also in right middle cerebral artery. Evoked flow velocity (FV) responses were evaluated by a control system approach for systolic and diastolic data. Parameters studied were baseline FV with eyes closed, stable FV under stimulation (gain), oscillatory feature (natural frequency) and damping (attenuation) of the control system model, rate time, and also systolic and diastolic BP and HR. ANOVA test was used for comparing the values of variables in different postural settings, inferring statistical significance at a p < 0,05 level. Although there was a significant variation on the different orthostatic conditions in systolic (p = 0,027) and diastolic (p = 0,001) BP and HR (p = 0,0001), there was no significant change in the basal or evoked CBF velocities. An intact CA compensates the different orthostatic conditions completely thus allowing an independent regulation of NC according to the metabolic needs of cortical stimulation.