Adaptation of cerebral pressure-velocity hemodynamic changes of neurovascular coupling to orthostatic challenge

Abstract

Neurovascular coupling (NVC), analysed by a control system approach, was shown to be unaffected by orthostatic challenge, but data is lacking regarding the mechanism of this interplay and the behaviour of other cerebrovascular reactivity parameters. We investigated the changes in different pressure-velocity models during functional transcranial Doppler (TCD), under different orthostatic conditions.Thirteen healthy volunteers performed a reading test stimulation task in sitting, supine and head-up tilt (HUT) positions. CBF velocity was monitored with TCD in the posterior cerebral artery, and blood pressure was monitored with Finapres. Cerebrovascular resistance index (CVRi) was compared to a two-parameter model including resistance-area product (RAP) and critical closing pressure (CrCP), in the maximal and in the stable phases of flow response to visual stimulation.All cerebrovascular resistance parameters decreased with visual stimulation but the magnitude of their variation in each orthostatic condition was not similar. From supine to HUT, CrCP variation decreased (both maximal and stable phase p = 0.001). CVRi variation increased from sitting to HUT positions (maximal p = 0.039; stable phase p = 0.033). RAP variation to visual stimulation did not change between the three positions (maximal p = 0.077; stable phase p = 0.188).A 2-parameter model of vascular resistance provided better discrimination for the effects of posture on NVC as shown by the adaptive changes in CrCP with orthostatic challenge, in comparison with the classical use of CVRi. These findings suggest that although NVC seemed unaffected by orthostatic challenge, more complex vasoregulative mechanisms are activated in different orthostatic conditions that could potentially be of diagnostic or prognostic value.

Assessing cerebrovascular autoregulation from critical closing pressure and resistance area product during upright posture in aging and hypertension

“…In addition, postulations that CrCP is sensitive to metabolic influences (36) and PCO 2 (7,55) provide evidence that autoregulatory responses driven by CrCP likely rely on multiple factors on top of fluctuations in arterial pressure. In opposition of the current findings, prior research has reported elevations in CrCP during seated and head-up tilt postures (4,8); however, it appears these studies used central pressure in the estimation of CrCP, rather than BP MCA . Increased CrCP in response to lower arterial pressure would exaggerate the reduction in cerebral perfusion pressure and lower CBF given a constant resistance, a paradoxical autoregulatory response.…”

Does gradual change in head positioning affect cerebrovascular physiology?

“…Despite these phasic changes, no significant differences in RAP were observed between averaged 5-min FLAT and SIT positions. This contrasts with a previous report by Robertson Castro et al (2012) recruited 13 healthy young volunteers, aged 26 AE 9 years, and performed a reading task in supine, sitting and head-up tilt positions, and reported a significant reduction in MCA CBV, and an associated significant increase in CrCP from supine to head-up tilt, but no such change in RAP.…”

“…Castro et al. () recruited 13 healthy young volunteers, aged 26 ± 9 years, and performed a reading task in supine, sitting and head‐up tilt positions, and reported a significant reduction in MCA CBV, and an associated significant increase in CrCP from supine to head‐up tilt, but no such change in RAP.…”

Neurovascular coupling response to cognitive examination in healthy controls: a multivariate analysis

“…Castro et al. () measured subcomponent changes in the PCA during a reading task in healthy volunteers. Measurements were undertaken in varying orthostatic positions and all parameters ( V CrCP , V RAP and CVRi) reduced, but responded differently to varying orthostatic conditions (Castro et al.…”