# The impact of posture changes on critical closing pressure and resistance-area product regulation in healthy subjects

## TL;DR

This study examines how posture changes affect cerebral blood flow regulation in healthy individuals using measurements like critical closing pressure and resistance-area product.

## Contribution

The study introduces a novel approach to assess dynamic cerebral autoregulation by analyzing step responses of critical closing pressure and resistance-area product during posture changes.

## Key findings

- Posture changes significantly affect cerebral blood velocity and resistance-area product step responses.
- Critical closing pressure step responses change with posture, but not consistently for all cerebral arteries.
- End-tidal CO2 levels decrease with posture changes and may influence cerebral autoregulation.

## Abstract

Cerebral blood flow (CBF) is affected by posture changes, but there is a paucity of research examining the effect of posture on dynamic cerebral autoregulation (dCA). The step responses of critical closing pressure (CrCP) and resistance area product (RAP) obtained from the cerebral blood velocity (CBv) signal can reflect the changes in dCA, enabling exploration of dCA changes in supine, sitting and upright postures.

In 22 participants (11 males, aged 30.2 ± 14.3 years), two recordings were made for each posture, corresponding to supine, sitting, and standing. Blood pressure (BP, Finometer), MCAv and PCAv (transcranial Doppler ultrasound), end-tidal carbon dioxide (EtCO2, capnography) and heart rate (ECG) were continuously recorded. CrCP and RAP were obtained for each cardiac cycle, and the step responses of CBv (SRVMCA/PCA), CrCP (SRVCrCP), and RAP (SRVRAP), for both arteries, were calculated after subcomponent and transfer function analysis.

Moving from supine to sitting, and then standing, led to reductions in mean MCAv (p < 0.001), PCAv (p = 0.037), BP (p < 0.001) and EtCO2 (p < 0.001), accompanied by changes in SRVMCA (p = 0.002), but not in SRVPCA (p = 0.78). For both arteries, SRVRAP and SRVCrCP reflected changes in posture (both p < 0.001).

Posture changes can significantly affect the step responses of MCAv, CrCP, and RAP. The interaction between posture and EtCO2 from the perspective of the CrCP and RAP step responses needs further exploration in future studies.