Asymmetry of cerebral autoregulation does not correspond to asymmetry of cerebrovascular pressure reactivity

Abstract

Background

Small cerebral vessels respond to variations of cerebral perfusion pressure (CPP) by changes of vessel diameter inducing changes of blood flow resistance and keeping cerebral blood flow constant. This mechanism is called cerebral autoregulation (CA). Recently stronger reactions of CA during pressure increase than during decrease were reported. Aim of this study was to assess the symmetry behavior of CA during spontaneous CPP changes and compare it to cerebrovascular pressure reactivity (CVR).

Methods

In 238 patients with traumatic brain injury or stroke, correlation indices between CPP and cerebral blood flow velocity (CBFV) were calculated during periods of increasing (upMx) and decreasing CPP (downMx). The indices range from −1 to +1, values ≤0 indicating intact, values >0 indicating impaired autoregulation. Similar correlation between arterial blood pressure (ABP) and ICP was calculated during increasing (upPRx) and decreasing ABP (downPRx), negative values indicating intact, positive values indicating impaired CVR. Only recordings with strong pressure changes (CPP/ABP > 10 mmHg) were evaluated.

Results

CA was assessed in 62 patients. On average (mean ± SD) upMx was 0.06 ± 0.52, downMx was 0.15 ± 0.55 (P < 0.005). CVR was assessed in 47 patients. On average upPRx was 0.45 ± 0.43, downPRx was 0.38 ± 0.48 (P < 0.05). In 40 patients both Mx and PRx were calculated. On average upMx was 0.21 ± 0.55 and downMx was 0.27 ± 0.56 (P = 0.05), upPRx was 0.35 ± 0.43 and downPRx was 0.27 ± 0.47 (P < 0.05).

Conclusions

During pressure increase the autoregulatory response was significantly stronger than during decrease, while in contrast the cerebrovascular reactivity was significantly weaker. The reason for this opposed behavior remains unclear and needs further exploration.