Cerebral autoregulatory performance and the cerebrovascular response to head-of-bed positioning in acute ischemic stroke

BACKGROUND AND PURPOSE: Cerebrovascular responses to head-of-bed positioning in patients with acute ischemic stroke are heterogeneous, questioning applicability of general recommendations on head positioning. Cerebral autoregulation is impaired to various extents after acute stroke, while it is unknown whether this affects cerebral perfusion during posture change. We aimed to elucidate whether the cerebrovascular response to head position manipulation depends on autoregulatory performance in ischemic stroke patients.

METHODS: In 39 patients with acute ischemic stroke and in 17 reference subjects from 2 centers the responses of bilateral transcranial Doppler ultrasound determined cerebral blood flow velocity (CBFV) and local cerebral blood volume (CBV) assessed by near-infrared spectroscopy total hemoglobin tissue concentration ([total Hb]) to head-of-bed lowering from 30° to 0° were determined. Cerebrovascular autoregulatory performance was expressed as the phase difference of the arterial pressure-to-CBFV transfer function.

RESULTS: Following head-of-bed lowering, CBV increased in the reference subjects only ([total Hb] +2.1±2.0 vs. +0.4±2.6 μM; p<0.05), whereas CBFV did not change in both groups. In patients' hemispheres with autoregulatory performance <50th percentile CBV increased upon head-of-bed lowering vs. a decrease in hemispheres with better autoregulatory performance ([total Hb]: +1.0±1.3 μM vs. -0.5±1.0 μM; p<0.05). The CBV response was inversely related to autoregulatory performance (r= -0.68; p<0.001) in the patients, while no such relation was observed for CBFV.

CONCLUSIONS: This study is the first to provide evidence that in patients with acute ischemic stroke cerebral autoregulatory performance affects the cerebrovascular response to changes in the position of the head. This article is protected by copyright. All rights reserved.