Directional sensitivity of dynamic cerebral autoregulation in squat-stand maneuvers.

Ronney B Panerai,Mintu Nath,Thompson G Robinson,Sam C Barnes,Victoria J Haunton,Naomi Ball

doi:10.1152/ajpregu.00010.2018

Ronney B Panerai, Mintu Nath + Show 4 more

Open Access

https://doi.org/10.1152/ajpregu.00010.2018

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Abstract

Dynamic cerebral autoregulation (CA), the transient response of cerebral blood flow (CBF) to rapid changes in arterial blood pressure (BP), is usually modeled as a linear mechanism. We tested the hypothesis that dynamic CA can display nonlinear behavior resulting from differential efficiency dependent on the direction of BP changes. Cerebral blood velocity (CBV) (transcranial Doppler), heart rate (HR) (three-lead ECG), continuous BP (Finometer), and end-tidal CO2 (capnograph) were measured in 10 healthy young subjects during 15 squat-stand maneuvers (SSM) with a frequency of 0.05 Hz. The protocol was repeated with a median (interquartile range) of 44 (35-64) days apart. Dynamic CA was assessed with the autoregulation index (ARI) obtained from CBV step responses estimated with an autoregressive moving-average model. Mean BP, HR, and CBV were different (all P < 0.001) between squat and stand, regardless of visits. ARI showed a strong interaction ( P < 0.001) of SSM with the progression of transients; in general, the mean ARI was higher for the squat phase compared with standing. The changes in ARI were partially explained by concomitant changes in CBV ( P = 0.023) and pulse pressure ( P < 0.001), but there was no evidence that ARI differed between visits ( P = 0.277). These results demonstrate that dynamic CA is dependent on the direction of BP change, but further work is needed to confirm if this finding can be generalized to other physiological conditions and also to assess its dependency on age, sex and pathology.

Highlights

Cerebral blood flow (CBF) is tightly controlled by metabolic, myogenic, and neurogenic mechanisms, usually assumed to optimize brain perfusion in response to changes in arterial blood pressure (BP), arterial carbon dioxide (CO2 reactivity), and oxygen demand [neurovascular coupling (NVC)]
For other cerebral autoregulation (CA) covariates, namely mean arterial BP, Heart rate (HR), end-tidal CO2 (EtCO2), cerebral blood velocity (CBV), and pulse pressure (PP), we investigated the effect of visit and maneuver using similar repeated measures models accounting for the correlation between measurements within the same subject
Using the autoregulation index (ARI), a well-established method to quantify the strength of dynamic CA [32], we have confirmed the recent results of Brassard et al [8], suggesting that the squatting phase of squat-stand maneuver (SSM) has a more efficient CA response than the corresponding standing phase

Summary

Introduction

Cerebral blood flow (CBF) is tightly controlled by metabolic, myogenic, and neurogenic mechanisms, usually assumed to optimize brain perfusion in response to changes in arterial blood pressure (BP) (autoregulation), arterial carbon dioxide (CO2 reactivity), and oxygen demand [neurovascular coupling (NVC)]. The speed at which these regulatory mechanisms respond to different stimuli can provide insight into the underlying physiology and potentially provide diagnostic and prognostic information in clinical studies. Address for reprint requests and other correspondence: R. Of Cardiovascular Sciences, Room 439, Robert Kilpatrick Clinical Sciences.

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