Directional sensitivity of dynamic cerebral autoregulation in squat-stand maneuvers

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology integrative and comparative physiology, 2018-10, Vol.315 (4), p.R730-R740
• Main Authors: Panerai, Ronney B, Barnes, Sam C, Nath, Mintu, Ball, Naomi, Robinson, Thompson G, Haunton, Victoria J
• Format: Article
• Language: English
• Subjects: Arterial Pressure; Autoregressive moving-average models; Blood flow; Blood Flow Velocity; Blood pressure; Brain; Carbon dioxide; Cerebral blood flow; Cerebrovascular Circulation; Dependence; Directional sensitivity; Echocardiography; EKG; Electrocardiography; Exercise - physiology; Female; Heart Rate; Homeostasis; Humans; Male; Maneuvers; Models, Cardiovascular; Muscle Contraction; Nonlinear Dynamics; Posture; Standing Position; Strong interactions (field theory); Time Factors; Ultrasonography, Doppler, Transcranial; Ultrasound; Young Adult
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00010.2018

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 CO (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.