Partial pharmacologic blockade shows sympathetic connection between blood pressure and cerebral blood flow velocity fluctuations

Abstract

Cerebral autoregulation (CA) dampens transfer of blood pressure (BP)-fluctuations onto cerebral blood flow velocity (CBFV). Thus, CBFV-oscillations precede BP-oscillations. The phase angle (PA) between sympathetically mediated low-frequency (LF: 0.03-0.15Hz) BP- and CBFV-oscillations is a measure of CA quality. To evaluate whether PA depends on sympathetic modulation, we assessed PA-changes upon sympathetic stimulation with and without pharmacologic sympathetic blockade. In 10 healthy, young men, we monitored mean BP and CBFV before and during 120-second cold pressor stimulation (CPS) of one foot (0°C ice-water). We calculated mean values, standard deviations and sympathetic LF-powers of all signals, and PAs between LF-BP- and LF-CBFV-oscillations. We repeated measurements after ingestion of the adrenoceptor-blocker carvedilol (25mg). We compared parameters before and during CPS, without and after carvedilol (analysis of variance, post-hoc t-tests, significance: p<0.05). Without carvedilol, CPS increased BP, CBFV, BP-LF- and CBFV-LF-powers, and shortened PA. Carvedilol decreased resting BP, CBFV, BP-LF- and CBFV-LF-powers, while PAs remained unchanged. During CPS, BPs, CBFVs, BP-LF- and CBFV-LF-powers were lower, while PAs were longer with than without carvedilol. With carvedilol, CPS no longer shortened resting PA. Sympathetic activation shortens PA. Partial adrenoceptor blockade abolishes this PA-shortening. Thus, PA-measurements provide a subtle marker of sympathetic influences on CA and might refine CA evaluation.

Sport-Related Concussion Alters Indices of Dynamic Cerebral Autoregulation

“…At a group level, key findings indicated transient post-injury impairments in the capacity of the cerebrovasculature to buffer BP oscillations occurring at 0.10 Hz, the timescale over which sympathetic contributions to CA are thought to operate ( 24 , 28 ). At a within-subject level, more substantial impairments in CA were related with poorer performance on the SAC, a brief cognitive screen for concussion.…”

“…Mounting evidence points to the importance of sympathetic innervation in the dynamic regulation of BP variability ( 51 ). Recently, pharmacological studies in healthy young adults have characterized sympathetic modulation of CA, whereby sympathetic activation has been shown to reduce both Phase and Gain at frequencies including 0.10 Hz, with even partial sympathetic blockade completely eliminating the Phase response ( 24 , 28 ). In accordance with the suggestion that progressive impairment of autoregulation likely first affects the latency of the response ( Phase ) before affecting the efficiency ( Gain ) ( 52 ), we observed significant changes in Phase only.…”

Dynamic cerebral autoregulation in anterior and posterior cerebral circulation during cold pressor test

“…In the present study, the RoR as an index of the dCA in the MCA and PCA was unchanged during CPT. In contrast to these results, Hilz et al [34] reported that CPT impaired the dCA in the MCA. One possible reason for this inconsistent result is that the foot was stimulated rather than the hand for the CPT.…”