Highlights
- •Cerebral autoregulation (CA) dampens blood pressure (BP)-fluctuations.
- •Thus, cerebral blood flow velocity (CBFV)-oscillations precede BP-oscillations.
- •Phase angle (PA) between sympathetic CBFV- and BP-oscillations measures CA quality.
- •Sympathetic stimulation shortens PA; sympathetic blockade abolishes PA-shortening.
- •PA measurements provide a subtle marker of sympathetic CA effects.
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: 0.03–0.15 Hz) 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 (25 mg). 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.
Abbreviations:
CA (cerebral autoregulation), BP (blood pressure), CBFV (cerebral blood flow velocity), CPS (cold pressor stimulation), ETCO2 (end-tidal carbon dioxide levels), HF (high-frequency), LF (low-frequency), PA (phase angle), RRI (RR-interval), SD (standard deviation), TCD (transcranial Doppler sonography)Keywords
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Article info
Publication history
Published online: April 17, 2016
Accepted:
April 7,
2016
Received in revised form:
March 24,
2016
Received:
October 30,
2015
Identification
Copyright
© 2016 Elsevier B.V. All rights reserved.
