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This Article Full Text Full Text (PDF) All Versions of this Article: 286/3/H863    most recent 00373.2003v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (5) Citing Articles via Google Scholar Google Scholar Articles by Zhang, R. Articles by Levine, B. D. Search for Related Content PubMed PubMed Citation Articles by Zhang, R. Articles by Levine, B. D.

Inhibition of nitric oxide synthase does not alter dynamic cerebral autoregulation in humans

Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Dallas 75231; and University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75235

Submitted 22 April 2003 ; accepted in final form 2 November 2003

The aim of this study was to determine whether inhibition of nitric oxide synthase (NOS) alters dynamic cerebral autoregulation in humans. Beat-to-beat blood pressure (BP) and cerebral blood flow (CBF) velocity (transcranial Doppler) were measured in eight healthy subjects in the supine position and during 60° head-up tilt (HUT). NOS was inhibited by intravenous N^G-monomethyl-L-arginine (L-NMMA) infusion. Dynamic cerebral autoregulation was quantified by transfer function analysis of beat-to-beat changes in BP and CBF velocity. Pressor effects of L-NMMA on cerebral hemodynamics were compared with those of phenylephrine infusion. In the supine position, L-NMMA increased mean BP from 83 ± 3 to 94 ± 3 mmHg (P < 0.01). However, CBF velocity remained unchanged. Consequently, cerebrovascular resistance index (CVRI) increased by 15% (P < 0.05). BP and CBF velocity variability and transfer function gain at the low frequencies of 0.07–0.20 Hz did not change with L-NMMA infusion. Similar changes in mean BP, CBF velocity, and CVRI were observed after phenylephrine infusion, suggesting that increase in CVRI after L-NMMA was mediated myogenically by increase in arterial pressure rather than a direct effect of cerebrovascular NOS inhibition. During baseline tilt without L-NMMA, steady-state BP increased and CBF velocity decreased. BP and CBF velocity variability at low frequencies increased in parallel by 277% and 217%, respectively (P < 0.05). However, transfer function gain remained unchanged. During tilt with L-NMMA, changes in steady-state hemodynamics and BP and CBF velocity variability as well as transfer gain and phase were similar to those without L-NMMA. These data suggest that inhibition of tonic production of NO does not appear to alter dynamic cerebral autoregulation in humans.

cerebral blood flow; head-up tilt; transcranial Doppler