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Articles in PresS, published online ahead of print July 12, 2002
J Appl Physiol, 10.1152/jap.00287.2002
Submitted on April 4, 2002
Accepted on June 26, 2002
1 Departments of Biomedical Engineering and Biological Sciences, Michigan Technological University, Houghton, MI, USA
2 Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Dallas, TX, USA; Department of Internal Medicine, University of Texas Southwestern Medical Center at Dallas, Dallas, TX, USA
3 Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Dallas, TX, USA
* To whom correspondence should be addressed. E-mail: benjaminlevine{at}texashealth.org.
Animal studies suggest that nitric oxide (NO) plays an important role in buffering short-term arterial pressure variability, but data from humans addressing this hypothesis are scarce. We evaluated the effects of NO synthase (NOS) inhibition on arterial blood pressure (BP) variability in eight healthy subjects in the supine position and during 60 head-up tilt (HUT). Systemic NOS was blocked by intravenous infusion of L-NMMA. ECG and beat-by-beat BP in the finger (Finapres) were recorded continuously for 6 min, and brachial cuff BP was recorded before and after L-NMMA in each body position. BP and R-R variability and their transfer functions were quantified by power spectral analysis in the low (LF; 0.05-0.15 Hz) and high frequency (HF; 0.15-0.35 Hz) ranges. L-NMMA infusion increased supine BP (systolic, 109±4 vs.122±3 mmHg, P = 0.03; diastolic, 68±2 vs.78±3 mmHg, P = 0.002), but did not affect supine R-R interval or BP variability. Before L-NMMA, HUT decreased HF R-R variability (P = 0.03), decreased transfer function gain (LF, 12±2 vs. 5±1 ms/mmHg, P = 0.007; HF, 18±3 vs. 3±1 ms/mmHg, P = 0.002), and increased LF BP variability (P < 0.0001). After L-NMMA, HUT resulted in similar changes in BP and R-R variability compared to tilt without L-NMMA. Increased supine BP after L-NMMA with no effect on BP variability during HUT suggests that tonic release of NO is important for systemic vascular tone and thus steady-state arterial pressure, but NO does not buffer dynamic BP oscillations in humans.
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