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1 Department of Integrative Physiology and Cardiovascular Research Institute, University of North Texas Health Science Center, Fort Worth 76107; and 2 Institute for Exercise and Environmental Medicine, Dallas, Texas 75231
This study was designed to investigate the importance of
vagal cardiac modulation in arterial blood pressure (ABP) stability before and after glycopyrrolate or atropine treatment. Changes in R-R
interval (RRI) and ABP were assessed in 10 healthy young (age, 22 ± 1.8 yr) volunteers during graded lower body negative pressure (LBNP)
before and after muscarinic cholinergic (MC) blockade. Transient
hypertension was induced by phenylephrine (1 µg/kg body wt), whereas
systemic hypotension was induced by bilateral thigh cuff deflation
after a 3-min suprasystolic occlusion. Power spectral densities of
systolic [systolic blood pressure (SBP)] and diastolic ABP
variability were examined. Both antimuscarinic agents elicited tachycardia similarly without significantly affecting baseline ABP. The
increase in SBP after phenylephrine injection (+14 ± 2 mmHg) was
significantly augmented with atropine (+26 ± 2 mmHg) or
glycopyrrolate (+27 ± 3 mmHg) and associated with a diminished reflex bradycardia. The decrease in SBP after cuff deflation
(
9.2 ± 1.2 mmHg) was significantly greater after atropine
(
15 ± 1 mmHg) or glycopyrrolate (
14 ± 1 mmHg), with
abolished reflex tachycardia. LBNP significantly decreased both SBP and
RRI. However, after antimuscarinic agents, the reduction in SBP was
greater (P < 0.05) and was associated with less
tachycardia. Antimuscarinic agents reduced (P < 0.05)
the low-frequency (LF; 0.04-0.12 Hz) power of ABP variability at
rest. The LF SBP oscillation was significantly augmented during LBNP,
which was accentuated (P < 0.05) after antimuscarinic
agents and was correlated (r =
0.79) with the decrease in SBP. We conclude that antimuscarinic agents compromised ABP
stability by diminishing baroreflex sensitivity, reflecting the
importance of vagal cardiac function in hemodynamic homeostasis. The
difference between atropine and glycopyrrolate was not significant.
baroreflex gain; glycopyrrolate; power spectral analysis; lower body negative pressure; phenylephrine; suprasystolic occlusion; Valsalva maneuver; vasomotion
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