Vagal modulation of RR intervals during head-up tilt and the infusion of isoproterenol.
Publication/Presentation Date
6-1-1995
Abstract
The objective of this study was to characterize the autonomic effects of 2 interventions, head-up tilt and isoproterenol infusion, which alter autonomic balance by different mechanisms but produce the same RR intervals. We compared the effect of head-up tilt with the effect of isoproterenol on autonomic balance as measured by power spectral analysis of RR variability. Fifteen normal subjects had baseline measurements and then underwent head-up tilt. After return to baseline supine values, isoproterenol was infused at a rate of 1 microgram/min (low-dose isoproterenol), which was then increased to 2.1 +/- 0.5 microgram/min (high-dose isoproterenol). All subjects underwent a second tilt during high-dose isoproterenol, and 9 subjects completed this second tilt study. During the experiment, normal RR intervals were recorded and 5-minute segments were used to calculate power spectra. High-frequency (HF) power (0.15 to 0.40 Hz) was used as a measure of vagal activity. The effects of head-up tilt were compared with the effects of low-dose isoproterenol. Despite nearly identical mean RR intervals (784 ms with tilt vs 792 ms with low-dose isoproterenol, p = NS), there was significantly (p < 0.05) less HF power during head-up tilt in the drug-free state (172 ms2) than during low-dose isoproterenol in the supine position (307 ms2). A second head-up tilt was performed during the infusion of high-dose isoproterenol. During high-dose isoproterenol, tilt caused a decrease in RR intervals (from 573 to 491 ms; p < 0.01) and a decrease in HF power (from 68 to 28 ms2; p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Volume
75
Issue
16
First Page
1145
Last Page
1150
ISSN
0002-9149
Published In/Presented At
Bloomfield, D. M., Bigger, J. T., Jr, Pavri, B. B., Han, J., Fleiss, J. L., Rolnitzky, L. M., & Steinman, R. C. (1995). Vagal modulation of RR intervals during head-up tilt and the infusion of isoproterenol. The American journal of cardiology, 75(16), 1145–1150. https://doi.org/10.1016/s0002-9149(99)80747-4
Disciplines
Business Administration, Management, and Operations | Health and Medical Administration | Management Sciences and Quantitative Methods
PubMedID
7762502
Department(s)
Administration and Leadership
Document Type
Article