Abstract 14278: Autonomic Nerve Activity and Blood Pressure Fluctuation in Ambulatory Dogs
Background: Orthostatic hypotension is a common phenomenon that can occur briefly in any individual. We hypothesize that orthostatic hypotension is caused by an abrupt simultaneous termination of stellate ganglion nerve activity (SGNA) and vagal nerve activity (VNA) at the time of postural change, and that β2 adrenoceptor blockade is an effective therapy.
Methods and Results: We used a radiotransmitter to record SGNA, VNA and blood pressure (BP) in 8 ambulatory dogs; 5 showed simultaneous sympathovagal discharges. The min-by-min integrated SGNA in these 5 dogs correlated with integrated VNA in a linear pattern (“Group 1”). In these dogs abrupt termination of simultaneous SGNA-VNA at the time of postural changes was followed by abrupt (>20 mmHg over 4 beats) drops in BP (Figure). Video imaging showed that the dogs changed their posture from prone (at green bar) to upright (at red bar). Dogs without simultaneous on/off firing (“Group 2”) did not have drastic drops in pressure. ICI 118,551 (ICI, a specific β2-blocker) infused at 3.1 μg/kg/hr for 7 days significantly increased integrated SGNA (p=0.0001) and also the BP from 126 (95% confidence interval, CI: 118 to 133) mmHg to 133 (95% CI 125 to141) mmHg (p=0.0001). The occurrence of hypotension (mean systolic BP < 100 mmHg) during baseline accounted for 7.1% of the recording. The percentage was reduced by ICI to 1.3% (p = 0.01, compared to baseline).
Conclusion: Abrupt simultaneous termination of SGNA-VNA at the time of postural changes underlies the mechanisms of orthostatic hypotension. Selective β2 adrenoceptor blockade may be a novel therapeutic approach for orthostatic hypotension.
- © 2013 by American Heart Association, Inc.