Jessica Hellyer1, A George Akingba2, Kyoung-Suk Rhee1, Alex Y Tan3, Kathleen A Lane4, Changyu Shen5, Jheel Patel1, Michael C Fishbein6, Peng-Sheng Chen7. 1. Division of Cardiology, Department of Medicine, Krannert Institute of Cardiology, Indianapolis, Indiana. 2. Division of Cardiology, Department of Medicine, Krannert Institute of Cardiology, Indianapolis, Indiana; Division of Vascular Surgery, Department of Surgery, Indiana University School of Medicine, Indianapolis, Indiana. 3. Hunter Holmes McGuire VA Medical Center, Virginia Commonwealth University, Richmond, Virginia. 4. Department of Biostatistics, Indiana University School of Medicine, Indianapolis, Indiana. 5. Department of Biostatistics, Indiana University School of Medicine, Indianapolis, Indiana; Fairbanks School of Public Health, School of Medicine, Indiana University, Indianapolis, Indiana. 6. Division of Cardiology, Department of Medicine, Krannert Institute of Cardiology, Indianapolis, Indiana; Department of Pathology and Laboratory Medicine, University of California, Los Angeles, California. 7. Division of Cardiology, Department of Medicine, Krannert Institute of Cardiology, Indianapolis, Indiana. Electronic address: chenpp@iu.edu.
Abstract
BACKGROUND: The relationship between cardiac autonomic nerve activity and blood pressure (BP) changes in ambulatory dogs is unclear. OBJECTIVE: The purpose of this study was to test the hypotheses that simultaneous termination of stellate ganglion nerve activity (SGNA) and vagal nerve activity (VNA) predisposes to spontaneous orthostatic hypotension and that specific β₂-adrenoceptor blockade prevents the hypotensive episodes. METHODS: We used a radiotransmitter to record SGNA, VNA, and BP in eight ambulatory dogs. Video imaging was used to document postural changes. RESULTS: Of these eight dogs, five showed simultaneous sympathovagal discharges in which the minute-by-minute integrated SGNA 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 (as documented by video imaging) was followed by abrupt (>20 mm Hg over four beats) drops in BP. 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 µg/kg/h for 7 days significantly increased BP from 126 mm Hg (95% confidence interval 118-133) to 133 mm Hg (95% confidence interval 125-141; P = .0001). The duration of hypotension (mean systolic BP <100 mm Hg) during baseline accounted for 7.1% of the recording. The percentage was reduced by ICI to 1.3% (P = .01). CONCLUSION: Abrupt simultaneous termination of SGNA-VNA was observed at the time of orthostatic hypotension in ambulatory dogs. Selective β₂-adrenoceptor blockade increased BP and reduced the duration of hypotension in this model.
BACKGROUND: The relationship between cardiac autonomic nerve activity and blood pressure (BP) changes in ambulatory dogs is unclear. OBJECTIVE: The purpose of this study was to test the hypotheses that simultaneous termination of stellate ganglion nerve activity (SGNA) and vagal nerve activity (VNA) predisposes to spontaneous orthostatic hypotension and that specific β₂-adrenoceptor blockade prevents the hypotensive episodes. METHODS: We used a radiotransmitter to record SGNA, VNA, and BP in eight ambulatory dogs. Video imaging was used to document postural changes. RESULTS: Of these eight dogs, five showed simultaneous sympathovagal discharges in which the minute-by-minute integrated SGNA 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 (as documented by video imaging) was followed by abrupt (>20 mm Hg over four beats) drops in BP. 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 µg/kg/h for 7 days significantly increased BP from 126 mm Hg (95% confidence interval 118-133) to 133 mm Hg (95% confidence interval 125-141; P = .0001). The duration of hypotension (mean systolic BP <100 mm Hg) during baseline accounted for 7.1% of the recording. The percentage was reduced by ICI to 1.3% (P = .01). CONCLUSION: Abrupt simultaneous termination of SGNA-VNA was observed at the time of orthostatic hypotension in ambulatory dogs. Selective β₂-adrenoceptor blockade increased BP and reduced the duration of hypotension in this model.
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