Baroreflex Function During Orthostatic Stress with Administration of a Somatostatin Analog

Open Access
Author:
Leone, David Michael
Area of Honors:
Kinesiology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • James Anthony Pawelczyk, Thesis Supervisor
  • Stephen Jacob Piazza, Honors Advisor
  • Karl Maxim Newell, Faculty Reader
Keywords:
  • Baroreflex Sensitivity
  • Baroreflex Effectiveness Index
  • Orthostatic Intolerance
  • Octreotide
  • Head Up Tilt
Abstract:
Arterial baroreflexes provide short-term blood pressure regulation during orthostatic stresses, such as standing. In this study we evaluated the magnitude and frequency of baroreflex engagement during orthostatic stress before and after blood volume was redistributed by constricting the splanchnic (gut) vasculature selectively with octreotide acetate, a somatostatin analog. Purpose: To evaluate the baroreflex sensitivity (BRS), and effectiveness index (BEI) during orthostatic stress, with and without pharmacological protection from orthostatic intolerance. Two procedures were employed with healthy, young subjects (n = 52; ages 18-37). In the first procedure, subjects were tilted upright to 70°, once with a placebo and once with octreotide. In the second procedure, subjects were tilted at intervals of 15°, 30°, and 50°. BRS and BEI were both evaluated post-tilt using the spontaneous association between changes in R-R Intervals and changes in systolic blood pressure. BRS was measured by the slope of the relationship. BEI was determined as the percentage of ramps in systolic blood pressure that elicited a baroreflex-mediated change in R-R interval. Results: In all protocols there was a significant decrease in BRS with increased orthostatic stress (p<0.0001). Conversely, there was a significant increase in BEI with increased stress (p=0.0018). Orthostatic tolerance was significantly increased (p=0.001) with octreotide, but BRS and BEI were unaffected. Conclusion: Passive tilt reduces the sensitivity of the baroreflex, but increases the frequency of engagement. The increased baroreflex activation is necessary to maintain blood pressure during orthostatic stress. We found that octreotide significantly increases orthostatic tolerance, but has no effect on BRS or BEI. These findings suggest that this improvement to tolerance was independent of arterial baroreflexes.&#8195;