Major Department

Health and Human Physiology

College

College of Liberal Arts & Sciences

Degree

BS (Bachelor of Science)

Session and Year of Graduation

Fall 2020

Honors Major Advisor

Elizabeth Rook-Panicucci

Thesis Mentor

Darren P. Casey

Abstract

When individuals encounter periods of low oxygen, hypoxia, the peripheral chemoreflex works to restore saturation to normal levels. The peripheral chemoreceptors are responsible for sensing such decreases in oxygen and signaling consequent increases in ventilation and sympathetic-mediated cardiovascular (CV) responses. Aside from oxygen, other molecules like glucose, insulin, leptin, carbon dioxide, and nitric oxide (NO) have been shown to affect this reflex. NO, specifically, exhibits a reflex blunting effect demonstrated by various animal studies. Obstructive sleep apnea (OSA), a disease characterized by repeated mechanical occlusions of the upper airway during sleep, demonstrates both a pathophysiological sensitization of the peripheral chemoreflex and a noted decrease in bioavailable NO. This study’s purpose was to analyze the effects of acute inorganic nitrate supplementation (beetroot juice), a dietary path for increasing bioavailable NO, on the heart rate and ventilatory response to acute hypoxia and brachial blood-pressure (BP) in subjects with OSA. We hypothesized that, inorganic nitrate would blunt chemoreflex responsiveness as observed through the ventilatory and cardiovascular (HR) biomarkers. The study followed a double-blind, randomized, placebo-controlled format in which 14 subjects with mild-to-moderate OSA, over the course of two study days, consumed both the placebo beetroot juice (BRP) and the nitrate beetroot juice (BRN;500mg inorganic-nitrate and 40mg nitrite). Peripheral chemoreflex responsiveness was analyzed as the absolute-change and the linear-regression against SpO2 for HR and VE. The ventilatory response was analyzed under two criteria: baseline to target 80% hypoxia (Bl-T) and baseline to peak response (Bl-P). The effects of BRP and BRN were analyzed as the comparison between the two bouts of acute hypoxia (pre-vs-post supplementation) conducted on each study day. The intervention successfully increased NO bioavailability (plasma-nitrate: pre:26±11μmol/L , post:292±90μmol/L, pE responsiveness increased in the absolute-change Bl-P-BRP (pre:3.1±1.2L/min, post:4.3±2.3L/min, p=0.03) but not BRN (pre:4.3±2.6L/min, post:4.8±2.7L/min, p=0.43). The VE Bl-T absolute-change (p=0.11), Bl-P linear-regression (p=0.33), and Bl-T linear-regression (p=0.08) also did not change. The HR response to hypoxia (linear-regression and absolute-change) was unaltered in either intervention (p=0.12, p=0.54 respectively). Systolic BP (SBP) increased under BRP (pre:120±9, post:127±10, pN (pre: 123±13 mmHg, post: 123±9 mmHg, p=0.96), DBP did not change in BRP or BRN (p=0.08). Holistically, these findings suggest no impact of nitrate supplementation on peripheral chemoreflex effectors (HR and ventilatory response) in OSA. Alternatively, the SBP response to nitrate supplementation may suggest inorganic nitrate can blunt diurnal increases in BP.

Keywords

inorganic nitrate, obstructive sleep apnea, acute hypoxia, hypertension, peripheral chemoreflex

Total Pages

30

Copyright

Copyright © 2020 Thomas Asama

COinS
 

URL

https://ir.uiowa.edu/honors_theses/345