The Effect of Inhaled Nitric Oxide on Maximal Oxygen Consumption in High-fit and Untrained Individuals

• Author / Creator

  Brotto,Andrew R

• Previous work suggests that endurance-trained athletes have superior pulmonary vasculature function as compared to untrained individuals, which may contribute to their greater maximal oxygen uptake (V̇O2max). Inhaled nitric oxide (iNO) improves pulmonary vascular compliance at rest in healthy individuals, which may translate to greater compliance during exercise and improved V̇O2max. The purpose of this study was to examine whether iNO improves V̇O2max in high-fit and untrained individuals. It was hypothesized that iNO will increase V̇O2max in untrained individuals, while no significant change would be observed in high-fit individuals. Sixteen high-fit and sixteen untrained individuals with normal lung function completed the randomized double-blind cross-over study over four sessions. On day 1, participants completed a pulmonary function and standard cardiopulmonary exercise test (CPET). Untrained was defined as a V̇O2max between 30-45 ml  kg-1  min-1, and high-fit was defined as a V̇O2max >55 ml  kg-1  min-1 for females and >60 ml  kg-1  min-1 for males. A cut-off of 45 ml  kg-1  min-1 was used as this represents from the 10th - 50th percentile of fitness in the general population, while a V̇O2max >55 ml  kg-1  min-1 for females and >60 ml  kg-1  min-1 for males has previously been associated with enhanced cardiac function. On days 2 and 3, participants completed experimental CPETs while breathing either normoxia (placebo, day 2) or 40 ppm of iNO (day 3, order of test day randomized). On day 4, echocardiography was performed during rest and sub-maximal exercise (60 Watts) while participants breathed either iNO or placebo. Expired gas was collected to determine V̇O2, carbon dioxide production (V̇CO2), and ventilation. Cardiac output was estimated by impedance cardiography and right ventricular systolic pressure (RVSP) was estimated using Doppler Echocardiography. RVSP was significantly reduced with iNO at rest (Placebo: 7.55 ± 0.86 mmHg vs. iNO: 6.35 ± 0.72 mmHg, p< 0.001) and exercise (Placebo: 10.15 ± 1.08 mmHg vs. iNO: 7.29 ± 0.84 mmHg, p= 0.011). V̇O2max was significantly different between groups (Untrained: 43.3 ± 1.0 ml  kg-1  min-1 vs. High-fit: 66.1 ± 1.0 ml  kg-1  min-1, p< 0.001), but there was no effect of condition (Placebo: 54.9 ± 1.0 ml  kg-1  min-1 vs. iNO: 54.5 ± 1.0 ml  kg-1  min-1, p= 0.788) and no group by condition interaction (p= 0.682). Peak cardiac output, ventilation and V̇CO2 were also unchanged by iNO in both groups. These data demonstrate that despite reductions in pulmonary vascular resistance, V̇O2max was unaffected by iNO in both high-fit and untrained participants. These results suggest that the pulmonary vasculature does not limit V̇O2max in young healthy individuals, regardless of aerobic fitness level.

• Subjects / Keywords

  • Maximal Oxygen Consumption
  • Nitric Oxide

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-67xq-7z90

• License

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