Dopamine receptor blockade improves pulmonary gas exchange during exercise in healthy humans (717.1)

Abstract

Impaired pulmonary gas exchange during heavy exercise, manifested as an increase in the alveolar‐arterial oxygen difference (A‐aDO2), may be due to anatomical intrapulmonary (IP) shunt recruitment. Dopamine (DA) has been shown to recruit IP shunts at rest and circulating DA increases with exercise, and thus may contribute to the increased A‐aDO2 during exercise. We hypothesized that gas exchange impairment during exercise will decrease with DA receptor blockade. Ten healthy males (Age: 25±6 yrs, VO2max: 56.3±6.6 ml∙kg‐1∙min‐1) performed two incremental staged cycling exercise sessions after ingestion of either placebo (P) or DA blockade (B) (Metoclopramide 20mg). Arterial blood gas sampling and cardiorespiratory data were obtained at rest and during 4 exercise intensities (30%, 50%, 75% and 90% of previously determined VO2max). At 90% VO2max, DA blockade decreased A‐aDO2 (P: 19.3±8.5 torr, B: 14.8±6.8 torr, p=0.038 and increased arterial O2 saturation (P: 95.4±1.0%, B: 96.2±0.9%, p=0.004). Blood gases were similar between the two groups at rest, 30%, 50% and 75% of VO2max. Compared to placebo, DA blockade did not change O2 consumption, CO2 production, or respiratory exchange ratio at any intensity. Administration of a DA receptor blockade decreased A‐aDO2 during near‐maximal exercise, suggesting that endogenous DA affects affects pulmonary gas exchange during exercise.Grant Funding Source: Supported by The National Sciences and Engineering Research Council of Canada