No effect of nitric oxide on pulmonary pressure response to SCUBA diving

Abstract

Some SCUBA diving time and depth profiles have been shown to increase pulmonary artery systolic pressure (PASP) post-dive. SCUBA diving while breathing compressed air results in a hyperoxic fraction of inspired oxygen and SCUBA divers are not hypoxic following a dive, so hypoxic pulmonary vasoconstriction is not responsible for the observed increase in PASP. In addition, no studies to date have examined whether the increased PASP is due to vasoconstriction or increased cardiac output (Q) following the dive. The purpose of this study was to examine whether nitric oxide availability post-dive is associated with the increased pulmonary pressure following SCUBA diving. 26 subjects completed the study (6 female). Subjects completed two dives (18 meters of sea water, 47 minute bottom time) on back-to-back days. Subjects were given sildenafil or placebo in a randomized and balanced crossover design upon resurfacing from their dive. Cardiac ultrasound for measurements of PASP and Q were done before diving and 1 hour after drug ingestion upon resurfacing. Total pulmonary resistance (TPR) was calculated as PASP/Q. PASP (p=0.0186) and TPR (p=0.0156), but not Q (p=0.779), increased on day 1 in the sildenafil group only. Irrespective of drug treatment, PASP was significantly higher by 2.58 mmHg at pre-dive on day 2 compared to pre-dive day 1 (p = 0.031). The increase in pulmonary pressure with SCUBA is likely independent of nitric oxide bioavailability. In addition, pulmonary pressure may remain mildly elevated for up to 24 hours after a SCUBA dive at 18m for 47 minutes. PADI Foundation Diving Physiology Grant (2021 - 2022), Title: Is SCUBA diving-induced pulmonary hypertension related to blood flow through patent foramen ovale and inflammation? AT Lovering (PI), Zeljko Dujic (Co-I); Fulbright Scholars Program (2019 & 2022), Title: Investigating the role of intrapulmonary and intracardiac shunts in mediating breath-hold diving-induced and SCUBA diving-induced pulmonary hypertension. A.T. Lovering (PI); University of Oregon College of Arts & Sciences International Research Travel Grant (2022), AT Lovering (PI); Global Oregon Faculty Research Travel program (2022), AT Lovering (PI) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.