M. Bryant-Ekstrand1, T. Kelly1, C. Brown2, R. Lord3, T. Dawkins3, A. Drane3, O. Barak4, T. Dragun5, M. Stembridge3, B. Spajić6, I. Drviš6, J.W. Duke7, G. Foster2, Z. Dujic5, AT. Lovering1

1University of Oregon, Eugene, OR, USA, 2University of British Columbia, Kelowna, BC, Canada, 3Cardiff Metropolitan University, Cardiff, Wales, UK, 4University of Novi Sad, Novi Sad, Serbia, 5University of Split School of Medicine, Split, Croatia, 6University of Zagreb, Zagreb, Croatia, 7Northern Arizona University, Flagstaff, AZ, USA

Breath-hold divers (BHD) routinely place themselves into extremely hypoxemic (low blood oxygen) conditions and therefore repeatedly expose themselves to intermittent bouts of hypoxia and consequently pulmonary hypertension and increased right heart work. PURPOSE: The purpose of this study was to 1) determine if pulmonary arterial pressure and right heart dysfunction in hypoxia were greater in BHD compared to controls, and 2) determine the role of a pulmonary vasodilator in alleviating the increased pulmonary pressure in response to hypoxia. METHODS: Subjects (n=24, 12 BHD, 12 Control) completed two 30-minute isocapnic normobaric hypoxic breathing challenges, after receiving either 50mg sildenafil or placebo, with a 48-hour minimum washout period between visits. Pulmonary arterial systolic pressure (PASP) and right heart function via tricuspid anular plane systolic excursion (TAPSE) measures were made using Doppler ultrasound, and total pulmonary resistance (TPR) was calculated with PASP and cardiac output (Qt). RESULTS: Compared to placebo, BHD had a reduction in TPR with sildenafil in normoxia (312.5 ± 92.8 vs 385 ± 122.6 dynes/sec/cm-5, respectively, p = .04). Compared to normoxia, PASP was increased with hypoxia in BHDc with placebo (22.9±6.0 vs. 32.4±8.9 mm Hg, respectively, p=0.0002) but not with sildenafil. Conversely, BHD had no changes in PASP with placebo, but had an increase in PASP from normoxia to hypoxia with sildenafil (22.3±4.8 vs. 31.5±6.9 mm Hg, respectively, p=0.0002). CONCLUSION: There was no effect of group or treatment on TAPSE. Our data suggest breath hold divers may have a previously unrecognized chronic pulmonary vasoconstriction in room air that is prevented with administration of sildenafil.

Funded by the Burroughs Wellcome Fund (BWF) 2018 Collaborative Research Travel Grant (CRTG) and the Fulbright U.S. Scholar Grant.

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Figure 1

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