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β1-Blockade increases maximal apnea duration in elite breath-hold divers

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posted on 2023-01-30, 16:40 authored by Ryan L. Hoiland, Philip N. Ainslie, Anthony R. Bain, David B. MacLeod, Michael StembridgeMichael Stembridge, Ivan Drvis, Dennis Madden, Otto Barak, Doug M. MacLeod, Zeljko Dujic

 We hypothesized that the cardioselective β1-adrenoreceptor antagonist esmolol would improve maximal apnea duration in elite breath-hold divers. In elite national-level divers (n = 9), maximal apneas were performed in a randomized and counterbalanced order while receiving either iv esmolol (150 μg·kg−1·min−1) or volume-matched saline (placebo). During apnea, heart rate (ECG), beat-by-beat blood pressure, stroke volume (SV), cardiac output (CO), and total peripheral resistance (TPR) were measured (finger photoplethysmography). Myocardial oxygen consumption (MV̇o2) was estimated from rate pressure product. Cerebral blood flow through the internal carotid (ICA) and vertebral arteries (VA) was assessed using Duplex ultrasound. Apnea duration improved in the esmolol trial when compared with placebo (356 ± 57 vs. 323 ± 61 s, P < 0.01) despite similar end-apnea peripheral oxyhemoglobin saturation (71.8 ± 10.3 vs. 74.9 ± 9.5%, P = 0.10). The HR response to apnea was reduced by esmolol at 10–30% of apnea duration, whereas MAP was unaffected. Esmolol reduced SV (main effect, P < 0.05) and CO (main effect; P < 0.05) and increased TPR (main effect, P < 0.05) throughout apnea. Esmolol also reduced MV̇o2 throughout apnea (main effect, P < 0.05). Cerebral blood flow through the ICA and VA was unchanged by esmolol at baseline and the last 30 s of apnea; however, global cerebral blood flow was reduced in the esmolol trial at end-apnea (P < 0.05). Our findings demonstrate that, in elite breath-hold divers, apnea breakpoint is improved by β1-blockade, likely owing to an improved total body oxygen sparring through increased centralization of blood volume (↑TPR) and reduced MV̇o2. 

History

Published in

Journal of Applied Physiology

Publisher

American Physiological Society

Version

  • AM (Accepted Manuscript)

Citation

Hoiland, R., Ainslie, P., Bain, A., Macleod, David, Stembridge, M., Drvis, I., Madden, D., Barak, O., Macleod, Doug & Dujic, Z. (2016) 'Beta 1-blockade increases maximal apnea duration in elite breath hold divers', Journal of Applied Physiology, 122 (4), pp. 899-906

Print ISSN

8750-7587

Electronic ISSN

1522-1601

Cardiff Met Affiliation

  • Cardiff School of Sport and Health Sciences

Cardiff Met Authors

Mike Stembridge

Cardiff Met Research Centre/Group

  • Cardiovascular Physiology

Copyright Holder

  • © The Publisher

Language

  • en

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