Beta 1-blockade increases maximal apnea duration in elite breath hold divers
American Physiological Society
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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 i.v. esmolol (150μg ⋅ 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 (MVO2) 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 to placebo (356±57 vs. 323±61 seconds; 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, while 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 MVO2 throughout apnea (main effect; P<0.05). Cerebral blood flow through the ICA and VA were unchanged by esmolol at baseline and the last 30 seconds 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 MVO2.
Journal of Applied Physiology
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
This article was published in Journal of Applied Physiology on 28 April 2016 (online), available at http://dx.doi.org/10.1152/japplphysiol.00127.2016
This study was funded through a Canadian Research Chair and NSERC Discovery grant held by Prof Ainslie. Drs. Dujic, Barak, and Ainslie were also funded through the Croatian Science Foundation (grant no. IP-2014-09-1937). We would like to specially acknowledge the apnea divers from the Croatia National Apnea team for their participation.
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