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β1-Blockade increases maximal apnea duration in elite breath-hold divers
Ryan L Hoiland1, Philip N Ainslie2, Anthony R Bain2
1Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia-Okanagan, Kelowna, British Columbia, Canada; ryanleohoiland@gmail.com.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|April 30, 2016
Summary
The beta-1 blocker esmolol improved maximal apnea duration in elite divers by reducing myocardial oxygen consumption and increasing total peripheral resistance. This beta-blockade enhances oxygen conservation, leading to longer breath-hold times.
Area of Science:
- Cardiovascular Physiology
- Human Performance
- Pharmacology
Background:
- Elite breath-hold divers push physiological limits, making interventions to extend apnea duration highly sought after.
- Anecdotal evidence suggests beta-blockers may enhance breath-hold capabilities, leading to competitive bans.
- The physiological mechanisms underlying potential beta-blocker effects on apnea remain unclear.
Purpose of the Study:
- To investigate the effect of the cardioselective beta-1 antagonist esmolol on maximal apnea duration in elite breath-hold divers.
- To elucidate the cardiovascular and cerebrovascular responses to esmolol during apnea.
- To determine if esmolol improves oxygen conservation during breath-hold.
Main Methods:
- A randomized, placebo-controlled, counterbalanced trial involving 9 elite national-level divers.
- Administration of intravenous esmolol or saline placebo prior to maximal apnea attempts.
- Continuous monitoring of heart rate, blood pressure, stroke volume, cardiac output, total peripheral resistance, and estimated myocardial oxygen consumption.
- Assessment of cerebral blood flow via Duplex ultrasound of internal carotid and vertebral arteries.
Main Results:
- Maximal apnea duration was significantly increased with esmolol compared to placebo (356 ± 57 s vs. 323 ± 61 s, P < 0.01).
- Esmolol reduced heart rate response, stroke volume, cardiac output, and myocardial oxygen consumption during apnea.
- Total peripheral resistance increased with esmolol, suggesting blood volume centralization, while cerebral blood flow was largely maintained until end-apnea.
Conclusions:
- Beta-1 blockade with esmolol improves maximal apnea duration in elite divers.
- The improvement is likely due to enhanced oxygen sparring via reduced myocardial oxygen consumption and increased peripheral resistance.
- These findings provide the first empirical evidence confirming the efficacy of beta-blockade in extending apnea duration.
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