title: β1-Blockade increases maximal apnea duration in elite breath-hold divers.
abstract: 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 MV̇o2throughout 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 MV̇o2NEW & NOTEWORTHYThe governing bodies for international apnea competition, the Association Internationale pour le Développment de l'Apnée and La Confédération Mondaile des Activités Subaquatiques, have banned the use of β-blockers based on anecdotal reports that they improve apnea duration. Using a randomized placebo-controlled trial, we are the first to empirically confirm that β-blockade improves apnea duration. This improvement in apnea duration coincided with a reduced myocardial oxygen consumption.
authors.affiliation: Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia-Okanagan, Kelowna, British Columbia, Canada; ryanleohoiland@gmail.com.
authors.forename: Ryan L
authors.identifier: http://orcid.org/0000-0002-5657-0059
authors.initials: RL
authors.lastname: Hoiland
authors.affiliation: Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia-Okanagan, Kelowna, British Columbia, Canada.
authors.forename: Philip N
authors.initials: PN
authors.lastname: Ainslie
authors.affiliation: Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia-Okanagan, Kelowna, British Columbia, Canada.
authors.forename: Anthony R
authors.initials: AR
authors.lastname: Bain
authors.affiliation: Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina.
authors.forename: David B
authors.initials: DB
authors.lastname: MacLeod
authors.affiliation: Cardiff School of Sport, Cardiff Metropolitan University, Cardiff, United Kingdom.
authors.forename: Mike
authors.initials: M
authors.lastname: Stembridge
authors.affiliation: University of Zagreb School of Kinesiology, Zagreb, Croatia.
authors.forename: Ivan
authors.initials: I
authors.lastname: Drvis
authors.affiliation: Department of Integrative Physiology, University of Split School of Medicine, Split, Croatia.
authors.forename: Dennis
authors.initials: D
authors.lastname: Madden
authors.affiliation: Department of Physiology, University of Novi Sad School of Medicine, Novi Sad, Serbia; and.
authors.forename: Otto
authors.initials: O
authors.lastname: Barak
authors.affiliation: Emory University, Atlanta, Georgia.
authors.forename: Douglas M
authors.initials: DM
authors.lastname: MacLeod
authors.affiliation: Department of Integrative Physiology, University of Split School of Medicine, Split, Croatia.
authors.forename: Zeljko
authors.initials: Z
authors.lastname: Dujic
mesh_terms: D058671:Adrenergic beta-1 Receptor Antagonists / Q000627:therapeutic use*; D000328:Adult; D001049:Apnea / Q000188:drug therapy* / Q000378:metabolism; D001794:Blood Pressure / Q000187:drug effects; D062485:Breath Holding / Q000187:drug effects*; D002302:Cardiac Output / Q000187:drug effects; D002343:Carotid Artery, Internal / Q000187:drug effects / Q000378:metabolism; D002560:Cerebrovascular Circulation / Q000187:drug effects; D004242:Diving / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects; D010108:Oxyhemoglobins / Q000378:metabolism; D011412:Propanolamines / Q000627:therapeutic use; D013318:Stroke Volume / Q000187:drug effects; D014655:Vascular Resistance / Q000187:drug effects; D014711:Vertebral Artery / Q000187:drug effects / Q000378:metabolism
chemical_list: D058671:Adrenergic beta-1 Receptor Antagonists; D010108:Oxyhemoglobins; D011412:Propanolamines; C036604:esmolol; D010100:Oxygen
keywords: breath-hold diving; cerebral blood flow; esmolol; rate pressure product