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

Abstract

47We hypothesized that the cardioselective β 1 -adrenoreceptor antagonist esmolol would improve 48 maximal apnea duration in elite breath hold divers. In elite national level divers (n=9), maximal 49 apneas were performed in a randomized and counterbalanced order while receiving either i.v. 50) or volume matched saline (placebo). During apnea, heart rate 51 (ECG), beat-by-beat blood pressure, stroke volume (SV), cardiac output (CO) and total 52 peripheral resistance (TPR) were measured (finger photoplethysmography). Myocardial oxygen 53 consumption (MVO 2 ) was estimated from rate pressure product. Cerebral blood flow through the 54 internal carotid (ICA) and vertebral arteries (VA) was assessed using Duplex ultrasound. Apnea 55 duration improved in the esmolol trial when compared to placebo (356±57 vs. 323±61 seconds; 56 P<0.01) despite similar end apnea peripheral oxyhemoglobin saturation (71.8±10.3% vs. 57 74.9±9.5; P=0.10). The HR response to apnea was reduced by esmolol at 10-30% of apnea 58 duration, while MAP was unaffected. Esmolol reduced SV (main effect; P<0.05) and CO (main 59 effect; P<0.05), and increased TPR (main effect; P<0.05) throughout apnea. Esmolol also 60 reduced MVO 2 throughout apnea (main effect; P<0.05). Cerebral blood flow through the ICA 61 and VA were unchanged by esmolol at baseline and the last 30 seconds of apnea; however, 62 global cerebral blood flow was reduced in the esmolol trial at end apnea (P<0.05). Our findings 63 demonstrate that, in elite breath hold divers, apnea breakpoint is improved by β 1 -blockade, likely 64 owing to an improved total body oxygen sparring through increased centralization of blood 65 volume (↑TPR) and reduced MVO 2 . 66 67 KEY WORDS: esmolol; rate pressure product; breath hold diving; cerebral blood flow 68 69 70 71Esmolol and Maximal Apnea Duration 3

Physiology of static breath holding in elite apneists

“…In the study by Hoiland et al. (), arterial oxygen saturations were similar at the breath‐hold breaking point, indicating that the increased duration of apnoea with cardiac‐selective β 1 ‐blockade was probably associated with reduced oxygen consumption. (The ergogenic effect of β‐blockers has not been lost in the competitive apnoea community, leading to its ban in all AIDA and CMAS organized competitions.)…”

“…In elite apneists, bradycardia in turn increases maximal breath‐hold duration. For example, administration of cardiac‐specific β 1 ‐blockade (esmolol), to accentuate reductions in HR, increases the maximal dry static breath‐hold duration in elite apneists by ∼10% (33 s) compared with a placebo (Hoiland et al., ). In the study by Hoiland et al.…”

Influence of lung volume on the interaction between cardiac output and cerebrovascular regulation during extreme apnoea

“…The lower heart rate can result in a reduction in cardiac work and may help oxygen sparing, thus prolonging apnoea duration (Hoiland et al . ). Despite the positive effects of bradycardia, a balance must exist between oxygen sparing whilst also maintaining the perfusion of important vascular beds.…”

“…; Hoiland et al . ). The authors would like to acknowledge that there is minor overlap in some of the parameters reported (e.g.…”

“…Therefore, volumetric flow was calculated from the velocity of the last successful velocity measurement multiplied by the percentage change in MCAv (ICA) or PCAv (VA) of the next stage, as previously described in detail (Hoiland et al . ) and used repeatedly within the literature (Fisher et al . ; Smith et al .…”