Blood Adenosine Increase During Apnea in Spearfishermen Reinforces the Efficiency of the Cardiovascular Component of the Diving Reflex.

Marion Marlinge,Jean-Claude Rostain,Mathieu Coulange,Marion Zavarro,Régis Guieu,Fabrice Joulia,François Billaut,Mohamed Chefrour

doi:10.3389/fphys.2021.743154

Abstract

The physiopathology consequences of hypoxia during breath-hold diving are a matter of debate. Adenosine (AD), an ATP derivative, is suspected to be implicated in the adaptive cardiovascular response to apnea, because of its vasodilating and bradycardic properties, two clinical manifestations observed during voluntary apnea. The aim of this study was to evaluate the adenosine response to apnea-induced hypoxia in trained spearfishermen (SFM) who are used to perform repetitive dives for 4–5 h. Twelve SFM (11 men and 1 woman, mean age 41 ± 3 years, apnea experience: 18 ± 9 years) and 10 control (CTL) subjects (age 44 ± 7 years) were enrolled in the study. Subjects were asked to main a dry static apnea and stopped it when they began the struggle phase (average duration: SFM 120 ± 78 s, CTL 78 ± 12 s). Capillary blood samples were collected at baseline and immediately after the apnea and analyzed for standard parameters and adenosine blood concentration ([AD]b). Heart rate (HR), systolic (SBP), and diastolic (DBP) blood pressures were also recorded continuously during the apnea. During the apnea, an increase in SBP and DBP and a decrease in HR were observed in both SFM and CTL. At baseline, [AD]b was higher in SFM compared with CTL (1.05 ± 0.2 vs. 0.73 ± 0.11 μM, p < 0.01). [AD]b increased significantly at the end of the apnea in both groups, but the increase was significantly greater in SFM than in controls (+90.4 vs. +12%, p < 0.01). Importantly, in SFM, we also observed significant correlations between [AD]b and HR (R = −0.8, p = 0.02), SpO2 (R = −0.69, p = 0.01), SBP (R = −0.89, p = 0.02), and DBP (R = −0.68, p = 0.03). Such associations were absent in CTL. The adenosine release during apnea was associated with blood O2 saturation and cardiovascular parameters in trained divers but not in controls. These data therefore suggest that adenosine may play a major role in the adaptive cardiovascular response to apnea and could reflect the level of training.

Highlights

The cardiovascular adaptive response to breath-hold diving, known as the diving response, has long been a matter of debate, especially since the popularization of recreational apnea and spearfishing
The activation of A1R can lead to bradycardia, sinus arrest, or atrioventricular block (ATVB), while the activation of A2 subtypes leads to strong vasodilation and hypotension
There were no significant differences between SFM and CTL regarding their anthropometric characteristics (Table 1) and the resting values of Heart rate (HR), DBP, SBP, pH, SpO2, PCO2, and [La] (Table 2)

Summary

Introduction

The cardiovascular adaptive response to breath-hold diving, known as the diving response, has long been a matter of debate, especially since the popularization of recreational apnea and spearfishing. These aquatic activities commonly involve hours of immersion with repeated voluntary dynamic apneic phases causing severe hypoxia streak (Marlinge et al, 2021). Adenosine (AD), an ATP derivative, is implicated in the response to hypoxemia during breath hold (Joulia et al, 2013, 2014; Marlinge et al, 2019). A3R are implicated in ischemia– reperfusion protection (Guieu et al, 2020; Paganelli et al, 2021)

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