Diving reflex: can the time course of heart rate reduction be quantified?

Abstract

In this meta-analysis of diving bradycardia in humans, we sought to quantify any heart rate (HR) reduction using a relatively simple mathematical function. Using the terms "diving reflex,""diving bradycardia,""diving response,""diving plus heart rate," databases were searched. Data from the studies were fitted using HR=c+aexp(-(t-t(0))/τ), where c is the final HR, a is the HR decrease, τ is the time constant of HR decay, and t(0) is the time delay. Of 890 studies, 220 were given closer scrutiny. Only eight of these provided data obtained under comparable conditions. Apneic facial immersion decreased HR with τ=10.4 s and in air alone it was less pronounced and slower (τ=16.2 s). The exponential function fitted the time course of HR decrease closely (r(2)>0.93). The fit was less adequate for apneic-exercising volunteers. During apnea both with and without face immersion, HR decreases along a monoexponential function with a characteristic time constant. HR decrease during exercise with and without face immersion could not readily be described with a simple function: the parasympathetic reaction was partially offset by some sympathetic activity. Thus, we succeeded in quantifying the early time course of diving bradycardia. It is concluded that the diving reflex is useful to diagnose the integrity of efferent cardiovascular autonomic pathways.

Cardiovascular Responses during Free-Diving in the Sea

“…Moreover, it is important to note that the bottom duration of SA is not exactly the same for all divers, which could affect the diving response and the related hemodynamic response. Time course of HR reduction during diving has been thoroughly analyzed by several authors and summarized in some reviews [3,17,20]. Without a doubt, the promptness of diving response is primarily related to the diver's ability.…”

“…Without a doubt, the promptness of diving response is primarily related to the diver's ability. In fact, the maximal bradycardiac response (i. e., HR decay) can occur within 10-24 s in elite divers [3], while it can take up to 146 s in well-trained divers under competition [17]. Finally, to evaluate the blunting of the diving response during dives, it would be useful in the future to make a comparison between our protocol and descents in both static apnea or in non-apneic exercise conditions.…”

Alveolar gas composition during maximal and interrupted apnoeas in ambient air and pure oxygen

“…Recently, some authors (Caspers et al, 2011;Costalat et al, 2015Costalat et al, , 2016 This study is affected by some limitations. First, the sample size estimation was not computed in this study, because power analysis cannot be carried out in the present experimental condition.…”

The Oxygen-Conserving Potential of the Trigeminocardiac Reflex

“…29 Bradycardia is a salient feature of the DR. Myocardial contractility and cardiac output decrease; however, because of peripheral vasoconstriction, the blood supply to the brain remains relatively unaffected. 19,[34][35][36][37] In contrast, artificial ventilation can significantly attenuate or even reverse divingrelated bradycardia. [31][32][33] As a result, whereas the blood supply to the heart meets myocardial oxygen demand, myocardial oxygen consumption decreases.…”