Cardiac vagal modulation during static and dynamic breathhold dives in elite divers

Abstract

Marked bradycardia occurs at the end of breath‐hold dives. However, vagal modulation of heart rate (HR) during maximal static (SA) and dynamic (DA) underwater apneas is not well‐known. HR, HR variability (SD1) and arterial oxygen saturation (SpO2) were analyzed at the immersed baseline and at initial‐, mid‐ and end‐apnea (each 30 s) of maximal underwater SA and DA in nine breath‐hold divers. DA lasted 78±8 s and SA 225±20 s (mean±SEM) and resulted in similar decreases in SpO2 (78±3 and 75±3 %, p=0.352, respectively). Initially, DA increased HR from 80±5 to 122±5 bpm (p<0.001), followed by decrease in HR at mid‐apnea and end‐apnea (101±6 and 80±8 bpm). During SA, HR decreased at mid‐apnea (from 78±4 to 66±3 bpm, p=0.004) but did not decrease further at end‐apnea phase. SD1 decreased at the initial phase of DA (from 28±5 to 10±4 ms, p=0.005) being lower compared with SA (24±4 ms, p=0.005). At the end of DA and SA, SD1 tended to increase above the baseline (67±16 and 66±10 ms, p=0.088 and p=0.093, respectively) and did not differ from each other (p=0.804). We concluded that apnea blunts the effects of exercise on HR variability at the end of DA when despite the higher HR. This indicates complex interplay between vagal and sympathetic responses to apnea and exercise. Supported by TEKES, Finland, Paavo Nurmi Foundation, Finland and Croatian Ministry of Science.