Abstract
The purpose of this study was to assess the differences in cardiac autonomic modulation
during maximal static (SA) and dynamic (DA) underwater apneas. Arterial oxygen saturation
(SpO2), heart rate (HR) and HR variability (SD1 from Poincaré plot and short-term fractal-like
scaling exponent, α1) were analyzed at the immersed baseline (3 min) and initial, mid- and end-phases (each 30 s) of SA and DA in nine elite breath-hold divers. DA and SA lasted 78±8 and 225±20 s (mean±SEM), respectively, and resulted in similar decrements in end-stage SpO2 (78±3 and 75±3%, p=0.352). During DA, initial increase in HR (from 80±5 to 122±5 bpm, p<0.001) was followed by gradual decrease towards the baseline at mid-apnea and end-apnea
phase (101±6 and 80±8 bpm, respectively). 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 (66±4 bpm). Decreased SD1 was observed 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 (62±16 and 66±10 ms, p=0.128 and p=0.093, respectively, p=0.602 DA vs. SA). α1 tended to be higher at the end of DA compared with SA (1.17±0.10 vs. 0.79±0.10, p=0.059). We concluded that apnea blunts the effects of exercise on cardiac vagal activity
at the end of DA. However, higher HR during DA compared with SA indicates larger cardiac
sympathetic activity during DA, as suggested also by slightly higher α1.
Keywords
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Article info
Publication history
Published online: June 11, 2012
Accepted:
May 17,
2012
Received in revised form:
March 28,
2012
Received:
December 21,
2011
Identification
Copyright
© 2012 Elsevier B.V. Published by Elsevier Inc. All rights reserved.
