Voluntary breath-holding in the morning and in the evening

Abstract

The aim of the present study was to determine whether or not voluntary breath-holding time (BHT) changes with the time of the day. BHT with airways closed at end-expiration was measured in six male subjects in the sitting position during the morning (08.00-12.00 hours, on days 1, 6, 7 and 8) and evening (20.00-24.00 hours, on days 2 and 4). BHT increased with the number of days of testing and, at day 8, the morning values averaged 160% of those on day 1. Also, Delta P ACO2 [the difference between end-tidal partial pressure of CO2 ( P CO2) and alveolar P CO2 ( P ACO2) at the breaking point] increased in proportion to BHT. Hence the BHT/Delta P ACO2 ratio remained nearly constant. Voluntary hyperventilation prolonged BHT and increased Delta P ACO2. Conversely, in hypoxia (13% O2 for 1-2 h), BHT and Delta P ACO2 were reduced proportionally. During the evening sessions, most of the BHT/Delta P ACO2 ratios in normoxia, hypoxia or after hyperventilation were higher than the corresponding morning values, with the group difference reaching statistical significance for the measurements in normoxia and hypoxia. In conclusion, voluntary BHT varies in both duration and its relationship with Delta P ACO2 between the morning and evening hours. The results should also imply that, with an interruption of breathing, changes in alveolar and arterial gases are not the same at different times of the day.

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Circulatory effects of apnoea in elite breath‐hold divers

“…To avoid effects of circadian variations on cardiovascular parameters (Bosco et al 2004), all measurements were performed in the morning. Heart rate (HR) and arterial blood oxygen saturation (SaO 2 ) were measured continuously with a pulse oximeter (NPB 40; Nelcor Puritan Bennett, Pleasanton, CA, USA) fixed on the left median finger.…”

Hypercapnic Ventilatory Response: A Comparison Between Elite and Novice Skin Divers

“…Two min after the fifth BH FI effort subjects performed a HCVR test. Taking into account the starting time of the HCVR in the 1 st visit, the starting time of the 2 nd laboratory visit was determined about ~ 30 min earlier so both HCVR tests were performed, at approximately the same time [18]. HCVR test in any condition was always conducted in a sitting position.…”