Arterial blood gases in divers at surface after prolonged breath-hold

Purpose Adaptations during voluntary breath-hold diving have been increasingly investigated since these athletes are exposed to critical hypoxia during the ascent. However, only a limited amount of literature explored the pathophysiological mechanisms underlying this phenomenon. This is the first study to measure arterial blood gases immediately before the end of a breath-hold in real conditions. Methods Six well-trained breath-hold divers were enrolled for the experiment held at the "Y-40 THE DEEP JOY" pool (Montegrotto Terme, Padova, Italy). Before the experiment, an arterial cannula was inserted in the radial artery of the non-dominant limb. All divers performed: a breath-hold while moving at the surface using a sea-bob; a sled-assisted breath-hold dive to 42 m; and a breath-hold dive to 42 m with fins. Arterial blood samples were obtained in four conditions: one at rest before submersion and one at the end of each breath-hold. Results No diving-related complications were observed. The arterial partial pressure of oxygen (96.2 +/- 7.0 mmHg at rest, mean +/- SD) decreased, particularly after the sled-assisted dive (39.8 +/- 8.7 mmHg), and especially after the dive with fins (31.6 +/- 17.0 mmHg). The arterial partial pressure of CO2 varied somewhat but after each study was close to normal (38.2 +/- 3.0 mmHg at rest; 31.4 +/- 3.7 mmHg after the sled-assisted dive; 36.1 +/- 5.3 after the dive with fins). Conclusion We confirmed that the arterial partial pressure of oxygen reaches hazardously low values at the end of breath-hold, especially after the dive performed with voluntary effort. Critical hypoxia can occur in breath-hold divers even without symptoms.