Arterial blood gas measurements during deep open-water breath-hold dives

Arterial blood gas (ABG) measurements at both maximum depth and at resurfacing prior to breathing have not previously been measured during free dives conducted to extreme depth in cold open-water conditions. An elite free diver was instrumented with a left radial arterial cannula connected to two sampling syringes through a low-volume splitting device. He performed two open-water dives to a depth of 60 m (197 0, 7 atmospheres absolute pressure) in the constant weight with fins competition format. ABG samples were drawn at 60 m (by a mixed-gas scuba diver) and again on resurfacing before breathing. An immersed surface static apnea, of identical length to the dives and with ABG sampling at identical times, was also performed. Both dives lasted approximately 2 min. Arterial partial pressure of oxygen (Pa-O2) increased during descent from an indicative baseline of 15.8 kPa (after hyperventilation and glossopharyngeal insufflation) to 42.8 and 33.3 kPa (dives 1 and 2) and decreased precipitously (to 8.2 and 8.6 kPa) during ascent. Arterial partial pressure of carbon dioxide (Pa-CO2) also increased from a low indicative baseline of 2.8 kPa to 6.3 and 5.1 kPa on dives 1 and 2; an increase not explained by metabolic production of C-O2 alone since Pa-CO2 actually decreased during ascent (to 5.2 and 4.5 kPa). Surface static apnea caused a steady decrease in Pa-O2 and increase in Pa-CO2 without the inflections provoked by depth changes. Lung compression and expansion provoke significant changes in both Pa-O2 and Pa-CO2 during rapid descent and ascent on a deep free dive. These changes generally support predictive hypotheses and previous findings in less extreme settings. NEW & NOTEWORTHY Arterial blood gas measurements at both maximum depth and the surface before breathing on the same dive have not previously been obtained during deep breath-hold dives in cold open-water conditions and competition dive format. Such measurements were obtained in two dives to 60m (197') of 2 min duration. Changes in arterial oxygen and carbon dioxide (an increase during descent, and a decrease during ascent) support previous observations in less extreme dives and environments.

Automated summary

Arterial blood gas measurements were obtained during extreme deep free dives, showing significant changes in both oxygen and carbon dioxide partial pressure during descent and ascent. These findings support previous observations in less extreme diving environments.