Arterial blood gases' analysis in elite breath-hold divers at extreme depths

To showcase results of arterial blood gases' analysis in elite breath-hold divers sampled at depths where their total lung capacities are below their residual lung volume on surface.

Three male elite breath-hold divers performed body plethysmographies to determine their lung volumes. Two dives were performed, one on normal inhalation to 60 m of depth and the second on complete exhalation to 10 m of depth. Blood samples were taken on five occasions; before the first dive, at 60 and 10 m of depth and immediately after resurfacing after both dives.

Arterial blood gases' analysis at 60 m of depth showed an increase in partial pressures of oxygen and carbon dioxide, a consequent decrease in pH and an increase in concentration of HCO₃^-. After resurfacing, in two divers, values mostly returned to normal; hypoxemia was observed in one diver. At 10 m of depth, all values showed similar variation, and hypoxemia was observed in the same diver but at depth. Upon resurfacing, all values returned to normal.

This is the first study performed at depths where the total lung capacities of participants are below their residual lung volumes at the surface. Partial pressure of carbon dioxide increases at depth to higher than normal values causing pH to decrease thus exceeding the buffering potential of the blood. In addition, previous assumptions that maximum depth in breath-hold divers is where total lung capacity is reduced to their residual volume proved wrong as our group of divers had no symptoms after resurfacing.