Cardiac function and oxygen saturation during maximal breath-holding in air and during whole-body surface immersion

The magnitude of the oxygen-sparing effect induced by the diving response in humans is still under debate. We wished to compare cardiovascular changes during maximal breath-holding (BH) in air and during whole-body immersion at the surface in a group of BH divers.

Twenty-one divers performed a maximal static apnea in air or during whole-body immersion. Dopplerechocardiography, arterial blood pressure and haemoglobin saturation (SaO₂) were obtained at the beginning of, and at 1/3, 2/3 and maximal BH time.

BH time was on the average 3.6 ± 0.4 min, with no differences between the two conditions. SaO₂ significantly decreased during BH in both conditions, but was significantly higher during immersion as compared to the dry (P = 0.04). In both conditions, BH induced a significant linear increase in right ventricular diameter (P < 0.001), left ventricular (LV) volumes (P < 0.001) and LV stroke volume (P < 0.001) but a significant linear decrease in LV ejection fraction (P = 0.033). In both conditions, Doppler diastolic parameters showed changes suggesting a constrictive/restrictive left ventricular filling pattern (i.e., an increase of early diastolic left ventricular filling velocity, P = 0.005, and a decrease in the deceleration time of early diastolic left ventricular filling. P < 0.001).

BH induces progressive LV enlargement both in air and whole-body immersion, associated with reduced LV ejection fraction and progressive hindrance to diastolic filling. For a similar apnea duration, SaO₂ decreased less during immersed BH, indicating an O₂-sparing effect of diving, suggesting that interruption of apnea was not triggered by a threshold critical value of blood O₂ desaturation.