Acute effects of a single open sea air dive and post-dive posture on cardiac output and pulmonary gas exchange in recreational divers

Objective: To evaluate the cardiopulmonary effects of open sea scuba air diving to 39 m (30 minutes bottom time) with standard decompression. To account for possible gravity dependent effects of venous gas bubbles, the variables were measured in different post-dive body postures and compared with the baseline values before the dive in the same posture. Methods: Eight male divers conducted two similar dives on successive days. Their posture before and after the dive was either sitting or supine, in random order. The divers were evaluated before and 30, 60, and 90 minutes after the dive. Venous bubbles were detected by precordial Doppler after the dive in four divers in the supine posture and two divers in the sitting posture. Results: Arterialised oxygen tension had decreased at all times after the dive (−11.3 mm Hg, p = 0.00006), due to decreased alveolar oxygen tension, irrespective of posture. Apart from an increase in the sitting posture 30 minutes after the dive, pulmonary capacity for carbon monoxide diffusion and cardiac index decreased, mostly 60 minutes after the dive (−9%, p = 0.0003 and −20%, p = 0.0002 respectively). The decrease in cardiac index was greater in the supine posture (p = 0.0004), and the physiological dead space/tidal volume ratio increased more in the sitting position (p = 0.006). Conclusions: Field dives are associated with moderate impairments in cardiac output and gas exchange. Some of these impairments appear to depend on the posture of the diver after the dive.