Ventilatory gas analysis in SCUBA divers using a surface-based measurement system.

The main technological problem associated with measuring gas exchange in submerged divers breathing from a self-contained underwater breathing apparatus (SCUBA) involves simulating ambient water pressure on the expired side of the SCUBA regulator without causing regulator free-flow. This report presents a method to acquire expired gas from exercising divers for analysis at the surface using a standard metabolic measurement system. We did this using a flat collapsible tube downstream from the expiration valve of the regulator. We tested 12 divers while swimming on the surface and during SCUBA at 1.8 m (6 ft) underwater using a tethered swim/counter weight system to provide graded exercise to exhaustion. Peak minute ventilation was not significantly different between surface swimming and SCUBA, but peak oxygen consumption (VO2) was lower (p < 0.0001) during SCUBA than for surface swimming. There was a significant correlation (p = 0.0002) between peak VO2 during SCUBA and surface swimming. These results show that VO2 and ventilation can be accurately measured in SCUBA divers during underwater exercise and the new and simple technique will be useful to those interested in the energy requirements of diving activities in shallow water.