Operation Everest III (Comex'97): altitude-induced decompression sickness during a hypobaric chamber experiment: necessity for circulating venous gas emboli monitoring for the investigators.

Acute exposure to altitude changes increases the risk of decompression sickness (DCS). Altitude-induced DCS incidence is from 15 to 20% and > 30% above 8,000 m. A particular risk occurs for scientific investigators during hypobaric chamber experiments.In the present study, we assess whether the detection of nitrogen venous gas emboli (VGE) could help to screen the investigators at risk for altitude-induced DCS.During a 32-day hypobaric chamber experiment, we collected clinical episodes of DCS symptoms in the investigators, and performed detection of VGE using two-dimensional (2D) echocardiography and pulsed Doppler ultrasonography guided by 2D images, graded from 0 to 5.Eight investigators made a total of 32 flights, including 8 flights above 8,000 m, with a 15.6% overall incidence of DCS symptoms and a 50% incidence above 8,000 m. VGE detections were systematically performed at or above 8,000 m (eight detections), and some detections were performed at 5,000 m, 6,000 m, and 7,000 m. VGE grades 3 and 4 were present in all but one subject with DCS symptoms and preceded the "bends" in all cases. VGE detection thus confirmed, in a more sensitive way compared to clinical examination, that our precautionary measures for DCS were not optimized.VGE monitoring for investigators during hypobaric chamber experiments increased the sensitivity for the detection of subjects at risk for DCS.