Exercise-induced altitude decompression sickness

Background: It has been known since World War II that exercise at altitude increases incidence of decompression sickness (DCS). However, data on the e ffects of specific exercise types at altitude are lacking. This research fo cused on the relative hazards of exercise without motion (isometric, strain ing) vs. dynamic exercise involving motion. The study also compared arm vs. leg exercise. Methods: There were 32 healthy male subjects exposed, while resting, to 29,500 ft(8992 m) for 4 h or until DCS occurred, at which time they were brought to ground level. If the subject developed DCS on this exp osure, he was exposed in successive months to lower altitudes, using the sa me procedure, until the subject was free of symptoms for the 4-h exposure. At this symptom-free altitude, as low as 20,000 Tt (6096 m), the subject pe rformed isometric arm, isometric leg, dynamic arm and dynamic leg exercises at less than 10% of maximal oxygen consumption, each during separate expos ure months. Precordial venous gas emboli (VGE) were monitored every 20 min during each exposure with a Hewlett-Packard SONGS 1000 Echo Imaging System. Results: Dynamic arm, dynamic leg, isometric arm, and isometric leg exerci se induced DCS in 50%, 38%, 41% and 31% of the subjects, respectively. VGE incidence varied from 47-66%. No significant differences in DCS or VGE were found. Conclusions: Under our test conditions, there was no difference bet ween dynamic and isometric exercise in eliciting DCS. Exercise during expos ure to the symptom-free altitude for 4 h produced a 40% incidence DCS.