ECG-CHANGES DURING THE EXPERIMENTAL HUMAN DIVE HYDRA-10 (71-ATM 7,200-KPA)

Electrocardiogram (ECG) analysis was performed in three human divers d uring a 71 atm (7,200 kPa) saturation dive (COMEX HYDRA 10 experiment) . The inhaled gas mixture was slightly hyperoxic; its composition was basically helium and oxygen. Hydrogen was introduced during compressio n and its partial pressure reached 20 atm. ECG changes were the same i n the three divers. Marked bradycardia rapidly appeared at the beginni ng of compression, then this response adapted throughout the dive. P-R , QRS, and Q-T intervals and the S-T segment did not change significan tly. The QRS axis remained stable. However, a rightward shift occurred in P and T vector angles. These changes were correlated with time and gas density, respectively. The modifications of ventricular repolariz ation during compression are similar to those we observed during the H YDRA 9 COMEX dive. They may correspond to changes in duration of myoca rdial cell repolarization due to increased intrathoracic pressure chan ges with dense-gas breathing. A marked global diminution of voltage oc curred during the decompression period. This suggests that accumulatio n of micro bubbles in tissues may influence the impedance, causing an artifact in the amplitude of ECG complexes.