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The effects of successive air and trimix dives on human cardiovascular function

Introduction The use of trimix (a mixture of oxygen, helium and nitrogen) has significantly increased among the diver population. However, data indicating how trimix dives at most common depths affect the cardiovascular function are sparse. The purpose of this study was to investigate the cardiovascular effects of trimix dives and compare them with air dives, as well as to determine whether the repetition of dives in successive days affects their extent. Methods Nine professional divers performed four dives in consecutive days where the dive depth was progressively increased to the maximum of 55 m. Divers used air in the 1st dive, nitrox 25 in the 2nd, and trimix 20/30 in the 3rd and 4th dive. Echocardiography was performed before and after each dive. Results After each dive, a significantly decreased left ventricular ejection fraction and fractional shortening, as well as increased end-systolic volume without a change in end-diastolic volume were found, indicating a depressed systolic function of the left heart. Assessment of the ratio between pulmonary artery acceleration time and right ventricular ejection time (used as an indicator of pulmonary artery pressure – PAP) revealed an increase in PAP after all the dives. No physiologically relevant cumulative effects of the multiple dives or signs of acclimatization were found. Conclusion The current study shows that the cardiovascular effects of trimix dives do not differ from those of the dives with compressed air. However, it suggests that even a very safe and conservative trimix diving profile exerts significant cardiovascular effects.

SCUBA; technical diving; systolic function; pulmonary artery pressure

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