[abstract] RESPIRATORY MECHANICS DURING HYDROX BREATHING AT 13 ATM.

Abstract

A mixture of 2% oxygen in hydrogen has, at 13 atm, a density that is only 17% higher than air at 1atm and 43% lower than 98/2 heliox at 13 atm. The low gas density of hydrox together with a low viscosity is expected to give improvements in respiratory mechanics. During a three day saturation dive on heliox at 120 m, three divers were exposed to a hydrox mix (98% H2,2% O2) for periods up to 1 h. Validyne transducers for oesophageal and maSk pressures and an Ohio rolling seal spirometer for respiratory volumes were used. Paired measurements of VC showed a 93ml larger VC and a 5% higher FEV% during hydrox breathing compared to heliox breathing. During heliox ventilation at rest the work of breathing was 0.57 joule per breath at a VT of 1.25 1 and a frequency of 14. The corresponding values for hydrox breathing were 0.30 joule per breath at a VT of 1.301 and a frequency of 13. As calculated from the work of breathing at a standardized resting ventilation, the functional lung resistance was 35% lower during hydrox breathing compared to heliox breathing. The experimental set up did not allow calculation of external work of breathing during bicycle ergometry but pressure fluctuations in the mask were smaller during hydrox periods than during heliox periods. The lower work of breathing during hydrox ventilation was subjectively noticed by all divers. The observed reduction in respiratory load should be an advantage when diving at great depths.