Influence of modified gas mixtures on the acoustic parameters of human forced exhalation

It was earlier demonstrated that the duration of tracheal noises of forced exhalation (FE) looks to be promising to determine adverse changes in the lung function after a dive. This study dealt with the parameters of tracheal expiratory noises (FE) as dependent of the composition of breathing gas mixtures. In the first type of experiments, 25 volunteers aged from 22 to 60 years carried out forced exhalation under a normal pressure of air or of an oxygen-helium or oxygen-krypton mixture. In the second type of experiments, six volunteers from 25 to 46 years of age performed forced exhalation with air in an altitude chamber under a normal pressure (0.1 MPa); the same subjects performed FE under an elevated pressure (0.263 MPa) while breathing air or an oxygen-helium mixture. In the first type of experiments, the total duration of tracheal FE noises in the frequency range 200?C2000 Hz and 200-Hz bands FE noises depended directly and linearly on the density of the gas mixture; this was not the case in the high-frequency band from 1400 to 2000 Hz. In the second type of experiments, the high-frequency durations and spectral energies of tracheal FE noises (1600?C2000 Hz) depended inversely and significantly on the adiabatic gas compressibility. In a simulated dive to a depth of 16.3 m (0.263 MPa), individual changes in the total duration of tracheal FE noises exceeded the diagnostic threshold of deterioration of the lung function in divers that was determined earlier under normal pressure.