Measurement and estimation of human forced expiratory noise parameters using a microphone with a stethoscope head and a lapel microphone.

OBJECTIVE: The time signature of tracheal noise in the 200-2000 Hz frequency band recorded during a forced expiratory manoeuvre (FETa) is a promising tool for diagnosis of bronchial obstructions. FETa is typically registered using a microphone with a stethoscope head placed on the neck over the trachea (stethoscope sensor). We studied basic time and spectral parameters of forced expiratory tracheal noises with a microphone placed near the mouth (lapel microphone, outside the flow of exhaled air) and compared these with measurements via stethoscope sensor, with the aim of providing patient home monitoring via standard personal computer facilities. APPROACH: FETa, 200 Hz band pass times, and frequency responses of signals recorded simultaneously with both sensors were analysed in a sample of 24 healthy volunteers. MAIN RESULTS: Averaged real transfer function of signals from a stethoscope sensor and a lapel microphone in the frequency range 200-1800 Hz was characterized by a slope of -7.2 dB/octave. This is near the slope of -6 dB/octave predicted via theoretical models of both sensors. The lapel microphone and stethoscope sensor were not interchangeable regarding spectral characteristics of forced expiratory tracheal noises. However, FETa measurements in healthy volunteers via stethoscope sensor and lapel microphone showed no significant differences according to U-Mann-Whitney test for independent samples. SIGNIFICANCE: The ability to measure FETa successfully with a lapel microphone placed near the mouth was experimentally demonstrated in healthy volunteers. Additional studies are needed to verify whether FETa measured near the mouth is acceptable for monitoring pulmonary status in patients with asthma or chronic obstructive pulmonary disease.

[Characteristics of flow standardized inspiratory lung sounds in healthy].

Objectification of respiratory sounds, recorded on chest surface, is important to assess human broncho-pulmonary system. The aim is to detail the objective characteristics of basic inspiratory sounds. The study involved 36 healthy men aged 19 to 80 years. Under flow rate 0.89 ± 0.18 L/s medians of spectral characteristics of basic inspiratory lung sounds are in the ranges: amplitude level -63.3... -56.5 dB, -3 dB cutoff frequency 269.5-359.4 Hz, -20 dB cutoff frequency 531.3-621.1 Hz, the slope of the spectrum curve between the cut-off frequencies -0.077... -0.050 dB/Hz. The high degree of bilateral symmetry of spectral characteristics is found. Significant upward trend in the cutoff frequencies is revealed between interscapular region and apices or basal areas of the lungs. The 90% limits of intersubject variability of the cutoff frequencies of the spectrum are identified in areas of chest used for lung auscultation.

[Influence of changed gas media on acoustic parameters of human forced exhalation].

In previous study it was shown that duration of tracheal forced expiratory noises is promising to reveal negative changes of lung function after dive. The objective is a study of parameters of tracheal forced expiratory noises in changed gas media. The first experiment involved 25 volunteers (22-60 years), performed forced exhalation under normal pressure with air, oxygen-helium and oxygen-krypton mixtures. The second experiment in the chamber involved 6 volunteers (25-46 years), which performed forced exhalation with air under normal pressure (0.1 MPa), and under elevated pressure 0.263 MPa with air and oxygen-helium mixture. In the first experiment the direct linear dependence on gas density was found for forced expiratory noises common duration in the band of 200-2000 Hz and for its durations in narrow 200-Hz bands, excluding high frequency range 1400-2000 Hz. In the second experiment a significant reversed dependence of high frequency durations and spectral energies in 200-Hz bands (1600-2000 Hz) on adiabatic gas compressibility. Individual dynamics of common duration of tracheal forced expiratory noises under model dive of 16.3 m (0.263 MPa) is more then the diagnostic threshold of this parameter for lung function decrease, previously obtained for divers under normal pressure.