Computer Evaluation of Tracheal Forced Expiratory Noise Time for Bronchial Obstruction Diagnostics

Computer analysis of respiratory noises provides a precise estimation of acoustic forced expiratory noises time (FETa). The objective is to analyze FET a diagnostic capability in revealing bronchial obstruction. A group of patients with bronchial asthma (BA) involved 50 males (16-24 years). Selection criteria: (a) diminution of FEV 1/FVC (VC) relation; (b) bronchodilator response to salbutamol; (c) diurnal variability of PEF. A group of 52 healthy volunteers were recruited as the control one. Spirometry and forced expiratory tracheal noises recording were sequentially accomplished for each person. FETa values were estimated by means of developed semiautomated procedure, including bandpass filtration (200-2000 Hz), waveform envelope calculation with accumulation period of 0.01 sec, measurement of FET a at 0.5% level from the peak value of the waveform. The value of FET a was significantly larger in BA patients group than in control one. Based on ROC-analysis the cutoff point FET a > 1.86 s was chosen as a sign of bronchial obstruction. Areas under ROC - curves of FETa and baseline spirometric index FEV1/FVC (VC) did not differ significantly. The mean intrasubject variability of FETa constituted 8.3% in the control group. Thus FETa is a reasonably sensitive, specific and quite repeatable test of bronchial obstruction in young men.