Limitations in the use of median frequency for lung sound analysis

The aim of this paper is to investigate methods of standardizing lung sound analysis, with a view to supplementing traditional spirometric air flow me asurements to help in the diagnosis of asthma and to provide a measure of t he effectiveness of treatment. Lung sounds were measured in nine patients w ith asthma and five control subjects, alongside air flow measurements of fo rced expiratory volume (FEV1) and forced vital capacity (FVC). The patients were administered the bronchodilator, salbutamol, to assess how effective these measurement techniques were for quantifying its effect. The results a gree with previous studies, that analysis of lung sounds is a potentially u seful tool for indicating air flow changes. The results, however, also demo nstrate that the emerging standard of 'F-50' or 'median frequency' should b e treated with great caution because of its high sensitivity to the measure ment frequency range. F-50 is very unlikely to provide a reliable single in dicator of lung condition.