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 measurements to help in the diagnosis of asthma and to provide a measure of the effectiveness of treatment. Lung sounds were measured in nine patients with asthma and five control subjects, alongside air flow measurements of forced 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 agree with previous studies, that analysis of lung sounds is a potentially useful tool for indicating air flow changes. The results, however, also demonstrate that the emerging standard of 'F50' or 'median frequency' should be treated with great caution because of its high sensitivity to the measurement frequency range. F50 is very unlikely to provide a reliable single indicator of lung condition.