Lung function interpolation by means of neural-network-supported analysis of respiration sounds

Respiration sounds of individual asthmatic patients were analysed in the scope of the development of a method for computerised recognition of the degree of airways obstruction. Respiration sounds were recorded during laboratory sessions of allergen provoked airways obstruction, during several stages of advancing obstruction. The technique of artificial neural networks was applied for relating sound spectra and simultaneously measured lung function values (spirometry parameter FEV1). The ability of feedforward neural networks was tested to interpolate obstruction levels of FEV1-classes of which no members were included in the set used for training a network. In this way, a situation was simulated of an existing network recognising a new asthmatic attack under the same physiological conditions. It appeared to be possible to interpolate FEV1 values, and it is concluded that a deterministic relationship exists between sound spectra and lung function parameter FEV1. Variance optimisation appeared to be important in optimising the neural network configuration.