MAXIMUM EXPIRATORY FLOW-VOLUME CURVE - MATHEMATICAL-MODEL AND EXPERIMENTAL RESULTS

A mathematical simulation of the maximum expiratory flow-volume (MEFV) curve was developed using a lumped parameter model The model uses a t heoretical approximation of an activation function representing the lu ng's pressure-volume relationship during maximally forced expiration. The waveforms obtained by the model were compared to the flow-volume c urves recorded from normal subjects and for patients with small airway s disease, asthma, and emphysema. We were able to reproduce the flow-v olume curves using the model and calculate new parameters that reflect the dependency of airways resistance on expired volume during FVC man oeuvre. These new parameters are based on, the entire information pres ented in the flow-volume curve and on the reduction in flow at all lun g volumes. We also calculated the mean slope of the resistance-expired volume curves (b) over bar obtained from the model by fitting a strai ght fine to the curve. Using representative data for normal and COPD p atients different mean slopes of 0.095, 0.13, 0.49 and 1.44 litre(-1) were obtained for normal subject, small airways disease, asthma and em physema patients, respectively. The model-based parameters may be appl icable to human studies. However, further studies in large groups of p atients are required to better define the true predictive value of the new indices described for the diagnosis of COPD.