The effect of the pulmonary time constant on the cough peak flow rate at two different inflation pressures: a bench test model

Supramaximal flow is characteristic of the cough manoeuvre and is thought to be the result of dynamic compression of collapsible airways. We investigated the effect of changing the pulmonary time constant on the peak flow rate produced by an in vitro cough manoeuvre. We used a prototype artificial cough generator and a simplified lung-airway model. The model consisted of a compliant bag with a resistor (internal diameter 3 mm to 7 mm) that emptied through a collapsible tube. The resulting range of emptying time constants (420 to 2800 ms) included those found in vivo (500 to 2000 ms). The lung-airway model was inflated to one of two pressures (31 cmH₂O or 55 cmH₂O) and then compressed within a glass container to a pressure of 45 cmH₂O. A mechanically-operated glottis opened rapidly and the resultant flow was measured by a pneumotachograph. The cough peak flow rate (CPFR) was recorded for 20 cough manoeuvres for each configuration and the values of the mean and standard deviation are shown in the Table.

The results from this bench-test model suggest that the pulmonary time constant has a profound effect on the magnitude of the cough peak flow rate.

Table