Airway dynamics, oesophageal pressure and cough.

This study hypothesizes that: peak supramaximal airflow during cough reflects expiratory muscle effort, and that expiratory muscle function during cough might be assessed from the airflow signal alone. We monitored airflow and oesophageal pressure (Poes) in normal subjects during cough generated under two conditions: 1) voluntarily from functional residual capacity (FRC); and 2) involuntarily after inhalation of citric acid (CA). Maximal expiratory cough flow was quantified as the quotient of maximal flow during a given cough divided by maximal flow at the matched volume of thoracic gas (Vtg) as identified on the maximal expiratory flow-volume curve. We found: flow ratios correlated poorly with Poes; the variance of flow ratios associated with a series of voluntary coughs was poorly explained by Poes. During CA inhalation, when the Vtg compressed during cough could not be controlled, correlation of Poes with flow ratio remained poor. We conclude that to study the motor limb of the cough reflex, measurements of both airflow and oesophageal pressure are required.