A SIMPLE METHOD TO MONITOR PERFORMANCE OF FORCED VITAL CAPACITY

The forced vital capacity (FVC) maneuver is the most common lung funct ion test. One of its major prerequisites is that it be performed with sufficient effort to achieve the maximal flows that are due to expirat ory flow limitation. To verify this, in nine normal subjects, short (0 .25-s) pulses of negative pressure (-5 to -20 cmH(2)O) were applied at the mouth at different times (0.25-1 s) after the onset of 1) FVC man euvers and 2) vital capacity expirations with submaximal expiratory ef forts (SVC). All subjects were experienced in FVC maneuvers. With FVC, the expiratory flow did not change with application and removal of ne gative-pressure pulses, apart from brief flow transients, mainly refle cting displacement of air from the compliant oral and neck structures. With SVC, flow increased throughout the application of the negative-p ressure pulses. Thus application of pulses of negative pressure provid es a simple method for on-line recognition of whether an FVC maneuver is performed with sufficient effort to achieve flow limitation.