CAN CAPNOGRAPHY DETECT BRONCHIAL FLAP-VALVE EXPIRATORY OBSTRUCTION

Objective. We have previously shown in a mechanical lung model [1] tha t bronchial flap-valve expiratory obstruction results in sequential lu ng expiration, best detected by prolonged and low magnitude tracheal e xpired flow ((V) over dot) from the obstructed lung. However, the norm al expiratory resistance oi clinical ventilation circuits might also g enerate prolonged, low value exhaled ii, that could be confused with b ronchial flap-valve obstruction. We reasoned that bronchial flap-valve obstruction would also cause sequential CO2 unloading from each lung and result in a biphasic tracheal capnogram. Methods. To test this hyp othesis, we ventilated (V-T, 650 ml, f, 10 br/min) a dual mechanical t est lung, with each side connected to a separate alcohol-burning chamb er. An airway adapter-monitor system measured airway (V) over dot, P, PCO2, and FO2. The circumference of the diaphragm in a respiratory one -way valve was trimmed to generate unidirectional resistance to expira tory (V) over dot. Measurement sequences were repeated after this flap -valve was interposed in the left ''main-stem bronchus.'' Results and Discussion. During moderate or severe left bronchial flap-valve obstru ction, left bronchial (V) over dot was delayed so that the left lung a natomical dead space (devoid of CO2) mixed with normal right exhalate to depress the expiratory upstroke or early plateau of the tracheal ca pnogram. During severe obstruction, decreased perfusion of the left lu ng caused lower alveolar PCO2. Then, prolonged low (V) over dot from t he left bronchus also resulted in depression of the end of the trachea l alveolar plateau. In general, the low magnitude of bronchial (V) ove r dot from the obstructed lung limited its effect on the tracheal capn ogram and the best marker oi sequential lung emptying during bronchial flap-valve obstruction may be late exhaled (V) over dot without reduc tion in total tidal volume.