Resistance measurement in normal and obstructed excised human lungs by means of the interrupter method

In 6 normal and 7 obstructed excised human lungs the interrupter resistance (APTA, Jaeger Company) with an airway occlusion period of 100 ms was determined, by measuring the equivalent of the alveolar pressure at the end of the occlusion period. To check the pressure equilibration between the tracheal pressure and the alveolar space, catheters were put in the most peripheral layer of the lung. The lungs were ventilated in an artificial thorax. The airway resistance determined from the transbronchial pressure difference by the catheters was taken as a reference. Compared with the reference method, an overestimation of the airways resistance by the interrupter technique in normal lungs was found which was caused by an overshoot of the pressure equilibration during the occlusion period. In contrast, in severely obstructed lungs the pressure equilibration was not complete which led to an underestimation of the airways resistance by the interrupter technique. The best approximation of the airways resistance by the interrupter method was found in lungs with a low degree of obstruction.