Experimental pendulum air in the flail chest.

Conditions for occurrence of pendulum airflow under spontaneous ventilation were studied in adult dogs with flail chest experimentally constructed by removing three ribs and the chest wall. Pendulum air flow was recorded pneumotachometrically from outside the body by intubation to the bronchi. Despite objections to the occurrence of pendulum air by many investigators, we found that pendulum airflow occurs under various conditions. The main factors facilitating the occurrence included 1) Significant differences in airway pressure and ventilatory volume between the lungs on the injured and the opposite side. 2) A high frequency of respiration. 3) Increased resistance in the upper airway. The pendulum airflow occurred not only at the area of tracheal bifurcation but also in the peripheral bronchial airway in the ipsi-lateral thorax of the flail chest. However, pendulum airflow was observed only transiently coinciding with the time of change from one phase of respiration to the other, and volume of pendulum airflow was considered to be so minimal that it had no significant deleterious influence on the alveolar ventilation. In cases of marked dysfunction of the chest wall or with increasing upper airway resistance, pendulum airflow may disturb alveolar ventilation to a considerable extent.