Abstract
To maintain an adequate level of arterial oxygen tension (PaO2), it is not necessary to remark that one of the most essential is the balance between ventilation and perfusion in the lung. This study tested how rapidly and effectively PaO2 recovers when an acutely distorted imbalance is repaired. The lungs of 31 mongrel dogs, anesthetized with sodium pentobarbital were divided with Carlens' tracheal divider under mechanical ventilation with 100 percent oxygen in a supine position. Arterial and mixed venous blood were consecutively sampled every one to three minutes and analysed with an electrode blood gas analyzer (IL 213), with simultaneous monitoring for other vital signs. With obstruction of the left main bronchus and induction of absorption atelectasis of the left lung, PaO2 decreased to the level of 81.1±32.4mmHg (QS/QT 45.8±13.6%) in about ten minutes from a control arterial tension level (PaO2 620±38mmHg, Qs/Qt 3.9±2.9%). However, PaO2 recove red almost instantaneously to the control level (PaO2 576±56mmHg, QS/QT 5.5±2.2%) when the ipsilateral pulmonary artery was obstructed at the trunk of the pulmonary artery with a balloon tip cardiac catheter. The magnitude of the PaO2 elevation by pulmonary artery obstruction was entirely dependent on at where the pulmonary artery was obstructed. When the pulmonary artery was obstructed in the peripheral portion, the rec overy of PaO2 was not sufficient (PaO2 203.2±116.1mmHg, QS/QT 31.4±11.1%). These results suggest that the level of PaO2 during acute im balance of ventilation and perfusion in the lung is entirely dependent on the geometrical balance between vascularand alveolar compartments and there is no active nervous or humoral regulation to readjust their balance in either the plumonary vasculature or ariway system.
