Relation between Pulmonary Arterial Pressure and Pleural Pressure during the Acute Asthmatic Attack

¹ Department of Environmental Medicine, The Johns Hopkins University School of Hygiene and Public Health, Baltimore

We suggest that the acute asthmatic attack can be characterized as follows. The segmental and smaller bronchi become markedly constricted with a tendency toward complete closure. The constriction can be opposed by an increase in the static transpulmonary pressure which increases the distending pressure of the bronchi. The increase in distending pressure is brought about by the patient breathing nearer his total lung capacity. If he can breathe at a high enough level, the bronchi approach their original dimensions. Even so, during forced expirations these same airways have a tendency to collapse more readily than normal bronchi as the pressure within them falls relative to the pleural pressure with increasing flow. Breathing much nearer total lung capacity is perhaps the principal cause of the early circulatory and metabolic changes: increased oxygen consumption, increased cardiac output, and pulmonary hypertension. If breathing can occur at a sufficiently high lung volume, gas exchange is unaltered; but some areas tend to remain underventilated with resulting hypoxia.