<i>Pressure-Volume Measurements on Dog Bronchi</i>

Abstract

Pressure-volume studies have been made on excised segments of dog trachea and bronchi with average outside diameter of 5 mm and 2 mm, both under static conditions and at a frequency of 12 cycles per minute to simulate normal breathing. The trachea, 5 mm bronchi and 2 mm bronchi, were 90% collapsed by pressures of 90, 15 and 7.5 cm of saline, respectively. If the pressure surrounding any bronchus is approximated by intrapleural pressure then the bronchi have a volume of 2 to 5 times their resting volume at end-expiration. Hence, the elastic retractive forces of the lungs and chest wall (as the determinants of end-expiratory intrapleural pressure) become extremely important in holding bronchi open and decreasing airway resistance. The bronchi are on a very steep portion of their pressure-volume curves at functional residual volume. Small changes in transmural pressure will cause large volume changes and hence significant alterations in airway resistance. Submitted on June 10, 1958