The Effect of Added External Resistance on Regional Pulmonary Filling and Emptying Sequences

Using the radioactive 133Xe technique, the effects of external resistances on the distribution of inspired gas and on the expiratory alveolar plateau were examined in four normal subjects. Subjects inhaled 133Xe boli one of three ways: slowly through minimum external resistance, with maximum speed through minimal resistance, and with maximal effort but at very low flow rates through a large external resistance. Also, always after a slow inspiration through low resistance, subjects expired in three different ways: slowly through minimal resistance, with maximum speed through minimal resistance, and finally with maximal effort through an external resistance which sharply limited flow rates. Both regional intrapulmonary 133Xe distribution and the shape of the alveolar plateau appeared to depend entirely on flow rate and to be independent of effort. These results were interpreted as indicating that variations in respiratory effort do not produce variations in dynamic pleural pressure between lung regions.