The Half-Second Expiratory Capacity Test: A Convenient Means of Evaluating the Nature and Extent of Pulmonary Ventilatory Insufficiency

¹ The Department of Internal Medicine, The University of Texas, Southwestern Medical School and the Cardio-Pulmonary Laboratory, Parkland Memorial Hospital.

A simple method employing single maximum expiratory efforts is presented as a means of defining the nature and extent of ventilatory insufficiency. The method involves the measurement of the 0.5 sec. expiratory capacity and the total vital capacity. Then by relating the 0.5 sec. expiratory capacity to the total vital capacity as a simple ratio, and expression of the maximum velocity of air flow during expiration, is obtained. The total vital capacity is a measure of maximum pulmonary stroke volume. Thus in a single test expressions of the velocity of pulmonary air flow as well as pulmonary stroke volume are found. If these functions are plotted against each other in a quadrant graphic system which is based on normal values for these two functions, a convenient and precise clinical method for defining the physiological nature of ventilatory insufficiency is obtained. This test is applicable even to the seriously debilitated patient who cannot perform the maximum breathing capacity test. Serial studies by this method provide a convenient and informative method of studying the nature of the change in ventilatory function during the course of the disease or resulting from therapy.