Relationships between fast vital capacity and various timed expiratory capacities

¹ Cardiopulmonary Laboratory of the Department of Internal Medicine, University of Texas Southwestern Medical School and Parkland Hospital, Dallas, Texas

Fast vital capacity, 0.5-second, 0.75-second and 1.0-second timed expiratory capacities were measured with a Gaensler-Collins timed vitalometer in 153 healthy subjects, including equal numbers of males and females ranging in age from 20 through 60 years. The timed expiratory capacities (TEC) were found to constitute a fairly constant proportion of the vital capacity (VC) and the linear relationship of the TEC to the VC establishes the validity of using the ratio TEC/VC as a means of expressing this function for purposes of comparative analyses of function. The mean 0.5-second EC ratio was found to be 67.8%, the 0.75-second EC 77.3%, and the 1.0-second EC 83.9% with no variation between sexes and no significant age regression in the 0.5-second EC ratio. Values obtained by this method were comparable to those obtained by pneumotachographic and special spirometric techniques (Bernstein). Formulas for predicting the expected fast vital capacity for both males and females, using height and age as parameters, were calculated from these data to provide more accurate prediction of the VC in both sexes when the VC is measured by this commonly used method. A convenient nomogram was constructed for this purpose.