Planimetric Measurement of Total Lung Capacity in Asthma

¹ Department of Medicine, National Jewish Hospital and Research Center and The Division of Pulmonary Medicine, University of Colorado Medical Center, Denver

This study was designed to evaluate the accuracy of a radiographic-planimetric method of estimating total lung capacity in asthma. The technique involved utilizes the routine posterior-anterior (PA) and lateral chest roentgenogram and a polarizing planimeter. Results of total lung capacity obtained by this method in 33 patients were compared with results obtained from conventional methods using helium dilution and body plethysmography combined with routine spirometry. Correlation coefficients of 0.93 for planimetry and helium dilution (p < .01) and 0.89 for planimetry and plethysmography (p < .005) were obtained. Planimetric measurement of total lung capacity is a simple procedure, which can be readily mastered. We conclude that this method affords accurate estimation of total lung capacity in asthma, and we suggest that sequential measurements thus obtained may be useful in following the course of the disease.