STUDIES OF TOTAL PULMONARY CAPACITY AND ITS SUB-DIVISIONS. I. NORMAL, ABSOLUTE AND RELATIVE VALUES

Abstract

I. The total pulmonary capacity and its subdivisions have been determined in 50 normal males using the Christie''s method of O2 dilution without forced breathing. There are wide variations in the absolute values found but the vital capacity, residual air and mid-capacity, expressed in percentage of the total capacity, fluctuate within definite limits. This suggests the possibility that alterations in these ratios may give a quantitative estimation of the degree of functional respiratory efficiency from the point of view of alveolar ventilation.[long dash]II. The total pulmonary capacity and its subdivisions determined in 50 normal males have been correlated with various physical and radiological measurements. A standard radiological technique was employed. The highest correlation was found between the vital capacity and the "radiological chest volume" (area of the lung fields at maximum inspiration multiplied by the antero-posterior diameter of the chest in the same respiratory position). A formula was derived which permits the prediction of the pulmonary capacity and its main subdivisions in a given case. The relationship between the pulmonary capacity and the chest expansion and shape has also been studied.[long dash]III. The influence of body posture on the pulmonary capacity and its subdivisions has been studied in 10 normal males. There was a slight decrease in the total capacity, vital capacity and residual air, and a marked reduction in the mid-capacity and reserve air on changing the posture from sitting to recumbency. The complementary air on the other hand increases. These changes are accompanied by proportional and parallel changes in the size of the chest as determined by radiological measurements.[long dash]IV. The total pulmonary capacity and its subdivisions have been determined in cases of pulmonary emphysema and pneu-moconiosis. (The methods and technique presented in previous papers were employed.) Definite alterations were found consisting mainly in a marked increase in the residual air and a corresponding decrease in the vital capacity (total capacity being about normal) in the emphysematous patients, and a marked reduction in the vital capacity with a moderate increase in the residual air (total capacity being decreased) in pneumoconiosis. The changes found were closely correlated to the degree of respiratory efficiency during physical activity, and also to the saturation of the arterial blood with oxygen, which is less than normal when the ratio of residual air to total capacity was abnormally high.