Pulmonary function in diseases of the chest.

Pulmonary function tests are designed to provide accurate information of the extent and location of disturbed function thereby making available additional information for use with the history, physical, and roentgenological examination in the clinical management of the individual case. A battery of physiological test measurements are used, each possessing a wide range between the normal and the abnormal, and each covering an essential aspect in the evaluation of the adequacy of the gas exchange. One group of tests concerns the bellows action of the chest and lungs and evaluates the ability to move air in and out of the alveoli during the process of breathing. The other group of tests relate to the blood gas exchange across the alveolar-capillary or pulmonary membrane (oxygen and carbon dioxide transport). Pulmonary function measurements assist in the interpretation of the meaning of pulmonary disease from the standpoint of disability, operative risk and treatment. The efficiency of the bellows action of the chest and lungs for moving air in and out of the alveoli is measured from spirogram tracings and from the residual capacity measurement.' Spirogram tracings provide measurements of total vital capacity, timed vital capacity, maximal breathing capacity, and a permanent graphic recording of the exhalation pattern. Evidence of air trapping in the lung is also obtained from the spirogram tracings by having the individual take a deep breath in and then blow out rapidly a few times. Total vital capacity is determined both in the supine and standing position, being the difference between the volume of the lung in the maximal distended position in inspiration and the minimal volume present a t the end of a forced maximal exhalation. The total vital capacity in a normal individual is usually slightly larger in the standing than in the supine position. A marked reduction in total vital capacity in the standing position as compared to the supine position indicates the presence of severe pulmonary insufficiency. However, vital capacity when recorded with respect to time becomes a much more significant measurement. The subject is instructed to take in as deep a breath as possible, hold the breath momentarily and then on command blow all of the air out of the lungs as rapidly and as completely as possible. The volume exhaled in the first three seconds measured from the exact beginning of expiration is recorded as the three second timed vital capacity. The three second timed vital capacity is normally the same as the individual's predicted total vital capacity, and represents the maximal functional portion of the vital capacity (a respiratory rate of 15 per minute allows