STUDIES IN MAN OF THE VOLUME OF THE RESPIRATORY DEAD SPACE AND THE COMPOSITION OF THE ALVEOLAR GAS1

Journal/Book: THE JOURNAL OF CLINICAL INVESTIGATION Vol. XXXIII No. 4 pp. 469-481 April 1954. 1954;

Abstract: From the Department of Medicine Columbia University College of Physicians and Surgeons and the Cardio-Pulmonary Laboratory of the First Medical and Chest Services (Columbia University Division) Bellevue Hospital New York N. Y. Submitted for publication July 44 1953; accepted November 18 1953 1This investigation was supported (in part) by a research grant (PHS Grant H-833 (C) from the National Heart Institute of the National Institutes of Flealth Public Health Service with additional support from the Life Insurance Medical Research Fund and the American Heart Association. 2Established Investigator of the American Heart Association. SUMMARY 1. The graphic. solution of the Bohr formula according to the method described by Pappenheimer Fishman and Borrero (1) has been applied to the determination of the volume of the respiratory dead (non-gas exchanging) space and the alveolar gas composition in eight normal subjects and in three patients with pulmonary disease. 2. The results confirm the previous observations on anesthetized dogs and normal human subjects and indicate that this dead space (VD) remains constant over a wide range of tidal volumes and during a variety of experimental conditions. The average VD in the seven male subjects was 164 ml. 3. An attempt has been made to identify the VD measured by the iso-saturation method. This well-defined VD containing inspired gas must be distinguished from the virtual physiological VD calculated from blood gas tensions which may vary during exercise and in pulmonary disease due to changes in the dynamics of alveolar ventilation and alveolar ventilation-perfusion relation-ships. 4. The alveolar gas compositions determined by this method were coupled with results of direct arterial blood gas analyses for the calculation of the alveolar-arterial (A-a) oxygen and carbon dioxide pressure gradients. In the normal subjects the A-a oxygen and carbon dioxide gradients averaged 6 and 0.5 mm.' Hg respectively. 5. The A-a gradients were applied to the calculation of the oxygen diffusion capacity of the lungs in the normal subjects; the DLO2 at rest was calculated to be 22 ml. per min. per mm. Hg.6. The A-a gradient and VD were similarly studied in three patients with three different types of pulmonary dysfunction. The A-a oxygen gradient and the VD were considerably increased in one subject with diffuse pulmonary granulomatosis but were within normal limits in one patient with chronic non-obstructive emphysema and in another patient with a single distended lung. The results of the VD measurements in the patient with diffuse pulmonary granulomatosis were used to emphasize the theoretical differences between the VD measured by the iso-saturation method and the "physiological" VD. ___MH

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