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dubois lung vol


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A RAPID PLETHYSMOGRAPHIC METHOD FOR MEASURING THORACIC GAS VOLUME: A COMPARISON WITH A NI- TROGEN WASHOUT METHOD FOR MEASURING FUNC- TIONAL RESIDUAL CAPACITY IN NORMAL SUBJECTS1 By ARTHUR B. DuBOIS, STELLA Y. BOTELHO, GEORGE N. BEDELL, ROBERT MARSHALL, AND JULIUS H. COMROE, JR. (From the Department of Physiology and Pharmacology, Graduate School of Medicine, University of Pennsylvania, Philadelphia, Pa.) (Submitted for publication October 3, 1955; accepted October 31, 1955) In general, two principles have been employed in the measurement of the volume of gas in the lungs. The dilution techniques, using either a closed (rebreathing) or open (non-rebreathing) system are the most commonly used; the physical methods, based on Boyle's law relating pressure and volume, require special equipment and have been used relatively infrequently. This report presents a rapid, practical physical method for measuring lung volumes plethysmographically; it has been found to give reproducible values which, in healthy subjects, do not differ signifi- cantly from values obtained by the dilution method of Darling, Cournand, and Richards (1). Two types of physical (pneumatometric) tech- niques have been described previously, both based on Boyle's law. One of these is the decompres- sion method used by Hitchcock, Edelmann, Shel- den, and Whitehorn (2), Willmon and Behnke (3), and Dejours and Rahn (4) ; it has been used in experimental animals (5, 6) as well as in nor- mal man. In the decompression method, the pres- sure about the body and in the trachea and lungs is raised equally above atmospheric so as to com- press the gas inside the lungs and outside the body. The total number of molecules is thereby increased in all parts of the lung in free communication with an open airway. The pressures in the chamber and in the trachea are then released simultane- ously. During return to normal atmospheric pres- sure, the amount of gas which flows out of the trachea is measured; this is the amount of gas which had been added to the lung gas by the previ- 'This investigation was supported in part by a re- search grant, H-406 from the National Heart Institute of the National Institutes of Health, U. S. Public Health Service. ous increment of pressure. The pulmonary gas volume at atmospheric pressure can then be cal- culated by application of Boyle's law. Since the method measures the gas volume which flows in and out of the trachea during compression and de- compression, it measures the volume of lung gas which is in communication with the trachea. The other type, based on voluntary compression or decompression of lung gas, was described in principle by Pfluger in 1882 (7). It requires measurements of changes in alveolar gas pressure and volume while the subject makes voluntary respiratory efforts against a closed airway.
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