Studies on the Intrapulmonary Mixture of Gases. Ii. Analysis of the Rebreathing Method (Closed Circuit) for Measuring Residual Air

Abstract

The closed rebreathing circuit has been widely used for residual air measurement (1, 2, 3, 4, 5, and others). The essential features of the apparatus and procedure were the same in all. A spirometer filled with high oxygen (or with a hydrogen-containing) gas mixture was attached to the test subject. The carbon dioxide was removed with soda lime or other alkali in the circuit and the subject breathed for a period of time until the nitrogen (or hydrogen) was redistributed in the circuit. The residual lung gas volume was calculated from the amount of redistributed gas.In most of the work it was assumed that at the end of five or more minutes of quiet breathing the gas in lungs and spirometer was uniform in composition, except for a slight excess concentration of inert gases in the lungs. This excess was assumed to be the same as that occurring during the breathing of room air. On the basis of these assumptions, the net change in spirometer gas concentration was considered the same as that in the lungs during the rebreathing. By actual measurement of the gas concentration in the various parts of the spirometer system and the alveolar gas, Lassen, Cournand, and Richards (6) concluded in the study of normal subjects that these assumptions were not valid. Rather than an excess, they found a lower concentration of nitrogen in the lungs than in the spirometer at the end of a breathing period. They explained these findings as due to the constantly increasing nitrogen concentration which resulted from the steadily diminishing spirometer volume. This effect they called the "oxygen storage" effect. To correct for it, they introduced alveolar air concentrations into the calculation and found that this correction made a

Studies on Intrapulmonary Mixture of Gases. V. Forms of Inadequate Ventilation in Normal and Emphysematous Lungs, Analyzed by Means of Breathing Pure Oxygen

“…In fact, principal emphasis has been placed on the increase in residual air, together with the fall in vital capacity, to explain the disability in pulmonary emphysema. From a critical analysis of usual residual air measurements in a previous paper (3), it was concluded that frequently, in such cases, the measurements gave falsely high residual air values due to the. factor of imperfect intrapulmonary mixture.…”

“…Marked variations in the gas concentrations of the different parts of an expired alveolar specimen, in such subjects, have led to the same conclusion (2). The authors (3), in the course of analyzing the rebreathing method for measuring residual air, found that the usual alveolar samples represent an imperfect measure of average pulmonary gas concentration under the changing conditions of a rebreathink experiment. From these experiments, imperfect intrapulmonary gas mixture was recognized as a factor in pulmonary disability; but it could not be measured and compared with the other factors, namely, pulmonary overdistension, diminished vital capacity, and impaired gas diffusion, in these subjects.…”

“…The formula describing this phenomenon has been derived. 3. Values for pulmonary concentration of nitrogen after breathing oxygen have been measured on 18 normal subjects and 5 patients with severe pulmonary emphysema.…”

Studies of Pulmonary Capacity and Mixing With the Nitrogen Meter 1

“…Although the closed circuit method appears to give somewhat higher values than open circuit (2) or constant volume (3)(4)(5) methods in normal individuals, such differences are not as apparent in pathological subjects where faulty mixing and other factors cause poor testing reproducibility in all methods. Since clinical adaptability rather than maximum accuracy was the goal in this study, a closed circuit method was adopted.…”

Multiple-breath nitrogen washout techniques: including measurements with patients on ventilators

“…The N 2 washout method for measuring lung volumes was developed into a clinical technique by DARLING and co-workers [23][24][25] in a series of papers published in 1940. The principle of the technique is that N 2 is washed out of the body by having the subject breathe 100% oxygen, starting the first inspiration of O 2 from FRC.…”