Lung Ventilation Patterns Determined by Analysis of Nitrogen Elimination Rates; Use of the Mass Spectrometer as a Continuous Gas Analyzer 1

Abstract

A quantitative measure of the effectiveness of lung ventilation and the significance of unequal mixing of the gases in the lung is of interest in many problems such as the measurement of lung volume and in studies of such processes as tissue denitrogenation which involve transport of gases through the lung.The present study involves the determination of the turnover rates attained in the lung from measurements of the rate at which nitrogen is washed out of the lungs while the subject is breathing pure oxygen. It has been recognized (1) that this rate depends upon the distribution of the tidal breath to the deeper pulmonary structures and that it offers a means of measuring the ventilatory process. Use of the method has, however, led to a number of different expressions for the effectiveness of ventilation none of which we believe is definitive of the process.Because the function of lung ventilation is to maintain physiological partial pressures of oxygen and of carbon dioxide in the alveoli it seems to us that the measure of the effectiveness of ventilation should be reciprocally related to the average time that a molecule remains in those spaces. The replacement rate or turnover rate, defined as the ratio of the number of new molecules which enter a space in unit time to the number present at the end of expiration is such a measure.Without attempting here to survey the extensive literature upon this subject we shall mention a few papers which bear most directly upon the interpretation of the present results.Cournand and his associates (1, 2) in testing the adequacy of the assumption of even pulmonary ' This work was supported in part by the Life Insurance Medical Research Fund and in part by the Army Air Force.2 Present address: Medical Department, Brookhaven National Laboratory, Upton, Long Island, New York. mixing found evidence of unequal mixing in emphysematous subjects and to some extent in normal ones. They develop the "pulmonary emptying rate" as a criterion for the effectiveness of lung ventilation. This is based upon the concentration of nitrogen remaining in the alveoli after seven minutes of oxygen breathing. In effect this establishes two points on the curve representing the concentration of nitrogen as a function of time, the initial point and the seven-minute one. This function is not, however, defined by these two points unless it is a simple function having only two constants, such as a single-termed exponential. Non-uniform mixing is not consistent with any simple function; with different degrees of mixing two curves differing appreciably can both pass through these two points but be quite different at other times. In a later paper Darling, Cournand, and Richards (3) compare the concentration of nitrogen remaining after a period of oxygen breathing to the concentration they predict would have been obtained had mixing been perfect and they express the effects of unequal mixing as the percentage failure of ventilation.Meneely and Kaltreider (4) consider the effects of mixing upon the time require...

Lung Function Studies. Viii. Analysis of Alveolar Ventilation by Pulmonary N2 Clearance Curves 12

“…This is in contrast with data obtained by continuous analysis reported here and by Robertson, Siri, and Jones (12). However, one of several requirements upon which experiments were rejected or accepted was the "definiteness of linear relationship between y and n"; that is, the definiteness with which the clearance process could be described by a single value of w. As Robertson points out, analysis of multiphasic pulmonary clearance or equilibration curves with equations containing only one exponential term (4,6,10) is inadequate and may lead to ambiguous or at times incorrect interpretation of the nature of ventilatory inefficiency (23,26).…”

“…First Tables I and II, based on multiphasic analysis of -pulmonary N2 elimination rates (12). However, we prefer to treat alveolar ventilation as a discontinuous rather than as a continuous process, as they have done.…”

“…To date, no method has been wholly satisfactory (3). One approach has been by study of the time course of equilibration of alveolar gas with a "foreign" inspired gas, such as H2 (4), He (5-7) or pure 02 (8)(9)(10)(11)(12)(13)(14)(15). A principal difficulty has been to differentiate between the effects of an enlarged respiratory dead space and of uneven alveolar ventilation, both of which can retard the completion of equilibration.…”

The bias flow nitrogen washout technique for measuring the functional residual capacity in infants

“…The Veff is converted to BTPS (Veff-BTPS) [24]. The switching errors above FRC should be corrected for by subtracting any volume above EEL (previously converted to BTPS conditions) from the VEFF-BTPS to obtain FRCN 2 [7,12]:…”

STUDIES OF THE VENTILATION-PERFUSION RELATIONSHIPS IN THE LUNGS OF SUBJECTS WITH CHRONIC PULMONARY EMPHYSEMA, FOLLOWING A SINGLE INTRAVENOUS INJECTION OF RADIOACTIVE KRYPTON (Kr85). I. PRESENTATION AND VALIDATION OF A THEORETICAL MODEL *

“…The study of the elimination of an inert gas from the lungs of human individuals has proven a useful tool in the determination of ventilation patterns (1,2). In particular it could be demonstrated that the lungs of emphysematous patients can be conceived as being composed of at least two different compartments, i.e., a relatively small space with good ventilation and a relatively large space with poor ventilation (3).…”