Nonuniform Ventilation Research Articles

Effect of ventilation and diffusion nonuniformity on DLCO (exhaled) in a lung model.

Recent studies have shown that diffusing capacities measured at multiple intervals during a single exhalation [DLCO(exhaled)] remained constant with lung volume in normal subjects, but decreased with decreasing lung volume in patients who may have had diffusion nonuniformity. We have examined the theoretical basis of these results by determining what factors affected DLCO(exhaled) in a computerized lung model in which diffusion in each compartment remained constant with lung volume. DLCO(exhaled) decreased with decreasing lung volume when a small lung region lacked diffusion. However, the change in DLCO(exhaled) with lung volume was also affected by nonuniform ventilation and these effects could not be eliminated by correcting the carbon monoxide decay and the simultaneous decay of helium. DLCO(exhaled) values were also influenced by the exhaled flow rate in the presence of nonuniform ventilation and/or nonuniform diffusion. However, prolonging the period of breath holding prior to exhalation reduced DLCO(exhaled) values at all lung volumes when non-uniform diffusion was simulated, but did not affect DLCO(exhaled) when only nonuniform ventilation was simulated.

Radiological diagnosis of nonuniform pulmonary ventilation.

Laboratory methods of determining many aspects of pulmonary function have become remarkably accurate and sophisticated in the past ten years. Application of these new tests, however, has been limited by the fact that many of them require expensive apparatus not readily available, skilled technicians, and considerable time and effort. In a previous paper (1) we described the qualitative information about disordered ventilatory capacity which one might obtain by appropriate roentgen methods which are easily available. In the present paper the author proposes to discuss another aspect of disturbed pulmonary function in which ventilation is uneven in relation to capillary blood flow and to show the radiologic evidence which suggests that this disturbance is present. The efficient performance of gas exchange (O2 and CO2), which is the primary function of the lungs, requires a nice matching between the amount of air circulating through alveoli and the quantity of blood passing along the alveolar walls. In the normal lung, the air-blood volume relationships are constant for any particular lung area although these constants vary somewhat depending on location within the chest (2). One might consider, however, the normal average situation to be one in which alveolar ventilation equaled 2 liters∕min.∕lung, and capillary blood flow 2.5 liters∕min.∕lung, resulting in a ratio of 0.8 (Fig. 1). When injury or disease affects a localized area of lung, either ventilation or blood flow may be impaired selectively (Figs. 2 and 3). This may be accompanied by a compensatory decrease in the reciprocal function, which, however, seldom produces a new balance with a normal ratio of 0.8. Thus, even though total lung volumes may be adequate, mismatching of ventilation and blood flow results in the hypoxemia that accompanies pulmonary insufficiency and failure in many different clinical conditions (3). Many years ago, Golden (4) showed that the pattern of the vascular markings in the lungs, as seen by fluoroscopy and films, reflected accurately the symmetrical changes which occur in the tracheobronchial tree during respiration in the normal person. Since the blood vessels parallel the branching of the airways, irregularity and asymmetry of the vascular shadows in any area of the lung mean that the distribution of air in that region is uneven. Therefore, close inspection of roentgenograms of the chest made in various projections may lead to a diagnosis of nonuniform ventilation, localized or generalized (Figs. 4 and 5). This evaluation of qualitative pulmonary dysfunction can be quite accurate when compared with laboratory tests of lung function (Fig. 6). Discussion Nonuniform pulmonary ventilation may lead to alveolar hypoventilation and result in chronic hypoxemia.

LUNG DIFFUSING CAPACITY: REBREATHING METHOD, APPLICABILITY IN NONUNIFORM VENTILATION.

We have calculated how the carbon monoxide concentration changes when subjects with different distributions of ventilation and lung diffusing capacity (Dl) respire in a small bag. The curve [loge CO concentration in the bag] versus [time] will sooner or later appear as a straight line. Dl is calculated from the slope of the rectilinear section of the curve and from lung and bag volume. If the curve becomes rectilinear within the period considered, Dl is calculated too low. In some cases the curve will not be rectilinear until more than 45 sec have passed, but will appear to be rectilinear during the period from 30 to 45 sec. If such an experiment is discontinued when 45 sec (the usual duration of experiment) have passed, Dl can be calculated at too high, at correct, or at too low values. nonuniform distribution of lung diffusing capacity Submitted on February 18, 1964

LUNG DIFFUSING CAPACITY: CYCLICALLY AND CONTINUOUSLY VENTILATED CLOSED SYSTEMS.

In previous communications, distribution of ventilation and lung diffusing capacity (Dl) were calculated from changes occurring in N2 and CO concentrations when a subject, whose lungs contained atmospheric air at the beginning of the experiment, respired in a spirometer containing oxygen and a little CO. In the calculations, the system was assumed to be continuously ventilated and without dead space. The present study examines which errors may arise from these simplifications. Equations for cyclic ventilation are derived. Definite values for dead space and for volumes, alveolar ventilation, and Dl of two nonuniformly ventilated lung regions are assumed. Thereupon it is computed how the concentrations of N2 and CO will change, if a subject with the assumed values respires in a spirometer of a given volume. From these changes in concentration, Dl and the distribution of ventilation are calculated using equations for continuous ventilation. The differences between the assumed and the calculated values of Dl are small. mathematics for cyclic ventilation; nonuniform ventilation; calculation of dead space; calculation of lung diffusing capacity Submitted on February 18, 1964

MEASUREMENT OF LUNG DIFFUSING CAPACITY BY MEANS OF C14O IN A CLOSED SYSTEM.

A method of measuring the lung diffusing capacity (Dl) with radioactive carbon monoxide (C14O) and nonuniformity of ventilation with nonabsorbable gas in a closed system is described. Treating ventilation as a continuous phenomenon and disregarding dead space, the mathematical equations for uniform and nonuniform ventilation (two lung regions ventilated in parallel) are derived. It is proved that sooner or later the curve for carbon monoxide, plotted on semilogarithmic paper, will be rectilinear. Experiments in six normal subjects and eight patients with chronic lung disease are described. Determinations of the distribution of the ventilation and the Dl are made in separate experiments. Since the method is unreliable at high Dl values, many of the Dl estimations are performed at high oxygen tension, which reduces the apparent Dl. It is shown that the assumption of a uniform distribution of Dl to lung volume explains the experimental findings better than the assumption of a uniform distribution of Dl to alveolar ventilation. Dl was decreased in four of the eight patients. mathematics of uniform and nonuniform ventilation; distribution of lung diffusing capacity in relation to lung volume and alveolar ventilation; N2 curve for use in calculating alveolar ventilation and regional lung volumes; CO curve for use in calculating lung diffusing capacity; diffusing capacity of lung determined with a closed system Submitted on October 15, 1962

MEASUREMENT OF THE LUNG DIFFUSING CAPACITY FOR CARBON MONOXIDE AND OF NON-UNIFORM VENTILATION BY MEANS OF A CLOSED SYSTEM.

(1963). Measurement of the Lung Diffusing Capacity for Carbon Monoxide and of Non-Uniform Ventilation by Means of a Closed System. Scandinavian Journal of Clinical and Laboratory Investigation: Vol. 15, No. 6, pp. 587-596.