Uneven Ventilation of the Lung Following Trauma

To evaluate the rate of gas mixing in human lungs during rebreathing maneuvers used to measure pulmonary tissue volume (Vt) and pulmonary capillary blood flow (Qc), we devised a method to determine the dead space during rebreathing (VRD). Required measurements are initial concentration of a foreign inert insoluble gas in the rebreathing bag, first mixed expired concentration, equilibrated concentration, volume inspired, and volume of the first expired breath. In subjects breathing rapidly at 30 breaths/min with inspired volumes in excess of 2 liters, VRD had values three or more times greater than the predicted anatomical dead space (VD). Breath holding after the first inspiration progressively diminished VRD so that after 10–15 s, it approximately equaled predicted VD. VRD measured with helium was smaller than VRD measured with sulfur hexafluoride. The reported degree of uneven ventilation from gravitational forces in normal humans can account for only about one-third of the difference between VRD and VD. These findings support the concept that mixing by diffusion between peripheral parallel airways is incomplete at normal breathing rates in humans and can result in errors as high as 25% in Vt and Qc.

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Estimation of pulmonary ventilation with nitrogen and helium, using the mass spectrometer

Journal of Applied Physiology ◽

10.1152/jappl.1959.14.4.499 ◽

1959 ◽

Vol 14 (4) ◽

pp. 499-506 ◽

Cited By ~ 1

Author(s):

K. Tokuyasu ◽

A. Coblentz ◽

H. R. Bierman

Keyword(s):

Tidal Volume ◽

Mass Spectrometer ◽

Functional Residual Capacity ◽

Pulmonary Ventilation ◽

Normal Subjects ◽

Alveolar Ventilation ◽

Pulmonary Lesions ◽

Normal Subject ◽

Residual Capacity ◽

Uneven Ventilation

Estimation of pulmonary ventilation was attempted by measuring the elimination of nitrogen and helium with the mass spectrometer. Exhalatory concentrations of nitrogen and helium were continuously recorded in each of 12 normal subjects and 10 patients with pulmonary enphysema or space-occupying pulmonary lesions. Uniform values for both slow and rapid uneven ventilation were found in all normal subjects but always less than in emphysematous states. Ratios of effective tidal volume (Vt) and alveolar ventilation volume (f·Vt) to functional residual capacity P = Vt/Vr and Q = f·Vt/Vr were one half or less than those in the normal subject. Smaller values of uneven ventilation were found for helium than nitrogen. Data computed by the theory of 'periodic' ventilation gave greater values for uneven ventilation (Q) and more accurately represented the physiologic conditions than derived by ‘continuous’ ventilation. Submitted on August 7, 1958

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Ventilation inhomogeneity during controlled ventilation. Which index should be used?

Journal of Applied Physiology ◽

10.1152/jappl.1988.65.5.2030 ◽

1988 ◽

Vol 65 (5) ◽

pp. 2030-2039 ◽

Cited By ~ 51

Author(s):

A. Larsson ◽

C. Jonmarker ◽

O. Werner

Keyword(s):

Tidal Volume ◽

Dead Space ◽

Mean Value ◽

Mixing Ratio ◽

Tracer Gas ◽

Ventilation Inhomogeneity ◽

Pulmonary Clearance ◽

Significant Difference ◽

Uneven Ventilation ◽

Spontaneously Breathing

Six indexes for diagnosing uneven ventilation by tracer gas washout were studied. The indexes were lung clearance index, mixing ratio, Becklake index, multiple-breath alveolar mixing inefficiency, moment ratio, and pulmonary clearance delay, all of which increase with impaired pulmonary gas mixing. In model lung tests, indexes that compared the actual washout curve with a calculated ideal curve (mixing ratio, multiple-breath alveolar mixing inefficiency, and pulmonary clearance delay) were unaffected by changes in tidal volume and series dead space, whereas the others varied markedly. In both spontaneously breathing and mechanically ventilated patients all indexes showed a significant difference between smokers and nonsmokers (P less than 0.002), but the indexes were somewhat different in their assessment of different ventilatory patterns. However, the mean value for all indexes, with the exception of mixing ratio, was smallest with a fast insufflation followed by an end-inspiratory pause. Any of the indexes may be useful if its limitations are recognized, but mixing ratio, multiple-breath alveolar mixing inefficiency, and pulmonary clearance delay seem preferable, because they are not affected by changes in tidal volume and dead space fraction.

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Airway resistance and uneven ventilation in bronchial asthma

Journal of Applied Physiology ◽

10.1152/jappl.1968.25.4.365 ◽

1968 ◽

Vol 25 (4) ◽

pp. 365-370 ◽

Cited By ~ 54

Author(s):

E. R. McFadden ◽

Harold A. Lyons

Keyword(s):

Bronchial Asthma ◽

Airway Resistance ◽

Uneven Ventilation

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Effects of uneven ventilation-diffusion ratios on pulmonary diffusing capacity in disease.

Journal of Applied Physiology ◽

10.1152/jappl.1967.23.1.1 ◽

1967 ◽

Vol 23 (1) ◽

pp. 1-10 ◽

Cited By ~ 13

Author(s):

C Hatzfeld ◽

F Wiener ◽

W A Briscoe

Keyword(s):

Diffusing Capacity ◽

Pulmonary Diffusing Capacity ◽

Uneven Ventilation

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A comparison of static volume-pressure relations of excised pulmonary lobes of dogs

Journal of Applied Physiology ◽

10.1152/jappl.1963.18.2.274 ◽

1963 ◽

Vol 18 (2) ◽

pp. 274-278 ◽

Cited By ~ 27

Author(s):

N. R. Frank

Keyword(s):

Technical Assistance ◽

Tissue Weight ◽

Uneven Ventilation ◽

The Right ◽

Gas Volume ◽

Subordinate Role

Comparison was made of essentially static volume-pressure relations of the lobes of excised dogs' lungs during stepwise deflation from a maximal distending pressure of 30 cm H2O. No systematic differences were found among the right apical, middle, and left apical lobes nor between the right and left lungs when gas volume was expressed per unit of tissue weight. However, the right mediastinal-lower and left lower lobes held smaller volumes for any pressure than did the others. The differences were small and appear to play a subordinate role in causing the uneven ventilation typical of healthy lungs. These observations relate only to elastic variations among lobes and are not intended to characterize variations that may exist within lobes. Note: (With the Technical Assistance of Eleanor Root) Submitted on August 13, 1962

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