A. Zwart

The sloping alveolar plateau at synchronous ventilation

We performed model calculations on the slope of the alveolar plateau at single breath washout of helium (He) and sulphurhexafluoride (SF6). Calculations were carried out on an extensible axissymmetric lung model, which was synchronously ventilated either equally or unequally. The calculated slopes of the alveolar plateau were small (<0.3%), which is in agreement with the results of other investigators. However, calculations carried out on a synchronously equally ventilated axis-asymmetric lung model related to the terminal lung unit (acinus), yielded slopes for the alveolar plateau ranging from 0 up to 14% per liter between 1.2 and 1.8 l expired volume. Even with a post inspiratory apnea of 1 s, we still found slopes ranging from 0–4%.Our findings are in contrast to the conclusions of Engel et al. (1979), who ascribe the slope of the alveolar plateau to asynchronous unequal ventilation.

Uptake of highly soluble gases in the epithelium of the conducting airways

Short duration washin and washout experiments were carried out with the gases ether (diethyl ether), ethyl acetate and acetone in order to study the excretion behaviour in the lung of gases highly soluble in blood and tissues. Carbon dioxide (CO2) was analyzed as a reference gas during the washout. The excretion values for acetone were generally the lowest, those for ether the highest, and intermediate ones were obtained for ethyl acetate. These results are in accord with the experimental data of others. Analysis of the washout curves shows that for acetone the volume of gas expired before the beginning of phase II is considerably smaller than found for CO2 and ether. During washout, the slope of the alveolar plateau for acetone is negative for the first few breaths and becomes positive thereafter; however, it remains lower than the slopes for CO2 and ether, which are always positive. These two phenomena occurring during washout clearly demonstrate that the acetone in the expired air must originate from the epithelial tissue lining the conducting airways. We conclude, therefore, that, in terms of gas transport, the conducting airways behave differently for poorly and highly soluble gases and this provides a physiological basis for the deviating excretion behaviour of highly soluble gases.

A Non-Invasive Determination of Lung Perfusion Compared with the Direct Fick Method

In 5 young pigs (7–9 kg each) data on effective lung perfusion were obtained using a sinusoidal forcing function in the inspired halothane concentration. These data were compared with the cardiac output measured by the direct Fick method for oxygen, corrected for venous admixture.To produce different levels of cardiac output during each experiment the respiratory and circulatory conditions were changed. For the 5 experiments taken together, the mean of the ratios between the noninvasively obtained effective lung perfusion and the venous admixture corrected Fick data was 1.01 (SD=0.14,n=55) withr=0.92.

A new ventilation inhomogeneity index from multiple breath indicator gas washout tests in mechanically ventilated patients

Objectivesa) To determine the validity of a new method to analyze indicator gas washout tests on mechanically ventilated patients. This method takes into account the difference between the end-expiratory gas fraction and the mean gas fraction in the lung and provides the end-expiratory lung volume and a new index of ventilation inhomogeneity called volumes regression index. b) To determine the validity of this index as a predictor of chronic obstructive pulmonary disease. c) To compare this index with the moment ratio index and Becklake index. DesignProspective study of diagnostic test. Criterium standards: Closed-circuit indicator gas dilution technique and Tiffeneau index. SettingSurgical intensive care unit of a university hospital. PatientsA total of 38 mechanically ventilated postoperative patients, divided into two groups: the obstructive group (n = 21) and the nonobstructive group (n = 17), based on their preoperative lung function. InterventionsNone. Measurements and Main Resultsa) The mean coefficient of variation of all lung volume measurements in a group of nine healthy volunteers was 5%, and the difference between this technique and the closed-circuit helium dilution measurements was −2 ± 5%. In patients, the mean coefficient of variation of the lung volume measurements was 3.5%. The volumes regression index was measured as 0.02 ± 0.04 in a dummy lung, 0.37 ± 0.08 in the healthy volunteers, 0.64 ± 0.23 in the nonobstructive patients, and 1.1 ± 0.3 in the obstructive patients. The volumes regression index provided a better correlation (r2 = .46) with preoperatively determined Tiffeneau index than the Becklake index (r2 = .11) or the moment ratio index (r2 = .18). ConclusionThe proposed technique provides a means for accurate measurement of the end-expiratory lung volume and the amount of ventilation inhomogeneity in mechanically ventilated intensive care unit patients. (Crit Care Med 1993; 21:1149–1158)

The excretion of highly soluble gases by the lung in man

AbstractThe excretion (E) of inert gases by the lung depends on, among other things, their blood-gas partition coefficients (λ). According to conventional gas exchange models, E should increase with increasing λ However, recent models that take into account the tidal character of breathing and the buffering capacity of lung tissue predict that E will show a minimum in the range of large λ values (λ>10). Further, this local minimum should shift to larger λ values in exercise conditions as compared to rest conditions. The aim of this study is to verify this predicted behaviour of E. The experiments were carried out with seven healthy subjects at rest and at three work loads (50 W, 100 W and 150 W) on a bicycle ergometer. The behaviour of E was determined from the results of a simultaneous washin of four tracer gases: ethyl acetate (λ≈75), acetone (λ≈330), ethanol (λ≈2000) and acetic acid (λ≈20000). The washin lasted 4 min, and E was calculated from E = 1−pĒ/pI, where pI and PĒ are the partial pressures of the tracer gas in inspired and mixed expired gas determined from the recordings obtained during the last minute of washin. pI and PĒ were measured with a mass spectrometer. Comparison of the E values of the four gases shows that at rest a minimum value for E is found for acetone. In exercise conditions, however, the smallest E value is found for the more soluble ethanol or acetic acid. Further, under exercise conditions the E values for ethyl acetate and acetone are larger than their respective values at rest. In general, the experimental findings are consistent with the predicted behaviour of E. This means that gas exchange in the airways between gaseous and dissolved tracer gas in the airway lumen and in the airway tissue, respectively, cannot be ignored for highly soluble tracer gases. In addition, the observed differences between the E values of the four highly soluble tracer gases imply that the dead space ventilation (

Diffusion-limited gas mixing in the lung and its consequences for transpulmonary gas transport

\dot V_{\text{D}}

Excretion-retention data of steady state gas exchange in tidal breathing

) depends on λ, i.e. the value of