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In healthy volunteers, the single-breath diffusing capacity of the lung for carbon monoxide (Dlco) decreases and Dlco normalized per liter alveolar volume (Va; Dlco/Va) increases if Va is decreased. We hypothesized that comparison of Dlco/Va with its predicted value at predicted total lung capacity (TLC) will result in an underestimation of the diffusion disorder in patients with a restrictive lung disease, if a similar relationship exists between Dlco/Va and lung volume as found in healthy volunteers. To test this hypothesis, we studied total gas transfer Dlco and Dlco/Va as functions of Va in patients who developed a restrictive lung disease and a diffusion disorder in a short period of time. An observational survey. Pulmonary function department. Thirteen patients without any initial pulmonary pathology who developed the mentioned pulmonary pathology due to bleomycin treatment. Bleomycin treatment. We performed the single-breath test at various Va levels before, during, and after bleomycin treatment. In the majority of the patients, the Dlco vs Va relationship remained parabolic, but shifted downwards during therapy. Therefore, the linear Dlco/Va vs Va relationship shifted downwards, while the negative slope was not changed, indicating the development of a decreased gas transfer. Six patients also developed a volume restriction. The agreement of the data with the hypothesis increased its probability. Consequently, to evaluate a diffusion disorder, Dlco/Va at a lower actual TLC of patients with a lung restriction should be compared to a reference Dlco/Va at a lung volume equal to the actual TLC.

To test the hypothesis that, during high-frequency oscillatory ventilation (HFOV) of pigs with acute lung injury, the oxygenation index (OI = Paw*FIO(2)*100/PaO(2)) is minimal at the lowest continuous distending pressure (Paw), where the physiological shunt fraction is below 0.1 (Paw(optimal)). Prospective, observational study in a university research laboratory. Eight Yorkshire pigs weighing 12.0+/-0.5 kg, with lung injury induced by lung lavage. After initiation of HFOV, the pigs were subjected to a stepwise increase of Paw to obtain under-inflation, optimal inflation and over-distension of the lungs (inflation) in series, followed by a similar decrease of Paw (deflation). At each Paw level, the OI and physiological shunt fraction were determined. The OI reached a minimum of 6.2+/-1.4 at Paw 30+/-4 cmH(2)O during inflation and a minimum of 2.4+/-0.3 at Paw 13+/-2 cmH(2)O during deflation. Paw(optimal) was 32+/-6 cmH(2)O on the inflation limb and 14+/-2 cmH(2)O on the deflation limb. The difference between the Paw at minimal OI and Paw(optimal) was -1.9+/-4.2 cmH(2)O (NS) during inflation and -1.5+/-1.6 cmH(2)O (p<0.05) during deflation. In 15 out of the 16 comparisons, the difference in Paw was within one step (+/-3 cmH(2)O). The minimal OI is indicative for the Paw where oxygenation is optimal during HFOV in surfactant-depleted pigs.