[Effect of pneumothorax on membrane diffusing capacity and pulmonary capillary blood volume].

OBJECTIVE: Investigating the effect of pulmonary membrane diffusing capacity(Dm) and pulmonary capillary blood volume(Vc) on carbon monoxide diffusing capacity (DLCO) in patients with pneumothorax before and after treatment, and clarifying the mechanism of hypoxemia due to pulmonary reexpansion.

METHODS: Pulmonary function test, DLCO, Dm, Vc and arterial blood gas analysis were determined in 21 cases of pneumothorax before treatment and one week after pulmonary reexpansion.

RESULTS: DLCO, Dm, Vc, partial pressure of arterial oxygen (PaO2), alveolar ventilation volume (VA), percentage of forced expiratory volume in one second to predicted value, and the ratio of dead space ventilation (VD) to tidal volume (VT) [VD/VT] were (64 +/- 4)%, (66 +/- 5)%, (70 +/- 5)%, (83.7 +/- 2.3) mm Hg, (4.4 +/- 0.2) L, (59 +/- 4)%, 0.340 +/- 0.020 respectively before treatment. After pulmonary reexpansion, they respectively were (71 +/- 4)%, (74 +/- 4)%, (80 +/- 6)%, (89.4 +/- 1.5) mm Hg, (5.40 +/- 0.20) L, (79 +/- 4)%, 0.210 +/- 0.010. They were significantly improved after treatment. Except for Dm, they were statistically different. Between Dm, Vc and DLCO, significant positive correlations were found during pneumothorax and one week after pulmonary reexpansion, especially correlation between Dm and DLCO was more apparent. Between Dm and DLCO significant positive correlations (r2 = 0.862, P < 0.0001; r2 = 0.728, P < 0.001) were found in study patients before and after treatment. So were Vc and DLCO (r1 = 0.643, P < 0.01; r2 = 0.52, P < 0.05). The correlation coefficient of Dm was markedly larger than Vc.

CONCLUSIONS: The decrease in pulmonary diffusing function is related to Dm and Vc during pneumothorax, while decrease of Dm plays a major role. The hypoxemia is still presented in a period of time after pulmonary reexpansion, which is not related to VA and abnormality of ventilation-perfusion ratio (V/Q). It is chiefly due to unrecovery of Dm.