Pulmonary parenchymal tissue volume and pulmonary capillary blood flow in normal subjects

We measured pulmonary parenchymal tissue volume (Vt) and pulmonary capillary blood flow (Qc) in 11 normal subjects by a rebreathing technique and end-tidal, dead-space correction (ETDS) method, using two soluble gases, acetylene (C2H2) and dimethyl ether (DME). We assessed the results using different intervals of measurement, inspired volumes and rebreathing frequencies. The mean values +/- SD of Vt were 559 +/- 58 and 511 +/- 52 ml, with C2H2 and DME, and of Qc were 3.67 +/- 0.44 and 4.18 +/- 0.54 liter/min/m2, respectively. Measurements with the interval between the 1st and the 6th end-tidal points and within the first 15 s yielded the best reproducibility. Data obtained from two satisfactory recordings from the same subject are sufficient to calculate Vt and Qc. Inspired volume shows a significant correlation with Vt values measured with both tracer gases, especially with DME. Rebreathing frequency also affects this latter gas. Despite some problems which are not easily explainable (dependence upon the inspired volume, rebreathing frequency and test gas species), we conclude that the methods allow measurements of Vt and Qc with acceptable reproducibility but that different variables may affect the results.