Recovery of ventilation distributions by gas wash-out of a mechanical pump.
A method for deriving virtually continuous distributions of ventilation in the lungs from multiple-breath wash-out of inert, insoluble gases has been tested using a mechanical pump in which two parallel compartments, simulating lung regions, could be differentially ventilated to any desired, and known, extent. With more than moderate non-uniformity, bimodal distributions were always recovered from wash-out data, and with high reproducibility. In a substantial proportion of wash-out experiments ventilation was recovered in regions of very low and very high turnover in addition to the expected modes. These spurious modes may be abolished by various computational devices, none entirely satisfactory. Simultaneous wash-out and wash-in of two or three gases of similar diffusivity give essentially identical solutions. When the pump is operated with the two cylinders out of phase, emptying patterns derived from gas wash-out correspond quite well with those expected from the pump setting. These results help to identify and clarify some of the errors which affect physiological wash-out studies.