Pulmonary blood flow and tissue volume. Assessment of a non-invasive technique of measurement.

Pulmonary blood flow and tissue have been measured by a rebreathing technique in which the disappearance of soluble and insoluble gases from an inhaled mixture is followed continuously using a respiratory mass spectrometer. Although measurements made with diethyl ether are more reproducible than those made with freon-22, they are inaccurate because ether (the more soluble gas) is taken up by the tissues surrounding the respiratory dead space. Experiments carried out on four normal subjects demonstrate that measurements of both pulmonary blood flow and tissue volume are influenced by the volume of gas in the lungs during the manoeuvre. Possible reasons for this are discussed and an exponential relationship between the two variables and lung volume is suggested.