Double indicator pulmonary edema measurement

Abstract

Patient monitoring method and apparatus for measurement of in vivo extra vascular lung water (pulmonary edema) and pulmonary circulatory system thermal bypass utilizing double indicator dilution with temperature and electrical conductivity modifiers. A thermal modifier is utilized for a primary indicator dilution measurement with electrical conductivity provided as a reference indicator which in turn is corrected for temperature effects produced by the thermal moderator as well as effects of plasma characteristics. Thermal and conductivity sensors are both placed upstream and downstream of the lungs in the pulmonary artery and thesystemic arterial system, and a thermal and conductivity moderator is injected at a site upstream from both. Temperature and conductivity are detected at both sites and the conductivity signal is converted to a volume dilution valve. Lung water is then determined as a function of the mean transit time difference of the two sensed temperatures less the mean transit time difference for the two conductivity based volume dilutions. Because the measurement is based on four sensors and mean transit time differences are used, in vivo error sources merely act as more signal and do not affect the final values. The detected signals are also analyzed in a manner to yield information on thermal bypass. The measurement technique disclosed is useful in correcting the effects of a conductivity indicator for thermal and blood effects however employed.