Thermal recovery after passage of the pulmonary circulation assessed by deconvolution

For indicator-dilution studies, complete thermal recovery after passage of heat through the pulmonary circulation would be desirable. However, the results in the literature obtained by extrapolation techniques are inconsistent. To overcome problems of the extrapolation approach, transport functions of the pulmonary circulation (including the left heart) were computed by deconvolution of pulmonary arterial and aortic pairs of thermodilution curves after central venous indicator injection (10 ml of an ice-cold blood indocyanine green dye mixture). Thermal recovery was determined as the finite integral of the transport function. Thirteen mongrel dogs under piritramid-N2O anesthesia were examined under base-line conditions, in orthostasis to alter the distribution of pulmonary blood flow (9 dogs), and in oleic acid edema (8 dogs). Using the deconvolution approach, thermal recovery was 0.97 +/- 0.04 under base-line conditions, 0.96 +/- 0.03 in orthostasis, and 0.96 +/- 0.05 in pulmonary edema. Thermal recovery determined from extrapolated dilution curves was greater than 100% in all groups, a physically impossible finding. It is concluded that thermal recovery is incomplete but insensitive with respect to the distribution of blood flow and to the size of the extravascular compartment. Monoexponential extrapolation is unsuited for the determination of thermal recovery.