Thermal recovery after passage of the pulmonary circulation assessed by deconvolution

Abstract

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.

Extravascular lung water measurements and hemodynamic monitoring in the critically ill: bedside alternatives to the pulmonary artery catheter

“…Given the broader shape of the curve during a transpulmonary thermodilution measurement than during a measurement with the PAC, recirculation effects may be present before monoexponential decay can be reliably established (10). Overcorrection for recirculation has the same effect as an unaccounted for loss of indicator: both will result in a smaller than expected area under the thermodilution curve (Eq.…”

Cardiac index measurements during rapid preload changes: a comparison of pulmonary artery thermodilution with arterial pulse contour analysis

“…This finding demonstrates the clinical applicability of the software version of the PiCCO device tested in our study. The still existing small overestimation of CI PC in contrast to CI PA may be explained by a loss of cold temperature of the injected saline during the transpulmonary passage [30]. In addition, Della Rocca et al proposed a temporary reduction of the heart rate after cold saline injection into the central vein to account for small differences between right heart and left heart CI and therefore a slightly higher arterial pulse contour CI than PA thermodilution CI [12].…”

Bronchial temperature reflects transcapillary heat transport of isolated blood-perfused rabbit lungs

“…In contrast, cold-based calculations of mean transit times measure the whole thermal volume including intravascular and extravascular lung water as well as further extravascular structures [14,15]. After one pass through the pulmonary circulation almost all cold is recovered [16,17]. One aspect to be considered in this context is that thermal volume changes with formation of oedema.…”