Interpretation of metabolic function of the lung. Influence of perfusion, kinetics, and injury

Quantitative assessment of pulmonary metabolic function has been shown to be a novel and important approach to obtaining specific and subtle biochemical information regarding endothelial cell function in the normal and diseased lung. A primary consideration in this measurement of whole organ metabolism, whether it be enzyme, transport, or binding functions, it is to be able to separate convective from kinetic aspects of endothelial cell physiology. Significant progress has been made in both our understanding of the influence of convective factors, as well as of possible solutions relying on mixed order kinetics. Nonetheless, the pervasive influence of surface area on these metabolic measurements and the distinct likelihood that this variable is simultaneously altered with endothelial cell function in acute lung injury makes definitive statements premature at this time. Several approaches to resolve this important issue have been attempted and include simultaneous measurement of nonmetabolic endothelial cell function including DLCO or permeability to urea; simultaneous measure of microvascular space for water or antipyrine; comparison with complex uptake and binding of a lipophilic basic amine such as propranolol; and multiple metabolic markers that may be selectively affected by injury. Other advances that should prove useful include an on-line computer registration of metabolic information, as well as gamma-scintigraphy for the purpose of obtaining regional information.