A noninvasive in vivo method of assessing the kinetics of XXXX metabolism in @entity1 .

@entity1 @entity5161 @entity1009 @entity1508
The authors describe a noninvasive method of estimating the kinetic constants that characterize metabolism of inhaled anesthetics in @entity1 . Ten healthy male volunteers breathed subanesthetic concentrations of @entity1508 and @entity5161 in a fixed inspired ratio of 20:1. @entity5161 served as a marker that identified changes in uptake in nonmetabolizing depots. Each study progressed through nine 30-min levels (numbered 0-8). At each level, inspired concentrations of both @entity1508 and @entity5161 were doubled, and alveolar concentrations and uptakes were determined. Clearance (uptake/alveolar concentration) of @entity5161 remained constant over a range of concentrations of 0.00006 to 0.008%. In contrast, clearance of @entity1508 decreased as the alveolar concentration increased from 0.0007 to 0.13%. On this basis, the authors assumed that the clearance of @entity1508 was a combination of linear clearance to depots and saturable metabolism, the former proportional to the clearance of @entity5161 , and the latter attributable to a Michaelis-Menten process. Applying such a model to @entity1508 , they estimated the mean (+/- SE) Vmax (the composite maximum rate of metabolism) to be 0.79 +/- 0.09 ml . @entity1009 . individual-1, and the Km (the composite concentration at which half-saturation of enzymes occurs) to be 0.029 +/- 0.003%. This model provides a significantly better data fit than that provided by two simpler submodels, one of which assumes that all clearance is linear, and the other of which allows a part of clearance to be saturable but ignores the @entity5161 marker data. The value of 0.029% for Km indicates that a wide range of clinical anesthetic concentrations will produce similar rates of metabolism; that metabolism will proceed at near maximum rates during the first several minutes of recovery; and that most metabolism probably occurs after, rather than during, anesthesia.
