Properties of the recirculation model: matrix description and conditions for a monotonic decreasing single pass response.

The recirculation equation is examined for the case in which the blood concentration is given by a polyexponential expression sigma Ai exp (-ait). A matrix is developed whose eigenvalues are the exponential coefficients of the single pass response. These eigenvalues are real and distinct, and the single pass response is monotonic decreasing, when the Ai are all positive. An ordering relatión for the eigenvalues is given.