ISEC - A PROGRAM TO CALCULATE INSULIN-SECRETION

ISEC (Insulin SECretion) is a computer program which calculates pre-he patic insulin secretion from plasma C-peptide measurements. The progra m uses a regression (population) model to derive parameters of C-pepti de kinetics from;subject's gender, type (normal, obese, non-insulin de pendent diabetes mellitus), age, weight, and height. Insulin secretion is calculated as a piece-wise constant (step) function with flexible step length allowing for a fine resolution of the secretion profile be tween measurements. A constrained regularisation method of deconvoluti on is employed to carry out the calculations. The calculated profile s atisfies three properties: (i) it fits the measurement within the give n level of the measurement error, (ii) it is non-negative, and (iii) i t has a minimum value of a regularisation criterion (norm of second di fferences) which quantifies the degree of deviation of the secretion p rofile from a straight line. Both theoretical aspects and specific fea tures related to ISEC are considered. To exemplify the use of ISEC, pr e-hepatic insulin secretion is calculated during meal tolerance test, frequently sampled intravenous glucose tolerance test, hyperinsulinaem ic euglycaemic glucose clamp, and basal conditions with frequent sampl ing.