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Am J Physiol Gastrointest Liver Physiol 257: G668-G675, 1989;
0193-1857/89 $5.00
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AJP - Gastrointestinal and Liver Physiology, Vol 257, Issue 4 668-G675, Copyright © 1989 by American Physiological Society

ARTICLES

Computerized curve fitting in the analysis of hydrogen gas clearance curves

E. H. Livingston, T. Reedy, F. W. Leung and P. H. Guth
Surgical Service, West Los Angeles, Veterans Administration Medical Center, California.

Hydrogen gas clearance curves obtained from the rat gastric corpus were digitized into a computer and then analyzed by three methods: 1) linear regression of log-transformed data, 2) direct curve fitting with a modified Gauss-Newton nonlinear regression algorithm, and 3) Zierler's height-over-area algorithm. For linear regression of log-transformed data, if the initial base-line estimate was inaccurate or normal amounts of experimental noise were present, the log-transformed data was skewed, leading to deviation of the regression line and incorrect estimation of blood flow. By utilization of the direct-fit routine, the initial estimate of the parameters or experimental noise had little influence on the blood flow determination because of iterative improvement of the parameters. In a study of isoproterenol-stimulated gastric blood flow, Zierler's algorithm underestimated the blood flow estimate. We conclude that analysis of hydrogen gas clearance curves by linear regression of log-transformed data or by Zierler's algorithm may potentially introduce errors in blood flow estimates that may be avoided by analysis with a direct-fitting, nonlinear regression algorithm.


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