Single-breath method for estimating pulmonary blood flow: data reduction based on nonlinear curve fitting
Grønlund, J.; Christensen, P.; Hansen, L.G.
Aviation Space and Environmental Medicine 58(11): 1097-1102
1987
ISSN/ISBN: 0095-6562 PMID: 3120685 Document Number: 301450
The single-breath method of Kim et al. for noninvasive estimation of pulmonary blood flow utilizes the PCO2 vs. PO2 curve recorded during a prolonged expiration. The calculation of pulmonary blood flow is complicated by the nonlinearity of the expression for the PCO2 vs. PO2 curve. In previous studies of the single-breath method, this problem has been solved by using a data reduction procedure which includes transformation of the nonlinear expression into a linear plot. The disadvantage of this data reduction procedure is that the transformation utilizes the first derivative of the PCO2 vs. PO2 curve, which is very sensitive to experimental noise. In the present study, we have examined an alternative data reduction procedure in which the nonlinear expression was fitted directly to the experimental curve. At an expiration length of 15 s, the two data reduction procedures gave almost identical standard deviations of 0.57 L.min-1 on repeated determinations of the pulmonary blood flow. However, the linear data reduction procedure was much more sensitive to omission of the PCO2 vs. PO2 curve segments obtained in the last part of the prolonged expiration.