Medicine of the Future in America

The Oxyhemoglobin Dissociation Curve in Liver Cirrhosis: Statistical Analysis

The Oxyhemoglobin Dissociation Curve in Liver Cirrhosis: Statistical AnalysisDuring this process, two variables were measured continuously: So2% by photometry, and Po2 using a Po2 electrode (Eschweiler; Kiel, Germany). A plot was continuously made of hemoglobin oxygen saturation as a function of Po2. In addition, 10 mL of blood was sampled for measurements of 2,3 DPG, plasma ions, and arterial and mixed venous blood gases. For each curve, one hundred pairs of Po2 and So2% values were processed by a homemade computer program in order to obtain the entire curve. The accuracy of the method, as expressed by the SD of the P50, was 0.1 mm Hg for six curves obtained from the same blood sample. Biological variation, estimated from 16 curves traced from four blood samples taken every Monday during 4 weeks from the same healthy nonsmoking volunteer, was 0.3 mm Hg.

The plasma concentration of inorganic phosphates was determined using a commercial kit (Phosphorus Inorganic Kit No. 670; Sigma Chemical; St Louis, MO). The plasma chloride concentration was determined by a titrimetric method (Merckotest; Merck; Darmstad, Germany). Plasma sodium, potassium, and calcium concentrations were assayed in a blood gas analyzer (model 288; Ciba-Corning Diagnostics; Medfield, MA). Hemoglobin and carboxyhemoglobin were measured by an oximeter (OSM III; Radiometer; Copenhagen, Denmark). 2,3 DPG was measured by an enzymatic method (kit No. 35-UV; Sigma). The hemoglobin oxygen capacity was measured by a Lex-O2-Con galvanic cell (Lexington Instrument Corporation; Waltham, MA).
A Student t test for unpaired data was applied to compare Po2 values at 11 levels of So2 in the two groups. To test the dispersion of the Po2 values for a single level of So2, we used the F Fisher one-tailed test, F = S2x/S2y, where S2x and S2y are the variances of the data.35 The effect of 2,3 DPG and ions on P50 was assessed using univariate linear regression. To select the plasma ions that independently affect the P50, all of them were submitted to a forward stepwise linear regression using T-to-enter statistics to check the significance of change in explained P50 variance (r2); p < 0.05 was considered significant (analysis of variance).

This entry was posted in Liver disease and tagged liver cirrhosis, oxyhemoglobin dissociation curve.
Copyright © 2012 Medicine of the Future in America