A technique to continuously measure arteriovenous oxygen content difference and P50 in vivo

Abstract

In hypoxemic high-altitude polycythemic natives whose arterial O2 saturation (SaO2) normally ranges between 70 and 80%, three polyurethane catheters with both optical and polarographic sensors were inserted into the radial artery to measure SaO2 and O2 tension (PaO2), and three thermodilution fiber-optic balloon-tipped catheters were floated into the pulmonary artery to measure mixed venous O2 saturation (SvO2). Correlation of the in vivo SaO2, PaO2, and SvO2 values with the in vitro measurements was high (r = 0.97, 0.99, and 0.98, respectively). Both catheters were inserted in one polycythemic subject before and 4 days after isovolemic hemodilution. Data from the sensors were used to calculate arteriovenous O2 content difference (CaO2 - CvO2) and the O2 half-saturation pressure of hemoglobin (P50). The mean +/- 1 SD of the in vivo and in vitro P50 calculated with the Hill equation was 27.61 +/- 2.15 Torr and 27.35 +/- 1.60 Torr, respectively. The mean +/- 1 SD of the absolute difference between the in vivo and in vitro measurements was 1.16 +/- 1.21 Torr. The in vivo CaO2 - CvO2 correlated well with the in vitro measurements (r = 0.93), and the mean +/- 1 SD of the error in the catheter CaO2 - CvO2 measurements was 0.47 +/- 0.50 ml/dl. This technique appears to provide a useful measurement of blood gas exchange parameters and should be applicable to the study of exercise physiology and clinical regulation of O2 transport.

MR Imaging–derived Oxygen-Hemoglobin Dissociation Curves and Fetal-Placental Oxygen-Hemoglobin Affinities

“…Oxygen affinity can be measured as the Po 2 partial pressure of oxygen level at which hemoglobin is 50% saturated with oxygen (P50). To obtain P50 values, Po 2 partial pressure of oxygen and So 2 oxygen saturation can be determined ex vivo from arterial and venous blood samples ( 9 ). However, during pregnancy, extraction of blood samples from the fetal umbilical cord is a highly invasive procedure, involving a great risk to the fetus ( 10 ).…”

Feasibility and accuracy of a fiberoptic catheter for measurement of venous oxygen saturation in newborn infants

“…A pulse generator sequentially activates each diode for 1 ms followed by an equal interval when no diodes are energized. This four period cycle occurs at a rate of 244 Hz (9).…”