Measurement of Blood Oxygen Tension

THE measurement of the blood oxygen tension is not as simple as the measurement of oxygen content but improved techniques are now available and one such method will be described after a review of earlier methods.The measurement of blood oxygen tension was first achieved by methods based upon the aerotonometer, in which a small bubble of gas is equilibrated with a large volume of blood, and the gas bubble subsequently analysed for oxygen.Krogh (1908) designed a micro-aerotonometer in which blood flowed from a cannulated artery around a bubble which was subsequently drawn into a capillary tube and analysed for oxygen.Barcroft and Nagahashi (1921) devised a method which was similar in principle but, being suitable for analysis of a blood sample contained in a syringe, it was the first method applicable to human experiments.Twenty years later Comroe and Dripps (1944) published a modification of this method and established its accuracy.Then Riley et al. (1945) described their use of the Roughton-Scholander syringe for the equilibra- tion of blood with a bubble of gas and for its subsequent analysis.The essential advance was that the whole procedure was carried out in the same syringe.This method has proved of great value in physiological studies but has some disadvantages.It is not for occasional use and requires constant practice, considerable skill and perfect attention to detail.An experimenter may attain repeatability of results and yet show systematic errors, so that it is essential that each individual should assess his own personal accuracy by means of a series of tonometer experiments.The method is most accurate in the range of PO2 between 40-100 mm Hg and is unsuitable for values above 100 mm Hg, which for many purposes is a serious limitation.