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Abstract
An indirect method of calibrating an ear oximeter using alveolar Po2measurements has been tested in 10 normal subjects. An oximeter calibration curve was constructed for each individual subject by comparing the output of an ear oximeter with arterial oxygen saturation calculated from alveolar Po2and PCO2during 10 to 20 seconds of hypoxia produced by breathing low oxygen mixtures in the supine position. Hypoxia is terminated by having the subject breathe oxygen, and it is assumed that arterial saturation reaches 100% and that discrepancies between end-expired and arterial gas tensions due to ventilation-perfusion imbalance, impaired diffusion, and right-to-left shunts are negligible under the conditions of calibration. The accuracy of the indirect calibration method was tested by comparing it with direct calibration using arterial blood samples. It is concluded that the indirect calibration method gives a reasonably accurate measure of arterial oxygen saturation in the range of 25–100%.