Introduction
The observation that the inhalation of a gas of low oxygen content may bring on angina pectoris, or specific electrocardiographic changes, has led to the induced anoxemia (hypoxemia) test for the study of coronary artery disease.* The type of anoxemia test most widely used is that of Levy and co-workers, in which a gas of fixed low oxygen concentration, 10%, is administered for a period up to 20 minutes.2In two previous papers, with Dr. Caroline Thomas, we described another type of test, the oximeter-controlled anoxemia test,3,4 in which the content of oxygen in the respired gas is varied to produce the desired degree of anoxemia, measured continuously by the oximeter.5 This overcomes the large variability in the oxygen saturation of the arterial blood known to result from the inhalation of 10% oxygen and other gas mixtures of fixed oxygen concentration.3,4,6-8 In subsequent papers, with