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with the technical assistance of Jacob Beser, B.M.E., Salle A. Lore and Grace Saltzer Cardiovascular responses were studied by means of the ballistocardiograph and electrocardiograph in 16 normal subjects and 11 patients with suspected coronary artery disease before, during and after the induction of oximetiicallv controlled anoxemia. Progressive and significant increases occurred in cardiac output, pulse rate, left ventricular work, maximum cardiac force and pulse pressure during anoxemia in all of the normal subjects and in the 5 patients whose ballistocardiograms allowed the calculation of these variables. The increase in carliac output resulte(l almost entirely from an acceleration of cardiac rate. In the normal subjects control ballistocardiograms were normal in form and remained normal throughout anoxemia. Of the patients, 1 with normal, 2 with borderline and 1 with abnormal ballistocardiograms became abnormal or more abnormal. Two of the patients had a positive electrocardiographic test for coronary insufficiency while the test was negative in all of the normal subjects.The linear relationship between left ventricular work and arterial oxygen saturation suggests that when cardiovascular function is tested by means of anoxemic stress the level of arterial desaturation should be controllable. This is made possible by the use of a variable oxygen-nitrogen mixture and an oximeter. SINCE THE Pike's Peak expedition by Douglas, Haldane, Henderson and Schnei-K-,., der1 in 1911, the physiologic effect of altitude and anoxemia has been the subject of considerable scientific interest; the studies conducted by these physiologists formed the basis for most of the investigative work which has followed. Interest in anoxemia has sprung not only from the frequency of its occurFrom the

The induced anoxemia test of cardiovascular function has been standardized according to the degree of anoxemia rather than the oxygen concentration of the gas mixture administered. The cardiovascular response of normal subjects at 80, 75 and 70 per cent arterial oxygen saturation is described. The changes can be closely correlated with the degree of anoxemia, as measured by the oximeter.AT THE present time the most widely used method of studying the effect of induced anoxemia on the cardiovascular system consists of giving the subjects low oxygen gas (usually 10 Each subject rested on a bed in a quiet room until his or her blood pressure and pulse rate became stabilized. Electrocardiograms were ma(le with a Cambridge electrocardiograph and standardized to give a 10-mm. deflection with 1 millivolt. In measuring the height of the RS-T segment, the P-Q or P-R segment was selected as the isoelectric line according to the method followed by Katz,4 Malmstrom,5 and others. Blood pressure was taken by the auscultatory method with a Tycos manometer; the heart rate was obtained from the electrocardiogram. The blood pressure, pulse rate, and electrocardiogram were taken before, during, and after the period of anoxemia.A total of 76 normal persons was studied. Seventytwo were medical students and the remainder. were laboratory assistants. All but 3 of the subjects were men. Seventy-three of the subjects were between 22 and 28 years of age; the other 3 subjects were 16, 17. and 34 years old. All subjects were of the white race and were free from any cardiovascular disease as far as could be determined by a preliminary examination, which included a detailed medical history, physical examination, and electrocardiogram. Eighty-one tests were performed on the 76 subjects. In most instances the arterial oxygen saturation was lowered in a "step-wise" manner3 so that a subject was studied at more than one level of saturation during the same test. The various readings (electrocardiogram, etc.)