THE USE OF CO2 INHALATION AS A TEST OF CIRCULATION TIME 1

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Abstract
Inhalation of 50% CO2 has been used clinically to estimate the "left heart" circulation time, lung to respiratory center. Previously this had been arrived at by subtracting the rate obtained by the ether method which measures anticubital vein to pulmonary capillaries from the rate obtained by methods which measure both right and left circulation time; i.e., cyanide, decholin, etc. When both methods were utilized in the same patient there was a close correspondence in results. The mixture is contained in a basal metabolism apparatus from which the lime chamber has been removed. The subject inhales deeply twice, the beginning of the first inhalation being considered the start of the test. The end point is announced subjectively by a feeling of warmth over the head and objectively by a quickening and deepening of respiration. Normal values range from 5-10 seconds. The left heart time is considerably prolonged in heart disease commensurate with the degree of left heart failure. Individual patients, followed throughout the period of hospitalization, showed variations which corresponded to their clinical status. Patients suffering from hyperthyroidism had rates which were more rapid than normal. The test is harmless, the effect transitory, it does not require injection and it may be used repeatedly in the same subject.