A new constant infusion radioisotopic technique for the noninvasive determination of cardiac output

A constant infusion radioisotopic method for the noninvasive determination of cardiac output is introduced and validated in a series of 22 patients by comparison with simultaneous dye dilution or Fick measurements. The new bedside radioisotopic technique utilizes peripheral venous infusion of indium-113m, detection by a single external probe, and analysis of the time-concentration curve by a specially designed, multivariate computer model. The technique is entirely atraumatic, requiring neither injection into the central circulation nor intra-arterial cannulation. The correlation coefficient was 0.72 (p less than 0.001) between the radioisotopic and standard methods for cardiac output determinations. In addition, results in five patients with valvular regurgitation or intracardiac shunts support the validity of the constant infusion radioisotopic technique in these clinical settings in which the standard dye dilution methods for determining cardiac output are invalid. The techniques is applicable in a variety of clinical conditions in which the invasive techniques for cardiac output measurement are either impractical or not available.