Indicator-dilution measurement of cardiac output with dissolved hydrogen.

Dissolved HL has been used as an indicator for measuring cardiac output by the techniques of constant-rate injection and sudden, single injection indicator dilution. Because of its low solubility, H2 is eliminated essentially quantitatively in the lungs and recirculates negligibly. The constant-rate injection technique involves the gas chromatographic measurement of pulmonary (or systemic) arterial H2 concentration during an infusion of dissolved H2 into a vena cava (or the left atrium). Measurements in anesthetized dogs agreed well with simultaneous measurements by dye dilution, direct Fick, and direct volumetric techniques. Measurements could be repeated several times a minute, and using a linearly responding platinum electrode, intravascular H2 concentrations could be recorded continuously. In the sudden, single injection technique, dissolved H2 was injected into a vena cava (or the left atrium) while monitoring pulmonary (or systemic) arterial H2 concentration with a chromatographically calibrated platinum electrode. Measurements again agreed with simultaneous measurements by dye dilution, constant-rate injection of H2, and the direct volumetric technique. Hydrogen curves could be repeated rapidly and integrated instantaneously. Hydrogen appears to be a useful indicator for rapidly repeated determinations of cardiac output and for measurements of output in situations in which recirculation of conventional indicators limits their usefulness. ADDITIONAL