Noninvasive determination of cardiac output by the inert-gas-rebreathing method--comparison with cardiovascular magnetic resonance imaging.

BACKGROUND: An easy, noninvasive and accurate technique for measuring cardiac output (CO) would be desirable for the diagnosis and therapy of cardiac diseases. Innocor, a novel inert-gas-rebreathing (IGR) system, has shown promising results in smaller studies. An extensive evaluation in a larger, less homogeneous patient collective is lacking.

METHODS: We prospectively assessed the accuracy and reproducibility of CO measurements obtained by IGR in 305 consecutive patients as compared to the noninvasive gold standard, cardiovascular magnetic resonance (CMR) imaging.

RESULTS: Bland-Altman analysis showed a good correspondence of the two methods for CO measurement with an average deviation of 0.2 +/- 1.0 liters/min (mean +/- SD) and a good reproducibility with a mean bias of 0.2 +/- 0.5 liters/min. The accuracy of the present measurements at rest was significantly better in the physiological range than in higher or lower CO ranges. The error levels set forth by current recommendations were exceeded.

CONCLUSION: The data show that IGR measurements are easy to perform and show good agreement with CMR; however, the technique appears to be less accurate in extreme CO ranges at rest. The clinical importance of the IGR method remains to be proven by further studies.