BACKGROUND: Cardiac Output (CO) is an important parameter in the diagnosis and 
therapy of heart diseases. Inert gas rebreathing (IGR) and continuous wave 
Doppler ultrasound (CWD) are among the most promising newer techniques aiming at 
a non-invasive, point of care measurement of CO. A direct comparison of the two 
methods has not yet been carried out.
METHODS: 63 consecutive patients were included in the study. CO was measured 
twice with both CWD and IGR to assess inter-method agreement and 
reproducibility. The statistical comparisons were performed as proposed by Bland 
and Altman.
RESULTS: There was a significant correlation between the CO measurements by both 
methods (r=0.53, p<0.001). Bland-Altman analysis showed a good agreement of 
measurements with a bias of 0.4+/-1.0 l/min (mean+/-standard deviation). Both 
methods showed a good reproducibility. CWD measurements were not possible in 14% 
of patients while IGR measurements were not possible in 5% of patients (p=0.13).
CONCLUSION: The determination of CO by IGR and CWD revealed a good agreement and 
reproducibility with a low rate of impossible measurements, suggesting that IGR 
and CWD can be used interchangeably in the clinical setting.