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Impedance cardiography measurement of cardiac output gained wide interest due to its ease of use and non-invasiveness. However, validation studies of different algorithms yielded diverging results. Bioreactance (BR) as a recent adaption differs fundamentally as the flow signal is derived from phase shifts. Our aim was to assess the accuracy and reproducibility of BR, as compared to the non-invasive gold standard--cardiac magnetic resonance imaging (CMR). We prospectively included 32 stable patients. BR was performed twice in the supine position and averaged over 30 seconds. Mean bias was 0.2 ± 1.8 l/minute (1 ± 28%, percentage error 55%) with limits of agreement ranging from  -3.4 to 3.7 l/minute. Reproducibility was acceptable with a mean bias of 0.1 ± 0.9 l/minute (1 ± 14%, 27%). Low cardiac output was significantly overestimated (-1.1 ± 1.5 l/minute), while high cardiac output was underestimated (1.5 ± 1.7 l/minute), ( P =0.001), although reproducibility was unaffected. Bias and weight were moderately correlated in men (r = 0.50, P =0.02). No differences for accuracy were found in nine patients who had an arrhythmia (0.3 ± 1.4 versus 0.1 ± 2.0 l/minute, P =0.76), while clinically relevant differences were found in patients with mild aortic valve disease (1.9 ± 2.2 versus -0.3 ± 1.7 l/minute, P =0.02). Overall, BR showed insufficient agreement with CMR, overestimating low and underestimating high cardiac output states. Reproducibility was acceptable and not negatively affected by the circulatory condition. Consequently, absolute values acquired with BR should be interpreted with caution and must not be used interchangeably in clinical practice.

Electrical velocimetry (EV) is one of the most recent adaptions of impedance cardiography. Previous studies yielded diverging results identifying several factors negatively influencing accuracy. Although electrode arrangement is suspected to be an influencing factor for impedance cardiography in general, no data for EV is available. We aimed to prospectively assess the influence of electrode position on the accuracy and reproducibility of cardiac output (CO) measurements obtained by EV. Two pairs of standard electrocardiographic electrodes were placed at predefined positions of the thorax in 81 patients. The inter-electrode gap was varied between either 5 or 15 cm by caudal movement of the lowest electrode. Measurements were averaged over 20 s and performed twice at each electrode position. Reference values were determined using cardiac magnetic resonance imaging (CMR). Mean bias was 1.2  ±  1.6 l min(-1) (percentage error 22  ±  28%) between COCMR and COEV at the 5 cm gap significantly improving to 0.5  ±  1.6 l min(-1) (8  ±  28%) when increasing the gap (p  <  0.0001). The mean difference between repeated measurements was 0.0  ±  0.3 l min(-1) for the 5 cm and 0.1  ±  0.3 l min(-1) for the 15 cm gap, respectively (p  =  0.3). The accuracy of EV can be significantly improved when increasing the lower inter-electrode gap still exceeding the Critchley and Critchley recommendations. Therefore, absolute values should not be used interchangeably in clinical routine. As the reproducibility was not negatively affected, serial hemodynamic measurements can be reliably acquired in stable patients when the electrode position remains unchanged.

A novel algorithm of impedance cardiography referred to as electrical velocimetry (EV) has been introduced for non-invasive determination of cardiac output (CO). Previous validation studies yielded diverging results and no comparison with the non-invasive gold standard cardiac magnetic resonance imaging (CMR) has been performed. We therefore aimed to prospectively assess the accuracy and reproducibility of EV compared to CMR. 152 consecutive stable patients undergoing CMR were enrolled. EV measurements were taken twice before or after CMR in supine position and averaged over 20 s (AESCULON(®), Osypka Medical, Berlin, Germany). Bland-Altman analysis showed insufficient agreement of EV and CMR with a mean bias of 1.2 ± 1.4 l/min (bias 23 ± 26 %, percentage error 51 %). Reproducibility was high with 0.0 ± 0.3 l/min (bias 0 ± 8 %, percentage error 15 %). Outlier analysis revealed gender, height, CO and stroke volume (SV) by CMR as independent predictors for larger variation. Stratification of COCMR in quintiles demonstrated a good agreement for low values (<4.4 l/min) with bias increasing significantly with quintile as high as 3.1 ± 1.1 l/min (p < 0.001). Reproducibility was not affected (p = 0.71). Subgroup analysis in patients with arrhythmias (p = 0.19), changes in thoracic fluid content (p = 0.51) or left heart failure (p = 0.47) could not detect significant differences in accuracy. EV showed insufficient agreement with CMR and good reproducibility. Gender, height and increasing CO and SV were associated with increased bias while not affecting reproducibility. Therefore, absolute values should not be used interchangeably in clinical routine. EV yet may find its place for clinical application with further investigation on its trending ability pending.

Objectives: A growing interest in monitoring cardiac output (CO) noninvasively has emerged; however, its determination has been difficult using the standard approaches. The aim of this study was to evaluate the accuracy and precision of pulse contour analysis (PCA) compared with cardiac magnetic resonance imaging (CMR)., Design: A single-center prospective study., Setting: A university hospital., Participants: Thirty-nine consecutive stable patients undergoing CMR., Interventions: CO was determined twice by PCA using the Nexfin monitoring system (BMEYE BV, Amsterdam, The Netherlands). Measurements were performed after 10 minutes of rest in a stable supine position immediately before or after the CMR examination., Measurements and Main Results: There was a mean bias of 0.2 ± 1.9 L/min between CMR and PCA and a reproducibility of 0.2 ± 0.6 L/min for PCA. Between 4.8 and 6.3 L/min (second quartile of COCMR), there was a good agreement (mean bias = -0.2 ± 1.3 L/min). Comparing quartile 1 (-1.3 ± 2.0 L/min) overestimating and quartiles 3 (1.4 ± 0.9 L/min) and 4 (0.9 ± 2.0 L/min) underestimating CO, a statistically significant difference was found. The reproducibility was not affected by the quartile (p = 0.23, analysis of variance), whereas there was a significant difference between the nonoutlier and outlier group when using the Mann-Whitney U test (p = 0.02)., Conclusions: Noninvasive PCA allows the safe and economic measurement of CO, yet it still has major limitations. Although the agreement with CMR was acceptable, there was a clinically unacceptable variation; absolute values should not be used interchangeably. These results suggest that therapeutic interventions and clinical decisions should not be based on noninvasive PCA measurements at the present time., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Cardiac output (CO) is an important parameter for diagnosis and therapy of heart diseases, but it is still difficult to determine. Innocor, a novel noninvasive inert gas rebreathing (IGR) system, has shown promising results. However, the impact of pulmonary diseases on IGR remains unclear. The aim of the study therefore was to assess the accuracy and reliability of IGR in patients with distinct chronic lung disease. A total of 96 patients were enrolled, including 48 consecutive patients with variant lung diseases (group A) and 48 pair-matched pulmonary healthy patients (group B). CO was measured with cardiac magnetic resonance imaging (CMR) and IGR. Lung function testing was done by spirometry [FEV(1)/FVC (forced expiratory volume in one second/forced vital capacity), VC (vital capacity)] and determination of the diffusing capacity of the lung for carbon monoxide divided by alveolar volume (DLCO/VA). In group A we found a mean CO of 4.7 ± 1.3 L/min by IGR and 4.9 ± 1.2 L/min by CMR. Group B showed a mean CO of 4.8 ± 1.4 L/min by IGR and 5.0 ± 1.3 L/min by CMR. Bland-Altman analysis revealed good correspondence between CMR and IGR, with an average deviation of 0.1 ± 1.0 L/min in group A and 0.1 ± 1.0 L/min in group B (p = 0.99). Multiple regression analysis for the pulmonary parameters did not show a statistically significant impact on the mean bias of CO measurements (FEV(1)/FVC: r = 0.01, p = 0.91; VC: r = -0.2, p = 0.13; and DLCO/VA: r = 0.04, p = 0.82). IGR allows a feasible determination of CO even in patients with lung diseases. The accuracy of the IGR method is not influenced by either pulmonary obstructive and restrictive diseases or a reduced DLCO.

Background: USCOM, a novel continuous wave Doppler (CWD) device, has been introduced for noninvasive determination of cardiac output (CO). The present study aimed to compare the accuracy and reproducibility of the new device, using cardiovascular magnetic resonance imaging (CMR) as the noninvasive gold standard., Methods and Results: The CO of 56 consecutive patients was prospectively determined by CWD either before or after CMR imaging. The CWD probe was placed in the suprasternal or supraclavicular notch aiming at the aortic valve. Valid CWD signals could be obtained in 45 patients yielding a CO of 5.3+/-1.1 L/min (range, 3.0-7.5 L/min) by CMR and 4.7+/-1.1 L/min by CWD (2.5-8.0 L/min, P = .004), respectively. CWD measurements showed an acceptable agreement with CMR (bias: 0.6+/-1.1 L/min) and a high reproducibility (bias: 0.1+/-0.4 L/min). Higher CO and body mass index (BMI) were identified as sources of inaccuracy in univariate analysis. By multivariate analysis, only CO(CMR) was found to be independently associated with larger variation. Estimated diameters of the left ventricular outflow tract (LVOT), a prerequisite for CO measurement by CWD, correlated only weakly with those measured by CMR., Conclusions: Continuous wave Doppler is a feasible technique for measuring cardiac function. Although the overall agreement with CMR was acceptable, CWD showed a trend to underestimate CO. The estimated LVOT diameter by CWD is likely to be an important source of error. Nevertheless, the CWD device could be of clinical use especially for detection of intraindividual hemodynamic changes since a high reproducibility could be demonstrated., (Copyright 2010 Wiley Periodicals, Inc.)

Background: Cardiac output (CO) is an important cardiac parameter, however its determination is difficult in clinical routine. Non-invasive inert gas rebreathing (IGR) measurements yielded promising results in recent studies. It directly measures pulmonary blood flow (PBF) which equals CO in absence of significant pulmonary shunt flow (Q(S)). A reliable shunt correction requiring the haemoglobin concentration (c(Hb)) as only value to be entered manually has been implemented. Therefore, the aim of the study was to evaluate the effect of various approaches to Q(S) correction on the accuracy of IGR., Methods: Cardiac output determined by cardiac magnetic resonance imaging (CMR) served as reference values. The data was analysed in four groups: PBF without correcting for Q(S) (group A), shunt correction using the patients' individual c(Hb) values (group B), a fixed standard c(Hb) of 14.0 g dl(-1) (group C) and a gender-adapted standard c(Hb) for male (15.0 g dl(-1)) and female (13.5 g dl(-1)) probands each (group D)., Results: 147 patients were analysed. Mean CO(CMR) was 5.2 +/- 1.4 l min(-1), mean CO(IGR) was 4.8 +/- 1.3 l min(-1) in group A, 5.1 +/- 1.3 in group B, 5.1 +/- 1.3 l min(-1) in group C and 5.1 +/- 1.4 l min(-1) in group D. The accuracy in group A (mean bias 0.5 +/- 1.1 l min(-1)) was significantly lower as compared to groups B, C and D (0.1 +/- 1.1 l min(-1); P<0.01)., Conclusion: IGR allows a reliable non-invasive determination of CO. Since PBF significantly increased the measurement bias, shunt correction should always be applied. A fixed c(Hb) of 14.0 g dl(-1) can be used for both genders if the exact c(Hb) value is not known. Nevertheless, the individual value should be used if any possible.

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.