Reproducibility Of Cardiac Output Measurements Research Articles

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.

Impedance Cardiography Derived Cardiac Output in Hemodialysis Patients: A Study of Reproducibility and Comparison with Echocardiography

Hemodialysis patients experience a variety of hemodynamic abnormalities that contribute to cardiovascular disease mortality which is the leading cause of death in these patients. Impedance cardiography has been utilized in order to monitor cardiac hemodynamics with lower cost and inconvenience, but it has not been appropriately validated in the hemodialysis population. We repeatedly used impedance cardiography to assess short- (48 hours) and long-term (15 days) reproducibility of cardiac output measurements and we compared baseline impedance cardiography measurements with echocardiographic measurements. We studied 109 stable hemodialysis patients, aged 59.70 +/- 11.97 years being on hemodialysis for 67.59 +/- 40.15 months, on a non-dialysis day. Cardiac output was obtained with the BioZ impedance cardiography system (Cardiodynamics, San Diego, Ca, USA). Baseline echocardiography was performed using a Hewlett-Packard Sonos 2500 (Andover, Mass., USA). The values of impedance cardiography derived cardiac output were 5.28 +/- 0.79, 5.27 +/- 0.75 and 5.25 +/- 0.74 l/min at baseline (107 patients), 48 hours (107 patients) and 15 days (98 patients) respectively, showing high reproducibility. Bland and Altman analysis estimated that bias at 48 hours and at 15 days were: -0.013 (95% confidence intervals = -0.045 to 0.019) and 0.028, (95% confidence intervals = -0.044 to 0.101), respectively. In addition baseline impedance cardiography derived cardiac output was significantly correlated with the echocardiographic derived cardiac output (r = 0.9, p < 0.0001). Impedance cardiography is a simple non invasive technique for cardiac output estimation in hemodialysis patients which has high reproducibility when performed under controlled conditions, and is closely correlated with echocardiographic measurements of cardiac output.

The effect of patient position on the reproducibility of cardiac output measurements

To determine the effect of patient position on the reproducibility of cardiac output measurements. Prospective, two-group quasi-experimental design. Convenience sample. The study involved two intensive care units in two adult acute care hospitals. Thirty patients admitted to the intensive care unit who had a thermodilution pulmonary artery catheter in place. Ages ranged from 39 to 80 years (mean of 66.4 +/- 11.3 years). Thermodilution cardiac output measurements. The subjects were placed in one of two groups, initially by flipping a coin then into alternate groups. Group A subjects were placed supine, and after 5 minutes had cardiac output measurements performed. They were then placed in the 45-degree upright position, and after an additional 5 minutes had cardiac output measurements performed. Group B subjects were first placed in the 45-degree upright position, and after 5 minutes had cardiac output measurements performed. They were then placed in the supine flat position, and after an additional 5 minutes had cardiac output measurements performed. Seventy percent (n = 30) of the sample population displayed a lower cardiac output in the 45-degree upright position than that obtained in the supine position, with the decrease ranging from 1% to 32% (mean decrease 11%). Forty percent (n = 30) of cardiac output measurements obtained in the 45-degree upright were greater than or equal to 10% less than those obtained in the supine flat position. The differences in cardiac output were analyzed with the paired t test. which produced a 95% confidence interval from -0.539 to -0.083. The two-group Wilcoxon test was used to analyze the mean cardiac output with the patient in the supine, flat position and in the 45-degree upright position. The mean cardiac output at 0 degrees was found to be statistically significant higher (p = 0.0083) than the mean cardiac output at 45 degrees. The effect of coexisting variables was analyzed with the Kruskal-Wallis. The use of vasoconstrictors was the only variable that had a statistically significant change in cardiac output associated with a change in position. These results indicate that cardiac output measurements are affected by alterations in patient position. To ensure accurate comparisons between consecutive cardiac output measurements, the researchers recommend that the position in which the cardiac output measurements are performed be documented and the cardiac output measurements be conducted in a uniform position.

Injectate port selection affects accuracy and reproducibility of cardiac output measurements with multiport thermodilution pulmonary artery catheters

To compare the accuracy and reproducibility of thermodilution cardiac output measurements obtained from the injectate and infusion ports of a multilumen pulmonary artery catheter. The thermodilution results were compared with an independent measure of flow obtained from an electromagnetic flow meter. In an experimental study conducted at an animal research laboratory of a health sciences university, two virgin western breed ewes were surgically instrumented with an inferior vena cava occluder, which reduced venous return and thus lowered cardiac output, and an ascending aortic electromagnetic flow probe, which provided an independent reference measure of cardiac output. On the day of study, a multilumen pulmonary artery catheter was inserted. Cardiac output was manipulated over a range of 2.9 to 12.1 L/min with i.v. isoproterenol or inferior vena cava occlusion. Approximately 30 simultaneous thermodilution and electromagnetic flow meter measurements of cardiac output were obtained from both the infusion and injectate ports in each of the two subjects. Correlation coefficients were lower and standard error of the estimates was higher for the infusion port (r = .83; SEE = 1.19 L/min) vs the injectate port (r = .94; SEE = .74 L/min), indicating reduced reproducibility with infusion port thermodilution cardiac output determinations. Accuracy was also adversely influenced in the infusion port results. The linear regression for the infusion port data intercepted the Y axis at +2.64 L/min, indicating significant overestimation of cardiac output at flows of less than 5 L/min and underestimation of flow when cardiac output exceeded 8 L/min. The use of the infusion port for the measurement of thermodilution cardiac output measurements may result in nonreproducible and inaccurate results.

Validation of impedance cardiography measurements of cardiac output during limited exercise in heart transplant recipients

Twenty-one patients were studied at rest and during exercise after heart transplantation to compare cardiac output measured by thermodilution and impedance cardiography. Exercise was performed on a bicycle ergometer over a limited range of work load (25 and 50 watt) whilst metabolic gas exchange was recorded. One patient was studied at rest whilst his circulation was maintained by a Jarvik-7 artificial heart. The values of cardiac output measured by impedance cardiography corresponded closely with the flow rate from the artificial heart. There was also close agreement between the impedance and thermodilution measurements of cardiac output at rest and during exercise. Both measurements followed the changes in heart rate and oxygen consumption. Both thermodilution and impedance cardiography methods elicited good reproducibility of cardiac output measurements at rest and during exercise. These observations suggest that the noninvasive and continuous record of cardiac output obtained by impedance cardiography can be used for the postoperative monitoring of heart transplant recipients.

Validation of impedance cardiography measurements of cardiac output during limited exercise in heart transplant recipients

Abstract. Twenty-one patients were studied at rest and during exercise after heart transplantation to compare cardiac output measured by thermodilution and impedance cardiography. Exercise was performed on a bicycle ergometer over a limited range of work load (25 and 50 watt) whilst metabolic gas exchange was recorded. One patient was studied at rest whilst his circulation was maintained by a Jarvik-7 artificial heart. The values of cardiac output measured by impedance cardiography corresponded closely with the flow rate from the artificial heart. There was also close agreement between the impedance and thermodilution measurements of cardiac output at rest and during exercise. Both measurements followed the changes in heart rate and oxygen consumption. Both thermodilution and impedance cardiography methods elicited good reproducibility of cardiac output measurements at rest and during exercise. These observations suggest that the noninvasive and continuous record of cardiac output obtained by impedance cardiography can be used for the postoperative monitoring of heart transplant recipients.

Signal processing strategies for enhancement of signal-to-noise ratio of thermodilution measurements.

Thermodilution measurements of clinically important cardiac parameters, such as cardiac output and stroke volume, are subject to many sources of error. The temperature fluctuations (thermal noise) normally found in the pulmonary artery constitute one of these sources of errors. To improve the signal-to-noise ratio of thermodilution flow measurements rather than increase the signal level, we investigated four signal processing strategies designed to reduce the thermal noise power. We applied the noise reduction strategies to thermal noise data, containing simulated thermodilution curves, obtained in a mock circulatory loop. We compared the accuracy and reproducibility of the curve area estimates produced by the algorithms to the area estimates obtained by numerical integration of the thermal signal. Our results show that a bandpass (BP) integration technique combined with a noise canceler can improve thermodilution curve area estimate reproducibility and accuracy. The BP integration technique improved the reproducibility of cardiac output measurements by roughly 16 dB and is directly applicable to most thermodilution hardware currently in use. The more accurate noise cancelers, combined with the BP integration technique, provided correspondingly improved signal-to-noise ratios, with the improvement ranging up to 50 dB.

Reproducibility of cardiac output measurements in the dog.

Studies were performed on dogs to determine the constancy of the cardiac output during a 4-hour period beginning from the moment the animal was anesthetized. The cardiac output fell to varying quantities during the first hour but finally became stabilized at approximately 50–75% of the values obtained within the first 2–3 minutes following induction. Considerable variability in this response among different animals was noted. Similar studies on other animals, beginning approximately 1 hour following induction, indicated a similar pattern, i.e. that relatively stable cardiac outputs could be anticipated after this time period. Submitted on July 16, 1958