Comparison of impedance cardiography and dye dilution method for measuring cardiac output

Comparative study of cardiac output measurement by regional impedance cardiography and thermodilution method in patients undergoing off pump coronary artery bypass graft surgery

Background:

An ideal CO monitor should be noninvasive, cost effective, reproducible, reliable during various physiological states. Limited literature is available regarding the noninvasive CO monitoring in open chest surgeries.

Aim:

The aim of this study was to compare the CO measurement by Regional Impedance Cardiography (RIC) and Thermodilution (TD) method in patients undergoing off pump coronary artery bypass graft surgery (OPCAB).

Settings and Design:

We conducted a prospective observational comparative study of CO measurement by the noninvasive RIC method using the NICaS Hemodynamic Navigator system and the gold standard TD method using pulmonary artery catheter in patients undergoing OPCAB. A total of 150 data pair from the two CO monitoring techniques were taken from 15 patients between 40-70 years at various predefined time intervals of the surgery.

Patients and Methods:

We have tried to find out the accuracy, precision and cost effectiveness of the newer RIC technique. Mean CO, bias and precision were compared for each pair i.e.TD-CO and RIC-CO as recommended by Bland and Altman. The Sensitivity and specificity of cutoff value to predict change in TD-CO was used to create a Receiver operating characteristic or ROC curve.

Results:

Mean TD-CO values were around 4.52 ± 1.09 L/min, while mean RIC- CO values were around 4.77± 1.84 L/min. The difference in CO change was found to be statistically not significant (p value 0.667). The bias was small (-0.25). The Bland Altman plot revealed a mean difference of -0.25 litres. The RIC method had a sensitivity of 55.56 % and specificity of 33.33 % in predicting 15% change in CO of TD method and the total diagnostic accuracy was 46.67%.

Conclusion:

A fair correlation was found between the two techniques. The RIC method may be considered as a promising noninvasive, potentially low cost alternative to the TD technique of hemodynamic measurement.

Lung-to-finger circulation time can be measured stably with high reproducibility by simple breath holding method in cardiac patients

Lung to finger circulation time (LFCT) has been used to estimate cardiac function. We developed a new LFCT measurement device using a laser sensor at fingertip. We measured LFCT by measuring time from re-breathing after 20 s of breath hold to the nadir of the difference of transmitted red light and infrared light, which corresponds to percutaneous oxygen saturation. Fifty patients with heart failure were enrolled. The intrasubject stability of the measurement was assessed by the intraclass correlation coefficient (ICC). The ICC calculated from 44 cases was 0.85 (95% confidence interval: 0.77–0.91), which means to have “Excellent reliability.” By measuring twice, at least one clear LFCT value was obtained in 89.1% of patients and the overall measurability was 95.7%. We conducted all LFCT measurements safely. High ICCs were obtained even after dividing patients according to age, cardiac index (CI); 0.85 and 0.84 (≥ 75 or < 75 years group, respectively), 0.81 and 0.84 (N = 26, ≥ or < 2.2 L/min/M²). These results show that our new method to measure LFCT is highly stable and feasible for any type of heart failure patients.

Modulation of left ventricular diastolic filling during exercise in persons with cervical motor incomplete spinal cord injury

PURPOSE

To characterize left ventricular diastolic function during an exertional challenge in adults with incomplete cervical spinal cord Injury (icSCI).

METHODS

In this cross-sectional study, a two-group convenience sample was used to compare left ventricular LV diastolic performance during a 5-10 W·min-1 incremental arm ergometer exercise protocol, using bioimpedance cardiography. Subjects were eight males with cervical incomplete spinal cord injury (icSCI; C5-C7: age 39 ± 14 years) versus eight able-bodied males (CON: age 38 ± 13 years). Left ventricular (LV) diastolic indices included end-diastolic volume (EDV) and early diastolic filling ratio (EDFR). LV ejection time (LVET), inotropic index (dZ/dT2) and stroke volume (SV) were compared between the groups at peak exercise, and maximum workload for the icSCI group (isomax).

RESULTS

EDV (at peak exercise:131.4 ± 7.3 vs 188.78 ± 9.4, p < 0.001; at isomax: 131.4 ± 7.3 vs 169 ± 23, p = 0.0009) and EDFR (at peak exercise 73 ± 14% vs 119 ± 11%, p = 0.006; at isomax 94 ± 10; p = 0.009) were significantly reduced in icSCI compared to CON, respectively. Significant differences in LVET (icSCI: 273 ± 48 vs CON: 305 ± 68; p = 0.1) and dZ/dT2 (icSCI: 0.64 ± 0.11 vs CON: 0.85 ± 0.31; p = 0.1) were not observed at isomax, despite a significant decrease in SV in the subjects with icSCI (77.1 ± 6.05 mL vs 105.8 ± 9.2 mL, p < 0.00) CONCLUSION: Left ventricular filling was impaired in the subjects with icSCI as evidenced at both peak exercise and isomax. It is likely that restrictions on the skeletal muscle pump mechanized the impairment but increased left ventricular wall stiffness could not be excluded as a mediator.

The PhysioFlow thoracic impedancemeter is not valid for the measurements of cardiac hemodynamic parameters in chronic anemic patients

The aim of the present study was to test the validity of the transthoracic electrical bioimpedance method PhysioFlow® to measure stroke volume in patients with chronic anemia. Stroke volume index (SVI), as well as cardiac index (CI) obtained by transthoracic electrical bioimpedance method and doppler echocardiography were compared in healthy subjects (n = 25) and patients with chronic anemia (i.e. mainly with sickle cell anemia; n = 32), at rest. While doppler echocardiography was able to detect difference in SVI between the two populations, the Physioflow® failed to detect any difference. Bland & Altman analyses have demonstrated no interchangeability between the two methods to assess CI and SVI in anemic patients and healthy subjects. While doppler echocardiography displayed a good concordance for SVI results with those obtained in the literature for anemic patients, the Physioflow® did not. Finally, in contrast to doppler echocardiography: 1) the CI obtained with the Physioflow® was not correlated with the hemoglobin level and 2) the stroke volume determined by the Physioflow® was highly influenced by body surface area. In conclusion, our findings indicate that the Physioflow® device is inaccurate for the measurement of SVI and CI in patients with chronic anemia and has a poor accuracy for the measurement of these parameters in African healthy subjects.

Investigation of Various Types of Neurocardiogenic Response to Head-Up Tilting by Extended Hemodynamic and Neurohumoral Monitoring

BACKGROUND

The pathophysiology of neurocardiogenic syncope is heterogeneous. This study aim was to analyze whether extended monitoring during tilt-table testing provided additional information on the hemodynamic and vegetative state prior to neurocardiogenic syncope.

METHODS

This retrospective analysis is based on data of head-up tilt-table testing of 40 unselected consecutive patients with a history of unexplained syncope. For optimized characterization of the type of syncope, monitoring included electrocardiogram (ECG), blood pressure measurements and cardiac output, peripheral vascular resistance and contractility index measurements by impedance cardiography, as well as epinephrine and norepinephrine plasma levels in supine position and every 5 min during tilting.

RESULTS

Seven of 40 patients were unsuitable for analysis because of incomplete data sets. Tilt-table was positive in 26 patients, negative in 7. Groups did not differ in hemodynamic and catecholaminergic parameters at baseline. Responses to tilting were VASIS 1 (mix of cardioinhibitory and vasodepressor) in 5 patients, VASIS 2B (cardioinhibitory with asystole >3 sec) in 3, VASIS 3 (vasodepressor) in 16, orthostatic dysregulation in 2. In VASIS 1, the catecholamine measurement 4 min before syncope showed a proportionally larger increase of the epinephrine level than of norepinephrine. This disproportion was not observed in VASIS 2B and 3. In VASIS 2B, strong vasoconstriction and negative inotropy were evident in the presyncopal period. In VASIS 3, vascular resistance decreased continuously before syncope, while contractility index increased inadequately. Presyncopal epinephrine surge or norepinephrine loss was not observed in this group, suspecting other vasodilating factors.

CONCLUSIONS

Extended monitoring by impedance cardiography and plasma catecholamine measurements during tilt-table testing gave further insight into different hemodynamic and neurohumoral presyncopal patterns among the various types of neurocardiogenic syncope and may thereby help to develop individualized therapeutic concepts.

Comparison of the effects of VVI versus DDD pacing on cardiac baroreflex function

INTRODUCTION

Conventional baroreceptor-heart rate (HR) reflex sensitivity cannot be examined in chronotropically incompetent patients or in pacemaker recipients. However, cardiac baroreceptor reflex sensitivity (BRS)-stroke volume (SV), which is closely and linearly correlated with BRS-HR, may be an alternative in that population. The aim of this study was to compare the BRS-SV in pacemaker recipients with a fixed HR paced in VVI versus DDD modes in the supine and upright positions.

METHODS

The pacing mode was set randomly to DDD or VVI with complete atrial and/or ventricular capture, then crossed over to the alternate mode in 9 recipients of dual-chamber pacemakers with atrioventricular (AV) block. Beat-to-beat mean blood pressure and SV were measured in the supine and upright positions, using a tilt table. The BRS-SV, expressed in %/mmHg, was the ratio of low-frequency (LF) power to total power (TP) of SV variability, measured by spectral analysis of spontaneous variations in mean blood pressure and SV.

RESULTS

BRS-SV was significantly lower in the VVI than in the DDD mode in the supine (37.2 +/- 26.7 vs 14.5 +/- 7.7%/mmHg) and upright (22.9 +/- 16.9 vs 10.6 +/- 6.6%/mmHg) positions (P < 0.05 for both comparisons).

CONCLUSIONS

VVI pacing is adverse from the standpoint of cardiac autonomic baroreflex function. A decreased BRS-SV may be one of the factors involved in the hemodynamic intolerance associated with VVI pacing.

Myocardial Contractility and Cardiac Filling Measured by Impedance Cardiography in Patients with Nitroglycerine-Induced Vasovagal Syncope

OBJECTIVE

Increased myocardial contractility and inadequate cardiac filling leading to activation of the Bezold-Jarisch reflex were proposed as possible triggering mechanisms of vasovagal syncope (VVS). In the present study noninvasive hemodynamic measurements were performed in order to examine the role of myocardial contractility and cardiac filling in pathogenesis of VVS.

METHODS

Hemodynamic parameters were measured during head-up tilt test (HUT) by impedance cardiography in 46 patients with unexplained syncope. Myocardial contractility was measured as index of contractility (IC), acceleration index (ACI), and ejection fraction (EF). Afterload was measured as systemic vascular resistance index (SVRI) and preload was expressed as end-diastolic index (EDI). Serial measurements were done 1 minute before HUT, during HUT at 1-minute intervals, and 1 minute after completion of HUT.

RESULTS

HUT was positive in 30 patients (10 men, 20 women, mean age 36 +/- 16 years) and negative in 16 patients (8 men, 8 women, mean age 31 +/- 14 years). No significant differences were observed between HUT(+) and HUT(-) groups in hemodynamic parameters at supine rest and during HUT until the development of syncope. SVRI was lower in HUT(+) than in HUT(-) group at syncope (122.7 + 66.3 vs 185.6 + 51.4 dyn sec cm(-5)/m2, P = 0.002) and after syncope (117.0 + 61.1 vs 198.0 + 95.7 dyn sec cm(-5)/m2, P = 0.007). ACI, IC, EF, and EDI did not differ between groups at syncope. After syncope EF was higher in HUT(+) group compared to HUT(-) group (59.2 + 6.1 vs 52.7 + 9.4%, P = 0.02).

CONCLUSION

The role of increased myocardial contractility and decreased cardiac filling is not confirmed in the present study.

An evaluation of a noninvasive cardiac output measurement using partial carbon dioxide rebreathing in children

Cardiac output (CO) is an important hemodynamic measure that helps to guide the therapy of critically ill patients. Invasive CO assessment in infants and children is often avoided because of the inherent risks. A noninvasive CO monitor that uses partial rebreathing has been recently developed to determine CO via the Fick principle for carbon dioxide. There have been no clinical studies confirming its accuracy in pediatric patients. This is a prospective observational study of 37 children <12 yr of age who underwent cardiac catheterization. Under general anesthesia via an endotracheal tube without a leak, we made multiple CO measurements using thermodilution and compared them with noninvasively determined CO measurements. Paired measurements were analyzed for bias, precision, and correlation via Bland-Altman plot and linear regression. Noninvasive measurements showed a linear correlation with thermodilution CO assessment with an r value of 0.83 (P < 0.03). Bland-Altman analysis yielded a bias of -0.27 L/min and a precision +/-1.49 L/min. Cardiac index measurements demonstrated a decreased r value of 0.67 (P = 0.15) and a bias of -0.18 L . min(-1) . m(-2) and precision of +/-2.13 L . min(-1) . m(-2). Differences between partial rebreathing measurements and thermodilution measurements were largest in children with a body surface area of </=0.6 m(2) ventilated with tidal volumes <300 mL. Based on these findings, noninvasive CO measurement using partial rebreathing may be clinically acceptable in children with >0.6 m(2) body surface area and >300 mL tidal volume.

A novel approach to measure cardiac output noninvasively: a comparison with the thermodilution method on critical care patients

OBJECTIVE

To compare the accuracy and reliability of cardiac output (CO) measurement by a Noninvasive Hemodynamic Analyzer (NHA) to the thermodilution cardiac output (COTD) technique in ICU patients of cardiac condition.

METHOD

ICU retrospective data collected in a 700-bed university-affiliated regional medical center. The data results from 203 patients who required invasive hemodynamic monitoring for clinical and/or surgical management.

RESULTS

The ranges of the two CO measurements were: CO(TD) = 2.06 to 8.8 l/min and CO(NHA) = 2.06 to 8.46 l/min, respectively. The Mean and SD of CO(NHA) = 4.819 l/min +/- 1.053 was near to CO(TD) = 4.902 l/min +/- 1.421. Variance was better for CO(NHA) = 1.110 l/min compared to CO(TD) = 1.421 l/min. Median of CO(NHA) showed 4.813 l/min and CO(TD) = 4.660 l/min. Bias was 0.083 l/min with 95% Confidence Interval (Precision): -0.26 to 0.040, and 95% Limits of Agreement was between -1.661 to 1.827 l/min.

CONCLUSIONS

The results of this retrospective study indicate that the CO(NHA) technique may be a promising screening method. Additional studies are needed to explore its diagnostic trending capability. This noninvasive CO technique has been proven to be clinically accurate and may be applicable for telemedicine applications.

Non-invasive measurement of cardiac output in patients with chronic heart failure

OBJECTIVES

The measurement of cardiac output by thoracic bioimpedance has been previously assessed in several studies. However, there continues to be disagreement as to whether this technique is sufficiently accurate for use in clinical practice or research. The current study aimed to compare thoracic bioimpedance (COTB) with thermodilution (COTD) in patients with stable chronic heart failure.

METHODS AND RESULTS

A total of 282 paired measurements of cardiac output from 11 patients were analysed. There was good correlation between COTB and COTD (r=0.76, P<0.0001). However, Bland-Altman analysis revealed an average difference between values of 0.3 (2.2) l/min (P=0.02), suggesting a small average bias but marked variability in results. There was no significant correlation when results were expressed as percentage change from baseline and a significant average difference between values of 10.1 (30.1)%. There was no difference in between-day repeatability between thermodilution and thoracic bioimpedance [-0.2 (1.2) versus 0.1 (1.0) l/min, P=0.7].

CONCLUSIONS

This study demonstrates a correlation between the techniques but shows a poor level of agreement. The method of COTB underestimated cardiac output compared with COTD, and this difference appeared greater with higher cardiac outputs. Agreement was worse when results were expressed as change from baseline. The present study does not support the use of thoracic bioimpedance in its current form as an alternative to thermodilution in stable patients with chronic heart failure.

Recent developments in cardiac output determination by bioimpedance: comparison with invasive cardiac output and potential cardiovascular applications

PURPOSE OF REVIEW

To describe recent developments in bioimpedance technique and its application in cardiovascular diseases. Cardiac output determination has been used selectively during recent years because of the need for invasive right heart catheterization. Hence, experience with its application in patients with cardiovascular diseases and especially heart failure is limited. Bioimpedance is a novel noninvasive technique determining changes in instantaneous (during one heartbeat) conductance of a small electrical current transferred through the body. By using different algorithms correcting for various body composition constants, it calculates the change in instantaneous arterial blood volume (that is, stroke volume) and cardiac output. Traditionally, bioimpedance cardiac output is determined using either thoracic or whole body techniques according to the location of the electrodes transmitting and receiving the small electrical current.

RECENT FINDINGS

Significant progress was achieved in recent years in cardiac output determination by bioimpedance. Newer algorithms using thoracic and whole body bioimpedance have demonstrated better correlation with invasive cardiac output determination. In a few preliminary studies bioimpedance-determined cardiac output was found useful in the diagnosis, risk stratification, and treatment titration of some cardiovascular conditions. Further, larger prospective studies are required to determine the true independent value of cardiac output measurement by bioimpedance for the evaluation of cardiovascular diseases and especially heart failure.

SUMMARY

Recently, significant improvement was achieved in cardiac output measurement by bioimpedance with both newer thoracic and whole body techniques. Preliminary studies imply that this measure may be of value in managing some cardiovascular disorders.

Cardiovascular effects of vasopressin following V(1) receptor blockade compared to effects of nitroglycerin

Studies to more clearly determine the mechanisms associated with arginine vasopressin (AVP)-induced vasodilation were performed in normal subjects and in quadriplegic subjects with impaired efferent sympathetic responses. Studies to compare the effects of AVP with the hemodynamic effects of nitroglycerin, an agent that primarily affects venous capacitance vessels, were also performed in normal subjects. Incremental infusions of AVP following V(1)-receptor blockade resulted in equivalent reductions in systemic vascular resistance (SVRI) in normal and in quadriplegic subjects. However, there were major differences in the effect on mean arterial pressure (MAP), which was reduced in quadriplegic subjects but did not change in normal subjects. This difference in MAP can be attributed to a difference in the magnitude of increase in cardiac output (CI), which was twofold greater in normal than in quadriplegic subjects. These observations are consistent with AVP-induced vasodilation of arterial resistance vessels with reflex sympathetic enhancement of CI and are clearly different from the hemodynamic effects of nitroglycerin, i.e., reductions in MAP, CI, and indexes of cardiac preload, with only minor changes in SVRI.