Stroke volume measurements by electrical bioimpedance and echocardiography in healthy volunteers

Comparison of Bioimpedance Versus Pulse Contour Analysis for Intraoperative Cardiac Index Monitoring in Patients Undergoing Kidney Transplantation

Background

Cardiac index (CI; cardiac output indexed to body surface area) is routinely measured during kidney transplant surgery. Bioimpedance cardiometry is a transthoracic impedance as the non-invasive alternative for hemodynamic monitoring, using semi-invasive uncalibrated pulse wave or contour (UPC) analysis.

Objectives

We performed a cross-sectional observational study on 50 kidney transplant patients to compare the CI measurement agreement, concordance rate, and trending ability between bioimpedance and UPC analysis.

Methods

For each patient, CI was measured by bioimpedance analysis (ICON^TM) and UPC analysis (EV1000^TM) devices at three time points: after induction, during incision, and at reperfusion. The device measurement accuracy was assessed by the bias value, limit of agreement (LoA), and percentage error (PE) using Bland-Altman analyses. Trending ability was assessed by angular bias and polar concordance through four-quadrant and polar plot analyses.

Results

From each time point and pooled measurement, the correlation coefficients were 0.267, 0.327, 0.321, and 0.348. Bland-Altman analyses showed mean bias values of 1.18, 1.06, 1.48, and 1.30, LoA of -1.35 to 3.72, -1.39 to 3.51, -1.07 to 4.04, and -1.17 to 3.78, and PE of 82.21, 78.50, 68.74, and 74.58%, respectively. Polar plot analyses revealed angular bias values of -10.37º, -15.01º, -18.68º, and -12.62º, with radial LoA of 89.79º, 85.86º, 83.38º, and 87.82º, respectively. The four-quadrant plot concordance rates were 70.77, 67.35, 65.90, and 69.79%. These analyses showed poor agreement, weak concordance, and low trending ability of bioimpedance cardiometry to UPC analysis.

Conclusions

Bioimpedance and UPC analysis for CI measurements were not interchangeable in patients undergoing kidney transplant surgery. Cardiac index monitoring using bioimpedance cardiometry during kidney transplantation should be interpreted cautiously because it showed poor reliability due to low accuracy, precision, and trending ability for CI measurement.

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

Background

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.

Aim

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.

Patients and Methods

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).

Results

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).

Conclusion

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.

A randomized study of the effects of exercise training on patients with atrial fibrillation

BACKGROUND

Exercise training is beneficial in ischemic and congestive heart disease. However, the effect on atrial fibrillation (AF) is unknown.

METHODS

Forty-nine patients with permanent AF (age [mean ± SD], 70.2 ± 7.8 years; male-to-female ratio, 0.75; body mass index [mean ± SD], 29.7 ± 4.3 kg/m(2)) were randomized to 12-week aerobic exercise training or a control group. Exercise capacity, 6-minute walk test (6MWT), cardiac output, quality of life, and natriuretic peptides were measured. Cardiac output was measured at rest and during ergometer testing, and atrial natriuretic peptide and N-terminal pro-B-type natriuretic peptide were measured before and after the training period. Quality of life was evaluated using the Short-Form 36 and Minnesota Living With Heart Failure (MLHF-Q) questionnaires.

RESULTS

Improved exercise capacity and 6MWT were observed in the active patients (P < .001), and at study end, there was a significant difference between the active patients and the controls (P = .002). Resting pulse decreased in the active patients (94.8 ± 22.4 to 86.3 ± 22.5 beats/min, P = .049) but remained unchanged in the controls. Cardiac output was unchanged from baseline to end-of-study period. The MLHF-Q score improved in the active group (21.1 ± 18.0 vs 15.4 ± 17.5, P = .03). Active patients showed progress in 3 of the 8 Short-Form 36 subscales: physical functioning (P = .02), general health perceptions (P = .001), and vitality (P = .02). Natriuretic peptides were unchanged.

CONCLUSION

Twelve weeks of exercise training increased exercise capacity and 6MWT and decreased resting pulse rate significantly in patients with AF. Overall quality of life increased significantly as measured by the cardiology-related MLHF-Q. Cardiac output and natriuretic peptides were unchanged in both groups.

Haemodynamic changes during craniotomy monitored by a bioimpedance plethysmographic noninvasive cardiac output monitor

BACKGROUND

Profound cardiovascular changes may occur at various stages during a craniotomy. These changes require a detailed haemodynamic analysis including cardiac output. In the present study, we used a monitor based on electrical bioimpedance method for noninvasive cardiac output measurement.

METHODS

In 17 ASA I and II patients undergoing elective craniotomies for supratentorial tumours, the following haemodynamic parameters were measured noninvasively: heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), stroke volume (SV), cardiac output (CO) and systemic vascular resistance (SVR). Haemodynamic changes in response to the following events were studied: (a) induction of anaesthesia with thiopentone, (b) 15 min of air-O(2)-isoflurane anaesthesia, (c) infiltration of the scalp with lidocaine adrenaline mixture, and (d) change of inspired gas mixture to N(2)O-O(2)-isoflurane.

RESULTS

HR increased (P < 0.001) and SV decreased (P < 0.001) while CO remained unchanged, one min after administration of thiopentone. After 15 min of isoflurane anaesthesia, HR increased (P < 0.001) and, SBP (P = 0.02), DBP (P = 0.002) and SV (P = 0.003) decreased significantly without change in CO. Three minutes after infiltration of the scalp with lidocaine-adrenaline mixture, there was an increase in SBP (P = 0.001), DBP (P = 0.007), SV (P = 0.007) and CO (P = 0.001) and a decrease in SVR (P < 0.001). Addition of nitrous oxide (60%) to the inspired gas mixture decreased SBP (P = 0.003) and DBP (P = 0.001) with a trend for decrease in CO (P < 0.1). The changes recorded in the present study conform to those that have been documented earlier by using invasive monitoring.

CONCLUSION

Bioimpedance plethysmography is a useful noninvasive technique for monitoring and detailed analysis of the rapidly changing systemic haemodynamics during a craniotomy. The device could be useful for investigating important haemodynamic changes in specific neurosurgical settings.

Microcirculatory alterations induced by sedation in intensive care patients. Effects of midazolam alone and in association with sufentanil

Introduction

Sedation is widely used in intensive care unit (ICU) patients to limit the risk of pulmonary barotrauma and to decrease oxygen needs. However, adverse effects of cc5128sedation have not been fully evaluated; in particular, effects of benzodiazepine and opiates on microcirculation have not been extensively studied. The aim of this study was to evaluate the microcirculatory effects of a sedation protocol commonly prescribed in the ICU.

Methods

Ten non-septic patients under controlled ventilation requiring sedation for therapeutic purposes were enrolled in a prospective observational study conducted in an ICU of a university hospital. Sedation was conducted in two successive steps: first, each patient received midazolam (0.1 mg/kg per hour after a bolus of 0.05 mg/kg, then adapted to reach a Ramsay score of between 3 and 5). Second, after one hour, sufentanil was added (0.1 μg/kg per hour after a bolus of 0.1 μg/kg). Arterial pressure, heart rate, cardiac output determined by transthoracic impedance, transcutaneous oxygen (tcPO₂) and carbon dioxide (tcPCO₂) pressures, and microcirculatory blood flow determined by laser Doppler flowmetry at rest and during a reactive hyperaemia challenge were measured before sedation (NS period), one hour after midazolam infusion (H period), and one hour after midazolam-sufentanil infusion (HS period).

Results

Arterial pressure decreased in both sedation periods, but heart rate, cardiac output, tcPO₂, and tcPCO₂ remained unchanged. In both sedation periods, microcirculatory changes occurred with an increase in cutaneous blood flow at rest (H period: 207 ± 25 perfusion units [PU] and HS period: 205 ± 25 PU versus NS period: 150 ± 22 PU, p < 0.05), decreased response to ischaemia (variation of blood flow to peak: H period: 97 ± 16 PU and HS period: 73 ± 9 PU versus NS period: 141 ± 14 PU, p < 0.05), and attenuation of vasomotion.

Conclusion

Sedation with midazolam or a combination of midazolam and sufentanil induces a deterioration of vasomotion and microvascular response to ischaemia, raising the question of whether this effect may further alter tissue perfusion when already compromised, as in septic patients.

Bioimpedance-derived Differences in Cardiac Physiology during Exercise Stress Testing in Low-risk Chest Pain Patients

BACKGROUND

Little has been written about the utility of thoracic electrical bioimpedance (TEB)-derived cardiac physiologic variables in evaluating patients with low-risk chest pain syndromes. Noninvasive bioimpedance can monitor cardiac physiology while a patient is performing an exercise stress test. In addition, the demographics of patients with chest pain, the incidence of coronary artery disease (CAD), and the methods used for evaluation have well-documented sex differences.

OBJECTIVE

The objectives are to show that there are different cardiac physiologic responses to exercise stress test in Chest Pain Evaluation Unit patients with and without true CAD that could be used to stratify patients and that there is a sex difference in TEB results.

METHODS

Patients 18 to 65 years of age with low-risk chest pain were eligible. Patients were attached to the TEB throughout the exercise stress test procedure. Heart rate (HR) was monitored. Primary dependent variables were TEB-measured cardiac output (CO, L/min) and stroke volume (SV, ml) at peak exercise. Secondary variables were TEB-measured ejection fraction (%), end-diastolic volume (EDV, ml), ventricular ejection time (ms), and thoracic fluid index (omega) at peak exercise. Outcome variables were either proved CAD or patient sex. CAD was proved by angiography, stress scintigraphy, or stress echocardiogram. Results were compared using a Student's t test assuming equal variances, with significance considered at a P < 0.05, and 95% confidence intervals were calculated for significant results.

RESULTS

Nine patients had proved CAD, 82 patients did not. Forty-three women and 48 men were included in the study. At peak exercise, patients with CAD had a significantly smaller increase in EDV than patients without CAD (32.8 +/- 59.5 ml versus 89.3 +/- 101.8 ml) without a significant change in CO, SV, or HR. At peak exercise, women had a significantly smaller increase in CO and SV without a significant change in HR. In addition, women had a significantly smaller increase in EDV.

CONCLUSION

When compared with patients without CAD, patients with CAD have a significantly smaller increase in EDV and a trend toward the same effect in CO and SV. Women have significantly smaller increases CO, SV, and EDV compared with men. Because there were no differences in HR, using HR as the sole end point would miss these differences. TEB is a practical means of measuring these variables.

Cardiovascular regulation during water immersion

Head-out water immersion at thermoneutral temperature (34-35 degrees C) increases cardiac output for a given O2 consumption, leading to a relative hyperperfusion of peripheral tissues. To determine if subjects immersed in water at a colder temperature show similar responses and to explore the significance of the hyperperfusion, cardiovascular functions were investigated (impedance cardiography) on 10 men at rest and while performing exercise on a leg cycle ergometer (delta M = approximately 95 W.m-2) in air and in water at 34.5 degrees C and 30 degrees C, respectively. In subjects resting in water, the cardiac output increased by approximately 50% compared to that in air, mainly due to a rise in stroke volume. The stroke volume change tended to be greater in 30 degrees C water than in 34.5 degrees C water, and this was due to a greater increase in cardiac preload, as indicated by a significantly greater left ventricular end-diastolic volume. Arterial systolic pressure rose slightly during water immersion. Arterial diastolic pressure remained unchanged in 34.5 degrees C water, but it rose in 30 degrees C water. The total peripheral resistance fell 37% in 34.5 degrees C water and 32% in 30 degrees C water. Both in air and in water, mild exercise increased the cardiac output, and this was mainly due to an increase in heart rate. Since, however, the stroke volume increased with water immersion, cardiac output at a given work load appeared to be significantly higher in water than in air. The arterial pressures did not decrease with water immersion, despite a marked reduction in total peripheral resistance. These results suggest that 1) during cold water immersion, peripheral vasoconstriction provides an additional increase in cardiac preload, leading to a further increase in the stroke volume compared to that of the thermoneutral water immersion, 2) the mechanism of cardiovascular adjustment during dynamic exercise is not changed by the persistent increase in cardiac preload in water immersion, and 3) a relatively high cardiac output during water immersion is to maintain a proper arterial pressure in the face of reduced vascular resistance.

A meta-analysis of three decades of validating thoracic impedance cardiography

OBJECTIVE

To provide a meta-analysis of current literature concerning the validation of thoracic impedance cardiography (TIC) and to explain the variations in the reported results from the differences in the studies.

DATA SOURCES

A computer-assisted search of English-language, German, and Dutch literature was performed for the period January 1966 to April 1997. Moreover, references from review articles were obtained.

STUDY SELECTION

A total of 154 studies comparing measurements of cardiac output or related variables obtained from TIC and a reference method were analyzed.

DATA EXTRACTION

Articles were classified by differences in TIC methodology, reference method, and subject characteristics. Fisher's Zf transformed correlation coefficients were used to compare results. Data were pooled using the random-effects method.

DATA SYNTHESIS

An overall pooled r2 value of .67 (95% confidence interval, 0.64-0.71) was found. However, the correlation was higher in repeated-measurement designs than in single-measurement designs (r2 = .53; 95% confidence interval, 0.43-0.62). Further research using analysis of variance revealed a significant influence of the reference method and the subject characteristics on the correlation coefficient. The correlation was significantly better in animals than in cardiac patients. Subgroup analysis revealed that TIC correlated significantly better to the indirect Fick method than to echocardiography in healthy subjects. No significant influence of the applied TIC methodology was found.

DISCUSSION

The overall r2 value of .67 indicates that TIC might be useful for trend analysis of different groups of patients. However, for diagnostic interpretation, a r2 value of .53 might not meet the required accuracy of the study. Great care should be taken when TIC is applied to the cardiac patient. However, because the applied reference method was of significant influence, differences between TIC and the reference method are incorrectly attributed to errors in TIC alone.

Noninvasive measurement of cardiac output: two methods compared in patients with mitral regurgitation

In search for the origin of the less reliable cardiac output (CO) estimations by means of electrical impedance cardiography (EIC), the authors hypothesized that cardiac valve pathology might be one of the reasons. Twenty-six patients were examined by means of echo Doppler (ED) and EIC. The cardiac valve status was obtained by means of echocardiography and color Doppler flow, while CO was obtained by means of both methods. Seventeen patients had no valve pathology (nVP) while nine patients had mild to moderate mitral regurgitation (MVR). The overall correlation between the calculation of CO by means of the two methods was good (r = 0.85, p < 0.001, mean difference and standard deviation: 0.20+/-0.74 L/min), while there was no significant difference between the paired values. After division into an nVP and an MVR population, the results showed an even closer agreement between the CO values in the nVP population (r = 0.88, p < 0.001, mean difference and standard deviation: 0.15+/-0.68 L/min). Furthermore, significant differences were found in the first derivative of the impedance (dZ/dt) signals of these groups. Although the agreement between ED and EIC was slightly lower in the MVR population, EIC reliably estimated CO, even in case of MVR. The impedance signal itself gave an indication for the existence of MVR.

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

OBJECTIVE

To assess the degree of agreement between impedance cardiography, using the NCCOM3-R7 device, and the gold standard--the dye dilution method--both under basal conditions and after stimulation of cardiac output.

PATIENTS

35 paired measurements in five healthy male volunteers.

INTERVENTIONS

To obtain higher levels of cardiac output, cardiac performance was stimulated with a dopamine infusion.

RESULTS

In 35 paired measurements, the mean of all the impedance values was higher than that of the dye dilution values, at 10.2 v 7.4 l/min (p < 0.0001). The mean discrepancy between the two methods was 3.3 l/min, and the mean bias -2.9 l/min, with limits of agreement of -9.0 and 3.2 l/min. A change in cardiac output could not adequately be predicted by the NCCOM3-R7. In 20 of 25 measurements obtained during continuous intravenous dopamine infusions there was a rise in dye dilution cardiac output (range 0.2 to 5.9 l/min). Neither the magnitude nor the direction of the change in dye dilution values corresponded with the change measured by impedance cardiography. The mean discrepancy here between the two methods was 1.8 l/min, and the mean bias -0.8 l/min, with limits of agreement of -4.9 and 3.3 l/min.

CONCLUSIONS

In healthy volunteers, impedance cardiography with NCCOM3-R7 is inadequate for assessing cardiac output when compared with the dye dilution method.

Comparison of cardiac output measurements by thermodilution and thoracic electrical bioimpedance in critically ill versus non-critically ill patients

Thoracic electrical bioimpedance (TEB) has been proposed as an alternative to thermodilution (TD) for the measurement of cardiac output in settings such as the Emergency Department where invasive monitoring is not available. Validation studies comparing TEB with TD suggest a wide range of variability in the agreement between the two methods. This prospective study tests the hypothesis that this variability may be related to the severity of patient illness. Fifteen non-critically ill patients undergoing cardiac catheterization and 13 critically ill patients who underwent Swan-Ganz catheterization in the medical intensive care unit (MICU) were enrolled. Fifty-one pairs of data from the catheterization laboratory and 49 pairs of data from the MICU were obtained. The patients were graded retrospectively according to the APACHE II scoring system. The mean difference (bias) between TEB and TD results was calculated for each patient using the method suggested by Bland and Altman. A pooled t-test was performed to determine whether there was any significant difference between the APACHE II scores or cardiac output measurements obtained by TEB and TD in the two groups. APACHE II scores were 4.7 +/- 1.2 for the catheterization laboratory and 14.2 +/- 5.0 for the intensive care unit patients (P < .001). The catheterization laboratory (cath lab) group bias was 0.23 +/- 2.19, whereas the MICU bias was .002 +/- 2.33. There was no significant difference in the bias between the two groups despite significant differences in the APACHE II scores. Standard deviations of the bias were less than 15% different from each other.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of impedance cardiography: comparison of NCCOM3-R7 with Fick and thermodilution methods

OBJECTIVE

To assess the degree of error of the BoMed NCCOM3 model revision seven (R7) impedance cardiograph in determining stroke volume and estimated cardiac output.

DESIGN

Three-group, within-subject, repeated measures design.

SAMPLE

Group 1: patients (n = 17) with heart disease undergoing an elective coronary angiogram; group 2: patients (n = 28) after elective heart surgery; and group 3: healthy volunteers (n = 28).

MEASUREMENT

Cardiac output was determined by the BoMed NCCOM3-R7 impedance cardiograph, Fick principle, and thermodilution method. The NCCOM3-R7 was compared with the direct Fick and thermodilution methods in groups 1 and 2, respectively, to estimate validity coefficients. In group 3, repeated measures were obtained with the NCCOM3-R7 to calculate reliability coefficients.

RESULTS

The NCCOM3-R7 underestimated Fick measurements by 1.050 +/- 1.529 L/min at rest and 1.505 +/- 2.214 L/min during exercise. Correlation coefficients of 0.684 at rest (p = 0.001) and 0.219 during exercise (p = 0.248) were obtained. The NCCOM3-R7 underestimated thermodilution values by 0.425 +/- 1.325 L/min in subjects initially after heart surgery and 0.358 +/- 1.235 L/min 2 to 4 hours later. Correlation coefficients of 0.547 (p = 0.002) and 0.505 (p = 0.004) were obtained for the two time periods, respectively. A reliability coefficient of 0.837 was calculated with healthy subjects.

CONCLUSION

The NCCOM3-R7 has a clinically unacceptable level of error for evaluating cardiac performance in patients with heart disease.

A review of impedance cardiography

OBJECTIVE

To review the reliability and validity estimates of impedance cardiography to assess its empirical precision and clinical usefulness.

DATA SOURCE

Empirical and theoretical literature mainly within the last 10 years.

DATA SYNTHESIS

Descriptive statistics used to summarize the accuracy and use of impedance cardiography to estimate stroke volume.

CONCLUSIONS

Estimation of cardiac output is presently a core component of optimizing cardiac function in many patient populations. Impedance cardiography, which initially used a formula developed by Kubicek et al. and recently a formula developed by Sramek and Bernstein, remains controversial with regard to its accuracy and use in research and clinical practice.

Pulsed Doppler transesophageal echocardiographic determination of cardiac output in human beings: comparison with thermodilution technique

Measurement of cardiac output is a clinically valuable and widely used index of cardiac function. Although transesophageal echocardiography has been used to assess left ventricular function, little data exist on the accuracy of this technique in the measurement of cardiac output. Therefore cardiac output derived by pulsed Doppler transesophageal echocardiography and thermodilution methods were compared in adult patients being mechanically ventilated. The left ventricular outflow tract diameter was determined from a transgastric long-axis view of the left ventricle by using the transverse plane and longitudinal plane of the transesophageal scope. The cross-sectional area of the left ventricular outflow tract was calculated from the diameter assuming a circular shape. Pulsed Doppler recordings were obtained at the left ventricular outflow tract. Doppler time-velocity integrals were measured from the leading edge of the velocity curve. Cardiac output derived by transesophageal echocardiography was calculated as time-velocity integral multiplied by left ventricular outflow tract area and heart rate. Cardiac output derived by transesophageal echocardiography from the transverse plane (n = 26) and longitudinal plane (n = 22) were correlated with simultaneous thermodilution measurements. Thermodilution-derived cardiac output demonstrated excellent correlation with cardiac output measured by using transesophageal echocardiography from the transverse plane (r = 0.97, SEE = 0.84 L/min; p < 0.0001) and longitudinal plane (r = 0.95, SEE = 0.97 L/min; p < 0.0001). Transesophageal echocardiography is a promising technique in the measurement of cardiac output and expands the clinical use of this modality in the assessment of cardiac function.

Validity of cardiac output measurement by computer-averaged impedance cardiography, and comparison with simultaneous thermodilution determinations

The accuracy and reproducibility of noninvasive cardiac output determinations by computer-averaged impedance cardiography were compared with those of simultaneously performed thermodilution cardiac output. In all, 43 patients (14 men and 29 women = 201 pairs) were studied by simultaneously performed impedance and thermal determinations. Individual impedance values correlated with paired thermodilution determinations (r = 0.75; p less than 0.0001). Each patient's average thermodilution values correlated with the average impedance values (r = 0.86; p less than 0.0001). Mean thermodilution output was 4.6 +/- 1.37 liters/min. Mean impedance output was 4.5 +/- 1.27 liter/min Reproducibility was comparable for impedance (0.0059 +/- 0.639) and thermodilution cardiac output (0.023 +/- 0.556). There was high agreement between methods by plot of the difference against mean of the 2 methods. Impedance cardiac output values agree and correlate highly with quality-controlled thermodilution outputs across a wide range of clinical conditions and hemodynamic values.