Impedance Cardiography In Patients Research Articles

Hemodynamic profiling with impedance cardiography in patients with heart failure and reduced ejection fraction improves clinical outcomes

Hemodynamic profiling with impedance cardiography in patients with heart failure and reduced ejection fraction improves clinical outcomes

Effects of early phase 1 cardiac rehabilitation on cardiac function evaluated by impedance cardiography in patients with coronary heart disease and acute heart failure.

PurposeThe purpose of the study was to access the impact of phase 1 cardiac rehabilitation (CR) on cardiac function and hemodynamic changes in patients with coronary heart disease (CHD) and acute heart failure (AHF).Materials and methodsA total of 98 patients with CHD and AHF were recruited and randomized into two groups. Control group received standard pharmacotherapy and CR group received standard pharmacotherapy combined phase 1 CR. NT-proBNP and hemodynamic parameters measured by impedance cardiography (ICG) were estimated at baseline and at the end of treatment period.ResultsPhase 1 CR combined routine medical treatment could lower NT-proBNP levels. The percentage of high-risk patients was significantly decreased in CR group, although the post-treatment NT-proBNP level between control group and CR group showed no significant differences. Similarly, most hemodynamic parameters improved in the CR group, but not in the control group, suggesting that phase 1 CR in combination with the standard pharmacotherapy improved hemodynamic characteristics by elevating cardiac output, ameliorating preload, improving systolic and diastolic function, and relieving afterload, although the post-treatment hemodynamic parameters showed no statistically significant differences between the control group and the CR group.ConclusionPhase 1 CR combined routine medication can improve cardiac function and hemodynamic characteristics in patients with CHD and AHF. Thus, recommendation of phase 1 CR to stable patients is necessary.

Acute hemodynamic effects of non-invasive ventilation in patients with obesity hypoventilation syndrome.

To evaluate the acute effects of volume-targeted non-invasive ventilation (NIV) on hemodynamic parameters assessed by impedance cardiography in patients with obesity hypoventilation syndrome (OHS). Despite the well-described beneficial effects of NIV using volume-targeted pressure support ventilation modes on respiration in OHS patients, questions were raised about the impact of this treatment on the cardiovascular system. In 15 patients (10 men; mean age, 55.8±9.3 years) impedance cardiography recordings were taken at baseline, after 120 minutes while on NIV and 20 minutes after NIV termination. A repeated-measures analysis of variance was used for comparisons. Compared to baseline, a reduction in heart rate (from 80±11 to 73±10 beats per min, p<0.05) was observed on NIV whereas the stroke volume and cardiac index remained stable throughout all three assessed intervals (p=0.347, p=0.344; respectively). The pre-ejection period increased on NIV (from 113±16 to 127±20 ms, p<0.05), and the left ventricular ejection time increased after NIV termination compared to baseline (from 259±25 to 269±25 ms, p<0.05). Volume-targeted NIV may acutely improve systolic time intervals without any negative impact on the left ventricular function in OHS patients (Tab. 2, Ref. 17).

The effects of cardiac rehabilitation on haemodynamic parameters measured by impedance cardiography in patients with coronary artery disease

Background/Aim. Well-organized cardiovascular rehabilitation (CVR) reduces cardiovascular burden by influencing cardiovascular risk factors, improving the quality of life, and reducing mortality and hospital readmission. However, its effects on hemodynamic status are largely unknown. The aim of our study was to evaluate the influence of a three-week CVR program on hemodynamic status and to investigate if there is a correlation between physical strain tolerance and hemodynamic parameters measured by impedance cardiography (ICG) before and after the CVR program in patients with coronary artery disease (CAD). Methods. Fifty-two patients attended a three-week CVR program. At the beginning and the end of the rehabilitation program, laboratory tests, exercise stress tests (EST), and ICG measurements were taken. Results. Patients showed better strain tolerance on the second exercise stress test (EST2) by achieving a higher strain level (Z = 2.315; p = 0.021) and a longer duration of the test (Z = 2.305; p = 0.021). There was a strong positive correlation between the level of EST2 and cardiac output (CO) (r = 0.538; p &lt; 0.001) and stroke volume (SV) (r = 0.380; p = 0.017) on the second ICG (ICG2). Moreover, there was a strong negative correlation between EST2 level and systemic vascular resistance (SVR) (r = -0.472; p = 0.002) and SVR index (SSVRI) (r = -0,407; p = 0.010) on ICG2. There was a strong positive correlation between EST2 duration and CO (r = 0.517; p = 0.001) as well as between EST2 duration and SV (r = 0.340; p = 0.034), and a strong negative correlation between EST2 duration and SVR (r = -0.504; p = 0.001) as well as between EST2 duration and SVRI (r = -0.448; p = 0.004), according to ICG2. Conclusion. Our study showed that a well-designed CVR program can lead to better physical strain tolerance in patients with CAD. Furthermore, CVR led to a significant positive correlation between EST and CO as well as between EST and SV measured by ICG. On the other hand, there was a significant negative correlation between EST and vascular-related parameters according to ICG at the end of the CVR program.

Limited usefulness of resting hemodynamic assessments in predicting exercise capacity in hypertensive patients.

Reliable assessments of reduced exercise capacity based on resting tests are one of the major challenges in clinical practice. The aim of this study was to evaluate the relationship between hemodynamic parameters obtained via resting tests (echocardiography and impedance cardiography (ICG)) and objective parameters of exercise capacity assessed via cardiopulmonary exercise testing and exercise ICG in patients with controlled arterial hypertension (AH). The left ventricular ejection fraction (LVEF), global longitudinal strain (GLS), diastolic function parameters (e', E/A, E/e'), cardiac output (CO), stroke volume (SV), and systemic vascular resistance index were evaluated for any correlations with selected parameters of exercise capacity, such as peak oxygen uptake (VO2) and peak CO in 93 people with AH (mean age 54 years, 47 women). Statistically relevant correlations occurred between indices of exercise capacity (peak VO2; peak CO) and only the following hemodynamic parameters: diastolic blood pressure (R = 0.23, p = 0.026; R = 0.24, p = 0.021; respectively), e' (R = 0.32, p = 0.002; R = 0.24, p = 0.027), E/e' (R = 0.35, p < 0.001; ns), E/A (R = 0.23, p = 0.030; R = 0.21, p = 0.047), SV at rest (ns; R = 0.24, p = 0.019), and CO at rest (ns; R = 0.21, borderline p = 0.052). No significant correlations between the exercise capacity parameters and either LVEF or GLS were observed. No hemodynamic parameter proved to be an independent correlate of either peak VO2 or peak CO. The association between hemodynamic parameters at rest and parameters of exercise capacity was weak and limited to selected parameters of diastolic function. Exercise capacity assessment in patients with AH based on resting tests alone is insufficiently reliable and should be supplemented with exercise tests.

Effects of the SGLT2 inhibitor dapagliflozin on cardiac function evaluated by impedance cardiography in patients with type 2 diabetes. Secondary analysis of a randomized placebo-controlled trial

Background and aimsCardiovascular outcome trials have documented a strong benefit of sodium glucose cotransporter-2 inhibitors (SGLT2i) on the risk of hospitalization for heart failure (HF) in patients with type 2 diabetes (T2D) with or without established cardiovascular disease or prior history of HF. The mechanisms, however, are not entirely clear. We aimed to evaluate whether treatment with SGLT2i affected cardiac function using impedance cardiography (ICG) in a randomized placebo-controlled trial.Materials and methodsThirty-three patients with T2D were randomized to receive blind dapagliflozin 10 mg or matching placebo for 12-week on top of their ongoing glucose lowering medication regimen. Cardiac function was evaluated by resting ICG at baseline and at the end of the 12-week treatment period. ICG is a non-invasive technology based on the continuous measurement of thoracic electrical conductivity to process a cardiodynamic parameters related to fluid content, blood flow, cardiac function, and circulatory function. We also evaluated changes in glycaemic control, blood pressure, and body weight.ResultsThirty-one patients completed the study, 1 was excluded because ICG data was missing. Patients included in the final analysis were on average 63.4-year-old, with a known diabetes duration of 14.1 years and a baseline HbA1c of 8.2% (66 mmol/mol). 63.3% of patients had established cardiovascular disease (symptomatic or asymptomatic) and 36.7% had microangiopathy, but none had a prior history of HF. After 12 weeks, patients randomized to dapagliflozin, as compared to those randomized to placebo, showed improvements in HbA1c (− 1.2%; 13 mmol/mol), systolic blood pressure (− 3.7 mmHg), and body weight (− 3.3 kg). Based on ICG, in both groups, we detected no significant change in parameters of blood flow (stroke volume, cardiac output, cardiac index), systolic function (ejection fraction, acceleration and velocity indexes, systolic time ratio), circulatory function (systemic vascular resistance index), and fluid status (thoracic fluid content) after treatment.ConclusionThis is the first study exploring cardiac effects of SGLT2i using ICG in T2D. We observed no change in cardiac function parameters estimated by ICG in T2D patients who received dapagliflozin versus placebo for 12 weeks.Trial registration ClinicalTrial.gov NCT02327039. Registered 30 December 2014

Reliability of Peak Exercise Stroke Volume Assessment by Impedance Cardiography in Patients with Residual Right Outflow Tract Lesions After Congenital Heart Disease Repair.

Global ventricular response to exercise may be useful in follow-up of patients with residual right outflow tract lesions after congenital heart disease repair. In this context, impedance cardiography is considered accurate for stroke volume (SV) measurement during exercise testing, however, to date, only partial assessment of its reliability has been reported. We retrospectively evaluated relative and absolute reliability of peak SV by impedance cardiography during exercise using intraclass correlation (ICC) and standard error of measurement (SEM) in this population. Peak SV was measured in 30 young patients (mean age 14.4years±2.1) with right ventricular outflow tract reconstruction who underwent two cardiopulmonary exercise tests at a mean one-year interval. SV was measured using a signal morphology impedance cardiography analysis device (PhysioFlow®) and was indexed to body surface area. ICC of peak indexed SV measurement was 0.80 and SEM was 10.5%. High heterogeneity was seen when comparing patients according to peak indexed SV; in patients with peak SV<50ml/m2 (15 patients), ICC rose to 0.95 and SEM dropped to 2.7%, while in patients with a peak SV>50ml/m2 relative and absolute reliability decreased (ICC=0.45, SEM=12.2%). Peak exercise SV assessment by a PhysioFlow® device represents a highly reliable method in patients with residual right outflow tract lesions after congenital heart disease repair, especially in patients with peak SV<50ml/m2. In this latter group, a peak SV decrease>7.3% (corresponding to the minimum "true" difference) should be considered a clinically-relevant decrease in global ventricular performance and taken into account when deciding whether to perform residual lesion removal.

OP-012 Assessment of Av Interval Optimisation Results With Echocardiography and Impedance Cardiography in Patients with Biventricular Pacemaker

OP-012 Assessment of Av Interval Optimisation Results With Echocardiography and Impedance Cardiography in Patients with Biventricular Pacemaker

Non-invasive evaluation of cardiac index by impedance cardiography in patients undergoing percutaneous nephrolithotomy.

IntroductionPercutaneous nephrolithotomy (PNL) is an endoscopic treatment of renal lithiasis. It is usually two-staged: it begins in the lithotomy position for ureteral catheter placement and retrograde pyelography, and subsequently an optimal renal access is obtained in the prone position. Some patients under epidural anesthesia do not tolerate the prone position and the PNL cannot be continued. This may be related to changes occurring within the circulatory system. The aim of this prospective randomized double-blind study was to evaluate the changes of the cardiac index (CI) during PNL.Material and methodsIn a group of 50 patients, with ASA physical status grade 1–2, epidural anesthesia with either 0.2% ropivacaine or 0.25% bupivacaine was performed and then the CI was evaluated by impedance cardiography.ResultsForty-five patients were included in the analysis; all tolerated the PNL well. After turning prone, a decrease in the CI was always recorded, a maximum after 10–15 min – 22.58 ±11.47%. There was significant variability of recorded values. The average CI dropped from 2.96 ±0.42 l/min/m2 to 2.28 ±0.39 l/min/m2. In 7 patients the decrease in the CI was greater than 35%. No correlation was observed with the arterial blood pressure or the heart rate. The decrease in the CI occurred irrespective of the type of local anesthetic used (p = 0.91).ConclusionsA decrease in the CI was observed in every case, and it should be taken into consideration during qualification for PNL in the prone position.

Association of N-terminal pro-brain natriuretic peptide and hemodynamic parameters measured by impedance cardiography in patients with essential hypertension

The aim of this study was to evaluate the association of NT-proBNP with clinical and hemodynamic assessment in 156 patients with arterial hypertension. NT-proBNP correlated positively with, i.e. age (r = 0.310, p = 0.00008), mean blood pressure (MBP; r = 0.199, p = 0.0136), Heather index (HI; r = 0.375, p < 0.00001) and negatively with thoracic fluid content (TFC; r = −0.300, p = 0.0002). The patients with higher NT-proBNP were older (46.1 versus 40.6 years, p = 0.001), with higher MBP (102.6 versus 98.5 mm Hg, p = 0.0043), HI (14.54 versus 11.93 Ohm s2, p = 0.009) and lower TFC (27.5 versus 29.4 1/kOhm, p = 0.0032). The independent predictors of higher NT-proBNP were: age, MBP and HI.

Comparison of cardiac output derived from FloTrac™/Vigileo™ and impedance cardiography during major abdominal surgery

Impedance cardiography (ICG) is a noninvasive technique that provides reasonably accurate measurements of cardiac output, but the usefulness of ICG in patients undergoing open abdominal surgery has not been validated. Cardiac output was measured while patients underwent open gastrectomy using an ICG monitor (niccomo™; ICG-CO); the results were compared with those measured using a FloTrac™/Vigileo™ monitor (Flo-CO), which measures cardiac output by analysing the arterial waveform. Data collection commenced at the beginning of anaesthetic induction and continued until the patient was awake. Data were compared using the Bland-Altman analysis, and the clinical significance of the difference between the two methods was evaluated by calculating the percentage error (%). Eleven patients were monitored during surgery. The bias of the Flo-CO and ICG-CO values was -0.45 l/min. The upper and lower limits of agreement were 0.96 l/min and -1.85 l/min, respectively. The percentage error was 28.5%. Electrocautery induced interference that transiently impaired the performance of the ICG monitor. ICG provided useful information in evaluating the cardiac output of patients during abdominal surgery.

Value of Impedance Cardiography in Patients Studied for Pulmonary Hypertension

The aim of this study was to evaluate the accuracy and precision of impedance cardiography as a method for noninvasive hemodynamic evaluation of patients with pulmonary hypertension (PH). We performed a prospective and blinded study of patients who underwent right heart catheterization (RHC) for evaluation of known or presumed PH at the University of Florida from August 2009 to March 2010. The cohort consisted of a total of 39 patients (age=57±14years, 87% women) with presumed (23%) or confirmed PH (77%) of different etiologies. Patients underwent RHC and impedance cardiography using the PhysioFlow PF-05. The PhysioFlow PF-05 measures cardiac output (CO) and LV end-diastolic volume (LVEDV), among other parameters. The median pulmonary artery pressure was 36 (IQR 26-56) mmHg. The CO (mean±SD) by thermodilution (CO-T) and by impedance cardiography (CO-IC) was 5.9±2.2 and 5.6±1.5L/min, respectively. Bland-Altman analysis of CO-T versus CO-IC revealed a mean of 0.3L/min (95% LoA: -2.2 to +2.8). In patients with PH, the correlation of CO-T and CO-IC had a mean of 0.4L/min (95% LoA: 2.9 and -2.2). Pulmonary artery occlusion pressure (PAOP) correlated with LVEDV (R (2)=0.2, p=0.005). By ROC analysis, EDV≥200ml had a sensitivity of 53% and a specificity of 86% for PAOP>15mmHg (AUC=0.78). In patients with PH, impedance cardiography had good accuracy and fair precision for CO determination when compared with thermodilution. Impedance cardiography may provide information about the preload status and has the potential to become a cost-effective and noninvasive method for the follow-up of patients with PH.

Correlation of impedance cardiography with invasive hemodynamic measurements in patients with advanced heart failure: The BioImpedance CardioGraphy (BIG) substudy of the Evaluation Study of Congestive Heart Failure and Pulmonary Artery Catheterization Effectiveness (ESCAPE) Trial

Impedance cardiography (ICG) is a noninvasive modality that uses changes in impedance across the thorax to assess hemodynamic parameters, including cardiac output (CO). The utility of ICG in patients hospitalized with heart failure is uncertain. The BioImpedance CardioGraphy in Advanced Heart Failure study was a prospective substudy of the Evaluation Study of Congestive Heart Failure and Pulmonary Artery Catheterization Effectiveness. A total of 170 subjects underwent blinded ICG measurements using BioZ (CardioDynamics, San Diego, CA); of these, 82 underwent right heart catheterization. We compared ICG with invasively measured hemodynamics by simple correlation and compared overall ICG hemodynamic profiles ("wet" [thoracic fluid content > or =47/kOhm in men and > or =37/kOhm in women] and "cold" [cardiac index < or =2.2 L min(-1)m(-2)) versus those determined by invasive measurements (wet [pulmonary capillary wedge pressure > or =22 mm Hg] and cold [cardiac index < or =2.2 L min(-1)m(-2)). We also determined whether ICG measurements were associated with subsequent death or hospitalization within 6 months. There was modest correlation between ICG and invasively measured CO (r = 0.4 to 0.6 on serial measurement). Thoracic fluid content measured by ICG was not a reliable measure of pulmonary capillary wedge pressure. There was poor agreement between ICG and invasively measured hemodynamic profiles (kappa < or =0.1). No ICG variable alone or in combination was associated with outcome. In hospitalized patients with advanced heart failure, ICG provides some information about CO but not left-sided filling pressures. Impedance cardiography did not have prognostic utility in this patient population.

Sleepiness in Obstructive Sleep Apnea: A Harbinger of Impaired Cardiac Function?

Daytime sleepiness is a common clinical presentation in both obstructive sleep apnea (OSA) and cardiovascular diseases. The purpose of this study was to assess the relationship between degree of subjective daytime sleepiness and cardiac performance in patients with obstructive sleep apnea. Observational study. General Clinical Research Center. The study sample was comprised of 86 patients (68 men and 18 women) with an average age of 47 years. All were suspected of having obstructive sleep apnea and underwent confirmatory diagnostic polysomnography (respiratory disturbance index > or = 15). Stroke volume and cardiac output were measured using impedance cardiography and corrected for body surface area to yield stroke index and cardiac index. Daytime sleepiness was quantified using the Epworth Sleepiness Scale. A higher Epworth Sleepiness Scale score, suggesting more daytime sleepiness, was significantly related to lower stroke index and cardiac index. In multiple regression analyses, the relationships of Epworth Sleepiness Scale score with both stroke index and cardiac index were significant (p < .05), even after controlling for age, sex, ethnicity, respiratory disturbance index, and mean sleep oxygen saturation. These results suggest that daytime sleepiness is independently associated with decreases in cardiac function as assessed by impedance cardiography in patients with obstructive sleep apnea.

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

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

Automated Impedance Cardiography for Detecting Ischemic Left Ventricular Dysfunction during Exercise Testing

Automated impedance cardiography (ICG) is an attractive method for noninvasive hemodynamic evaluation. The objective of our study was to evaluate the feasibility and diagnostic value automated ICG in patients with suspected coronary artery disease (CAD). We measured stroke index (SI) and cardiac index (CI) in 65 patients with suspected CAD at rest and during bicycle exercise testing. All patients underwent subsequent cardiac catheterization including coronary angiography (CA). Depending on the results of CA, patients were divided into three groups, patients without significant CAD (group 0), single vessel disease (group 1) or multivessel disease (group 2–3). In a subset of 20 patients, automated ICG was compared to measurements of CI by the thermodilution (TD) method. Results: There were no significant differences in SI and CI at baseline between the three groups. At 75- and 100-watt exercise, patients in group 2–3 showed significantly lower mean values of SI and CI as compared to patients of group 0 and group 1 (all p < 0.05), indicating exercise-induced ischaemic left ventricular (LV) dysfunction. Three patients had to be excluded because of inappropriate quality of the ICG signals during exercise. Comparison of automated ICG with TD measurements of CI showed good correlations between both methods at rest (r = 0.73) and during exercise (r = 0.89–0.91). Conclusions: We conclude that hemodynamic monitoring by automated ICG is both feasible and practical during exercise testing. Automated ICG can provide reliable and valuable additional diagnostic information on LV function during exercise which is helpful for selecting those patients for angiography who are likely to benefit from coronary interventions.

Impedance cardiography in cardiac surgery patients: abnormal body weight gives unreliable cardiac output measurements.

To study the accuracy of cardiac output measurement by means of Electrical Impedance Cardiography (EIC) in post-cardiac surgery patients. In a prospective study, we compared cardiac output measurements by means of thermodilution (COTD) with impedance cardiographic-derived values (COEIC) in 37 mechanically ventilated patients after cardiac surgery. Both methods were used simultaneously. COEIC values were weakly correlated with COTD in the total group when the equation of Sramek-Bernstein was employed to calculate COEIC (r = 0.60, P < 0.001, mean difference and standard deviation: -0.06 +/- 1.25 l.min-1). After exclusion of the 12 patients whose body weight differed > 15% from their ideal body weight, no significant difference was found between the mean values (5.40 +/- 1.80 l.min-1 (COEIC) vs 5.31 +/- 1.69 l.min-1, n = 25) while the correlation coefficient increased substantially (r = 0.85, P < 0.001, mean difference and standard deviation: 0.09 +/- 0.96 l.min-1). The results of this study indicate that weight is a very important factor in unreliable measurement of CO by impedance cardiography in cardiac surgery patients. The calculation equation as proposed by Sramek and Bernstein is not accurate enough in patients with more than 15% of weight deviation. Therefore, the use of impedance cardiography in these patients is of limited value until an accurate correction factor has been developed.

The intra- and interobserver variability of impedance cardiography in patients at rest and during exercise

We studied the intra- and interobserver variability in the calculation of stroke volume by the impedance technique, using the recently proposed refinements in the electrode configuration and signal processing. Three groups of patients were included in this study: ten stable cardiac patients who underwent a diagnostic heart catheterization, ten patients 24 - 26 h after coronary artery bypass surgery and ten patients with severe chronic obstructive pulmonary disease (COPD). The first two groups were studied at rest and the COPD group during sub-maximal exercise. The intra-observer variability was 4.2%, 3.9 - 4.0% and 6.0 - 6.9% for the catheterized, surgical and COPD groups, respectively. The interobserver variability was 4.3%, 2.6% and 2.4%, respectively. It is concluded that highly reproducible data can be obtained with the newly proposed impedance technique in patients at rest and exercise which may be comparable or superior to other techniques used in clinical settings. Keywords: stroke volume, impedance cardiography, variability

Monitoring of Pulmonary Fluid Volume and Stroke Volume by Impedance Cardiography in Patients on Hemodialysis

Changes of intrathoracic fludi volume during maintenance therapy with hemodialysis were studied in ten patients with the aid of impedance cardiography. It was found that there was a statistically significant correlation between the decrease in body weight and the increase in basic thoracic impedance in the individual patients, but the values differed considerably from one patient to another. Therefore, comparison of sequential measurements is feasible only in one and the same patient. Out of 16 patients with overhydration undergoing dialysis, the stroke volume could not be determined by impedance cardiographic studies in eight, owing to the abnormal morphology of the dZ/dt curve. Moreover, because the basic thoracic impedance was not constant during treatment, the calculated changes in stroke volume did not appear to be reliable. This has to be taken into account when repeated measurements are made under clinical conditions. In some of the patients, the dZ/dt curve displayed interesting anomalies, probably resulting from hemodynamic alterations. The diagnostic meaning of these features is not yet known.

Measurement of cardiac output by impedance cardiography in patients with myocardial infarction. Comparative evaluation of impedance and dye dilution methods.

The cardiac output was measured simultaneously by the impedance cardiography and dye dilution methods in 10 patients with acute myocardial infarction 2-3 weeks after admission to the Coronary Care Unit. The impedance cardiac output was on the average 9.7% higher than the dye dilution cardiac output. The reproducibility of impedance cardiac output 4.1%, compared with 5.1% for the dye dilution method. The study showed a satisfactory reliability of impedance in predicting the relative changed of cardiac output in response to tilting from the supine to the 30 degrees head-up position, to a 10 degrees head-down position, and to the intravenous administration of propranolol.