Preoperative levosimendan infusion in combined aortic valve and coronary bypass surgery.

BACKGROUND: Cardiopulmonary bypass may have detrimental effects on intestinal function and decrease the concentrations of the active, long-acting metabolites of levosimendan, an inodilator used to improve cardiac function. The aim of this study was to evaluate the haemodynamic effects of preoperative levosimendan in patients undergoing high-risk cardiac surgery. METHODS: Twenty-four patients were randomized to receive levosimendan (12 µg bolus followed by an infusion of 0.2 µg kg(-1) min(-1)) or a placebo 24 h before surgery. The inclusion criteria were left ventricular ejection fraction (LVEF) <50% or LV hypertrophy indicated by a wall thickness of >12 mm. Haemodynamics were recorded every hour for 24 h (pulmonary artery catheter) and daily until postoperative day 4 (whole-body impedance cardiography). Doppler echocardiography with tissue Doppler imaging was used to assess systolic and diastolic cardiac function. RESULTS: The cardiac index (CI) and stroke volume index (SI) were higher in the levosimendan group (LG) for the 4 day postoperative period (P<0.05); on the fourth postoperative day, the CI was 3.0 litre m(-2) min(-1) in the LG compared with 2.4 litre m(-2) min(-1) in the control group (CG) and the SI was 30 vs 25 ml m(-2), respectively. The LVEF measured at baseline and on the fourth postoperative morning decreased in the CG, but was maintained in the LG. CONCLUSIONS: Levosimendan improved haemodynamics compared with a placebo in patients undergoing high-risk cardiac surgery. The concentrations of levosimendan's metabolites were higher compared with earlier studies using perioperative dosing.

The influence of hemodynamic factors on left ventricular mass.

We evaluated the relationship between the variability in the left ventricular mass index (LVMI) and different hemodynamic factors. LVMI was associated with blood pressure and, in one subgroup, strongly to arterial pulse wave velocity (PWV). High physical activity was connected to increased LVMI, and a combination of low stroke index (SI) and high heart rate (HR) to decreased LVMI.

The prognostic value of haemodynamic parameters in the recovery phase of an exercise test. The Finnish Cardiovascular Study.

We tested the hypothesis that the change from the peak to recovery values of systolic arterial pressure (SAP recovery) and rate-pressure product (RPP recovery) can be used to predict all-cause and cardiovascular mortality, as well as sudden cardiac death (SCD) in patients referred to a clinical exercise stress test. As a part of the Finnish Cardiovascular Study (FINCAVAS), consecutive patients (n=2029; mean age+/-SD=57+/-13 years; 1290 men and 739 women) with a clinically indicated exercise test using a bicycle ergometer were included in the present study. Capacities of attenuated SAP recovery, RPP recovery and heart rate recovery (HRR) to stratify the risk of death were estimated. During a follow-up (mean+/-s.d.) of 47+/-13 months, 122 patients died; 58 of the deaths were cardiovascular and 33 were SCD. In Cox regression analysis after adjustment for the peak level of the variable under assessment, age, sex, use of beta-blockers, previous myocardial infarction and other common coronary risk factors, the hazard ratio of the continuous variable RPP recovery (in units 1000 mm Hg x b.p.m.) was 0.85 (95% CI: 0.73-0.98) for SCD, 0.87 (0.78-0.97) for cardiovascular mortality, and 0.87 (0.81 to 0.94) for all-cause mortality. SAP recovery was not a predictor of mortality. The relative risks of having HRR below 18 b.p.m., a widely used cutoff point, were as follows: for SCD 1.28 (0.59-2.81, ns), for cardiovascular mortality 2.39 (1.34-4.26) and for all-cause mortality 2.40 (1.61-3.58). In conclusion, as a readily available parameter, RPP recovery is a promising candidate for a prognostic marker.

Pulse wave velocity reference values in healthy adults aged 26-75 years.

The stiffening of arteries is associated with various cardiovascular diseases. Arterial stiffening can be studied utilizing arterial pulse wave velocity (PWV), but the absence of reliable reference values for PWV has limited its use in clinical practice. The aim of this study was to establish a range of reference values for PWV. PWV was examined by measuring the time difference of systolic pulse waves in arteries from the aortic arch to the popliteal artery using whole-body impedance cardiography (ICG). The study population consisted of 799 individuals (age range 25-76 years), 283 of whom had no evidence of cardiovascular disease, and a low burden of risk factors was selected to represent an apparently healthy population. In healthy study population, PWV was higher in males (8 x 9 +/- 1 x 8 m s(-1)) than females (8 x 1 +/- 2 x 0 m s(-1), P<0 x 001). Young males had lower PWV values than old males. Correspondingly, young females also had lower PWV values than old females. PWV was clearly associated with age, and PWV was higher in young and middle-aged males than in females. There was no statistically significant difference between old males and females in PWV. In conclusion, whole-body ICG provides a practical method for PWV measurement. Reference values can be useful in the clinical management of patients, especially in detecting early vascular disease or an increased risk of cardiovascular complications.

Lead field theoretical approach in bioimpedance measurements: towards more controlled measurement sensitivity.

This study was conducted to demonstrate the potentiality of lead field theoretical approach in analyzing bioimpedance (BI) measurements. Anatomically accurate computer models and the lead field theory were used to develop BI measurement configurations capable of detecting more localized BI changes in the human body. The methods were applied to assess the measurement properties of conventional impedance cardiography (ICG) and such BI measurement configurations as can be derived using (i) the 12-lead electrocardiography (ECG) and (ii) the international 10-20 electroencephalography (EEG) electrode systems. Information as to how various electrode configurations are sensitive to detecting conductivity changes in different tissues and organs was thus obtained. Theoretical results with the 12-lead system suggested that, compared to conventional ICGs, significantly more selective ICG configurations can be derived for cardiovascular structures. In addition to theoretical investigations, clinical test measurements were made with the 12-lead system to establish whether characteristic waveforms are available. Sensitivity distributions obtained with the 10-20 electrode system give promise of the possibility of monitoring noninvasively cerebrospinal fluid (CSF) impedance changes related to impending epileptic seizures.

Non-invasive measurement of cardiac output: whole-body impedance cardiography in simultaneous comparison with thermodilution and direct oxygen Fick methods.

OBJECTIVE: To determine the reliability of whole-body impedance cardiography (ICGWB), with electrodes attached to wrists and ankles, in the measurement of cardiac output (CO) on the basis of simultaneous comparison with thermodilution (TD) and direct oxygen Fick (Fick) methods. DESIGN: Prospective clinical study. SETTING: A surgical intensive care unit at a university hospital. PATIENTS: Thirty consecutive subjects undergoing a coronary artery bypass surgery were investigated preoperatively. MEASUREMENTS: ICGWB derived CO was measured simultaneously with the TD and Fick methods to establish the biases and limits of agreement (LA) between the methods. RESULTS: The results obtained by ICGWB and the invasive methods showed good agreement. The bias and LA between COTD and COICG were 0.00 l/min: 1.37 and 1.37 l/min, respectively, and were close to those obtained between COTD and COFICK, 0.32 l/min; 1.74 and -1.10 l/min. The bias and LA between the COFICK and COICG were -0.32 l/min; -2.24 and 1.60 l/min respectively. The repeatability value of consecutive single measurements for ICGWB (RVICG = 0.57 l/min) was much better than for the TD method (RVTD = 1.10 l/min). CONCLUSION: There was close agreement between the results of the three methods in the measurement of CO. In sedated preoperative patients the accuracy of ICGWB is within clinically acceptable limits and its repeatability is excellent. ICGWB provides a useful alternative to the TD and Fick methods in cases where the pressures supplied by the pulmonary artery catheter are not essential.

Hemodialysis causes changes in dynamic vectorcardiographic ischemia monitoring parameters.

AIMS: The aim of this study was to establish whether changes in parameters reflecting myocardial ischemia QRS vector difference (QRS-VD), ST change vector magnitude (STC-VM) and ST vector magnitude (ST-VM6) during hemodialysis (HD) registered by MIDA (myocardial infarction dynamic analysis) are related to changes in blood volume (BV), extracellular water (ECW) and blood biochemistry. PATIENTS AND METHODS: Fifteen hemodialysis (HD) patients were studied. Computerized vectorcardiography was used for on-line dynamic analysis of ST segment and QRS complex changes. BV changes were monitored non-invasively and continuously with the CRIT-LINE instrument. Bioelectric impedance analysis (BIA) was used for ECW estimation. Blood samples were taken before and after hemodialysis for hemoglobin (B-Hb), hematocrit (B-Hcr), sodium (P-Na), chloride (P-Cl), magnesium (P-Mg), potassium (P-K), ionized calcium (P-iCa), phosphate (P-Pi) and astrup measurement. RESULTS: During dialysis treatment QRS-VD, ST-VM6 and STC-VM did not change in parallel. According to the linear mixed model, no statistically significant changes were noted in ST-VM6 during dialysis (time effect p = 0.5635). On the other hand, QRS-VD and STC-VM showed a statistically significant linear trend (time effect for QRS-VD p = 0.0001 and for STC-VM p = 0.0004). Changes in both ECW and BV affected the change in QRS-VD and in STC-VM. CONCLUSION: During HD treatment changes in the vectorcardiographic ischemia monitoring parameters QRS-VD and STC-VM are mostly related to ECW and BV changes and may give a false positive impression of myocardial ischemia. The ST-VM6 trend is less markedly influenced by volume changes.

Isolated ultrafiltration affects dynamic vectorcardiographic ischemia monitoring parameters.

AIMS: The present study was undertaken to assess the role of isolated ultrafiltration (UF phase) and hemodialysis with minimal ultrafiltration (HD phase) in changes in parameters reflecting myocardial ischemia: QRS vector difference (QRS-VD), ST change vector magnitude (STC-VM) and ST vector magnitude (ST-VM6) registered by MIDA (myocardial infarction dynamic analysis). PATIENTS AND METHODS: Twelve patients on maintenance hemodialysis were first ultrafiltrated for 2.5 h without dialysis (UF) followed by a 2.5-hour session of hemodialysis with minimal ultrafiltration (HD). Computerized vectorcardiography (VCG) was used for on-line dynamic analysis of ST segment and QRS complex changes. Blood volume (BV) changes were monitored non-invasively and continuously with the CRIT-LINE instrument. Whole-body bioelectric impedance analysis (BIA) was used for extracellular water (ECW) estimation. RESULTS: During the UF phase QRS-VD and STC-VM showed a statistically significant increasing linear trend (time effect for both QRS-VD and STC-VM p < 0.0001, while no changes were noted in ST-VM6; time effect p = 0.986). During the HD phase none of these parameters changed (time effect for QRS-VD p = 0.855, for STC-VM p = 0.275 and for ST-VM6 p = 0.976). During the UF, phase changes in QRS-VD were in close relation to those in ECW. CONCLUSION: Isolated ultrafiltration leads to an increase in the VCG ischemia monitoring parameters QRS-VD and STC-VM. The increase of QRS-VD is related to changes in ECW. Hemodialysis with minimal ultrafiltration has no effect on VCG ischemia monitoring parameters.

Influence of captopril, propranolol, and verapamil on arterial pulse wave velocity and other cardiovascular parameters in healthy volunteers.

OBJECTIVE: The effects of antihypertensive agents on cardiovascular parameters, especially on arterial pulse wave velocity, remain largely unknown in normotensive subjects. Therefore, the present investigation was designed to evaluate acute effects of ACE inhibitor captopril,beta-adrenoceptor blocker propranolol and calcium entry blocker verapamil on cardiovascular and ventilatory function in healthy volunteers. MATERIAL: The influence of single doses of captopril (25 mg), propranolol (40 mg), and verapamil (80 mg) on cardiovascular function and exercise capacity were compared in healthy volunteers in a randomized, double-blind, placebo-controlled fashion. METHODS: Cardiac output and beat-by-beat blood pressure were estimated non-invasively before and after the drug administrations by whole-body impedance cardiography and Finapres finger blood pressure monitoring, respectively. Arterial pulse wave velocity was obtained from the time delay between flow pulses measured from the root of the aorta and the popliteal artery, and systemic vascular resistance was calculated from cardiac output and mean arterial pressure. In addition, a progressive maximal exercise test was performed after the treatments. RESULTS: Propranolol reduced heart rate, cardiac output and arterial pulse wave velocity, and increased systemic vascular resistance clearly more effectively than placebo. In addition, captopril effectively decreased arterial resistance and pulse wave velocity. However, the influence of verapamil on cardiovascular parameters did not significantly differ from those observed in placebo-treated subjects. Exercise peak heart rate, peak blood pressure, and minute ventilation were reduced in subjects treated with propranolol, but not in those treated with captopril and verapamil, when compared to placebo. CONCLUSIONS: Acute administration of captopril and propranolol but not verapamil clearly modulated cardiovascular parameters in rest, suggesting differential effects of these compounds on cardiovascular function in healthy volunteers. These drugs seem to have disparate effects on arterial pulse wave propagation as an indicator of arterial compliance after short-term administration in healthy subjects. Captopril and verapamil had no effect on cardiovascular and ventilatory function during maximal exercise, while propranolol markedly altered also these variables in the present study.

Scatter correction for first-pass radiocardiography.

The effect of the dual window scatter subtraction method was tested for first-pass radiocardiography using 99Tcm. The photopeak window of 126-154 keV (20%) and Compton window of 93-125 keV (30%) were used. The set of scattered images was multiplied by a factor of 0.4 and subtracted from the primary images. The size of the correction was tested by recalculation among a group of 16 patients sent for cardiac output studies for various reasons. The average of the percentage increase following correction was 4.0% (range -1.1 to 11.7%). The size of scatter correction was rather small in individual patients, but consistent for the group of patients as a whole. There was a statistically significant difference between the raw and corrected cardiac output values.

Multiple lead recordings improve accuracy of bio-impedance plethysmographic technique.

We have developed the theory and instrumentation of multiple multi-electrode bio-impedance (BI) measurements based on lead field theoretical approach. To derive reliable information based on BI data, a quantity of measurements should be taken with electrode configurations possessing regional measurement sensitivity. An apparatus has been developed with an eye to the requirements imposed by the theoretical aspects of achieving multiple multi-electrode BI measurements. It has features compensating electrode-contact related errors and errors due to imbalance between the conductive pathways when multiple electrodes are utilised for BI measurement. The proposed design allows simultaneous multi-electrode BI and bioelectric recording with the same electrode system. Initial operation experiences in clinical environment indicate that the device functions as intended, and allows user-friendly utilisation of multiple BI measurements. Contributions presented to BI methodology and instrumentation improve the reliability of BI measurements.

Application of computer modelling and lead field theory in developing multiple aimed impedance cardiography measurements.

Conventional impedance cardiography (ICG) methods estimate parameters related to the function of the heart from a single waveform that reflects an integrated combination of complex sources. We have previously developed methods and tools for calculating measurement sensitivity distributions of ICG electrode configurations. In this study, the methods were applied to investigate the prospects of recording multiple aimed ICG waveforms utilizing the 12-lead electrocardiography (ECG) electrode locations. Three anatomically realistic volume conductor models were used: one based on Visible Human Man cryosection data and two on magnetic resonance (MR) images representing end diastolic and end systolic phases of the cardiac cycle. Based on the sensitivity distributions obtained, 236 electrode configurations were selected for preliminary clinical examination on 12 healthy volunteers and 9 valvular patients. The model study suggested that a variety of configurations had clearly enhanced sensitivity to the cardiovascular structures as compared to conventional ICGs. Simulation data and clinical experiments showed logical correspondence supporting the theoretically predicted differences between the configurations. Recorded 12-lead ICG signals had characteristic waveforms and landmarks not coinciding with those of conventional ICG. Furthermore, configurations showing resemblance to invasive data and morphological variations in disease are of interest. The results indicate the applicability of the modelling approach in developing ICG measurement configurations. However, the level of clinical relevance and potential of the 12-lead method remains to be explored in studies employing dynamic modelling and acquisition of invasive reference data.

Computational and physiological background of the baroreflex sensitivity.

All the commonly used definitions of baroreflex sensitivity (BRS) are based on a slope of linear relationship between systolic blood pressure and pulse interval (R-R interval). However, heart rate (HR) and R-R interval bear an inverse non-linear relationship, which distorts determination of BRS when different HR levels are present. We analysed data of 117 healthy, normal-weight, non-smoking men and women aged 23-77 to show how BRS depends on the initial HR. In this data, 43% of variation in BRS is solely explained by HR. Comparisons of BRS between patients with different HR and even within the same patient with changing HR (e.g. tilt-table test and nocturnal changes in HR) should be questioned. Consideration of the baseline HR is even more crucial, if the patients are subjected to an intervention affecting not only baroreflexes but also HR. If baseline HR is not taken into account, using the R-R interval in the estimation of BRS may lead to partially misleading values and possibly also to misinterpretation of physiological processes. We discuss alternative definitions of BRS to allow varying HRs.

Potassium channel KCNH2 K897T polymorphism and cardiac repolarization during exercise test: The Finnish Cardiovascular Study.

OBJECTIVE: Cardiac repolarization is regulated, in part, by the KCNH2 gene, which encodes a rapidly activating component of the delayed rectifier potassium channel. The gene expresses a functional single nucleotide polymorphism, K897T, which changes the biophysical properties of the channel. The objective of this study was to evaluate whether this polymorphism influences two indices of repolarization--the QT interval and T-wave alternans (TWA)--during different phases of a physical exercise test. MATERIAL AND METHODS: The cohort consisted of 1,975 patients undergoing an exercise test during which on-line electrocardiographic data were registered. Information on coronary risk factors and medication was recorded. The 2690A>C nucleotide variation in the KCNH2 gene corresponding to the K897T amino acid change was analysed after polymerase chain reaction with allele-specific TaqMan probes. RESULTS: Among all subjects, the QTc intervals did not differ between the three genotype groups (p> or =0.31, RANOVA). Women with the CC genotype tended to have longer QT intervals during the exercise test, but the difference was statistically significant only at rest (p = 0.011, ANOVA). This difference was also detected when the analysis was adjusted for several factors influencing the QT interval. No statistically significant effects of the K897T polymorphism on TWA were observed among all subjects (p = 0.16, RANOVA), nor in men and women separately. CONCLUSIONS: The K897T polymorphism of the KCNH2 gene may not be a major genetic determinant for the TWA, but the influence of the CC genotype on QT interval deserves further research among women.

Maternal haemodynamics in pre-eclampsia compared with normal pregnancy during caesarean delivery.

OBJECTIVE: To determine how pre-eclampsia modifies maternal haemodynamics during caesarean delivery. DESIGN: Prospective study. SETTING: Tampere University Hospital, Finland. POPULATION: Ten pre-eclamptic parturients and ten healthy parturients with uncomplicated pregnancies scheduled for elective caesarean section under spinal anaesthesia. METHODS: Haemodynamic parameters were assessed by whole-body impedance cardiography noninvasively. MAIN OUTCOME MEASURES: Stroke index (SI), heart rate (HR), cardiac index (CI), systemic vascular resistance index (SVRI) and mean arterial pressure (MAP) were recorded before operation, continuously during caesarean section, during the period of dissipation of anaesthesia and on the second to fifth postpartum day. RESULTS: Baseline haemodynamics in women with pre-eclampsia differed significantly from healthy women in higher SVRI and MAP and lower SI and CI. In women with pre-eclampsia, preload infusion increased both SI and HR, causing a significant rise in CI, while in healthy parturients, only HR rose. In both the groups, spinal blockade reduced SVRI but CI remained stable. At the moment of delivery, CI increased in both groups. In uncomplicated pregnancies, both SI and HR increased, but in women with pre-eclampsia, SI was not altered and the rise in CI was due to an increase in HR only. After the reversal of anaesthesia, haemodynamics in the control group returned to baseline values, whereas in women with pre-eclampsia, SI and CI fell to levels that were significantly lower than the levels observed before surgery. CONCLUSIONS: In women with pre-eclampsia, inability to increase SI at the moment of delivery may suggest dysfunction of the left ventricle to adapt to volume load caused by delivery and prompts concern for the increased risk of pulmonary oedema.

Ten-year prognosis of Puumala hantavirus-induced acute interstitial nephritis.

Nephropathia epidemica (NE) is a hemorrhagic fever with renal syndrome caused by Puumala hantavirus. Its long-term prognosis is considered favorable. There are, however, some reports about subsequent hypertension, glomerular hyperfiltration, and proteinuria after previous hantavirus infection. Therefore, we studied 36 patients 5 and 10 years after acute NE, with 29 seronegative controls. Office blood pressure, ambulatory 24-h blood pressure (ABP), glomerular filtration rate (GFR), and proteinuria were examined. Hypertensive subjects were defined as those patients having increased ambulatory or office blood pressure, or receiving antihypertensive therapy. Office blood pressure was used to define hypertension only if ABP was not determined. At 5 years, the prevalence of hypertension was higher among NE patients than in controls (50 vs 21%, P=0.020). At 10 years, the difference between the groups was no more significant (39 vs 17%, P=0.098). Five years after NE, patients showed higher GFR (121+/-19 vs 109+/-16 ml/min/1.73 m(2), P=0.012) and urinary protein excretion (0.19 g/day, range 0.12-0.38 vs 0.14 g/day, range 0.09-0.24, P=<0.001) than controls. At 10 years, there were no more differences in GFR or protein excretion between the groups (GFR: 113+/-20 vs 108+/-17 ml/min/1.73 m(2), P=0.370; proteinuria: 0.14 g/day, range 0.07-0.24 vs 0.13 g/day, range 0.06-0.31, P=0.610). In conclusion, the 10-year prognosis of NE is favorable, as glomerular hyperfiltration and slight proteinuria detected at 5 years disappeared during the longer follow-up. However, the possibility exists that NE may predispose some patients to the development of hypertension.

Non-invasive cardiac output determination: state of the art.

This review deals with recent developments in non-invasive cardiac output measurement. In the past few years significant progress has been made with semi-invasive transoesophageal echocardiography; the method now provides advanced facilities to measure cardiac output and other important characteristics of cardiac function. The method is, however, operator-dependent and the equipment used is expensive, which means that large-scale use on intensive care patients is not feasible. Whole-body impedance cardiography has recently shown good accuracy and flexibility in use, and seems to be the most promising method for the non-invasive measurement of cardiac output.

Can stroke volume and cardiac output be determined reliably in a tilt-table test using the pulse contour method?

The applicability of the finger pressure-derived pulse contour (PC) technique was evaluated in the measurement of stroke volume (SV), cardiac output (CO) and their changes in different phases of the tilt-table test. The reference method was whole-body impedance cardiography (ICG). A total number of 40 physically active patients, aged 41 +/- 19 years, were randomly chosen from a pool of 230. Specifically speaking, 20 of the patients experienced (pre)syncope (tilt+ patients) during the head-up tilt (HUT), and 20 did not (tilt-). A total number of three measurement periods, 30-60 s each, were analysed: supine position, 5 min after the commencement of HUT, and 1 min before set down. SV and CO values measured by PC underestimated significantly those measured by ICG (biases +/- SD 19 +/- 14 ml and 1.55 +/- 1.14 l min-1, respectively) in agreement with earlier reports. The bias between the methods was almost the same in the different phases of the test. However, the SD of the bias was bigger for tilt+ (P < 0.05). When the bias between the methods was eliminated by scaling the first measurement to 100%, the agreement between the methods in the second and third measurements was clearly better than without scaling. Both methods showed a physiological drop in SV after the commencement of HUT. These results indicate that PC suffices in tracking the changes in CO and SV, but for absolute values it is not reliable.

Effects of hypertonic saline (7.5%) on extracellular fluid volumes in healthy volunteers.

This study evaluated the effects of 7.5% saline on plasma and other extracellular fluid volumes. After baseline measurements, eight healthy postmenopausal female volunteers received 4 ml.kg-1 of hypertonic saline over 30 min. After the fluid infusion, the volunteers were studied for 60 min. Plasma volume was measured using a dilution of 125-iodine-labelled human albumin. Extracellular water and cardiac output were measured by whole body impedence cardiography. The infused volume was 4 ml.kg-1 (average 260 ml). Plasma volume increased rapidly during the infusion (mean +/- standard deviation, 442 +/- 167 ml). At the end of the 1-h follow-up period, plasma volume had increased by on average 465 ml (SD 83). The increase of extracellular water at the end of infusion and at the end of study was 650 ml (SD 93) and 637 ml (SD 192), respectively. The highest serum sodium recorded in the volunteers was 158 mmol.l-1. The effect of 7.5% saline on plasma volume was rapid and lasted for at least 1 h. Plasma volume remained elevated by more than the infused volume at the end of the study. The increase in plasma and extracellular fluid volumes was partly achieved by mobilizing intracellular water to extracellular compartment.

Segmental composition of whole-body impedance cardiogram estimated by computer simulations and clinical experiments.

Whole-body impedance cardiography (ICGWB) has been proposed as a feasible means of measuring cardiac output (CO). However, the source distribution of heart-related impedance variations in the whole body is not known. To establish how much of a signal originates in each segment of the body and what the contribution of each is to stroke volume (SV) in ICGWB, impedance in the extremities and trunk were investigated in 15 healthy volunteers. In addition, the theoretical measurement properties of ICGWB were studied using a computer model of the whole-body anatomy as a volume conductor. The model confirmed the expected result that most of the basal impedance originates from the extremities. Clinical experiments revealed that the heart-related amplitude variations in the ICGWB signal originate more evenly from various body segments, the trunk slightly more than the arms or legs. The heart-related ICGWB signal represents a weighted sum of segmental pulsatile events in the body yielding physiologically meaningful data on almost the whole circulatory system.