Impedance cardiography

The maximum rate of change of the thoracic impedance waveform (max dZ/dt) was compared with left-ventricular stroke volume (s.v.), maximum aortic blood flow (m.a,f ), enddiastolic pressure (e.d.p.) and the maximum rate of rise of ventricular pressure (max dP/dt) in 27 experiments performed on chloralose-anaesthetised mongrel dogs. In this study, cardiac performance was altered by acute hypoxia or drugs, Although when max dZ/dt was compared with s.v. and m.a.f., positive correlations (P < 0.01) were found in 80% of the experiments, the correlation coefficients varied greatly (0.324 to 0.986) and negative correlations were observed in two experiments. Positive correlations (P < 0.05) were found in 77% of the experiments where max dZ/dt was compared with max dP/dt, and no consistent correlation was found when max dZ/dt was compared with e.d.p. This study suggests that left-ventricular pump performance may not be the sole factor influencing max dZ/dt, and that max dZ/dt may be a source of error in the presently accepted empirical formula for calculating cardiac output by impedance cardiography.

La cardiografía de impedancia es una técnica no invasiva que permite una determinación rápida, continua y reproducible del gasto cardiaco latido a latido. Mide los cambios en la resistencia eléctrica del tórax que se producen por las variaciones en el volumen sanguíneo en la aorta durante el ciclo cardiaco. La medición continua del cambio en la impedancia o las fluctuaciones del volumen sanguíneo durante la sístole y la diástole, permite determinar el volumen latido, el gasto cardiaco, la contractilidad miocárdica y el contenido total de fluido del tórax. Entre las ventajas de esta técnica se incluyen su fácil implementación y asequibilidad, así como la posibilidad de ser realizada por prácticamente cualquier miembro del equipo de salud. La precisión de la cardiografía de impedancia ha sido validada en numerosos estudios en diferentes escenarios clínicos: hipertensión arterial, falla cardiaca, hipertensión pulmonar, optimización de la terapia de resincronización cardiaca y en pacientes críticos, situaciones en las que provee información sobre el estado hemodinámico sin los riesgos de otras técnicas invasivas o mínimamente invasivas. Es además un método de fácil aplicación y costo-efectivo para el diagnóstico y seguimiento de la respuesta a las intervenciones terapéuticas en múltiples patologías. La técnica representa así un cambio en los paradigmas del monitoreo hemodinámico.

Epidemiological studies have shown a progressive increase in insulin resistance (IR) accompanying body weight gain and blood pressure (BP) increase. This has led to the consideration that hemodynamic effects of IR might depend on its relationship with body mass index (BMI) and BP. The aim of our study was to determine whether IR is associated with changes in hemodynamic indices of cardiovascular function across different categories of BMI (normal weight, overweight, and obese), and BP levels (normal, high normal, and hypertension). This was a cross-sectional study conducted in a population sample of nondiabetic individuals (n ϭ 731). Measures: Insulin resistance was evaluated with the homeostasis model assessment of insulin resistance (HOMA) and subjects were classified into quartiles according to HOMA index values. Synchronized beat-to-beat recordings of stroke volume (impedance cardiography) and R-R interval, along with repeated auscultatory BP measurements were performed. Derived hemodynamic parameters were computed and averaged. Results: Analysis of covariance adjusting for confounders showed significant differences for most hemodynamic parameters among different quartiles of HOMA index both in the general population and within each BMI and BP category. Overall, increasing values of HOMA index were associated with significantly higher BP; and reduced R-R interval, stroke index, cardiac index, pre-ejection period and left ventricular ejection time (P Ͻ .01) across different categories of BMI and BP. Conclusions: These findings suggest that even small increases in HOMA index (not necessarily in the range to define IR) may induce significant changes on indices of cardiovascular function even in normal-weight and normotensive subjects, emphasizing the importance of IR at an early stage of the cardiovascular risk continuum. (

Transthoracic electrical impedance (TEI) was used to assess the relative effectiveness of a 60 mg sustained‐release furosemide preparation (FR) and a 40 mg standard furosemide tablet (F), in reducing the fluid content in the thoracic cavity. A double‐blind crossover study was performed, in which 12 men with a history of one or more myocardial infarctions and mild left heart failure treated with 40 mg furosemide once daily participated. The trial, lasting 28 days, was divided into two 14‐day periods. Each participant received one active drug and one placebo preparation daily, the same regimen being maintained for 14 days, when the active substances were switched. TEI, body weight, serum potassium, sodium, creatinine, and urate were measured immediately prior to the start of the study, after 14 days, and at the end of the study. TEI was measured at frequencies of 1 and 100 kHz with a constant current of 100 m̈Å, during a period of one hour following an intravenous injection of 40 mg f...

Principal component analysis (PCA) Valvular heart disease (VHD) Random forest (RF) a b s t r a c t Valvular heart diseases (VHDs) are an abnormal activity of the heart caused by a damage of one of the four heart valves. The impedance cardiography (ICG) is a non-invasive method employed to identify and classify the heart abnormalities. Despite its importance, there are not many works in scientific literature that use the ICG method in order to diagnose VHDs. Therefore, this paper deals with the ICG signal processing for the classification of normal (N) and various VHDs classes of heartbeats. In this work, six types of heartbeat classes of VHD are used, namely: aortic insufficiency (AOI), aortic stenosis (AOS), aortic disease (AOD), mitral disease (MD), mitral-aortic heart disease (MAOHD) and tricuspid insufficiency + mitral disease (TI + MD). The classification of these heartbeat classes is performed using a combination among statistical, morphological and spectral features. For each ICG heartbeat, the statistical features (median, mean, standard deviation, kurtosis, skewness, central moment and Shannon entropy) are computed from the first four intrinsic mode functions (IMFs) calculated using the empirical mode decomposition (EMD) technique. These statistical features are subjected to principal component analysis (PCA) to reduce the dimensionality. Then, the morphological features are extracted by calculating maximums and minimums of the peaks existing in the ICG heartbeat signal and determining the intervals which separate these peaks. Besides, the spectral features are calculated from the first three harmonics of each heartbeat ICG spectrum. From these three types of features, we selected the most significant of them by applying the analysis of variance (ANOVA) test. In order to obtain the best classification performance, three combination of the selected features are investigated and tested using the decision tree (DT), the random forest (RF) and the support vector machine (SVM) classifiers: i) spectral + morphological, ii) statistical + morphological, iii) statistical + morphological + spectral. The achieved results showed that the use of the third combination of features coupled with the RF classifier gave the highest overall accuracy of 96.34 %, average classaccuracy of 98.95 %, average specificity of 99.38 %, average positive predictivity of 96.73 % and average negative predictivity of 99.44 % using 10-fold cross validation. Thus, our developed method seems robust and very efficient for automatic detection of normal and VHDs ICG classes.

This study explored divergence (error) between ultrafiltration volumes (UFV) and intradialytic changes in extracellular volume (ΔECV) in hemodialysis (HD) patients measured by whole body (wBIS) and sum of segmental bioimpedance spectroscopy (sBIS). The primary aim of the study was to evaluate the effect of different ultrafiltration rates (UFR) on error of estimation of ΔECV by changes in their distribution in body segments (arm, trunk, and leg). Forty-four HD patients (26 men, age 63.5 ± 14.3 yr) were studied twice in the same week following high and low UFR treatments. ΔECV and distributions (segmental ΔECV/∑segmental ΔECV, %) in arm, trunk, and leg were measured. ΔECV by wBIS underestimated UFV (0.58 ± 0.43 in high vs. 0.36 ± 0.5 liters at low UFR; P &lt; 0.001, respectively); however, using sBIS no significant difference between UFV and ΔECV was present. Divergence using wBIS but not sBIS correlated positively with UFR. ΔECV distribution in trunk and leg at high UFR (44.1 ± 8.3, ...

Impedance cardiography (IC) has been used to monitor the pumping function of the heart in terms of stroke volume or cardiac output. We explored the extent to which IC can be used for monitoring transient effects of cardiac alterations on a beat-to-beat basis. A four-spot-electrode configuration was used in the present design. The spatial arrangement of the four electrodes was carefully selected to obtain an optimal result. A constant current source provided a 4 mA, 20 kHz sinusoidal excitation current. Analog signal processing was developed to demodulate and amplify the resultant impedance information, eliminate low frequency motion artifacts and incidental breathing artifacts. Experiments were performed on normal healthy volunteers. Impedance waveforms were recorded from each subject beginning from a supine position then moving to an upright position. Breath holding was maintained throughout the procedure. The impedance waveform, Z, its first derivative dZ/dt, the DC component, Z(0...

The minute ventilation/carbon dioxide production relationship is relevant to a number of patientrelated outcomes in COPD. Minute ventilation/carbon dioxide production, therefore, should be valued in the clinical management of these patients.

Background: The aim of this study was to ascertain whether individual atrioventricular delay (AVD) optimization using impedance cardiography (ICG) offers beneficial hemodynamic effects as well as improved exercise tolerance and quality of life in patients with requiring constant right ventricular pacing. Methods: There were 37 patients with advanced AV block included in the study. Several examinations were performed at the beginning. Next, the optimization of AVD by ICG was done. The next step of the study patients have been randomized into optimal AVD group (AVDopt) or factory setting group (AVDfab). After 3 months, the follow-up all data were collected again and crossover was performed. After another 3 months, during the final follow-up all these measures were repeated. Results: In 87.5% patients, AVDopt were different than factory value. Cardiac output (CO), cardiac index (CI), and stroke volume (SV) were significantly (P < 0.001) higher in AVDopt group than in AVDfab group (CO: 6.0 ± 1.4 L/minute vs. 5.3 ± 1.2 L/minute; SV: 85.8 ± 25.7 mL vs.76.9 ± 22.5 mL; CI: 3.2 ± 0.7 L/minute/m 2 vs. 2.7 ± 0.6 L/minute/m 2). There was a statistical significant (P < 0.05) reduction of proBNP and NYHA class in patients with AVDopt compared to AVDfab (proBNP: 196.4 ± 144.7pg/mL vs. 269.4 ± 235.8 pg/mL; NYHA class: 1.7 ± 0.5 vs. 2.3 ± 0.6). Six-minute walking test was significantly (P < 0.05) higher in AVDopt group (409 ± 90 m) than in AVDfab group (362 ± 93 m). There were no statistically significant differences in echocardiographic parameters between AVDopt and AVDfab settings. Conclusion: Our study results suggest that AVD optimization in patients with DDD pacemaker with ICG improves hemodynamic when compared to the default factory settings. Furthermore, optimally programmed AVD reduces BNP and improves exercise tolerance and functional class.

Background: Device optimization is not routinely performed in patients who underwent cardiac resynchronization therapy (CRT) device implantation. Noninvasive optimization of CRT devices by measurement of cardiac output (CO) can be used as a simple method to assess ventricular systolic performance. The aim of this study was to assess whether optimization of atrioventricular (AV) and interventricular (VV) delay can improve hemodynamic response to CRT and whether this optimization should be performed for each patient individually. Methods: Twenty patients with advanced heart failure New York Heart Association (NYHA) class III/IV, left ventricular ejection fraction ≤ 35% and left bundle branch block (QRS ≥ 120 ms) in sinus rhythm were evaluated from 24 h to 48 h after implantation of a CRT device by means of impedance cardiography (ICG). CO was fi rst measured at each patient's intrinsic rhythm. Patients then underwent adjustments of AV and VV delay from 80 ms to 140 ms and from-60 ms to +60 ms, respectively in 20 ms increment steps and CO at each setting was measured by ICG. Both AV and VV delays were programmed according to the greatest improvement in CO compared to intrinsic rhythm. Results: There was a statistically signifi cant increase in CO measured at the intrinsic rhythm compared to different AV delay by mean of 21% (3.8 ± 1.0 vs. 4.6 ± 0.1 L/min, p < 0.05). Optimal AV/VV delays with left ventricle-preexcitation or simultaneous biventricular pacing caused additional increased CO from intrinsic rhythm by mean of 32.6% (3.8 ± 1.0 vs. 5.04 ± ± 1.0 L/min, p < 0.05). Optimal AV/VV setting delays also resulted in improved hemodynamic responses compared to VV factory setting delay. Conclusions: Both AV and VV delay optimization should be performed in clinical practice. Optimal AV delay improved outcome. However, combination of optimized AV/VV delays provided the best hemodynamic response. Optimized AV/VV delays with left ventricle-preexcitation or simultaneous biventricular pacing increased hemodynamic output compared to intrinsic rhythm and VV factory setting delay.

Background and objectives The 6-minute walk test (6MWT) is a field test commonly used to predict peak oxygen consumption (VO2peak) in people after stroke. Inclusion of cardiodynamic variables measured by impedance cardiography (ICG) during a 6MWT has been shown to improve prediction of VO2peak in healthy adults but these data have not been considered in people after stroke. This study investigates whether the prediction of VO2peak can be improved by the inclusion of cardiovascular indices derived by impedance cardiography (ICG) during the 6MWT in people after stroke. Methods This was a cross-sectional study. Patients diagnosed with stroke underwent in random order, a maximal cardiopulmonary exercise test (CPET) and 6MWT in separate dates. Heart rate (HR), stroke volume (SV) and cardiac output (CO) were measured by ICG during all tests. Oxygen consumption was recorded by a metabolic cart during the CPET. Recorded data were subjected to multiple regression analyses to generate VO2peak...

The 6-minute walk test (6MWT) is a field test commonly used to predict VO2peakin people after stroke. Inclusion of cardiodynamic variables measured by impedance cardiography (ICG) during a 6MWT has been shown to improve prediction of peak oxygen consumption (VO2peak) in healthy adults but these data have not been considered in people after stroke. This study investigates whether the prediction of VO2peak can be improved by the inclusion of cardiovascular indices derived by impedance cardiography (ICG) during the 6MWT in people with strokeThis study investigates whether the prediction of VO2peak can be improved by the inclusion of cardiovascular indices derived by impedance cardiography (ICG) during the 6MWT in people with stroke This study investigates whether the prediction of VO2peak can be improved by the inclusion of cardiovascular indices derived by impedance cardiography (ICG) during the 6MWT in people with stroke. Our study showed that inclusion of SV and CO measured during t...

Accurate prediction of aerobic capacity is necessary to guide appropriate exercise prescription. It is common to use 6-minute walk distance (6MWD) to predict peak oxygen uptake (VO2peak) in the clinical environment. The aim of this study was to determine whether prediction of VO2peak can be improved by the inclusion of cardiovascular indices derived by impedance cardiography (ICG) during the 6MWT. A total of 62 healthy university students aged 21±1 years completed in separate days, a cardiopulmonary exercise test (CPET) and two 6MWTs (30 min apart), during which heart rate (HR), stroke volume (SV) and cardiac output (CO) were measured by ICG (PhysioFlow® PF07 EnduroTM). The CPET was conducted with the Ergoselect 200 Ergoline and oxygen consumption measured by a MasterScreenTM CPX breath-by-breath metabolic cart. Multiple regression analyses were conducted to generate VO2peak prediction equations using 6MWD with, or without the cardiovascular indices recorded at the end of the best p...

almost statistically significant differences (p values ranging from 0.07 and 0.13) could only be recorded consistently in the 40-49 age class concerning PWV/ cSBP/ cPP / AI. Authors discuss the relevance of these findings concerning risk stratification in a Portuguese population with high incidence of stroke.

Background-Clinical experience suggests that atrial tachyarrhythmias (ATs) are a frequent comorbidity in heart failure patients with left ventricular systolic dysfunction and that volume overload may increase AT susceptibility. However, substantiating this apparent relationship in free-living patients is difficult. Recently, certain implantable cardioverterdefibrillators provide, by measuring transpulmonary electric bioimpedance, an index of intrathoracic fluid status (OptiVol index [OI]). The goal of this study was to determine whether periods of greater intrathoracic fluid congestion (as detected by OI) correspond with increased AT event frequency. Methods and Results-This analysis retrospectively assessed the relation between AT events and OI estimate of volume overload in patients with left ventricular systolic dysfunction and OI-capable implantable cardioverter-defibrillators. OI values were stratified into 3 levels: group 1, Ͻ40; group 2, 40 to 60; and group 3, Ͼ60. An OI threshold-crossing event was defined as OIՆ60, a value previously associated with clinically significant volume overload. Findings in 59 patients (mean left ventricular ejection fraction, 24%) with 225 follow-up visits (mean, 3.8 visits per patient) were evaluated. AT prevalence was 73%. AT frequency (percent of patients visits with at least 1 episode of AT since previous device interrogation) was greater in group 3 versus group 1 (Pϭ0.0342). Finally, in terms of temporal sequence, AT episodes preceded OI threshold-crossing event in 43% of incidences, followed threshold-crossing event in 29%, and was simultaneous or indeterminate in the remainder. Conclusions-These findings not only support the view that worsening pulmonary congestion is associated with increased AT frequency in patients with left ventricular dysfunction but also suggest that AT events may be responsible for triggering episodic pulmonary congestion more often than previously suspected. (Circ Arrhythmia Electrophysiol. 2009;2:488-494.) Key Words: bioimpedance Ⅲ heart failure Ⅲ atrial tachyarrhythmias Ⅲ volume overload A trial tachyarrhythmias (AT), particularly atrial fibrillation (AF), are a frequent comorbidity in patients with left ventricular (LV) systolic dysfunction and heart failure. 1-5 Further, clinical experience suggests that AT may be triggered by periods of volume overload in such patients. 1-5 In part, AT episodes in this setting may be the consequence of increased atrial wall stress and/or neurohumoral changes that often accompany periods of volume overload. Alternatively, however, it is possible that in certain cases, spontaneous AT events may be the trigger, by initiating a period of hemodynamic deterioration and ensuing volume overload.

Clinical experience suggests that atrial tachyarrhythmias (ATs) are a frequent comorbidity in heart failure patients with left ventricular systolic dysfunction and that volume overload may increase AT susceptibility. However, substantiating this apparent relationship in free-living patients is difficult. Recently, certain implantable cardioverter-defibrillators provide, by measuring transpulmonary electric bioimpedance, an index of intrathoracic fluid status (OptiVol index [OI]). The goal of this study was to determine whether periods of greater intrathoracic fluid congestion (as detected by OI) correspond with increased AT event frequency. This analysis retrospectively assessed the relation between AT events and OI estimate of volume overload in patients with left ventricular systolic dysfunction and OI-capable implantable cardioverter-defibrillators. OI values were stratified into 3 levels: group 1, &lt;40; group 2, 40 to 60; and group 3, &gt;60. An OI threshold-crossing event was...

Introduction: Intradialytic hypotension is one of the most common complications to be observed during hemodialysis, occurring in about 15-20% of all sessions. The risk factors like interdialytic weight gain, UF rate, net ultrafiltration, pyrexia, food intake, cardiac events dialyzer type etc have been controlled due to modern hemodialysis equipments like hemodialysis machines with their better volumetric controls, sodium profiling, temperature control and patient counseling but still intradialytic hypotension is a major dialysis related complication. Objectives: Identify the risk factors responsible for intradialytic hypotension. Subjects and Methods: This cross-sectional study was comprised of one hundred patients of end stage renal disease carried out in the Department of Nephrology, Shaikh Zayed Hospital, Lahroe between 1 st January 2010 to 31 st March 2010. All adult patients on maintenance hemodialysis were included in this study. The patients on maintenance hemodialysis <3 months duration and vomiting, diarrhea or bleeding episodes pre-hemodialysis were excluded. These dialysis sessions were categorized in two groups (Group I and Group II). Group I included those dialysis sessions in which the patients developed hypotension during dialysis and Group II included those dialysis sessions in which patients did not develop intradialytic hypotension. Following factors were noted like interdialytic weight gain, ultrafiltration rate, dialyzer type, cardiac events, antihypertensive medication, food intake during dialysis, pyrexia. Results: Total 1907 hemodialysis sessions were included there were 103 (5.4%) patients of symptomatic hypotension (Group I) and 1804 (94.6%) patients of no symptomatic hypotension (Group II). The mean weight gain in group I was 2.2±0.7 kg and 2.1±0.9 kg in group II. The mean ultrafiltration rate in group I was 978±636 ml/h and in group II was 636±367ml/h. In group I, 4 (3.8%) and in group II, 20 (1.1%) sessions had cardiac events during dialysis (P= 0.04). Change in mean pulse rate was -2.1±14.1 in group l and -2.4±11.1 in group ll (p=0.8). the Odd ratios for total time of dialysis was 5.50 (3.59 -8.43), for lowest systolic blood pressure 5. 43(3.55 -8.32), and lowest diastolic blood pressure 4. 85(3.14 -7.48). Conclusions: We found that interdialytic weight gain, net ultrafiltration, ultrafiltration rate and acute cardiac event were responsible factors causing intradialytic hypotension. Autonomic dysfunction was also a contributing factor among symptomatic hypotensive group.

A case in which apparent undersensing was caused by detection of low amplitude impedance‐measuring pulses emitted by a thoracic impedance‐sensing rate‐modulated pacemaker is described. The detection of these high frequency pulses was interpreted as “noise” by the pacemaker and led to asynchronous pacing in the interference reversion mode. Increasing the sensitivity /ailed to correct the problem. Decreasing the sensitivity eliminated oversensing of the low amplitude pulses and the apparent undersensing. Recognition of (his phenomenon is important to prevent a misdiagnosis of undersensing.

OBJECTIVES This study sought to assess the potential utility of impedance cardiography (ICG) in predicting clinical deterioration in ambulatory patients with heart failure (HF). BACKGROUND Impedance cardiography uses changes in thoracic electrical impedance to estimate hemodynamic variables, but its ability to predict clinical events has not been evaluated. METHODS We prospectively evaluated 212 stable patients with HF and a recent episode of clinical decompensation who underwent serial clinical evaluation and blinded ICG testing every 2 weeks for 26 weeks and were followed up for the occurrence of death or worsening HF requiring hospitalization or emergent care. RESULTS During the study, 59 patients experienced 104 episodes of decompensated HF (16 deaths, 78 hospitalizations, and 10 emergency visits). Multivariate analysis identified 6 clinical and ICG variables that independently predicted an event within 14 days of assessment. These included three clinical variables (visual analog score, New York Heart Association functional class, and systolic blood pressure) and three ICG parameters (velocity index, thoracic fluid content index, and left ventricular ejection time). The three ICG parameters combined into a composite score was a powerful predictor of an event during the next 14 days (p ϭ 0.0002). Visits with a high-risk composite score had 2.5 times greater likelihood and those with a low-risk score had a 70% lower likelihood of a near-term event compared with visits at intermediate risk. CONCLUSIONS These results suggest that when performed at regular intervals in stable patients with HF with a recent episode of clinical decompensation, ICG can identify patients at increased near-term risk of recurrent decompensation.

Noninvasive cardiac output (CO) measurement can be useful in many clinical settings where invasive monitoring is not desired. Bioimpedance (intrabeat measurement of changes in transthoracic voltage amplitude in response to an injected high-frequency current) has been explored for this purpose but is limited in some clinical settings because of inherently low signal-to-noise ratio. Since changes in fluid content also induce changes in thoracic capacitive and inductive properties, we tested whether a noninvasive CO measurement could be obtained through measurement of the relative phase shift of an injected current (i.e., bioreactance). We constructed a prototype device that applies a 75-kHz current and determines the relative phase shift (dΦ/d t) of the recorded transthoracic voltage. CO was related to the product of peak dΦ/d t, heart rate, and ventricular ejection time. The preclinical study was done in nine open-chest pigs put on right heart bypass so that CO could be varied at kno...

A software implemented bio-impedance signal simulator (BISS) which can imitate real bio-impedance phenomena for analyzing the performance of various signal processing methods and algorithms is proposed. The underlying mathematical models are built by means of a curve-fitting regression method. Three mathematical models were compared, i.e. polynomial, Fourier series and sum of sine waves with four different measured impedance cardiography (ICG) datasets and two clean ICG and impedance respirography (IRG) datasets that were taken as the basis of the signals. Statistical analysis (sum of squares error, correlation and execution time) implies that Fourier series is the best suited. The models of the ICG and IRG signals are integrated into the proposed simulator. In the simulator the correlation between heart rate and respiration rate are taken into account by means of ratio between them (5:1, respectively).

Aim:  The aim of the study was to examine the central and peripheral cardiovascular adaptation and its coupling during increasing levels of hyperoxaemia. We hypothesized a dose‐related effect of hyperoxaemia on left ventricular performance and the vascular properties of the arterial tree.Methods:  Oscillometrically calibrated arterial subclavian pulse trace data were combined with echocardiographic recordings to obtain non‐invasive estimates of left ventricular volumes, aortic root pressure and flow data. For complementary vascular parameters and control purposes whole‐body impedance cardiography was applied. In nine (seven males) supine, resting healthy volunteers, aged 23–48 years, data was collected after 15 min of air breathing and at increasing transcutaneous oxygen tensions (20, 40 and 60 kPa), accomplished by a two group, random order and blinded hyperoxemic protocol.Results:  Left ventricular stroke volume [86 ± 13 to 75 ± 9 mL (mean ± SD)] and end‐diastolic area (19.3 ± 4.4...

Objective: To evaluate the role of bioelectrical impedance vector analysis (BIVA) and brain natriuretic peptide (BNP) in detecting peripheral congestion in heart failure (HF). Background: BIVA/BNP are biomarkers for congestion in acute (ADHF) and chronic HF. Methods: 487 ADHF and 413 chronic HF patients underwent BIVA and BNP tests. Results: BIVA was more accurate than BNP in detecting peripheral congestion both in ADHF (AUC 0.88 vs 0.57 respectively; p < 0.001) and chronic HF patients (AUC 0.89 vs 0.68, respectively; p < 0.001). In ADHF patients, the optimal BNP cutoff for discriminating presence or absence of edema was >870 pg/mL (PPV ¼ 48% and NPV ¼ 58%) whereas in chronic HF it was >216 pg/mL (PPV ¼ 18% and NPV ¼ 95%). The BIVA detected edema when the vector fell into the lower pole of 75th percentile tolerance ellipse (PPV ¼ 84% and NPV ¼ 78%) in ADHF, the lower pole of 50% (PPV ¼ 68% and NPV ¼ 95%) in chronic HF. Conclusions: In HF patients, BIVA is an easy, fast technique to assess peripheral congestion, and is even more accurate than BNP.

Preeclampsia is a severe disorder that can complicate pregnancy with serious consequences for mother and newborn. Although a specific hemodynamics profile can be observed during normal pregnancy, preeclampsia ischaracterized by several specific changes like increased cardiac output, sodium and water retention leading to blood volume expansion, reductions in systemic vascular resistance and systemic blood pressure. Impedance cardiography is a noninvasive method which can provide hemodynamic parameters in pregnancy. We present two cases of pregnancy complicated with preeclampsia and the hemodynamic particularities each of them has. The first one includes a patient with early onset of preeclampsia. She was monitored with impedance cardiography. We observed thatheather index decreased in the second trimester of pregnancy. The second case is focused on recurrent preeclampsia. The hemodynamic profile determined by impedance cardiography showed increased systemic vascular resistance beginningin the second trimester of pregnancy until delivery. Impedance cardiography is a noninvasive method, but its' accuracy in monitoring patients with high risk of preeclampsia should be proved with randomized control trials.

Background: Methods for stroke volume (SV) and ejection fraction (EF) measurements require the presence of qualified physicians and are not suited for continuous monitoring. Aim: To develop an automated non-invasive method for the measurement and continuous monitoring of SV and EF. Methods: We have designed a method for the measurement of EF and SV using multiple-site-impedance (z0) measurements, applying multiple frequencies of 5, 40 and 200 kHz whereby various segments of the human body, including volume changes within these segments, could be defined electrically. The obtained variables were used to train neuronal nets and related by multiple regression analyses to cardiac output (CO) as measured by a partial rebreathing Fick method (CO r-fick ) or EF as measured by echocardiography (EF echo ), respectively. A total of 129 subjects (48 with normal heart function and 81 with CHF, NYHA I-IV) were investigated. The multiply derived values of z0 and of change of impedance (dz/dt) were shown, by multiple regression analysis, to be significantly related to CO r-fick and to EF echo , (total r=0.77, n=35, pb0.001, and r=0.81, n=47, pb0.001, respectively.). By training a neuronal net with the electrical data of 67 (out of 94) subjects, EF echo could be predicted in the remaining 27 subjects which were unknown to the neuronal net with a combined r=0.71 ( pb0.001,n=27). In contrast, conventional impedance cardiography (ICG) was unable to predict either CO r-fick or EF echo . The new method, which we call multi-site-frequency electromechanocardiography (msf-ELMC) appears promising for the automated electrical measurement of the mechanical heart action in patients with normal and reduced cardiac function.

The goal of the present study was to develop and evaluate algorithms for non-invasive, real-time, beat-to-beat monitoring of stroke index (SI), blood pressure (BP) and total peripheral resistance index (TPRI) which has a menu-driven interface, suitable for routine use by unskilled sta. In addition, it was our aim to include a meta-analysis for the evaluation of autonomic function derived from the above haemodynamic data. This includes spectral analysis of heart rate (HR), BP, SI and TPRI and the automatic calculation of baroreceptor re¯ex sensitivity. Impedance cardiography was used for beat-tobeat SI determination, Finapres2 corrected by an oscillometric blood pressure measurement (Dinamap 1) on the upper arm for beat-to-beat BP measurement. We demonstrate noise free recordings during physiological (head up tilt) and pharmacological intervention (a 1-, b 2-adrenoreceptor agonists, insulin induced hypoglycemia). The newly developed software should prove valuable for physiological, pharmacological and clinical studies.

The effects of a single dose of 2 mg/kg amrinone (60min constant rate IV infusion) have been assessed in a double-blind, placebo-controlled, withinsubject cross-over study in six healthy volunteers. Combined impedance cardiography, phonocardiography and electrocardiography revealed a protracted drop in mean ventricular ejection time and electromechanical systole together, with a protracted rise in the "contractility" indices dZ/dtmax and the Heather index HI. The profile is compatible with combined venous vasodilation and positive inotropic action. In spite of the methodological constraints, endpoints were reached that were both detectable and relevant. The profiling permitted a better distinction to be made between the possible levels of action than systolic time intervals alone could have done. Therefore, these methods may be of value in the early development of "inodilator" drugs.

The reproducibility and agreement of the estimates of stroke volume (SV), cardiac output (CO) and total peripheral resistance (TPR) by transthoracic impedance cardiography (ZCG) and M-mode echocardiography (ECHO) were analyzed before and after the placebo-controlled administration of ascending doses of isosorbide dinitrate and nicorandil in 12 healthy subjects. There was no biostatistical agreement between the two methods in estimating cardiovascular function either before or after dosing (ZCG estimated substantially larger SV, CO and lower TPR). But, ZCG and ECHO estimated about similar overall treatment related changes (across treatments and periods) and reached substantially better agreement when the values were expressed as ratio of the baseline before dosing. Such improvement did not occur when the data were expressed as arithmetic difference from baseline. In spite of the improvement of agreement by expressing the data as ratio of baseline, the coefficients of reproducibility between the two methods (circa 25% of baseline) remained too large to judge the methods interchangeable.

Impedance cardiography is a well-established noninvasive method to assess withinsubject changes of cardiovascular function. We compared the standard approach (ZCG) which requires tedious signal analysis with an automated approach (TEB: NCCOM 3®) with its own specific equipment, algorithms and equations in order to assess agreement of the method-specific measurements and calculations. 2 Ten healthy men were studied on two occasions with either ZCG or TEB, at rest and at the end of 5 min i.v.-infusions with 1 ,ug min-' isoprenaline and 100 p,g min-' phenylephrine. 3 There was good agreement for the method-independent changes (HR, SBP/DBP), but there were large differences for method-specific measurements: dZ/dtmax [TEB-ZCG] =-0.68, CI:-0.83 to-0.53 f s-1, PEP [TEB-ZCG] =-22.1, CI:-35.0 to-9.2 ms and QS2c [TEB-ZCG] =-16.5, CI:-32.4 to-0.6 ms and for the calculated stroke volume SV [TEB-ZCG] = 30.3, CI: 15.5 to 45.2 ml. The responses of dZ/dtmax and SV to isoprenaline and phenylephrine, although qualitatively similar, reached no quantitative agreement either. A substantial disagreement was evident for the STI responses to isoprenaline where TEB failed to detect the expected reduction of VETC and thus grossly underestimated the shortening of QS2c. 4 It is concluded that TEB-measurements and-calculations did not agree with standard ZCG, that the methods, albeit related, cannot be considered as interchangeable and that suspicion is justified that TEB might yield erroneous results under specific cicumstances.

Relative sensitivity of four noninvasive methods in assessing systolic cardiovascular effects of isoproterenol in healthy volunteers Study objective: The study was performed to evaluate the relative sensitivity of various noninvasive methods to detect and describe the systolic cardiovascular effects of stepwise increasing doses of isoprotere- nol: two-dimensional left ventricular echocardiography (main variable, ejection fraction), ACVF (atten- uation compensated volume flow)dual-beam Doppler echoaortography (time-averaged mean velocity), electrical impedance cardiography [(dZ/dt,na,c)/RZ index], and systolic time intervals from mechanocardiography (PEP and QS2J. Methods: Isoproterenol was administered by constant rate intravenous infusion in consecutive steps of 0.1, 0.2, 0.4, 0.75, and 1.5 Rg/min (each for 15 minutes). Saline control infusions were given in analog fashion. The treatments (isoproterenol and saline solution) were administered in a period-balanced two- way crossover design with randomly allocated sequences. The subjects, observers, and analysts were blinded to the treatment protocol. Study subjects were 10 healthy male volunteers (age range, 23 to 31 years; mean age, 26.6 years). Results: Compared with saline solution, isoproterenol caused a dose-related increase in ejection fraction, (dz/dt)/RZ index, and time-averaged mean velocity and a dose-related shortening of PEP and QS2c The responses are congruent with an enhancement of cardiac systolic performance caused by a positive ino- tropic stimulation and an afterload reduction ("inodilatory" response). The effects on systolic time inter- vals reached statistical significance (a = 0.05) at the first isoproterenol dose step, the effects on the im- pedance cardiography and the Doppler echoaortography variables reached statistical significance at the second dose step, and the effects on the two-dimensional echocardiography reached statistical signifi- cance at the third dose step. Conclusions: All methods allowed to detect isoproterenol-related changes. Systolic time intervals were the most sensitive, followed by impedance cardiography, ACVF dual-beam Doppler echoaortography, and two-dimensional echocardiography. The practical convenience and high sensitivity of the systolic time intervals makes them suitable to evaluate investigational systolic inodilatory changes in humans. (CLINT

The contribution of computerized impedance cardiography in monitoring and differentiating cardiovascular responses to pharmacologic stress after the administration of dipyridamole (group 1 , n = 24) or dobutamine (group 2, n = 26) was investigated during stress echocardiography. Heart rate, stroke volume index, cardiac index and systemic vascular resistance index were evaluated continuously with an automated, computerized, signal-averaged impedance cardiography system. Dipyridamole had little average effect on heart rate, stroke volume index, and cardiac index. The responses were similar in patients with positive (n = 9) or negative (n = 15) stress echocardiography test results (as characterized by echocardiographic wall-motion abnormalities). Dobutamine induced a similar mean increase in heart rate in patients with negative (n = 13) or positive (n = 13) results on stress echocardiography. The mean increase in stroke volume index induced by dobutamine wasgreater in patients with negative stress echocardiograp h y test results than in patients with stress-induced wall-motion abnormalities. This distinction was also seen in the cardiac index; the mean change in patients with negative stress echocardiography test results was larger than in patients with positive results. It is concluded that automated computerized impedance cardiography not only allows surveying and monitoring hemodynamic changes during pharmacologic stress echocardiography but also contributes to differentiation of pathologic stress responses. tress echocardiography (SE) is a well-established S noninvasive technique for the diagnosis and functional evaluation of patients with suspected or proven ischemic coronary heart disease. Stress-induced left ventricular wall-motion abnormalities (WMA) detectable by echocardiography indicate hemodynamically relevant coronary artery disease. However, physical stress testing cannot be performed in all patients because of concomitant diseases (e.g., limb ischemia, gonarthrosis) or other fac-

Rationale: Normoxic heliox (mixture of 79% He and 21% O 2) may enhance exercise tolerance in patients with chronic obstructive pulmonary disease (COPD). It remains to be determined whether part of these beneficial effects could be ascribed to increased O 2 delivery (O 2 DEL) to locomotor muscles. Objectives: To investigate the effects of heliox on peripheral O 2 DEL and utilization during exercise in moderate to severe COPD. Methods: Twelve mildly hypoxic or nonhypoxemic men (FEV 1 5 45.0 6 13.0% predicted) underwent constant-work rate tests (70-80% peak) to the limit of tolerance while receiving heliox or room air. Near-infrared spectroscopy determined changes (D) in leg muscle deoxygenation (deoxyhemoglobin concentration [HHb], an index of fractional O 2 extraction), and surface electromyography estimated muscle fiber recruitment (n 5 5). _ Q and Sp O 2 were monitored by impedance cardiography and pulse oximetry, respectively. Measurements and Main Results: Heliox significantly decreased dynamic hyperinflation and increased exercise tolerance compared with room air (640 6 95 s vs. 371 6 100 s; P , 0.01). Heliox also accelerated on-exercise dynamics of _ Q, which were accompanied by faster O 2 uptake kinetics and slower D[HHb] responses (P , 0.05). During steady-state exercise, Sp O 2-corrected D[HHb] values decreased with heliox despite no significant changes in cardiac output. Muscle fiber recruitment and leg effort scores were also diminished (P , 0.05). On a multiple regression analysis, reductions in dynamic hyperinflation, dyspnea, and D[HHb] were independently related to improvements in exercise tolerance with heliox (R 2 5 0.91; P , 0.01). Conclusions: Heliox increases lower limb O 2 DEL and utilization during dynamic exercise in patients with moderate to severe COPD. These effects enhance exercise tolerance in this patient population.

Background: Wearable technologies for monitoring cardiovascular parameters, including electrocardiography (ECG) and impedance cardiography (ICG), propose a challenging research subject. The expectancy for wearable devices to be unobtrusive and miniaturized sets a goal to develop smarter devices and better methods for signal acquisition, processing, and decision-making. Methods: In this work, non-standard electrode placement configurations (EPC) on the thoracic area and single arm were experimented for ECG signal acquisition. The locations were selected for joint acquisition of ECG and ICG, targeted to suitability for integrating into wearable devices. The methodology for comparing the detected signals of ECG was developed, presented, and applied to determine the R, S, and T waves and RR interval. An algorithm was proposed to distinguish the R waves in the case of large T waves. Results: Results show the feasibility of using non-standard EPCs, manifesting in recognizable signal waveforms with reasonable quality for post-processing. A considerably lower median sensitivity of R wave was verified (27.3%) compared with T wave (49%) and S wave (44.9%) throughout the used data. The proposed algorithm for distinguishing R wave from large T wave shows satisfactory results. Conclusions: The most suitable non-standard locations for ECG monitoring in conjunction with ICG were determined and proposed.

ICG (impedance cardiography) is in parallel to ECG (electrocardiography) an important indicator of the functioning of the heart and of the overall cardiovascular system. Adding the ICG to ECG measurement functionality into the wearable devices improves the quality of health monitoring, as the ICG reflects relevant hemodynamic parameters (informative time intervals, but also the stroke volume and cardiac output and their variability). The most challenging task of the ICG signal processing is to extract the key points B, C, X of the cardiac periodstart, peak-location, and value at this point and the end of the LVET (left ventricular ejection time) sub-period in the cardiac cycle. A novel block diagram and analog implementation of it has been proposed, analyzed, and discussed, with discussion of the benefits of the proposed solution. The proposed solution enables developing of relatively simple very power-efficient solutions, monitoring the ICG values of the person with smart and efficient data acquisition and processing.

Background: The deep breathing test (DB) and Valsalva maneuver (VM) are used to detect autonomic dysfunction. The VM induces sympathetically mediated changes in blood pressure (phase II late, phase IV, and recovery time) and both tests induce vagally mediated heart rate changes. There is limited information on effects of key variables, compliance with testing and the effects of non-compliance This study has twin goals of evaluating compliance with standard instructions and the effects of changes in key variables. We also evaluated the effect of position on the VM. Material and methods: Forty healthy males performed DB at air exchange volumes of 50, 80, and 100% of vital lung capacity (VLC). The VM was performed at 40 and 30 mm Hg expiratory pressure for 15 and 10 s in sitting and supine position, respectively. Results: Participants performed DB at lower volumes than intended and were not able to maintain 100% VLC for the duration of the test. The DB heart rate response decreased 6.3 beats/min per liter below VLC. During the VM, subjects blew at lower pressures than instructed. The VM responses were significantly larger with longer expiration durations, higher expiratory pressures and when performed sitting. Performing the VM at 40 mm Hg for 10 s in supine position increased the odds ratio of experiencing flat-top responses. Conclusion: The ability of subjects to strictly comply with methodological guidelines significantly improves results. Recording of both test parameters and ensuing results is suggested.

We measured resting and exercise haemodynamics, as well as 24-hour ambulatory blood pressure, so as to study the influence on development of hypertension in children after repair of coarctation by either construction of a subclavian flap or end-to-end anastamosis. The patients in both groups were studied a mean time of 13 years after surgery. Thus, we divided 43 children who had undergone surgical repair of coarctation, and who were not on antihypertensive therapy, into a group of 22 patients who had undergone subclavian flap repair, with a mean age of 14 plus or minus 2.6 years, and another group of 21 patients undergoing end-to-end anastomosis, with a mean age of 13.5 plus or minus 3.9 years. We examined blood pressure at rest and during exercise, along with the measurement of cardiac output using impedance cardiography, and during 24-hour ambulatory monitoring. We recorded systolic and diastolic blood pressures, pulse pressure, cardiac output and total peripheral vascular resista...

Adaptive systems are employed in the cancelation of noises and estimation of periodic and quasiperiodic signals. Amongst these signals are the electrocardiogram (ECG), impedance cardiography (ZCG), brain evoked potentials and modulated signals in telecommunication applications. In this paper we study the behavior of the weights of the LMS algorithm when used to estimate the coefficients of the discrete Fourier transform (DFT) of a signal under influence of low frequencies. We show theoretically that low frequency noise affects the estimation of the weights at higher frequencies. The simulation results obtained are in agreement with theoretical results. Moreover, we exemplify the problem with impedance cardiography (ZCG) signals.

Stroke is still the third cause of death worldwide. It has been established that the main risk factors of stroke are: age, hypertension, atrial fibrillation, ischaemic heart disease, obesity, lipid disorders and diabetes. Diabetes not only increases the risk of stroke but also is associated with worse outcome. Factors leading to these process are: chronic and acute hyperglycaemia, hypertension, ischaemic heart disease, obesity, blood coagulation disorders, dyslipidaemia and hyperhomocysteinemia. Although diagnostic and therapeutic advances, stroke in diabetic patients is one of the worse complication and the main cause of disability. It has been demonstrated that the risk of stroke in diabetic is much higher than in non-diabetic subjects because of chronic hyperglycemia, hyperinsulinism and frequent coexistence with diabetes other disorders i.e. hypertension, coronary heart disease, dyslipidaemia and obesity. It has also been proved that thigh metabolic control and first of all reduction of blood pressure and administration of antiplatelet drugs can significantly decrease the frequency of stroke in diabetes.

Background: The deep breathing test (DB) and Valsalva maneuver (VM) are used to detect autonomic dysfunction. The VM induces sympathetically mediated changes in blood pressure (phase II late, phase IV, and recovery time) and both tests induce vagally mediated heart rate changes. There is limited information on effects of key variables, compliance with testing and the effects of non-compliance This study has twin goals of evaluating compliance with standard instructions and the effects of changes in key variables. We also evaluated the effect of position on the VM. Material and methods: Forty healthy males performed DB at air exchange volumes of 50, 80, and 100% of vital lung capacity (VLC). The VM was performed at 40 and 30 mm Hg expiratory pressure for 15 and 10 s in sitting and supine position, respectively. Results: Participants performed DB at lower volumes than intended and were not able to maintain 100% VLC for the duration of the test. The DB heart rate response decreased 6.3 beats/min per liter below VLC. During the VM, subjects blew at lower pressures than instructed. The VM responses were significantly larger with longer expiration durations, higher expiratory pressures and when performed sitting. Performing the VM at 40 mm Hg for 10 s in supine position increased the odds ratio of experiencing flat-top responses. Conclusion: The ability of subjects to strictly comply with methodological guidelines significantly improves results. Recording of both test parameters and ensuing results is suggested.

A comparison of pulmonary, cardiovascular and metabolic responses was made in 32 subjects consisting of 11 able-bodied, 8 paraplegics (T4-L3 lesions) and 13 quadriplegics (C5-C8 lesions) during maximal arm cranking exercise. A progressive continuous arm cranking test, modified for each group, was employed to elicit maximal responses with pulmonary and metabolic determinations made with open circuit spirometry and selected cardiovascular measurements made by impedance cardiography. Additionally, non-exercise static and dynamic lung function assess ments were made. Quadriplegics had significantly lower (p < 0•05) tidal volumes, vital capacities, forced expiratory volumes at 1 seconds, and maximal breathing caapacities than the other two groups. The mean peak V02 during maximal arm cranking was 28•2, 25•3 and 12•0 ml/kg.min for the able-bodied (AB), paraplegics (PP) and quadriplegics (QP), respectively. Furthermore, reduced cardiovascular function was observed in the QP as evident in the low peak HR (109 b/min), peak SV (52 ml/b) and peak Q (5•71/min). Values for the QP were 64°0 and 64°0 peak HR, 89°() and 50°0 peak SV and 54()() and 33 () o peak Q of values observed for the PP and AB groups, respectively. The peak SV and Q values were significantly lower (P < 0•05) for the PP group when compared with the AB group. Although not statistically significant the estimated a-v O2 dzfference was higher for both spinal cord injured groups (14•0 and 14•6 ml O2/100 ml, PP and QP respectively). The impaired work capacity and reduced oxygen transport and utilisation of the QP group can be attributed to impaired sympathetic cardiac stimulation and a smaller available active muscle mass.

espanolIntroduccion: La preeclampsia (PE) se acompana de cambios en la funcion cardiovascular (FCV). Sin embargo, es desconocido si los cambios preceden y persisten a la manifestacion clinica de PE. Objetivos: Evaluar las diferencias en la FCV, en la semana 22 de gestacion (22sg) y un ano posterior al parto (1app) en las pacientes que evolucionaron a la PE vs. a la normotension (N). Tambien, la asociacion entre la FCV en 22sg y la evolucion a PE. Material y metodos: Estudio prospectivo, que incluyo 260 primiparas normotensas. Se midio en la semana 22sg y a 1app: laboratorio de rutina, proteinuria de 24horas, presion arterial (PA). Por cardiografia por impedancia: indice cardiaco (IC) y de resistencia vascular sistemica (IRVS), velocidad de onda de pulso (VOP). Se formaron 3 grupos segun la evolucion a: PE, G1, HTA gestacional (HG) G2, y N, G3. Los resultados se presentan como media ± DS, ANOVA y test post hoc, p Resultados: 12 pacientes evolucionaron a PE, 18 a HG y 220 a N. El G1 p...

Introduction and objective. Difficult-to-control blood pressure can be attributed to a mismatch between the haemodynamic type of hypertension and the drug class used in treatment. Impedance cardiography may be a useful tool for enabling the individualization of antihypertensive therapy. The aim was to investigate the distribution of haemodynamic types of HT among hypertensive patients in an outpatient clinic. Materials and method. This was a prospective, observational study of patients with primary hypertension at an outpatient clinic. A 10-minute ICG examination was performed in 189 consecutive, patients (118 men and 71 women). Patients were divided into groups based on whether their hypertension was well-controlled (140/90 mmHg, n=95). They were also stratified according to haemodynamic states. Results. Patients with poorly controlled blood pressure compared to patients with well controlled blood pressure had a high haemodynamic output in 6.3% vs. 2.1% (p=0.153), and high vascular resistance in 41.1% vs. 27.7% (p=0.037), and balanced haemodynamic states in 52.6% vs. 70.2% (0 80 beats/min) and fluid retention (p<0.01). Conclusions. Half of the examined patients did not achieve the therapeutic goals for hypertension treatment. Differences in haemodynamic state of well and poor controlled hypertension groups suggests the usefulness of impedance cardiographytargeted hypertension treatment.

Impedance Cardiography (ICG) is a non-invasive tool for continuous hemodynamic monitoring. Aims of our study were to assess the utility of ICG to evaluate the hemodynamic impact of 6 mg (GL6) vs 8 mg (GL8) levobupivacaine combined with fentanyl in healthy patients undergoing elective cesarean section; secondary, to compare the duration and quality of analgesia and anesthesia. Sixty-two women receiving combined spinal-epidural (CSE) for elective cesarean delivery were randomly allocated to GL6 or GL8 groups. Mean arterial pressure (MAP), cardiac index (CI), systemic vascular resistance index (SVRI), heart rate (HR), stroke volume index (SVI) were recorded from Tbaseline to 31 min after CSE by ICG. Sensory and motor blocks, patients and surgeons satisfaction, neonatal data were also recorded. Fifteen of 32 patients in GL6 and 15 of 30 patients in GL8 experienced hypotension at T2 vs Tbaseline (P &lt; .001) and SVRI reduction (P = .035 and P &lt; .001 respectively). MAP, CI and SVRI we...