Transthoracic Impedance Cardiography Research Articles

Prognostic Value of Transthoracic Impedance Cardiography, Amino-Terminal Pro-B-Type Natriuretic Peptide Levels, The Six-Minute Walk Test, and Chest X-Ray in Elderly Patients with Chronic Heart Failure: A Comparative Study in Lithuania.

BACKGROUND Chronic heart failure (CHF) is a complex clinical syndrome associated with frequent, recurrent, and long-term hospitalizations. This study from a single center in Lithuania aimed to evaluate outcomes in 87 elderly patients hospitalized with CHF. The methods used included comparing transthoracic impedance cardiography (ICG), amino-terminal pro-B-type natriuretic peptide (NT-proBNP) levels, the six-minute walk test (6MWT), and dilatation of the right pulmonary artery on chest X-ray (dRPAcXR). MATERIAL AND METHODS The study sample consisted of 87 patients (49 men and 38 women). All subjects underwent 6MWT and ICG in addition to the standard CHF tests. The median duration of the follow-up was 23 months. Data about patient outcomes were gathered from the National Medical Record Database. RESULTS By multivariate Cox proportional analysis, thoracic fluid content (TFC) ≥41.1 1/kΩ (hazard ratio [HR] 32.354, 95% confidence interval [CI] 2.758-379.488), NT-proBNP ≥332.0 pmol/L (HR 4.739, 95% CI 1.656-13.559), 6-minute walk distance (6MWD) ≤203.5 m (HR 3.975, 95% CI 1.002-15.770), and dRPAcXR (HR 5.555, 95% CI 1.714-18.005) were associated with a poor prognosis in CHF patients (all P<0.05). The correlations between ICG and 6MWD and other non-invasive diagnostic tests examined in this study were weak to moderate. CONCLUSIONS TFC ≥41.1 1/kΩ, NT-proBNP ≥332.0 pmol/L, 6MWD ≤203.5 m, and dRPAcXR had a combined prognostic value in predicting cardiovascular death in patients with CHF. Therefore, these parameters may be of value in the assessment of the diagnosis and prognosis in this patient cohort.

The prognostic value of systemic vascular resistance in heart failure patients with permanent atrial fibrillation: a retrospective study

Heart failure (HF) and permanent atrial fibrillation (AF) interact mutually, exacerbating hemodynamic effects and causing adverse outcomes and increased healthcare costs. Monitoring hemodynamic indicators in patients with these comorbidities is crucial for effective clinical management. Transthoracic impedance cardiography (ICG) has been widely employed in assessing hemodynamic status in clinical settings. Given the limited research on the prognostic significance of ICG parameters in HF with permanent AF, we undertook this study. A total of 66 HF patients with permanent AF were included in this retrospective study, and the primary outcome was rehospitalization due to worsening HF within 180-day post-discharge. Cox regression analysis was performed to explore the connection between ICG-evaluated parameters and the outcome risk. Receiver operating characteristic (ROC) curve analysis determined the optimal cutoff values of risk factors, subsequently applied in plotting Kaplan Meier (KM) survival curves. Multivariate Cox regression analysis revealed that systemic vascular resistance (SVR) both on admission and at discharge independently predicted rehospitalization for worsening HF. ROC analysis established optimal SVR cutoff values: 320.89 (kPa s/L) on admission and 169.94 (kPa s/L) at discharge (sensitivity 70%, specificity 94.4%, area under the curve (AUC) 0.831, respectively, sensitivity 90%, specificity 55.6%, AUC 0.742). KM survival curves analysis showed that patients with SVR > 320.89 (kPa s/L) on admission had an 8.14-fold (P < 0.001) increased risk of the end-point event compared with those with SVR ≤ 320.89 (kPa s/L). Similarly, patients with SVR > 169.94 (kPa s/L) at discharge faced a risk elevated by 6.57 times (P = 0.002) relative to those with SVR ≤ 169.94 (kPa s/L). In HF patients with permanent AF, SVR measured by ICG emerges as an independent risk factor and clinical predictor for HF deterioration-related readmission within 180 days after discharge. Higher SVR levels, both upon admission and at discharge, correlate with an incremental rehospitalization risk.

Single-Center Study in Lithuania to Evaluate the Role of Transthoracic Impedance Cardiography in the Diagnosis and Outcome Evaluation of 301 Patients with Chronic Heart Failure Exacerbation.

BACKGROUND Scientific data regarding transthoracic impedance cardiography (ICG) parameters and its utility in patients with heart failure (HF) remains controversial. This study from a single center in Lithuania aimed to evaluate the role of ICG in the diagnosis and outcome evaluation of patients who were admitted to the hospital due to HF exacerbation. MATERIAL AND METHODS The sample consisted of 301 consecutive patients with a previous chronic HF diagnosis (166 men, 135 women) hospitalized for HF flare-ups. ICG data were compared to other noninvasive HF diagnostic tests. Data about patient outcomes were gathered from the Lithuanian Medical Record Database. RESULTS A weak correlation of amino-terminal pro-brain natriuretic peptide (NT-proBNP) with thoracic fluid content (TFC) and thoracic fluid content index (TFCI) was found (r=0.204, P<0.001 and r=0.207, P<0.001, respectively). There was weak to moderate correlation of 6-min walk distance with main ICG data. There was weak correlation between left ventricular ejection fraction (LVEF) with TFCI (r=-0.163, P=0.005), systolic index (r=-0.137, P=0.017), and systolic time ratio (r=0.236, P<0.001). By multivariate Cox proportional analysis, the following parameters were independently associated with cardiac death (P<0.001): NT-proBNP ≥425.5 pmoL/L (hazard ratio (HR), 5.104, 95% confidence interval (CI) 3.326-7.832), TFC ≥36.9 1/kOhm (HR, 4.604, 95% CI 2.701-7.849), LVEF ≤40% (HR, 4.942, 95% CI 2.8256-8.647). CONCLUSIONS The combination of non-invasively measured TFC, LVEF, and NT-proBNP showed great prognostic value for predicting readmissions and cardiac death in patients with HF.

Effect of acupuncture on the haemodynamic system in men.

Acupuncture stimulation decreases heart rate (HR) through somato-autonomic reflexes. However, the mechanisms responsible for other cardiovascular changes induced by acupuncture, such as its effects on stroke volume (SV) and blood pressure (BP), remain obscure. To evaluate continuously the comprehensive cardiovascular changes occurring during acupuncture. 20 healthy men participated in the study. HR, SV and BP were measured in the supine position using electrocardiogram, transthoracic impedance cardiography and continuous non-invasive finger blood pressure, respectively. Manual acupuncture stimulation using a stainless steel needle was performed at LI10 for 60 s after resting periods of approximately 15 min. HR was reduced and SV increased, in parallel, during the period of acupuncture stimulation (P<0.01, respectively). Diastolic blood pressure (DBP) decreased in the 10 s period of acupuncture stimulation compared with the 120 s pre-stimulation period (P<0.01) and recovered close to the pre-stimulation reading instantly after the transient reduction. No change was observed in cardiac output (CO) derived from HR and SV. This study indicates that HR reduction during acupuncture does occur, as previous reports have indicated. SV increased during acupuncture stimulation in parallel with HR reduction and CO was maintained during these changes. Any reduction in DBP caused by acupuncture recovered to baseline, likely due to baroreflexes.

Diagnostic and Outcome Prediction Value of Transthoracic Impedance Cardiography in Heart Failure Patients During Heart Failure Flare-Ups.

BackgroundThis study aimed at evaluating the diagnostic and outcome prediction value of transthoracic impedance cardiography (ICG) in heart failure (HF) patients admitted for in-hospital treatment due to flare-ups of their condition.Material/MethodsIn total, 120 patients of intensive care units who were admitted due to HF flare-ups were involved to the study. The findings of ICG were compared to data obtained by other methods used for diagnosing HF.ResultsStatistically significant (p<0.001) results were obtained when evaluating differences in ICG data between admission and discharge from the intensive care unit. In addition, a correlation was detected between brain natriuretic peptide (BNP) and thoracic fluid content index (r=0.4, p<0.001). Differences in ICG values, and BNP data emerged after the participants were grouped according to NYHA classes (p<0.05). The evaluation of lethal outcome during 6 months after the discharge yielded statistically significant results: BNP ≥350 pg/mL (Odds Ratio (OR) 4.4), thoracic fluid content ≥34 1/kOhm (OR 4.3), and systolic time ratio ≥0.55 (OR 2.9), p<0.05.ConclusionsICG data might be applied for the diagnosis and prognosis of HF, although the links between ICG and HF need further evaluation.

Applicability of Impedance Cardiography During Heart Failure Flare-Ups.

BackgroundHeart failure (HF) accounts for about 5% of all causes of urgent hospital admissions, and the overall mortality of HF patients within 1 year after hospitalization is 17–45%. Transthoracic impedance cardiography (ICG) is a safe, non-invasive diagnostic technique that helps to detect various parameters that define different cardiac functions. The aim of this study was to investigate the value of ICG parameters in patients hospitalized due to HF flare-ups.Material/MethodsThe study included 60 patients (24 women and 36 men) who were admitted to intensive care units because of an acute episode of HF without signs of myocardial infarction. The diagnosis of HF as the main reason for hospitalization was verified according to the universally accepted techniques. ICG data were compared to those obtained via other HF diagnostic techniques.ResultsA moderately strong relationship was found between the ejection fraction (EF) and the systolic time ratio (STR) r=−0.4 (p=0.002). Findings for STR and thoracic fluid content index (TFCI) differed after dividing the subjects into groups according to the EF (p<0.05). A moderately strong relationship was found between brain natriuretic peptide and TFCI r=0.425 (p=0.001), left cardiac work index (LCWI) r=−0.414 (p=0.001). Findings for TFCI, LCWI, and cardiac output differed after dividing the subjects into groups according to HF NYHA classes (p<0.05).ConclusionsTransthoracic impedance cardiography parameters could be applied for the diagnostics and monitoring of HF, but further studies are required to evaluate the associations between ICG findings and HF.

A hybrid approach for quantifying aortic valve stenosis using impedance cardiography and echocardiography.

BackgroundImpedance cardiography (IC) is a noninvasive modality that utilizes changes in impedance across the thorax to assess hemodynamic parameters, including stroke volume (SV).This study compared aortic valve area (AVA) as assessed by a hybrid approach of transthoracic echocardiography (TTE) and impedance cardiography (IC) to AVA determined at cardiac catheterization using the Gorlin equation.MethodsA total of 30 patients with moderate to severe aortic stenosis underwent AVA measurement using two different approaches: using the continuity equation (CE) in a hybrid method combining IC and TTE (AVA = stroke by volume impedance cardiography/trans-aortic-VTI) and using the Gorlin equation. Patient age ranged from 37 to 82 years (mean 48); there were 21 men and 9 women. Twenty-five patients were in sinus rhythm, and five had atrial fibrillation.ResultsThere was no statistically significant difference for the mean AVA between the two methods (0.7 ± 0.24 cm2 using the Gorlin equation versus 0.7 ± 0.23 cm2 using the hybrid approach, p = 0.17; r = 0.76, p < 0.001). The mean difference was 0.004 cm2, and the limits of agreement were −0.33 to 0.37.ConclusionThe hybrid method using impedance cardiography and TTE is a reasonable, clinically applicable approach to evaluate AVA and has significant correlation to invasive measurement using the Gorlin equation.

Use of transthoracic impedance cardiography and tissue Doppler echocardiography in the cardiovascular assessment of atrial fibrillation patients subjected to electroversion

Atrial fibrillation (AF) is the commonest complex cardiac arrhythmia, affecting approximately 2% of the general population. To describe cardiovascular changes in tissue Doppler echocardiography (TDE) and impedance cardiography (ICG) in AF patients subjected to cardioversion. Forty-one patients (22 males and 19 females) with acute or persistent AF were examined by means of TDE and transthoracic ICG before electroversion, and then one week following the restoration of sinus rhythm. Additionally, the preand post-cardioversion serum levels of B-type natriuretic peptide (BNP) were determined. The restoration of sinus rhythm was reflected by a significant increase in the following ICG parameters (average changes are presented): stroke volume (+25 mL), stroke volume index (+11.8 m/m²), contractility index (+12.6/s), end-diastolic index (+12.3 mL/m²), acceleration index (+6/s²), and left ventricular ejection time (+56 ms). These changes were accompanied by a significant increase in the TDE parameters of tricuspid annular systolic velocity and mitral annular systolic velocities. Moreover, a significant decrease in early diastolic velocities was also observed following the restoration of sinus rhythm, along with significantly lower levels of BNP. Both TDE and ICG are modern, valuable diagnostic methods that complementarily explain changes occurring in the cardiovascular system of AF patients subjected to electroversion.

Bioimpedância transtorácica comparada à ressonância magnética na avaliação do débito cardíaco

Cardiac magnetic resonance imaging is considered the gold-standard method for the calculation of cardiac volumes. Transthoracic impedance cardiography assesses the cardiac output. No studies validating this measurement, in comparison to that obtained by magnetic resonance imaging, are available. To evaluate the performance of transthoracic impedance cardiography in the calculation of the cardiac output, cardiac index and stroke volume using magnetic resonance imaging as the gold-standard. 31 patients with a mean age of 56.7 ± 18 years were assessed; of these, 18 (58%) were males. Patients whose indication for magnetic resonance imaging required pharmacologic stress test were excluded. Correlation between methods was assessed using the Pearson's coefficient, and dispersion of absolute differences in relation to the mean was demonstrated using the Bland-Altman's method. Agreement between methods was analyzed using the intraclass correlation coefficient. The mean cardiac output by transthoracic impedance cardiography and by magnetic resonance imaging was 5.16 ± 0.9 and 5.13 ± 0.9 L/min, respectively. Good agreement between methods was observed for cardiac output (r = 0.79; p = 0.0001), cardiac index (r = 0.74; p = 0.0001) and stroke volume (r = 0.88; p = 0.0001). The analysis by the Bland-Altman plot showed low dispersion of differences in relation to the mean, with a low amplitude of agreement intervals. Good agreement between the two methods was observed when analyzed by the intraclass correlation coefficient, with coefficients for cardiac output, cardiac index and stroke volume of 0.78, 0.73 and 0.88, respectively (p < 0.0001 for all comparisons). Transthoracic impedance cardiography proved accurate in the calculation of the cardiac output in comparison to cardiac magnetic resonance imaging.

No relevant cardiac, pharmacokinetic or safety interactions between roflumilast and inhaled formoterol in healthy subjects: an open-label, randomised, actively controlled study.

BackgroundRoflumilast is an oral, selective phosphodiesterase 4 inhibitor with anti-inflammatory effects in chronic obstructive pulmonary disease (COPD). The addition of roflumilast to long-acting bronchodilators improves lung function in patients with moderate-to-severe COPD. The present study investigated drug-drug interaction effects between inhaled formoterol and oral roflumilast.MethodsThis was a single-centre (investigational clinic), open, randomised, multiple-dose, parallel-group study. In Regimen A, healthy men were treated with roflumilast (500 μg tablet once daily; Day 2-18) and concomitant formoterol (24 μg twice daily; Day 12-18). In Regimen B, healthy men were treated with formoterol (24 μg twice daily; Day 2-18) and concomitant roflumilast (500 μg once daily; Day 9-18). Steady-state plasma pharmacokinetics of roflumilast, roflumilast N-oxide and/or formoterol (Cmax and AUC0-τ) as well as pharmacodynamics - blood pressure, transthoracic impedance cardiography (ZCG), 12-lead digital electrocardiography, peripheral blood eosinophils, and serum glucose and potassium concentrations - were evaluated through Day 1 (baseline), Day 8 (Regimen B: formoterol alone) or Day 11 (Regimen A: roflumilast alone), and Day 18 (Regimen A and B: roflumilast plus formoterol). Blood and urine samples were taken for safety assessment at screening, pharmacokinetic profiling days and Day 19. Adverse events were monitored throughout the study.ResultsOf the 27 subjects enrolled, 24 were evaluable (12 in each regimen). No relevant pharmacokinetic interactions occurred. Neither roflumilast nor formoterol were associated with significant changes in cardiovascular parameters as measured by ZCG, and these parameters were not affected during concomitant administration. Formoterol was associated with a slight increase in heart rate and a corresponding shortening of the QT interval, without changes in the heart rate-corrected QTc interval. There were small effects on the other pharmacodynamic assessments when roflumilast and formoterol were administered individually, but no interactions or safety concerns were seen after concomitant administration. No severe or serious adverse events were reported, and no adverse events led to premature study discontinuation.ConclusionsNo clinically relevant pharmacokinetic or pharmacodynamic interactions were found when oral roflumilast was administered concomitantly with inhaled formoterol, including no effect on cardiac repolarisation. Roflumilast was well tolerated.Trial RegistrationClinicaltrials.gov NCT00940329

Noninvasive Hemodynamic Monitoring by Transthoracic Impedance Cardiography During Different Ventricular Activation Sequences in CRT Patients

Background: Echocardiography-based programming of conduction delays in cardiac resynchronisation therapy is complex and time-consuming. Impedance cardiography (ICG) may be an alternative method. However, it is unknown whether ICG is sensitive enough to detect haemodynamic changes due to different pacing-induced ventricular activation modes. The aim of this study was to determine the ability of ICG to measure haemodynamic changes during different ventricular pacing modes in patients with a cardiac resynchronisation therapy (CRT). Methods: 18 patients were evaluated. Stroke volume (SV), cardiac output (CO) and total peripheral resistance (TPR) were measured by means of ICG. Continuous blood pressure (cBP) was recorded with the vascular unloading technique. Haemodynamic measurements of 10-minute-sampling periods, taken in the supine position, were compared during biventricular (BIV), right (RV) and left ventricular (LV) pacing and intrinsic rhythm (IR). Results: One patient was excluded from the analysis (serious haemodynamic deterioration during IR). The age of the study population was 67 ± 10 years (94% male) with a LV ejection fraction of 26 ± 6%. The majority had left-bundle-branch block (82%). Compared to IR, BIV increased SV (58 ± 11 vs 67 ± 12 ml; p = 0.0007), CO (3.6 ± 0.7 vs 4.2 ± 0.8 l/min; p = 0.0007) and reduced TPR (1975 ± 410 vs 1694 ± 390 dyn*s/cm5). cBP remained unchanged during different ventricular pacing modes. Conclusion: ICG is able to detect intraindividual changes of haemodynamic parameters induced by different pacing modes. However, its sensitivity to detect haemodynamic changes through conduction delay variations, as performed for device optimisation, remains unclear. Introduction

Impedance cardiography: a role in vasovagal syncope diagnosis?

vasovagal syncope is the most common cause of syncope in all age groups, with diagnosis usually based on history, examination and basic investigations to exclude alternative causes of syncope. Where doubt exists, the head-up tilt (HUT) test is used for diagnosis but is time consuming and lacks a gold standard to accurately assess sensitivity and specificity. Alternative methods of diagnosing vasovagal syncope would thus be useful. to investigate the potential for impedance cardiography (ICG)-derived haemodynamic measures to predict HUT test outcome in unexplained syncope. prospective controlled study. eighty-six patients with unexplained syncope and 43 non-syncopal controls. all subjects underwent continuous heart rate, blood pressure and ICG measurements during 10 min supine rest and during HUT. Vasovagal syncope was diagnosed when patients experienced symptom reproduction with concomitant haemodynamic derangements. during rest prior to HUT, the syncopal group had higher mean heart rate (P = 0.0008) and lower baroreceptor effectiveness index (P < 0.0001) compared to non-syncopal controls. On comparing patients who presented with unexplained syncope who subsequently had a positive HUT (therefore a diagnosis of vasovagal syncope 55 [64%]; mean age 47 years, range 17-85) to those having a negative tilt test (n = 31; mean age 47 years, range 17-88), there were no significant differences found in cardiovascular or autonomic parameters prior to HUT. A predictive ROC curve model at a 85% threshold allowed using cardiac index (CI), end-diastolic index (EDI) and left ventricular work index (LVWI) would identify those who would have a positive HUT from baseline cardiovascular measurements (CI >3.5, EDI > 77, LVWI >4.7) with 93% sensitivity and 17% specificity. supine haemodynamic measures derived from transthoracic ICG can simply, non-invasively and sensitively differentiate HUT-positive patients from those with negative tilt tests. Further work is needed, particularly in older patients, before this technique can be used in clinical practice.

Cardiovascular effects of (R)- and (S)-verapamil and racemic verapamil in humans: a placebo-controlled study

To characterise the comparative potency of optically pure (R)- and (S)-verapamil as regards negative dromotropic effects on atrioventricular (AV) node conduction and to compare the hemodynamic effects of single doses of the enantiomers in healthy volunteers. Eight healthy volunteers received a single oral dose of 120 mg (S)-verapamil, 480 mg (R)-verapamil, 240 mg racemic verapamil (rac-verapamil) or placebo on 4 separate occasions. Serum concentrations of (R)- and (S)-verapamil were measured up to 24 h. Cardiovascular effects were assessed by electrocardiography, measurement of blood pressure and transthoracic impedance cardiography (cardiac output and total peripheral resistance). The comparative potency of (R)- and (S)-verapamil with regard to prolongation of the PR interval in the surface ECG was estimated by use of the areas under the effect-time and serum concentration-time curves and linear regression analyses of per cent change in PR interval from baseline versus the logarithm of serum (R)- or (S)-verapamil concentration. The PR interval was significantly prolonged after all verapamil treatments as compared with placebo. (S)-verapamil was 20.6-21.8 times more potent than (R)-verapamil with regard to negative dromotropic effects. (R)-verapamil caused a significantly greater maximum reduction in the mean arterial pressure (MAP) than placebo [15.9+/-6.8 versus 8.7+/-3.2 mmHg (mean+/-SD); 95% CI on the difference, 0.79-13.7 mmHg; p<0.05], whereas MAP was not affected by the other verapamil treatments. No significant changes were observed in heart rate, cardiac output and total peripheral resistance after any verapamil treatment as compared with placebo. (S)-verapamil was about 20 times more potent than (R)-verapamil with regard to negative dromotropic effects on AV node conduction. (R)-verapamil but not (S)-verapamil significantly reduced the MAP as compared with placebo.

Early Diagnosis of Pulmonary Circulatory Disorders in Acute Lung Lesions in Critically Ill Patients

The most severe sequels of acute lung lesions are manifested by the impairment of ventilation-perfusion relations, by the development of primary pulmonary hypertension, by circulatory disorders and the increased content of extravascular fluid in the lung, whose diagnosis is extremely difficult. The purpose of the study was to access the capacities of early diagnosis of systemic hemodynamic and pulmonary circulatory disorders in acute lung lesion in patients with critical states. Hydro- and hemodynamics was evaluated in 32 persons in the early phase of intoxications with neurotropic poisons, in 15 with severe concomitant injury, and in 22 patients with critical states intensively treated cardiac surgery. Hemodynamics was determined, by concomitantly using the integral body rheography technique after M. I. Tishchenko and transthoracic impedance cardiogra-phy. The rheographic techniques could evaluate the state of systemic hemodynamics, the nature and effectiveness of pulmonary pulsatile blood flow, that depended on pulmonary hypertension, and increased thoracic fluid. The determination of the level of lactate and its arterial and venous blood ration with consideration of lactate clearance enabled the authors to evaluate both the effectiveness of systemic perfusion and impaired metabolic processes in the lung. Drastically decreased pulsatile blood flow, ineffective volumetric load, low oxygenation index, increased thoracic fluid volume, and the ratios of the arterial to venous blood concentration of lactate with its normal clearance may be early signs of acute lung lesion.

Oscillations in Stroke Volume and Cardiac Output Arising from Oscillatory Ventilation in Humans

Oscillations in the cardiovascular system have been observed in patients with periodic breathing. It is not clear whether these are driven by primary oscillations in the respiratory system or whether an intrinsic cardiovascular instability is required, as previous studies with subjects performing voluntary periodic breathing have failed to produce the cardiovascular oscillations. We investigated whether cardiovascular oscillations occurred in healthy controls performing voluntary periodic breathing. Six healthy subjects performed voluntary periodic breathing with guidance from a real-time computer display. We measured ventilation, end-tidal partial pressures of O2 (PO2) and CO2 (PCO2), heart rate, blood pressure (BP), arterial oxygen saturation and stroke volume and cardiac output by transthoracic impedance cardiography. Fourier analysis was used to quantify the size and phase of the periodic breathing-induced oscillations in these parameters. Periodic breathing (amplitude 30% of mean ventilation) induced oscillations in end-tidal PO2 (amplitude 0.8 kPa), end-tidal PCO2 (amplitude 0.3 kPa), R-R interval (amplitude 32.6 ms), systolic BP (amplitude 3 mmHg), diastolic BP (amplitude 3 mmHg), stroke volume (amplitude 8.0 ml, mean 79.5 ml) and cardiac output (amplitude 0.6 1, mean 5.9 l x min(-1)). The oscillations in stroke volume and cardiac output were nearly in phase with ventilation, with their peaks occurring 5.6 and 6.1 s, respectively, after the peak in ventilation. An oscillatory ventilatory pattern entrains the cardiovascular system in healthy controls into fluctuations, not only in heart rate and BP, but also in stroke volume and cardiac output.

Impedance cardiography applied to maximal arm cranking exercise: a matter of sampling and processing strategy.

A new ensemble-averaging (EA) approach was developed with the goal of investigating central hemodynamics by transthoracic impedance cardiography during maximal arm cranking. This EA procedure of the first time derivative of impedance changes (dZ/dt) over several cardiac cycles differs from previously reported techniques with respect to cycle selection strategy, according to fixed criteria, and processing methods. First, the primary elements of the Kubicek stroke volume (SV) formula, as determined by EA, were compared with the values determined by the standard hand-processing (HP) method over a large range of cardiac outputs. Results showed a very high reliability for ventricular ejection time (r = 0.996), (dZ/dt)min (r = 0.995), SV (r = 0.977), and heart rate (r = 0.999). Second, the EA procedure was applied to six subjects performing a continuous, multistage arm cranking test to volitional fatigue. The present technique allowed for an effective filtering of movement and breathing artifacts of the original signal. Thus, interpretation of the dZ/dt wave form was convenient, even at maximal arm cranking power outputs up to 120 W. Stroke volume ranged from 63.83 to 127.18 mL.beat-1, showing no significant variations with oxygen consumption. Cardiac output increased linearly with oxygen uptake, reaching a mean maximal value of 16 L.min-1. The present procedure opens a new field of application to impedance cardiography, permitting to measure cardiac output during maximal arm cranking exercise.

HEMODYNAMIC RESPONSES TO EXERCISE IN CHILDREN OF HYPERTENSIVE PARENTS 91

This study was designed to investigate whether children with a positive parental history of hypertension exhibit an elevated resting blood pressure(BP) or an exaggerated BP response during dynamic submaximal exercise. We studied 11 children (12.0 ± 2.4 yrs) of at least one hypertensive parent and 11 children (12.2 ± 1.8 yrs; M ± SE) of normotensive parents who served as the control group. On separate days, each subject completed a graded cycle test to maximal effort and a submaximal exercise bout consisting of 6 min each of steady state cycling at 50 and 80% of maximal heart rate reserve. BP, cardiac output (CO), and total peripheral resistance(TPR) were measured at rest and during the last 3 min of each submaximal exercise stage. CO was determined using transthoracic impedance cardiography, BP was measured by auscultation, and TPR was calculated as mean arterial pressure (MAP) divided by CO. The data were analyzed using an independent t-test and a 2-way (group x intensity) ANOVA. The groups were similar in age, weight, height, and body fatness (p<0.05). At rest, the positive history group had higher systolic BP, diastolic BP (DBP), and MAP (p<0.05). MAP and DBP remained significantly higher throughout exercise. Although differences between groups were not statistically significant, TPR was consistently higher(15-20%) in the positive history group at rest and during exercise, while CO tended to be slightly lower during exercise (p>0.05). In conclusion, children of at least one hypertensive parent exhibit a significantly higher MAP and DBP at rest and during submaximal exercise. The elevated BP in the positive history group may be due to an early trend towards a higher TPR at rest and during exercise.

Non-Invasive Monitoring of Hemodynamic Parameters during Hemodialysis

We studied in 13 hemodialysis patients intradialytic variations of blood volume (BV) and cardiac output, by means of non-invasive methods. We found a weak correlation, r 0.2 or less, between BV variations and intradialysis blood pressure variations. The sensitivity of the former in describing the variations of the latter was only 32%. During the 30 min preceeding the hypothensive crisis the percent BV variations did not show any predictive trend. On the contrary, refilling increased as blood pressure dropped and a weak inverse relation (r -0.35) was found between these two parameters. Unstable patients had predialytic blood volume values significantly lower than stable ones and comparable to healthy subjects. On the contrary, the correlation between percent variations of cardiac output index and MAP was 0.68 with a sensitivity and specificity of 90% and 59%, respectively. Unfortunately these promising results were obtained only with an estimate of cardiac output obtained by echocardiography and not by transthoracic impedance cardiography, which is much more feasible than the former as on-line monitoring of cardiac output. On-line monitoring of hemodynamic parameters is an appealing but still unsolved task.

Competitive sports activities improve cardiocirculatory performance in insulin‐dependent diabetics

By means of noninvasive transthoracic impedance cardiography, the cardiovascular profile of two groups of male asymptomatic and glycometabolic‐compensated insulin‐dependent diabetics (IDD), one composed of five untrained patients (UD) and the other of five athletes trained for aerobic‐anaerobic sports (TD), was studied during a cycle ergometer progressive exercise up to a submaximal work rate corresponding to a heart rate (HR) of 130 beats/ min (W 130). At rest, although HR and arterial blood pressure were similar in the two groups, values for TD were higher than for UD in stroke volume (SI, +14%) and cardiac output (CI, +26%) index expressed per m2 of body surface area, impedance‐derived cardiac work indicator (CWI, +24%), impedance‐derived heart mechanical efficiency indicator (HEI, +16%), impedance‐derived ventricle preload indicator (PLI, +12%), and those for TD were lower than for UD in impedance‐derived total peripheral resistance indicator (TPRI, ‐24%) and impedance‐derived myocardial contractility...

Impedance cardiography by use of a spot-electrode array to track changes in cardiac output in anesthetized dogs

Summary Transthoracic impedance cardiography is a noninvasive method to determine changes in cardiac output on the basis of the cardiac-induced impedance change measured across the thorax. In this report, we describe a new, easily applied, tetrapolar spot-electrode configuration for use in canine transthoracic impedance cardiography. The array is a convenient alternative to use of the traditional circumferential band-electrode array which, in the dog, is prohibitive because of the extensive skin preparation required. The spot-electrode array was used to compare changes in cardiac output measured by transthoracic impedance cardiography, with changes measured by a reference indicator-dilution technique. A spot-electrode array, composed of 4 standard ECG electrodes, was used to measure transthoracic impedance in 10 anesthetized dogs. Variations in cardiac output were produced by controlled hemorrhage (200- to 250-ml increments). Simultaneous reference measurements of cardiac output were made before hemorrhage (control) and at each level of hemorrhage, using the saline-dilution method. The beat-by-beat impedance changes were measured by use of a Minnesota impedance cardiograph, which also recorded the first derivative of impedance (dZ/dt). An index of cardiac output was defined as the product of the maximal value of the first time derivative of impedance, ejection time, and heart rate for each beat during inscription of a saline-dilution curve. The average of the beat-bybeat indices was calculated and then normalized relative to the initial control value. Linear regression analysis was performed to evaluate the correlation of the index of cardiac output with the reference cardiac output. The slope and correlation coefficient for the pooled data were 0.90 and 0.92, respectively. These results indicate that changes in cardiac output can be tracked reliably in anesthetized dogs by transthoracic impedance cardiography by use of a convenient spotelectrode configuration.