Non-invasive assessment of stroke volume and cardiovascular parameters based on peripheral pressure waveform.

Cardiovascular diseases are the leading cause of death globally, making the development of non-invasive and simple-to-use tools that bring insights into the state of the cardiovascular system of utmost importance. We investigated the possibility of using peripheral pulse wave recordings to estimate stroke volume (SV) and subject-specific parameters describing the selected properties of the cardiovascular system. Peripheral pressure waveforms were recorded in the radial artery using applanation tonometry (SphygmoCor) in 35 hemodialysis (HD) patients and 14 healthy subjects. The pressure waveforms were then used to estimate subject-specific parameters of a mathematical model of pulse wave propagation coupled with the elastance-based model of the left ventricle. Bioimpedance cardiography measurements (PhysioFlow) were performed to validate the model-estimated SV. Mean absolute percentage error between the simulated and measured pressure waveforms was 4.0% and 2.8% for the HD and control group, respectively. We obtained a moderate correlation between the model-estimated and bioimpedance-based SV (r = 0.57, p<0.05, and r = 0.58, p<0.001, for the control group and HD patients, respectively). We also observed a correlation between the estimated end-systolic elastance of the left ventricle and the peripheral systolic pressure in both HD patients (r = 0.84, p<0.001) and the control group (r = 0.70, p<0.01). These preliminary results suggest that, after additional validation and possibly further refinement to increase accuracy, the proposed methodology could support non-invasive assessment of stroke volume and selected heart function parameters and vascular properties. Importantly, the proposed method could be potentially implemented in the existing devices measuring peripheral pressure waveforms.

Non-Invasive Assessment of Cardiodynamics by Impedance Cardiography during the Six-Minute Walk Test in Patients with Heart Failure. / Avaliação Cardiodinâmica Não Invasiva por Cardiografia de Impedância durante o Teste de Caminhada de Seis Minutos em Pacientes com Insuficiência Cardíaca.

BACKGROUND: Central Illustration: Non-Invasive Assessment of Cardiodynamics by Impedance Cardiography during the Six-Minute Walk Test in Patients with Heart Failure. The six-minute walk test (6MWT) is commonly used to evaluate heart failure (HF) patients. However, several clinical factors can influence the distance walked in the test. Signal-morphology impedance cardiography (SM-ICG) is a useful tool to noninvasively assess hemodynamics. OBJECTIVE: This study aimed to compare cardiac output (CO), heart rate (HR), and stroke volume (SV) acceleration and deceleration responses to 6MWT in individuals with HF and reduced ejection fraction (HFrEF) and healthy controls. METHODS: This is a cross-sectional observational study. CO, HR, SV and cardiac index (CI) were evaluated before, during, and after the 6MWT assessed by SM-ICG. The level of significance adopted in the statistical analysis was 5%. RESULTS: Twenty-seven participants were included (13 HFrEF and 14 healthy controls). CO and HR acceleration significantly differed between groups (p<0.01; p=0.039, respectively). We found significant differences in SV, CO and CI between groups (p<0.01). Linear regression showed an impaired SV contribution to CO change in HFrEF group (22.9% versus 57.4%). CONCLUSION: The main finding of the study was that individuals with HFrEF showed lower CO and HR acceleration values during the submaximal exercise test compared to healthy controls. This may indicate an imbalance in the autonomic response to exercise in this condition.

FUNDAMENTO: Figura Central: Avaliação Cardiodinâmica Não Invasiva por Cardiografia de Impedância durante o Teste de Caminhada de Seis Minutos em Pacientes com Insuficiência Cardíaca. O Teste de Caminhada de seis Minutos (TC6M) é comumente usado para avaliar pacientes com insuficiência cardíaca. No entanto, vários fatores clínicos podem influenciar a distância percorrida pelos pacientes no teste. A cardiografia de impedância (CI) na avaliação morfológica é uma ferramenta útil para avaliar a hemodinâmica cardíaca de maneira não invasiva. OBJETIVO: Este estudo teve como objetivo comparar as respostas de aceleração e desaceleração do Débito Cardíaco (DC), da Frequência Cardíaca (FC), e do Volume Sistólico (VS) ao TC6M de indivíduos com insuficiência cardíaca e fração de ejeção reduzida (ICFEr) com as de controles sadios. MÉTODOS: Este é um estudo transversal observacional. O DC, a FC, o VS e o Índice Cardíaco (IC) foram avaliados antes, durante e após o TC6M por CI. O nível de significância adotado na análise estatística foi 5%. RESULTADOS: Foram incluídos 27 participantes (13 com ICFEr e 14 controles sadios). A aceleração do DC e da FC foi significativamente diferente entre os grupos (p<0,01 e p=0,039, respectivamente). Encontramos diferenças significativas no VS, no DC e no IC entre os grupos (p<0,01). A regressão linear mostrou uma contribuição deficiente do VS à mudança no DC no grupo com ICFEr (22,9% versus 57,4%). CONCLUSÃO: O principal resultado deste estudo foi o fato de que indivíduos com ICFEr apresentaram valores mais baixos de aceleração do DC e da FC durante o teste de exercício submáximo em comparação a controles sadios. Isso pode indicar um desequilíbrio na resposta autonômica ao exercício nessa condição.

Hemodynamic differences between women and men with elevated blood pressure in China: A non-invasive assessment of 45,082 adults using impedance cardiography.

BACKGROUND: Whether there are sex differences in hemodynamic profiles among people with elevated blood pressure is not well understood and could guide personalization of treatment. METHODS AND RESULTS: We described the clinical and hemodynamic characteristics of adults with elevated blood pressure in China using impedance cardiography. We included 45,082 individuals with elevated blood pressure (defined as systolic blood pressure of ≥130 mmHg or a diastolic blood pressure of ≥80 mmHg), of which 35.2% were women. Overall, women had a higher mean systolic blood pressure than men (139.0 [±15.7] mmHg vs 136.8 [±13.8] mmHg, P<0.001), but a lower mean diastolic blood pressure (82.6 [±9.0] mmHg vs 85.6 [±8.9] mmHg, P<0.001). After adjusting for age, region, and body mass index, women <50 years old had lower systemic vascular resistance index (beta-coefficient [ß] -31.7; 95% CI: -51.2, -12.2) and higher cardiac index (ß 0.07; 95% CI: 0.04, 0.09) than men of their same age group, whereas among those ≥50 years old women had higher systemic vascular resistance index (ß 120.4; 95% CI: 102.4, 138.5) but lower cardiac index (ß -0.15; 95% CI: -0.16, -0.13). Results were consistent with a propensity score matching sensitivity analysis, although the magnitude of the SVRI difference was lower and non-significant. However, there was substantial overlap between women and men in the distribution plots of these variables, with overlapping areas ranging from 78% to 88%. CONCLUSIONS: Our findings indicate that there are sex differences in hypertension phenotype, but that sex alone is insufficient to infer an individual's profile.

A method for suppressing respiratory noise in impedance cardiography and comprehensive assessment of noise reduction performance.

Cardiac Output (CO) is a significant hemodynamic index for the diagnosis and treatment of cardiovascular diseases. Impedance cardiography (ICG) is one of the non-invasive methods widely investigated for its simplicity, cost-effectiveness and ability to measure cardiac output continuously. However, measured ICG signals are contaminated by the respiratory artefact leading to difficulties in determining characteristic points in the signal waveform, thereby lowering the accuracy of measurement results. Thus, suppressing this artefact plays an important role in ICG signal processing. This paper aims to propose a method of noise filtering to improve the quality of the signal as well as a model to evaluate the noise filtering efficiency of the method. The proposed algorithm showed promising results with the output SNR values of 21.99 ± 3.20 dB, 20.40 ± 2.88 dB, 15.57 ± 4.79 dB for normal breathing, forced breathing, and rapid breathing respectively. The root mean square percentage error (RMSPE) values of the output signals processed by the proposed algorithm compared to the standard ICG signal source for normal breathing, forced breathing, and rapid breathing are 24.13 ± 22.66%, 18.09 ± 12.98%, 32.13 ± 20.40% respectively. The quality-enhanced ICG signal could be effective tool for assisting doctors to detect cardiac abnormalities via evaluating the morphology of ICG signal waveforms as well as improving accuracy in calculating beat-to-beat and averaged hemodynamic parameters.

Cushing's Disease: Assessment of Early Cardiovascular Hemodynamic Dysfunction With Impedance Cardiography.

Background: Cushing's disease is a rare condition associated with a high cardiovascular risk and hypercortisolemia-related hemodynamic dysfunction, the extent of which can be assessed with a noninvasive method, called impedance cardiography. The standard methods for hemodynamic assessment, such as echocardiography or ambulatory blood pressure monitoring may be insufficient to fully evaluate patients with Cushing's disease; therefore, impedance cardiography is being currently considered a new modality for assessing early hemodynamic dysfunction in this patient population. The use of impedance cardiography for diagnosis and treatment of Cushing's disease may serve as personalized noninvasive hemodynamic status assessment and provide a better insight into the pathophysiology of Cushing's disease. The purpose of this study was to assess the hemodynamic profile of Cushing's disease patients and compare it with that in the control group. Material and Methods: This observational prospective clinical study aimed to compare 54 patients with Cushing's disease (mean age 41 years; with 64.8% of this population affected with arterial hypertension) and a matched 54-person control group (mean age 45 years; with 74.1% of this population affected with arterial hypertension). The hemodynamic parameters assessed with impedance cardiography included the stroke index (SI), cardiac index (CI), systemic vascular resistance index (SVRI), velocity index (VI), (ACI), Heather index (HI), and thoracic fluid content (TFC). Results: The Cushing's disease group was characterized by a higher diastolic blood pressure and a younger age than the control group (82.9 vs. 79.1 mmHg, p=0.045; and 41.1 vs. 44.9 years, p=0.035, respectively). Impedance cardiography parameters in the Cushing's disease group showed: lower values of SI (42.1 vs. 52.8 ml/m2; p ≤ 0.0001), CI (2.99 vs. 3.64 l/min/m2; p ≤ 0,0001), VI (42.9 vs. 52.1 1/1000/s; p=0.001), ACI (68.7 vs. 80.5 1/100/s2; p=0,037), HI (13.1 vs. 15.2 Ohm/s2; p=0.033), and TFC (25.5 vs. 27.7 1/kOhm; p=0.006) and a higher SVRI (2,515 vs. 1,893 dyn*s*cm-5*m2; p ≤ 0.0001) than those in the control group. Conclusions: Cushing's disease is associated with significantly greater vasoconstriction and left ventricular systolic dysfunction. An individual assessment with impedance cardiography may be useful in Cushing's disease patients in order to identify subclinical cardiovascular complications of chronic hypercortisolemia as potential therapeutic targets.

OptiVol for Volume Assessment in Patients With Continuous Flow Left Ventricular Assist Device.

OptiVol (Medtronic PLC, Minneapolis, MN) is a diagnostic feature of some cardiac implantable electronic devices (CIEDs) based on changes in thoracic impedance (TI) over time. Changes in TI can predict heart failure (HF) hospitalizations and mortality in HF populations. However, the utility of this feature is unknown in patients with a left ventricular assist device (LVAD). To determine if OptiVol and TI correlate with clinical HF events in a population of LVAD patients, hospitalization outcomes were collected retrospectively from the electronic health records at a single academic medical center in 80 LVAD patients with an OptiVol-capable CIED. Demographics, medical history, and available clinical data were reviewed and reported. The primary outcomes of interest were TI and OptiVol trends before and after hospitalization, and association of trends before and after these events was evaluated. Most patients had a HeartMate II LVAD and most CIEDs were defibrillators, and 23 (29%) had at least one HF hospitalization during the study period. HF hospitalizations were preceded by signs of volume overload in Optivol (60%) and TI (78%) with recovery of these measures post hospitalization in 33% and 25% of patients, respectively. Monitoring of TI and OptiVol may be one effective component of HF management in LVAD patients as part of a comprehensive program.

Non-invasive assessment of haemodynamic parameters in patients after Fontan procedure.

INTRODUCTION AND OBJECTIVE: Single ventricle anomaly is one of the complex congenital heart defects. A dependable non-invasive method of evaluation of Fontan circulation haemodynamics for early diagnosing unstable patients is hardly available in routine clinical practice. The aim of the study is non-invasive evaluation of the haemodynamic parameters in patients after Fontan operation. MATERIAL AND METHODS: The study involved 11 participants (age 24.4±4.3 years) with functionally univentricular hearts after Fontan operation. Evaluation of haemodynamic parameters was performed in supine and sitting positions using the impedance cardiography method. RESULTS: In comparative analysis, heart rate (70.1 vs.78.3 1/min; p=0.001), diastolic blood pressure (73.9 vs. 76.7 mm Hg; p=0.026), mean arterial blood pressure (84.5 vs. 88.0 mm Hg; p=0.013), systemic vascular resistance (1284.8 vs. 1334.9 dyn*s*cm-5; p=0.024), systemic vascular resistance index (2178.7 vs. 2272.8 dyn*s*cm-5*m2 ; p=0.018), pre-ejection period (124.2 vs. 136.2 ms; p=0.009), systolic time ratio (0.43 vs. 0.53; p=0.0001), and Zo (26.2 vs. 28.7 Ω; p<0.00001), were significantly higher in the sitting position. Stroke volume (75.4 vs. 68.5 ml; p=0.013), stroke index (42.7 vs. 39.0 ml*m-2; p=0.014), thoracic fluid content (38.5 vs. 35.4 1*kΩ-1; p=<0.00001), thoracic fluid content index (22.8 vs. 21.0 1*kΩ-1*m-2; p=<0.00001), and leftventricular ejection time 291.1 vs. 260.1 ms; p <0.00001, were significantly higher in the supine position. CONCLUSIONS: In patients after Fontan procedure, impedance cardiography can be a useful tool the assessment of shortterm haemodynamic changes provoked by postural changes. Its clinical value in patients with congenital heart defects should be further investigated.

Clinical Use of Impedance Cardiography for Hemodynamic Assessment of Early Cardiovascular Disease and Management of Hypertension.

This article is for clinicians considering impedance cardiography (ICG) for secondary prevention. ICG is an inexpensive noninvasive technology that can be used to assess hemodynamic function of the central cardiovascular system. Diverse abnormalities of ventricular function, systolic and diastolic, can be detected by ICG. Additional data pertaining to decompensation can be obtained by taking ICG readings with the patient performing postural change, from upright to supine, to quantify the compensatory response. Vascular load consists of resistive and pulsatile loads. Systemic vascular resistance can provide a measure of resistive load. Pulsatile load has two components: arterial stiffness and wave reflection. ICG can be used to calculate arterial compliance and detect aortic wave reflection. For stage 1 hypertension, a significant issue is whether a treating clinician should add pharmacotherapy to lifestyle modification. Adults who have multiple cardiovascular risk factors with stage 1 hypertension have early cardiovascular disease. ICG can be used to identify the functional abnormalities associated with the cardiovascular disease. For the management of hypertension, ICG can be used to calculate the underlying hemodynamic parameters of cardiac index and systemic vascular resistance associated with a patient's blood pressure. There can be wide ranges for cardiac index and systemic vascular resistance, with many patients having low cardiac index with high systemic vascular resistance or vice versa. These hemodynamic data can be used to customize pharmacotherapy. Drug titration can be guided by patient response to treatment using the initial hemodynamic data as a baseline for comparison to subsequent measurements from serial office visits.

A Clinically Evaluated Interferometric Continuous-Wave Radar System for the Contactless Measurement of Human Vital Parameters.

Vital parameters are key indicators for the assessment of health. Conventional methods rely on direct contact with the patients' skin and can hence cause discomfort and reduce autonomy. This article presents a bistatic 24 GHz radar system based on an interferometric six-port architecture and features a precision of 1 µm in distance measurements. Placed at a distance of 40 cm in front of the human chest, it detects vibrations containing respiratory movements, pulse waves and heart sounds. For the extraction of the respiration rate, time-domain approaches like autocorrelation, peaksearch and zero crossing rate are compared to the Fourier transform, while template matching and a hidden semi-Markov model are utilized for the detection of the heart rate from sphygmograms and heart sounds. A medical study with 30 healthy volunteers was conducted to collect 5.5 h of data, where impedance cardiogram and electrocardiogram were used as gold standard for synchronously recording respiration and heart rate, respectively. A low root mean square error for the breathing rate (0.828 BrPM) and a high overall F1 score for heartbeat detection (93.14%) could be achieved using the proposed radar system and signal processing.

Accuracy of Impedance Cardiography for Hemodynamic Assessment During Rest and Exercise in Wheelchair Rugby Players.

Purpose: The aim of the study was to analyze the accuracy of impedance cardiography (ICG) for hemodynamic assessment in wheelchair rugby players during rest and exercise. Method: The study included 21 players (mean age 33.0 ± 5.4, 86% male) with posttraumatic tetraplegia. ECG, echocardiography, and gas exchange analysis during rest and exercise were used to obtain heart rate (HR), stroke volume (SV), and cardiac output (CO) for comparison with PhysioFlow®. Results: There was a good correlation between reference methods and ICG for HR, SV, CO at rest and CO at peak exercise (r = 0.69-0.77, p < .001) and a very good correlation for peak HR (r = 0.91, p < .0001). ICG overestimated SV at rest, CO at rest, and peak CO, which resulted in low intraclass correlation coefficients (ICC = 0.250 and 0.570). Conclusions: ICG can serve as a good estimate of basic hemodynamic parameters during rest and exercise in wheelchair rugby players but overestimates stroke volume and cardiac output.

Noninvasive assessment of Cardiac Index using impedance cardiography during liver transplantation surgery: a comparison with pulmonary artery thermodilution.

BACKGROUND: Liver transplantation (LT) is a high-risk surgery associated with significant hemodynamic changes requiring advanced hemodynamic monitoring. Pulmonary Artery Catheter (PAC) is still considered as a gold-standard for Cardiac Index (CI) measurement during LT despite association with an increased risk of complications. Noninvasive impedance cardiography (ICG) could be an interesting alternative tool for CI monitoring. The aim of this study was to compare the precision and trending ability of ICG versus PAC methods during LT. METHODS: Patients undergoing LT were prospectively included. CI was measured with PAC and ICG at 4 time points (T1: before surgical incision, T2: during anhepatic phase, T3: after portal reperfusion, T4: during wound closure). Bias and percentage error (PE) between CI measured with PAC and ICG were analyzed with the Bland-Altman method for repeated measurements. Trending ability was studied with 4-quadrant and polar plots and correlation coefficient. RESULTS: We included 43 patients with 156 measures. Mean bias was -0.95 L.min-1.m-2, SD±1.07, limits of agreement -3.73 to 1.83 L.min-1.m-2 and PE 58%. There was a significant increase in bias during LT (P<0.001). Assessment of trending ability displayed a concordance rate of 72% on the 4-quadrant plot and a mean angular bias of -8.4° (SD±28°) and radial limits of agreement ±55° on the polar plot. CONCLUSIONS: CI measurements using ICG exhibited a low precision and a poor trending ability when compared to thermodilution method during LT. Consequently, ICG is not an adequate hemodynamic tool to monitor CI during LT.

Complex assessment of patients with decompensated heart failure: The clinical value of impedance cardiography and N-terminal pro-brain natriuretic peptide.

BACKGROUND: Acute decompensated heart failure (ADHF) is a serious clinical problem and a condition requiring immediate diagnostics, supporting the therapeutic decision adequate to the specific ADHF mechanism. N-terminal pro-brain natriuretic peptide (NT-proBNP) is an established biochemical marker of heart failure, strongly related to hemodynamic status. Impedance cardiography (ICG) provides non-invasive hemodynamic assessment that can be performed immediately at the bedside and revealed to be useful diagnostic tool in some clinical settings in cardiology. OBJECTIVES: The aim of this study was to evaluate the usefulness of ICG in the admission diagnostics and monitoring the effects of treatment in patients hospitalized due to ADHF, with special emphasis on its relation to NT-proBNP. METHODS: This study enrolled 102 patients, aged over 18 years, hospitalized due to ADHF. The subjects underwent detailed clinical assessment, including ICG and NT-proBNP at admission and at discharge day. RESULTS: Among all analyzed ICG parameters thoracic fluid content (TFC), a marker of chest overload, was the most significantly correlated with NT-proBNP level (R = 0.46; p = 0.000001). In comparison with patients with low thoracic fluid content (TFC ≤ 35/kΩ), those with higher TFC values (>35/kΩ) exhibited a greater severity of symptoms (NYHA functional class); higher NT-proBNP levels; lower left ventricular ejection fraction (LVEF), stroke index (SI), and cardiac index (CI); as well as significantly higher systemic vascular resistance index (SVRI). These TFC-based subgroups showed no significant differences in terms of heart rate (HR), systolic blood pressure (SBP), or diastolic blood pressure (DBP). CONCLUSIONS: The evaluation of hemodynamic parameters, especially TFC, seems to be a worthwhile addition to standard diagnostics, both at the stage of hospital admission and while monitoring the effects of treatment. Impedance cardiography is a useful method in evaluating individual hemodynamic profiles in patients with ADHF.

Cardiovascular and Self-Regulatory Consequences of SES-Based Social Identity Threat.

This work examined the effects of socioeconomic status (SES)-based social identity threat on cardiovascular indexes of challenge and threat and self-regulatory strength. Participants ( N = 104) took an exam described as either diagnostic of intellectual ability (identity threat) or framed as a problem-solving task (control) while we recorded cardiovascular reactivity and assessed participants' physical self-control. Under identity threat, lower SES students exhibited impaired performance, reduced self-control, and cardiovascular threat reactivity. In contrast, higher SES students under threat exhibited the reverse pattern-a boost in performance, no change in self-regulation, and cardiovascular challenge reactivity. Furthermore, while measures of general arousal (heart rate and pre-ejection period) were unrelated to performance, cardiovascular patterns of challenge and threat were significantly associated with performance under identity threat. Results provide evidence that SES-based stigma influences physiological and self-regulatory processes.

Multiparameter assessment of exercise capacity in patients with arterial hypertension.

Introduction: Arterial hypertension (AH) can lead to the development of heart failure. Aim: Evaluating the relationship between parameters of exercise capacity assessed via a six-minute walk test (6MWT) and cardiopulmonary exercise test (CPET), with a hemodynamic assessment via impedance cardiography (ICG), in patients with AH. Methods: Exercise capacity was assessed in 98 hypertensive patients (54.5 ± 8.2 years) by means of oxygen uptake (VO2) get from CPET, 6MWT distance (6MWTd) and hemodynamic parameters measured by ICG: heart rate (HR), stroke volume (SV), cardiac output (CO). Correlations between these parameters at rest, at anaerobic threshold (AT) and at peak of exercise as well as their changes (Δpeak-rest, Δpeak-AT, ΔAT-rest) were evaulated. Results: A large proportion of patients exhibited reduced exercise capacity, with 45.9% not reaching 80% of predicted peak VO2 and 43.9% not reaching predicted 6MWTd. Clinically relevant correlations were noted between the absolute peak values and AT values of VO2 vs HR and VO2 vs CO. Furthermore ΔVO2(peak-AT) correlated with ΔHR(peak-AT), ΔCO(peak-AT) and ΔSV(peak-AT); ΔVO2(peak-rest) with ΔHR(peak-rest) and ΔCO(peak-rest); ΔVO2(AT-rest) with ΔHR(AT-rest) and ΔCO(AT-rest). Stronger correlations between changes in the evaluated parameters were demonstrated in the subgroup of subjects with peak VO2 < 80% of the predicted value; particularly ΔVO2(peak-AT) correlated with ΔSV(peak-AT) and ΔCO(peak-AT). Conclusions: The hemodynamic parameters show significant correlations with more measures of cardiovascular capacity of proven clinical utility. Impedance cardiography is a reliable method for assessing the cardiovascular response to exercise.

Stroke Volume, Ejection Fraction and Cardiac Health Monitoring using Impedance Cardiography.

In recent years occurrence of cardiac ailments have seen an exponential rise. In view of this it is highly important to monitor one's cardiac health. Currently employed methods for cardiac health monitoring are costly, require expert supervision and are available only at central hospitals. In order to overcome these obstacles, we have proposed a novel, non-invasive, cardiac health monitoring mechanism based on Impedance Cardiography (ICG). In this work we have proposed a methodolgy for determination of stroke volume (SV), left ventricular ejection fraction (LVEF), left ventricular end systolic volume (LVESV), and iso-volumetric relaxation time (IVRT), based on ICG. The proposed models report $\mathrm{r}^{2}$ values of 0.86, 0.97, 0.99, and 0.96 for SV, LVESV, LVEF, and IVRT, respectively. The proposed methodology also provides us an insight into the use of ICG for cardiac health monitoring, and diagnosis of critical cardiac ailments.

Circulation assessment by automated external defibrillators during cardiopulmonary resuscitation.

AIM: To design and evaluate a simple algorithm able to discriminate pulsatile rhythms from pulseless electrical activity during automated external defibrillator (AED) analysis intervals, using the ECG and the transthoracic impedance (TI) acquired from defibrillation pads. METHODS: ECG and TI signals from out-of-hospital AED recordings were retrospectively analysed. Experts annotated the cardiac rhythm during AED analysis intervals and at the end of each episode. We developed an algorithm to classify 3-s segments of non-shockable and non-asystole rhythms as either pulsatile rhythm or pulseless electrical activity. The algorithm consisted on a decision tree based on two features: the mean power of the TI segment and the mean cross-power between ECG and TI segments. RESULTS: From the 302 annotated episodes, 167 contained segments eligible for the study. The circulation detector algorithm presented a sensitivity (ability of detecting pulsatile rhythms) of 98.3% (95% CI: 95.1-100) and a specificity (ability to detect pulseless electrical activity) of 98.4% (95% CI: 97.1-99.8) in the validation subset. Absence of pulsatile rhythm was confirmed during the first AED analysis interval in 98.9% of the episodes, and presence of a pulse was confirmed in the first 3 s of all intervals with annotated return of spontaneous circulation. CONCLUSION: Accurate automated detection of circulation based on TI and ECG is possible during AED analysis intervals. This functionality could potentially contribute to enhance patient's care by laypersons using AEDs.

Toward a better noninvasive assessment of preejection period: A novel automatic algorithm for B-point detection and correction on thoracic impedance cardiogram.

Impedance cardiography is the most common clinically validated, noninvasive method for determining the timing of the opening of the aortic valve, an important event used for measuring preejection period, which reflects sympathetic beta-adrenergic influences on the heart. Automatic detection of the exact time of the opening of the aortic valve (B point on the impedance cardiogram) has proven to be challenging as its appearance varies between and within individuals and may manifest as a reversal, inflection, or rapid slope change of the thoracic impedance derivative's (dZ/dt) rapid rise. Here, a novel automatic algorithm is proposed for the detection of the B point by finding the main rapid rise of the dZ/dt signal, which is due to blood ejection. Several conditions based on zero crossings, minima, and maxima of the dZ/dt signal and its derivatives are considered to reject any unwanted noise and artifacts and select the true B-point location. The detected B-point locations are then corrected by modeling the B-point time data using forward and reverse autoregressive models. The proposed algorithm is validated against expert-detected B points and is compared with different conventional methods; it significantly outperforms them by at least 54% in mean error, 30% in mean absolute error, and 27% in standard deviation of error. This algorithm can be adopted in ambulatory studies requiring beat-to-beat evaluation of cardiac hemodynamic parameters over extended time periods where expert scoring is not feasible.

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

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

[Current status of noninvasive hemodynamics in hypertension]. / Estado actual de la hemodinamia no invasiva en hipertensión arterial.

Hypertension is a haemodynamic disorder resulting from a persistent mismatch between cardiac output and peripheral resistance. Hypertension undergoes haemodynamic progression during its natural history. Impedance cardiography is a method of evaluating the cardiovascular system that obtains haemodynamic information from beat to beat through the analysis of variations in the impedance of the thorax on the passage of an electric current. Impedance cardiography unmasks the haemodynamic deterioration underlying the increase in blood pressure as age and systolic blood pressure increases. This method may help to improve blood pressure control through individualized treatment with reduction of peripheral resistance, maintenance of cardiac output or its increase, improvement of arterial compliance and preservation of organ-tissue perfusion. It is useful in the management of patients with resistant hypertension, since a greater percentage of patients controlled with changes in the treatment in relation to the haemodynamic measurements are obtained. Impedance cardiography is important and has prognostic utility in relation to a haemodynamic deterioration pattern and increased cardiovascular events.

Good agreement between echocardiography and impedance cardiography in the assessment of left ventricular performance in hypertensive patients.

BACKGROUND: Impedance cardiography (ICG) is a noninvasive hemodynamic monitoring tool which can define hypertensive patients' hemodynamic profiles and help to tailor antihypertensive therapy. This study assesses the concordance between ICG-derived indexes used to evaluate left ventricular performance and transthoracic echocardiography (TTE) in hypertensive patients. METHODS: In this IMPEDDANS post-hoc analysis, the ICG-derived indexes are compared with TTE by Bland-Altman method. Statistical significance of the relationship between the values obtained was assessed by generalized linear mixed-effects models. RESULTS: In supine position, Bland-Altman analysis showed good concordance for cardiac output (CO) (mean difference of 0.006 mL/min [-0.120; 0.133]), cardiac index (CI) (mean difference of 0.016 mL/min/m2 [-0.471; 0.504]), pre-ejection period (PEP) (mean difference of -0.216 ms [-4.510; 4.077]), left ventricular ejection time (LVET) (mean difference of -0.140 ms [-6.573; 6.293]), and systolic time ratio (STR) (mean difference of -0.00004 [-0.008; 0.008]). In orthostatic position, good concordance was found for CO (mean difference 0.028 mL/min [-2.036; 1.980]), CI (mean difference -0.012 mL/min/m2 [-1.063; 1.039]), and STR (mean difference -0.101 [0.296; 0.094]). No significant difference between methods was identified by the linear mixed-effects models. CONCLUSION: The ICG-derived indexes CO, CI, PEP, LVET, and STR in supine position have good agreement with TTE. Therefore, ICG can be used to accurately evaluate left ventricular performance.