Impedance cardiography: Recent advancements

The aim of this paper is the presentation of recent advancements in impedance cardiography regarding methodical approach, applied equipment and clinical or research implementations. The review is limited to the papers which were published over last 17 months (dated 2011 and 2012) in well recognised scientific journals. (Cardiol J 2012; 19, 5: 550-556

Test-retest reliability of noninvasive ambulatory impedance cardiography during aerobic exercise

Impedance cardiography is an important tool in determining a person\u27s hemodynamic properties. The makers obtained through thoracic impedance have been shown to be of great importance when monitoring critical care patients. Technological developments have made this process noninvasive and ambulatory, opening up new possibilities for potential use. A study was conducted by remotely monitoring healthy subjects (n=5), who performed an 8-minute mild-to-moderate aerobic exercise protocol, followed up by a four minute cognitive stress test. Testing was conducted onsite at Kennedy Space Center in association with the National Aeronautics and Space Administration using the MW1000A (MindWare Technologies LTD, Gahanna, OH) ambulatory impedance cardiography monitoring (ICG) device. The current study was conducted in order to establish the test-retest reliability of the ICG during aerobic exercise and cognitive stress across a 2 week period. For the purpose of this study Heart Rate (HR), Left Ventricular Ejection Time (LVET) Stroke Volume (SV), Cardiac Output (CO), and Pre-Ejection Period (PEP) were acquired and analyzed during three phases. The phases were, walking on a level treadmill, walking at incline, and an at rest mental arithmetic stress test. Testing has shown that the MW1000A device can provide accurate ambulatory impedance cardiography monitoring with no significant difference between testing intervals. The simple application of electrodes makes this device easy to use and requires little training. Its non-invasive properties render employing ICG both a simple and effective means of determining the hemodynamic properties of a subject

Evaluating the RZ Interval and the Pre-ejection Period as Impedance Cardiography Measures of Effort-Related Cardiac Sympathetic Activity

Research on effort and motivation commonly measures how the sympathetic branch of the autonomic nervous system affects the cardiovascular system. The cardiac pre-ejection period (PEP), assessed via impedance cardiography, is a widely-used sympathetic outcome, but assessing PEP requires identifying subtle points on cardiac waveforms. The present research examined the value of the RZ interval (RZ), which has recently been proposed as a measure of sympathetic activity, for effort research. Also known as the initial systolic time interval (ISTI), RZ is the time (in ms) between the ECG R peak and the dZ/dt Z peak. Unlike PEP, RZ involves salient waveform points that are easily and reliably identified. Data from three experiments evaluated the suitability of RZ for effort research and compared it to a popular, automated PEP method. Participants completed a standard mental effort task in which correct responses earned a small amount of money. As expected, incentives significantly affected PEP and RZ in all three experiments. PEP and RZ were highly correlated (all rs = .89), and RZ consistently yielded a larger effect size than PEP. A quantitative synthesis of the experiments indicated that the effect size of RZ’s response to incentives (Hedges’s g = .387 [.248, .527]) was roughly 20% larger than PEP’s effect size (g = .323 [.185, .461]). RZ thus appears promising for future research on sympathetic aspects of effort-related cardiac activity

Psychopathology, everyday behaviors, and autonomic activity in daily life: an ambulatory impedance cardiography study of depression, anxiety, and hypomanic traits

Discrepancies regarding the link between autonomic nervous system (ANS) activity and psychopathology may be due in part to inconsistent measurement of non-psychological factors, including eating, drinking, activity, posture, and interacting with others. Rather than sources of noise, behaviors like being active and being with others may be the behavioral pathways that connect psychopathology symptoms to autonomic activity. The present study examined whether behaviors mediate the association of depression, anxiety, and hypomanic traits with ANS by using experience sampling methodology and ambulatory impedance cardiography. Participants (n?=?49) completed measures of affect and one day of experience sampling and ambulatory impedance cardiography. The association of hypomanic traits with heart rate variability and heart rate was mediated by physical activity, and social activity mediated the association of depressive symptoms and respiration. These results highlight the importance of considering the pathways between psychopathology and ANS and the mediating role that everyday behaviors play

Creative motivation: Creative achievement predicts cardiac autonomic markers of effort during divergent thinking

Executive approaches to creativity emphasize that generating creative ideas can be hard and requires mental effort. Few studies, however, have examined effort-related physiological activity during creativity tasks. Using motivational intensity theory as a framework, we examined predictors of effort-related cardiac activity during a creative challenge. A sample of 111 adults completed a divergent thinking task. Sympathetic (PEP and RZ) and parasympathetic (RSA and RMSSD) outcomes were assessed using impedance cardiography. As predicted, people with high creative achievement (measured with the Creative Achievement Questionnaire) showed significantly greater increases in sympathetic activity from baseline to task, reflecting higher effort. People with more creative achievements generated ideas that were significantly more creative, and creative performance correlated marginally with PEP and RZ. The results support the view that creative thought can be a mental challeng

Impedance cardiography: A valuable method of evaluating haemodynamic parameters

This year marks 40 years since the technique was designed of measuring and monitoring the basic haemodynamic parameters in humans by means of impedance cardiography (ICG), also known as "impedance plethysmography of the chest", "electrical bioimpedance of the chest" or "reocardiography". The method makes it possible to denote stroke volume and cardiac output. It also enables the factors to be assessed that influence the following: preload (measurement of thoracic fluid content), afterload (measurement of systemic vascular resistance), the systemic vascular resistance index, contractibility (measurement of the acceleration index), the velocity index, the pre-ejection period, left ventricular ejection time, systolic time ratio and heart rate. Advances in hardware and software, including digital signal tooling and new algorithms, have certainly improved the quality of the results obtained. The accuracy and repeatability of the results have been confirmed in comparative studies with results obtained through invasive methods and echocardiography. Not only are haemodynamic changes monitored by means of ICG in intensive care units, in operating theatres and at haemodialysis stations, but repeated measurements also provide haemodynamic information during the treatment of patients with hypertension and heart failure and pregnant women with cardiological problems and gestosis. A single ICG investigation makes a great contribution to the basic information available about the circulatory system, which is helpful in the initial evaluation of patients in a severe general condition (for example in the admission room), and also makes it possible to make a swift diagnosis of the cause of complaints such as dyspnoea and hypotonia. A particular application of ICG is the assessment of haemodynamic parameters during the programming of atrioventricular and CRT pacemakers. Besides these uses, ICG is a valuable investigative tool. It is defect-free and does not have pulmonary artery pressure monitoring limitations. Moreover, it is not as time-consuming as echocardiography and the examination can be performed by trained technicians or nurses. (Cardiol J 2007; 14: 115-126

Effort deficits and depression: The influence of anhedonic depressive symptoms on cardiac autonomic activity during a mental challenge

Motivational approaches to depression emphasize the role of dysfunctional motivational dynamics, particularly diminished reward and incentive processes associated with anhedonia. A study examined how anhedonic depressive symptoms, measured continuously across a wide range of severity, influenced the physiological mobilization of effort during a cognitive task. Using motivational intensity theory as a guide, we expected that the diminished incentive value associated with anhedonic depressive symptoms would reduce effort during a “do your best” challenge (also known as an unfixed or self-paced challenge), in which effort is a function of the value of achieving the task’s goal. Using impedance cardiography, two cardiac autonomic responses were assessed: pre-ejection period (PEP), a measure of sympathetic activity and our primary measure of interest, and respiratory sinus arrhythmia (RSA), a measure of parasympathetic activity. As expected, PEP slowed from baseline to task as anhedonic depressive symptoms increased (as measured with the Depression Anxiety Stress Scale), indicating diminished effort-related sympathetic activity. No significant effects appeared for RSA. The findings support motivational intensity theory as a translational model of effort processes in depression and clarify some inconsistent effects of depressive symptoms on effort-related physiology found in past work

Novel concepts for non-invasive telemonitoring in chronic heart failure

Background: The morbidity and mortality from chronic heart failure (HF) remains alarmingly high, in part due to failure to apply substantial disease modifying strategies to halt disease progression. Telemonitoring has been proposed as a potential disease management strategy to deal with the burden posed by HF. While treatment decisions guided by invasive telemonitoring data have shown early promise, it is unclear whether non-invasively derived surrogates of haemodynamics could be reliable enough to guide therapeutic interventions.Aims: The principal aim of this thesis is to investigate whether non-invasive “smart technologies” could accurately detect and track subtle changes in surrogates of cardiovascular haemodynamics in response to challenges posed by activities of daily living and non-adherence to therapy. Methodology: A series of prospective clinical studies were conducted in stable patients with chronic heart failure, on optimum tolerated guideline directed therapy for heart failure. Studies were performed under clinically adapted conditions to mimic the patient’s own habitat.Results: Significant systemic haemodynamic perturbations were detected non-invasively with variations in environmental temperature. Additionally, music, which modulates the sympathetic tone, led to modest changes in systemic blood pressure and heart rate, although the changes did not reach statistical significance. Non-adherence to cardiovascular therapy led to striking adverse changes in systemic haemodynamics. Smart technologies demonstrated a remarkable consistency in detecting haemodynamic perturbations.Conclusion: Non-invasive detection and tracking of changes in haemodynamics is feasible with smart technologies. The results need to be validated in larger multicenter clinical trials, with particular emphasis on using the data to guide therapeutic decisions

The complex nature of arterial stiffness in patients with arterial hypertension

Wstęp. Sztywność naczyniowa jest obecnie celem interwencji terapeutycznych u pacjentów z chorobami układu sercowo-naczyniowego. Dlatego możliwość oceny właściwości układu naczyniowego okazuje się szczególnie istotna. Celem pracy była ocena charakteru powiązań prędkość fali tętna (PWV) z parametrami klinicznymi oraz hemodynamicznymi u chorych z nadciśnieniem tętniczym. Materiał i metody. Analizą objęto grupę 150 pacjentów (w tym 111 mężczyzn; średni wiek 43,5 roku) z nadciśnieniem tętniczym, bez istotnych schorzeń współistniejących. U wszystkich badanych po wstępnej ocenie klinicznej wykonano 10-minutową rejestrację parametrów hemodynamicznych metodami kardiografii (ICG) i pletyzmografii impedancyjnej z oceną między innymi PWV, średniego ciśnienia tętniczego (MAP), częstości rytmu serca (HR), wskaźnika wyrzutowego (SI), całkowitej podatności naczyniowej (TAC), wskaźnika systemowego oporu naczyniowego (SVRI), okresu przedwyrzutowego (PEP) i czasu wyrzutu z lewej komory (LVET). Wyniki. Wartość PWV okazała się istotnie większa u kobiet niż u mężczyzn (6,18 ± 0,77 v. 5,91 ± 0,99 m/s; p = 0,035). W ocenie wzajemnych relacji wartość PWV najistotniej korelowała z wiekiem (R = 0,41), MAP (R = 0,32), HR (R = 0,32), SI (R = –0,47), TAC (R = –0,31), SVRI (R = 0,38) oraz podokresami skurczu serca: PEP (R = 0,59) i LVET (R = 0,28). W modelu wieloczynnikowym (R2 = 0,61) niezależnymi zmiennymi związanymi z PWV okazały się: wiek, MAP, PEP i LVET. Wnioski. Metody bioimpedancyjne okazują się przydatne w ocenie złożonej natury sztywności naczyniowej. Prędkość fali tętna wykazuje powiązania z innymi parametrami hemodynamicznymi charakteryzującymi interakcję lewej komory mięśnia sercowego z układem naczyniowym, w tym najsilniejsze z ciśnieniem tętniczym (BP), SVRI, TAC oraz wskaźnikami funkcji mięśnia sercowego jako pompy (HR, SI, PEP, LVET). Otrzymane wyniki wskazują, że wartość rokownicza PWV powinna być interpretowana z uwzględnieniem bieżącego stanu hemodynamicznego badanej osoby. Introduction. The arterial stiffness has become the target of therapeutic interventions in patients with cardiovascular diseases and the ability to characterize and quantify arterial properties turned out to be of importance. Aim of this study was to evaluate the association of arterial stiffness and peripheral blood flow with clinical characteristics and hemodynamics in patients with arterial hypertension (AH). Material and methods. The study included 150 patients (111 men; mean age 43.5 years) with AH that underwent clinical evaluation and hemodynamic assessment by impedance plethysmography (IPG) and cardiography (ICG), with analysis of i.e. pulse wave velocity (PWV), mean arterial pressure (MAP), heart rate (HR), stroke index (SI), total artery compliance (TAC), systemic vascular resistance (SVRI), pre-ejection period (PEP) and left ventricular ejection time (LVET). Results. In comparative analysis PWV was significantly higher in women than men (6.18 ± 0.77 vs 5.91 ± 0.99 m/s; p = 0.035). PWV was also associated with age (R = 0.41), MAP (R = 0.32), HR (R = 0.32), SI (R = –0.47), arterial elasticity (TAC, R = –0.31), vascular resistance (SVRI, 0.38) and sub-periods of heart contraction (PEP, R = 0.59 and LVET, 0.28). Age, MAP, PEP and LVET revealed to be the independent covariates in the multivariate regression model for PWV estimation (R square 0.61). Conclusions. Bioimpedance methods are complementary for the assessment of complexity of the arterial stiffness. PWV revealed to be associated with hemodynamic parameters characterizing ventricular-vascular interactions, including BP, SVRI, TAC, and characteristics of left ventricle performance (HR, SI, PEP, LVET). In view of the classifying value of PWV in cardiovascular risk evaluation the current patient’s hemodynamic state should be carefully considered