ECG Measurements Research Articles

Reference values for time- and frequency-domain heart rate variability measures

The analysis of heart rate variability (HRV) has become an established procedure in recent decades. Because there are no appropriate reference values available, HRV findings can still only be compared within a group or in individuals in longitudinal studies. The objectives of the present study were to examine a group of healthy subjects of different ages and sexes and to identify reference values for common HRV parameters. Long-term 24-hour electrocardiograms of 695 voluntary subjects were recorded by using a 2-channel Holter system over a period of 24 hours during daily activities. Reference values for men and women in 10-year age groups were calculated for standard deviation of NN intervals, root mean square of successive differences of NN intervals, standard deviation of the average of all consecutive 5-minute NN intervals, percentage of consecutive NN intervals that deviate from one another by more than 50 ms, low-frequency power normalized unit, high-frequency power normalized unit, low frequency/high frequency ratio, SD1, and SD2. The 5th and 95th percentiles were given for each sex and for the age groups 20-30, 30-40, 40-50, and 50-60 years. We observed a consistent decrease in HRV measures with increasing age as well as a sex dependency of HRV findings. We studied a large group of healthy subjects and identified reference values for commonly used HRV measures for 24-hour ECG measurements. The reference values differed considerably from the values published in 1996 in the Guidelines of the Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. In the future, steps should be taken to expand the database and define reference values for the age groups under 20 and over 60 years. It would be desirable to obtain reference values for short-term recordings (eg, 5-minute recordings) as well.

Monitoring Cardiomyocyte Functional Indices with Hybrid Mea-Impedance Technology

The recent progress in biosensor technology combined with availability of human stem cell-derived cardiomyocytes (SC-CMs) provides an exciting possibility to assess novel biomarkers of cardiac function in vitro. CardioExcyte 96 (Nanion Technologies GmbH, Germany) is a new screening platform combining impedance and extracellular field potential (EFP) recordings, which allows label-free simultaneous assessment of electrical activity, beating and electromechanical coupling in a variety of multi-cellular cardiac preparations.The goal of the present study was to evaluate the utility of the new hybrid instrument for multi-parameter profiling of endogenous responses in human SC-CMs. Cor.4U iPS-derived cardiomyocytes (Axiogenesis, Germany) cultured over a week were treated with reference drugs from various pharmacological classes affecting cardiac ion channels, pumps, adrenergic receptors and intercellular communication to evaluate their effect on various parameters of impedance and EFP signals. In addition to the pharmacological effects, dynamics of the cell growth and development in culture were monitored to derive an analytical expression for the system. Detailed investigation of the cellular beat signal facilitated multi-parameter evaluation allowing integrative assessment of cardiomyocyte behavior. The resulting multiplex signatures can be used as a fingerprint tool to highlight changes in cardiac function and potentially to categorize drugs based on their mechanisms of action.The hybrid impedance-EFP measurements in human SC-CMs exemplify a novel screening method for early and sensitive multi-parameter profiling in vitro. This integrative approach meliorates the screening pipeline by bridging single cell-based assays and ECG measurements for translational assessment.

The β1-Adrenergic Receptor Blocker, Metoprolol, Improves Survival and Electrical Remodeling in Rats with Pulmonary Artery Hypertension

Right ventricular (RV) failure is the leading cause of death in patients with pulmonary arterial hypertension (PAH). Pre-clinical studies have shown that β-blockers can improve survival in PAH and RV failure, however effects on electrical remodeling are unknown.Male Wistar rats were injected with saline (controls, CON) or 60mg/kg of monocrotaline (MCT) to induce PAH and RV failure. Metoprolol (10mg/kg) or placebo was administered daily from day 15 post MCT injection. For the acquisition of in vivo ECG measurements telemetric devices were implanted in CON, placebo treated MCT (FAIL) and β-blocker treated MCT (BB). Rats were removed when heart failure symptoms developed. Recordings occurred daily during light and dark cycles.Survival of the BB rats was significantly improved with a median time to failure of 32 days post injection compared to the FAIL rats median of 23 days (P BB > CON with all groups significantly different to each other (P< 0.05-0.001). The time from T-wave peak to end (Tpe) followed the same pattern but FAIL and BB were not significantly different from each other (P< 0.05-0.01), N = 9-10 animals in each group.We show that β1-blockade delays the onset of HF in PAH rats. In addition it partially reverses the increase in action potential duration (QT interval) possibly by reversing effects on K+ channel expression. There also was a trend for reduced dispersion of repolarisation (Tpe). These effects could help reduce pro-arrhythmic substrates of PAH rat hearts.Supported by the British Heart Foundation

Multimodal monitoring (MMM) in the perioperative period

Routine anaesthesia monitoring until the mid-1980s often consisted of just a finger on the pulse, primitive ECG and intermit-tent blood pressure (MAP) measurement using a cuff and aneroid gauge or me-chanical oscillotonometer. Then in quick succession an explosion of new monitors was introduced including pulse oximetry (SpO2), end tidal carbon dioxide (EtCO2) and anaesthetic agent monitoring as well as automated non-invasive blood pres-sure (NIBP) machines. These were all rou-tinely in place in many hospitals by the late 1980’s, but then progress came to a halt with no advances in routine anaesthetic monitoring for over 25 years.&nbsp;This paper concentrates on three classes of non- or minimally invasive monitors which have become additionally avail-able in the last 10 to 15 years and if used in combination their potential impact on improving outcome following surgery in high risk patients:tary information which should improve perioperative haemodynamic manage-ment and outcome and form part of a multi-modal monitoring (MMM) strategy which is the subject of this article.&nbsp

A Schematic Simulation for Health Economic Feasibility Studies: Results from a Model for Cardiac Remote Monitoring

The market for active implants and biosensors is of high economic and medical interest. As health economic considerations get into focus in terms of business planning and reimbursement, valid and flexible economic feasibility studies get more important. Unfortunately, literature mostly provides only single economic views on specific aspects like cost savings from reduced rehabilitation in a special patient cohort. To make planning and technology value negotiation more effective and more valid, a methodology to collect relevant data from different studies and normalize it to a common set of parameters was developed for the field of cardiac monitoring in a mixed example population with an approach of simple external weight, ECG and blood-pressure measurement or implanted devices for cardiac monitoring. The target entities taken into account by the simulation model were the impacts on heart attack, stroke, heart failure and the process of implant monitoring. Simulation took place at an example population of 500 patients with specific morbidity criteria. The health economic value was calculated over a period of three years and was split into a technology effectiveness measurement in Quality-adjusted-Lifetime-Years (QALYs) and a “cost- saving-part”. QALYs were chosen as technology effectiveness parameter for a combined and weighted mortality- and morbidity-reduction. Allocating 24.000 Euro to a saved QALY, 42% of the cost would be allocated to QALYs meaning money being spent for gained lifetime-years. The remaining 58% would be the different real cost savings: a per patient gross saving of 3.308 € per year would result for that part (21% on heart attack, 3% on stroke, 68% on heart failure and 8% on implant monitoring). Up-to-date studies do not provide a simple mechanism to allow custom-tailored health economic feasibility study results in terms of other specific population mixes or outcome parameters. Target audiences for the methodology of the described simulation are payors and solution providers targeting a specific patient population or specific telemedical situations. This way product development can address market-related needs more specific and healthcare providers can compare different outcome parameters in the given entities.

Hypotensive and antihypertensive effects of a hydroalcoholic extract from Senecio nutans Sch. Bip. (Compositae) in mice: Chronotropic and negative inotropic effect, a nifedipine-like action

Ethnopharmacological relevanceSenecio nutans Sch. Bip. (Compositae) is an endemic plant of South America used in the management of acute mountain sickness in the Andean communities. Currently, the direct effects of hydroalcoholic extract from S. nutans on the cardiovascular system are unknown. The aim of this study was to determine the effects and mechanism of action of S. nutans on cardiovascular function in normotensive and Angiotensin II (1μg/mL) hypertension mice models. Material and methodsBlood pressure and ECG measurements were simultaneously carried out on the mice and rats. The isolated right atrium, papillary muscle of the left ventricle and isolated heart of rat were used to study the cardiac functions and mechanisms. ResultsS. nutans (40mg/Kg) induced a 30% and 12% significant (p<0.05) reduction of the mean arterial pressure (MAP) in normotensive and hypertensive mice respectively. This decrease was as a result of decrease in heart rate (HR) in normotensive (25%) and hypertensive model (31%). It also decreased the sinus rhythm in isolated right atrium of rat. Compared with Losartan, a known anti-hypertensive, S. nutans caused a dose-dependent negative inotropic effect (dP/dtmax) on Langendorff isolated heart system. While Losartan, decreased the MAP by 30% but had no effect on heart rate. The calcium blocker nifedipine had similar effects as S. nutans, decreasing the beat frequency of isolated right atrium and contractility of papillary muscle of the left ventricle of rat. ConclusionThe results suggest an important clinical function in hypertension therapy, as S. nutans could decrease the blood pressure in hypertensive mice by decreasing the HR and contractility, leading to a reduction in myocardial oxygen demand.

Use of power-line interference for adaptive motion artifact removal in biopotential measurements

Motion artifacts (MA) have long been a problem in biopotential measurements. Adaptive filtering is widely used for optimal noise removal in many biomedical applications. However, the existing adaptive filtering methods involve the use of additional sensors, limiting the applicability of adaptive filtering for MA reduction. In the present study, a novel adaptive filtering method without need for additional sensors is proposed. In biopotential measurements, movement of the electrodes and their leads may cause variations not only in the skin and half-cell potential (motion artifacts), but also in the electrode-skin impedance. Such impedance variations may also cause power-line interference modulation (PLIM), resulting in additional spectral components around the power-line interference (PLI) in the frequency domain. Demodulation of the PLI may reflect the movement-induced electrode-skin impedance variation, and can therefore represent a reference signal for the adaptive filter. Preliminary validation on ECG measurements with seven volunteers showed a high correlation coefficient (R = 0.97) between MA and PLIM, and excellent MA removal by the proposed adaptive filter, possibly leading to improved analysis of biopotential signals.

Abstract 14124: A Marked Increase in Myocardial Oxidative Stress Associated With Sympathetic Hyperactivity is Related to Transient Myocardial Dysfunction in Patients With Takotsubo Cardiomyopathy

Introduction: Sympathetic hyperactivity is considered as one of the most likely pathogenic mechanism in takotsubo cardiomyopathy (TC). However, little is known about the relationship between sympathetic hyperactivity and myocardial oxidative stress (OS). Hypothesis: We hypothesized that cardiac sympathetic hyperactivity was associated with cardiac myocardial OS, and OS related to transient myocardial dysfunction in patients with TC compared with acute anteroseptal myocardial infarction (AMI). Methods: In 8 TC patients and 8 AMI patients (NYHA 3), ECG, echocardiography, cardiac catheterization and serial measurements of plasma catecholamines, urinary (U) 8-hydroxy-2’-deoxyguanosine (8-OHdG) as a marker of OS and plasma CPK were performed for two weeks from onset. Results: Blood sampling from coronary sinus (CS) and aorta (Ao) at 1st day showed that norepinephrine (NE) levels and 8-OHdG level in CS were significantly higher than those in Ao and peripheral blood, indicating that an increase in myocardial OS was associated with cardiac sympathetic hyperactivity. NE levels in peripheral blood were peaked out at 1st day and 2-times higher in TC than in AMI within a week, while the max CPK value in TC was significantly lower than that in AMI. Dual scintigraphy of 201Tl and 123I-meta-iodobenzylguanidine was performed at 7th day showed that cardiac sympathetic nervous injury was much larger than myocardial perfusion damage in all TC patients. U-8OHdG level (ng/mg Cr; normal range:&lt;10.0) in TC was elevated in parallel with the profile of plasma NE level (1st day: 65.6±24.5, 4th day: 19.1±8.3, 7th day: 16.4±9.1), while it was decreased to almost normal range after percutaneous coronary intervention for left anterior descending artery in AMI (1st day: 24.3±13.8, 4th day: 9.8±3.4, 7th day: 12.3±2.7). Interestingly, difference in serum 8-OHdG levels (CS vs Ao) in TC increased proportionally with wall motion score (WMS) as an index of LV dysfunction (R=0.93, p&lt;0.001), while difference in serum NA levels (CA vs Ao) in TC did not. U-8OHdG level in TC was positively correlated with WMS at each day (1st day, 7th day). Conclusions: These findings suggest that myocardial OS induced by cardiac sympathetic hyperactivity may play a critical role in transient LV dysfunction in TC.

Abstract 16803: Relationships Between Invasive and Non-invasive Measures of Cardiac Function During Exercise in Heart Failure With Preserved or Reduced Ejection Fraction

Introduction: Assessment of cardiac function during exercise is critical in the clinical evaluation of patients with heart failure with preserved (HFpEF) or reduced (HFrEF) ejection fraction. Direct invasive measurement of cardiac power (CP) and stroke work (SW) are robust measures of cardiac function. Non-invasive gas exchange based surrogates may provide practical means of assessing cardiac function in clinical and research settings; however, the relationship between invasive and non-invasive measurement of CP or SW during exercise is unclear in HFpEF and HFrEF. We aimed to assess relationships between invasive and non-invasive measures of CP and SW during exercise in HFpEF and HFrEF. Methods: HFpEF (n=47) and HFrEF (n=29) (age 71±10 vs 55±10 yrs; EF% 62±8 vs 21±6%; BSA 2.1±0.3 vs 2.1±0.2 m 2 ; weight 99±22 vs 87±15 kg; peak work 36±14 vs 37±13 watts (W), respectively; all p&lt;0.05, except peak work) underwent peak exercise testing during right heart catheterization. Invasive measurement of cardiac pressures, hemodynamics, and arterial pressures were recorded at rest, 20 W, and peak work. Continuous measurement of HR and VO 2 occurred from rest to peak work via 12-lead ECG and metabolic measurement system, respectively. Invasive measurements were calculated as, CP=(MAP–RAP) x Q x 2.22х10 -3 ; SW=(MAP–PCWP) x SV I x 0.133; and non-invasive as, CP=VO 2 x MAP; SW=VO 2 /HR x MAP. All indices adjusted for body surface area. Results: At rest, there were moderate relationships between invasive and non-invasive measures of CP and SW in HFpEF (r=0.56 and 0.48) and HFrEF (0.57 and 0.73), respectively (all p&lt;0.05). At 20 W, relationships between invasive and non-invasive measures of CP and SW strengthened in HFpEF (r=0.74 and 0.69) and HFrEF (0.74 and 0.72), respectively (all p&lt;0.05). The relationships noted between invasive and non-invasive measures of CP and SW at 20 W persisted at peak work in HFpEF (r=0.74 and 0.67) and HFrEF (0.78 and 0.69), respectively (all p&lt;0.05). Conclusion: These data suggest that non-invasive estimates of CP and SW correlate closely with invasive measures and may be reasonable surrogates for these indices during peak exercise testing in both HFpEF and HFrEF patients.

Bilan cardiorespiratoire préopératoire

Preoperative assessment before lung resection is based on cardiac assessment, lung function testing and prediction of the residual lung function. An exercise test would be prescribed in patients with compromised lung function. Cardiac risk assessment is based on a well validated score system. The calculation of this index is simple, since it is based on the medical history, physical examination, baseline ECG and plasma creatinine measurement. Lung function testing includes forced expiratory volume in one second (FEV1) and diffusing capacity of the lung for carbon monoxide (DLCO) measurements. Before lobectomy, the calculation using lung segment counting can predict postoperative

Validation of continuous QTc measurement in critically ill patients

IntroductionProlongation of the corrected QT interval (QTc) can lead to torsades de pointes. This study is designed to determine the validity of the continuous QTc (cQTc) measurement in critically ill patients. MethodsIn a retrospective cohort study, QTc analysis was performed with manual measurements on a single selected lead from a 12-lead ECG and cQTc measurement obtained at the same time. In addition, automated QTc measurement from the 12-lead ECG was also included in the study. Validation was performed by calculating intraclass correlation coefficient (ICC), Pearson’s correlation and Bland–Altman plot. Results119 patients with QRS<120ms were included with a mean cQTc of 468ms (standard deviation (SD) 37) and mean manually measured QTc of 449ms (SD 41) (p<0.001). Pearson’s correlation was 0.65 (p<0.01), ICC was 0.65 (95% CI: 0.53–0.74). Bland–Altman plot shows a mean difference of 19.5ms (limits of agreement (LOA) −44.6 to 83.7). For cQTc compared to automated QTc from the 12-lead ECG the intraclass correlation coefficient was 0.77 (95% CI: 0.68–0.83, p<0.001) and the Bland–Altman plot shows a mean difference of 7.8ms (LOA −40.2 to 55.8). ConclusioncQTc measurement in critically ill patients with a QRS duration shorter than 120ms shows an acceptable accuracy to be used in routine care.

Validation of Non-invasive Method for Electrocardiogram Recording in Mouse using Lead II

Electrocardiogram measures the electric impulses generated by the heart during its cycle. Recently genome-wide association studies on electrocardiogram traits revealed many relevant genetic loci. Therefore, these findings need to be validated and investigated to determine the underlying mechanisms using mouse models. Invasive radiotelemetry has been widely used to record the electrocardiogram in mice because it has several advantages over non-invasive measurements. However, radiotelemetry is expensive and requires complicated surgery. On the other hand, a non-invasive method using 3 electrodes (one for earth) for lead II is easy to establish and allows for rapid measurement. In this study, eleven mice were measured with this non-invasive method and no statistical difference among them was found in any ECG measurements. In addition, repeat measurement in the same mouse was performed in 9 sets of experiment and the results indicated that non-invasive method was reliable for reproducibility. Further it was shown that measurements for 1, 5, 10, and 15 minutes were not different so that a short recording such as 5 minutes was enough to estimate the ECG values including heart rate. Further this method was validated by measuring the ECG of Balb/c and FVB that were previously shown to differ in ECG values by radiotelemetry. Significant differences were found in heart rate, PR interval and corrected QT interval between these mouse strains. This study partially proved that non-invasive method also could provide the accuracy and reproducibility. Based on these results, the non-invasive ECG recordings of lead II is recommended as a useful method for quick test in mouse model.

Abstract CT117: Evaluation of the effect of crizotinib (CRZ) on the QT interval in patients with ALK-positive non-small cell lung cancer (NSCLC)

Abstract Background: CRZ is an oral tyrosine kinase inhibitor approved for the treatment of ALK-positive NSCLC at a starting dose of 250 mg BID. An ECG substudy was conducted to evaluate and quantitate any potential impact of CRZ on corrected QT interval (QTc). This ECG substudy enrolled patients with ALK-positive advanced NSCLC at selected sites from the phase III trial PROFILE 1007 and the phase II trial PROFILE 1005. Methods: All patients enrolled in the ECG substudy received CRZ 250 mg BID orally on a continuous basis. Triplicate 12-lead ECG measurements, approximately 2 minutes apart, were collected after a fast of at least 1 hour at predose, 4 and 8 hours following morning CRZ dosing on Day 1 of Cycle 1, and predose, 2, 4, 6 and 8 hours following morning CRZ dosing on Day 1 of Cycle 2 (1 Cycle = 21 days). All ECG tracings from this substudy were sent to an independent ECG laboratory for blinded manual interval measurements. Plasma PK samples for CRZ and its metabolite, PF-06260182, were collected at respective times immediately following each ECG measurement. ECG endpoints included QT interval corrected for heart rate (HR) using Fridericia's (QTcF) (primary endpoint) and Bazett's (QTcB) formulas and a model-based study-specific correction factor (QTcS), PR interval, RR interval, and QRS complex. Categorical analysis was conducted for all QTc endpoints. ANOVA was performed for QTcF and QTcS, the QTc with the most appropriate HR correction. These analyses were performed using the ECG Evaluable Population (EEP), defined as all treated patients with an adequate baseline assessment and at least 1 adequate ECG measurement on Cycle 2 Day 1 (at CRZ steady state). A pharmacokinetic/pharmacodynamic analysis was performed using the ECG-PK matched dataset. Results: A total of 65 patients were enrolled in the ECG study, and 52 were in the EEP. ANOVA revealed that all upper limits of the 90% confidence intervals for the least squares mean changes from baseline in QTcF at all Cycle 2 Day 1 time points were &amp;lt;20 ms. The largest LS mean change from baseline was an increase of 12.3 ms, reported at 6 hours post morning dose on Cycle 2 Day 1. No patients had a maximum QTc ≥500 ms and 1 (1.9%) patient had a QTc increase from baseline of ≥60 ms. Consistently with previous findings, mean steady state predose (Ctrough) and maximum plasma concentrations (Cmax) of CRZ were 271 ng/mL and 345 ng/mL, respectively, and mean steady state Ctrough and Cmax of metabolite PF-06260812 were 86.7 ng/mL and 107 ng/mL, respectively. A relationship was observed between CRZ plasma concentration and QTc. HR decreased with increasing CRZ plasma concentration, as reported previously in other studies. Conclusions: Based on ANOVA results from this substudy, a large QTc effect (≥ 20 ms) by CRZ can be excluded however a smaller increase in QTc cannot be ruled out. Periodic ECGs monitoring should be considered for patients who have a history of QTc prolongation or who are taking medications that prolong QT. Citation Format: Weiwei Tan, Keith D. Wilner, Silvana Lanzalone, Anna Polli, Matthew L. Zierhut, Dana Nickens, Kenneth J. O'Byrne, Fiona H. Blackhall, Alice T. Shaw, Ravi Salgia, Jesus Correl Jaime, Dong-Wan Kim. Evaluation of the effect of crizotinib (CRZ) on the QT interval in patients with ALK-positive non-small cell lung cancer (NSCLC). [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr CT117. doi:10.1158/1538-7445.AM2015-CT117

A novel ultra-wideband 80 GHz FMCW radar system for contactless monitoring of vital signs.

In this paper an ultra-wideband 80 GHz FMCW-radar system for contactless monitoring of respiration and heart rate is investigated and compared to a standard monitoring system with ECG and CO(2) measurements as reference. The novel FMCW-radar enables the detection of the physiological displacement of the skin surface with submillimeter accuracy. This high accuracy is achieved with a large bandwidth of 10 GHz and the combination of intermediate frequency and phase evaluation. This concept is validated with a radar system simulation and experimental measurements are performed with different radar sensor positions and orientations.

Using affective and behavioural sensors to explore aspects of collaborative music making

Our research considers the role that new technologies could play in supporting emotional and non-verbal interactions between musicians during co-present music making. To gain a better understanding of the underlying affective and communicative processes that occur during such interactions, we carried out an exploratory study where we collected self-report and continuous behavioural and physiological measures from pairs of improvising drummers. Our analyses revealed interesting relationships between creative decisions and changes in heart rate. Self-reported measures of creativity, engagement, and energy were correlated with body motion; whilst EEG beta-band activity was correlated with self-reported positivity and leadership. Regarding co-visibility, lack of visual contact between musicians had a negative influence on self reported creativity. The number of glances between musicians was positively correlated with rhythmic synchrony, and the average length of glances was correlated with self-reported boredom. Our results indicate that ECG, motion, and glance measurements could be particularly suitable for the investigation of collaborative music making.

Amiodarone and Trypanosoma cruzi parasitemia in patients with Chagas disease

Amiodarone and Trypanosoma cruzi parasitemia in patients with Chagas disease

Wireless power source for implantable telemetry devices

Recent advancements in biotelemetry systems allow measurements of blood flow, blood pressure, ECG and temperature in small animals such as rats (EG3‐Vx‐Sx‐Mx, Transonic EndoGear Inc) with minimal intrusion into their environment. However, these implants cannot be used continuously for extended periods of time, because they use finite capacity batteries. Different size batteries maybe used for different size animals, which also dictates the maximum duration of measurements. To provide telemetry monitoring over extended periods of time, we developed Wireless Power Supply (WPS) that uses inductive power technology to send power to an implanted 3‐dimentional Wireless Power Receiver (WPR) that is used instead of the battery. This WPR can provide continuous power to a telemetry system used in small animals such as rats. The WPS uses a self‐tuning design that adjusts for maximum power delivery even when multiple animals are present in the same cage. This is also possible due to the self‐regulation of the WPR that does not depend on back‐telemetry and regulation of the WPS. These advancements make it possible to have two, or more instrumented animals in the same cage. The WPR receives a maximum of 20mA at 3.5V up to a distance of 15cm, in all 3 dimensions, in a standard size rat cage. This is more than enough to power a telemetry system with the capability to measure advanced cardiovascular parameters such as blood flow, blood pressure, ECG and temperature.

A Low-Voltage Chopper-Stabilized Amplifier for Fetal ECG Monitoring With a 1.41 Power Efficiency Factor.

This paper presents a low-voltage current-reuse chopper-stabilized frontend amplifier for fetal ECG monitoring. The proposed amplifier allows for individual tuning of the noise in each measurement channel, minimizing the total power consumption while satisfying all application requirements. The low-voltage current reuse topology exploits power optimization in both the current and the voltage domain, exploiting multiple supply voltages (0.3, 0.6 and 1.2 V). The power management circuitry providing the different supplies is optimized for high efficiency (peak charge-pump efficiency = 90%).The low-voltage amplifier together with its power management circuitry is implemented in a standard 0.18 μm CMOS process and characterized experimentally. The amplifier core achieves both good noise efficiency factor (NEF=1.74) and power efficiency factor (PEF=1.05). Experiments show that the amplifier core can provide a noise level of 0.34 μVrms in a 0.7 to 182 Hz band, consuming 1.17 μW power. The amplifier together with its power management circuitry consumes 1.56 μW, achieving a PEF of 1.41. The amplifier is also validated with adult ECG and pre-recorded fetal ECG measurements.

Electrocardiographic Changes During Exercise in Acute Hypoxia and Susceptibility to Severe High-Altitude Illnesses

The goals of this study were to compare ECG at moderate exercise in normoxia and hypoxia at the same heart rate, to provide evidence of independent predictors of hypoxia-induced ECG changes, and to evaluate ECG risk factors of severe high-altitude illness. A total of 456 subjects performed a 20-minute hypoxia exercise test with continuous recording of ECG and physiological measurements before a sojourn above 4000 m. Hypoxia did not induce any conduction disorder, arrhythmias, or change in QRS axis. The amplitude of the P wave in V1 was lower in hypoxia than in normoxia. The amplitudes of the R, S, and T waves and the Sokolow index decreased in hypoxia. Under hypoxia, the amplitude of the ST segment decreased in II and V6 and increased in V1, the ST slope rose in V5 and V6, and the J point was lower in II, V5, and V6. Multivariate regression of hypoxic/normoxic ratios of electrophysiological parameters and clinical characteristics showed a correlation between the decrease in Sokolow index and T-wave amplitude in V5 with desaturation at exercise. Trained status and low body mass index were associated with a smaller decrease in T-wave amplitude in V5 and V6. Comparison of ECG between subjects suffering or not suffering from severe high-altitude illness failed to show any difference. During a hypoxia exercise test, a dose-dependent hypoxia-induced decrease in the amplitude of the P/QRS/T waves was observed. No standard ECG characteristic predicted the risk of developing severe high-altitude illness. Further studies are required to clarify the cause of these electric changes and their potential predictive role in cardiac events.

Motion artifacts in capacitive ECG measurements: reducing the combined effect of DC voltages and capacitance changes using an injection signal.

Capacitive electrodes are a promising alternative to the conventional adhesive electrodes for ECG measurements. They provide more comfort to the patient when integrated in everyday objects (e.g., beds or seats) for long-term monitoring. However, the application of capacitive sensors is limited by their high sensitivity to motion artifacts. For example, motion at the body-electrode interface causes variations of the coupling capacitance which, in the presence of a dc voltage across the coupling capacitor, create strong artifacts in the measurements. The origin, relevance, and reduction of this specific and important type of artifacts are studied here. An injection signal is exploited to track the variations of the coupling capacitance in real time. This information is then used by an identification scheme to estimate the artifacts and subtract them from the measurements. The method was evaluated in simulations, lab environments, and in a real-life recording on an adult's chest. For the type of artifact under study, a strong artifact reduction ranging from 40 dB for simulated data to 9 dB for a given real-life recording was achieved. The proposed method is automated, does not require any knowledge about the measurement system parameters, and provides an online estimate for the dc voltage across the coupling capacitor.