Estimation of the liquid water saturation in PEM fuel cells: A low-power peaking-free dead-zone observer approach.

Water management in polymer electrolyte membrane fuel cells (PEMFCs) is one of the most challenging issues affecting PEMFC efficiency and lifetime. The unavailability of reliably liquid water saturation sensors hinders the applicability of liquid water active control and supervision techniques. A promising technique that can be applied in this context are high-gain observers. However, the performance of this type of observer is significantly limited by the peaking phenomena and its noise sensibility. In general, this performance is not adequate for the considered estimation problem. For this reason, this work proposes a new high-gain observer without peaking and with reduced noise sensibility. The convergence of the observer is proven through rigorous arguments. Moreover, the algorithm is shown to be applicable in PEMFC systems through numerical simulations and experimental validation. It is shown that the proposed approach achieves a reduction of 32.3% of the mean square error in the estimation while maintaining the convergence rate and robustness of classical high-gain observers.

Offline and online parameter estimation of nonlinear systems: Application to a solid oxide fuel cell system.

In this paper, an offline tuning strategy and an online parameter estimation method are exploited to calibrate the solid oxide fuel cell mathematical model. Different to existing offline tuning strategy, the developed strategy is designed in order to tune the model under various operation conditions. First, the particle swarm optimization method combined with the gradient-based search method is applied to tune unknown parameters in the state-space model and the steady-state model for each operation condition. Then, the sensitive parameters are expanded to the polynomial equations. Moreover, the reconstructed model including coefficients in the polynomial equations are determined by using the particle swarm optimization method with gradient-based search method for whole operation conditions. To show the slowly time-varying performance of a solid oxide fuel cell, an adaptive optimal learning law based on the optimization technology is proposed to online minimize a cost function with the information of the estimation error. The estimation error is extracted through several low-pass filters and simple algebraic calculation. Finally, the proposed offline tuning strategy and the developed online adaptive estimation method are verified by conducting experiments on a practical solid oxide fuel cell test bench.

Prognostic Utility of Stress Testing and Cardiac Biomarkers in Menopausal Women at Low to Intermediate Risk for Coronary ARTery Disease (SMART Study): 5-Year Outcome.

BACKGROUND: In women with low to intermediate risk of coronary artery disease (CAD), prognostic detection strategies have been controversial. We present the follow-up data of the SMART trial in peri/postmenopausal women at low to intermediate risk of CAD. OBJECTIVES: To determine the value of contrast stress echocardiography (CSE), stress electrocardiogram (sECG), and serum biomarkers for prediction of cardiovascular events (CE) in peri/postmenopausal women at low to intermediate risk of CAD. MATERIALS AND METHODS: From January 2004 to August 2007, 400 peri/postmenopausal women were prospectively enrolled. All women had detailed risk factor assessment, and underwent simultaneous CSE (Definity®, Lantheus Medical Imaging) and sECG. Laboratories included brain natriuretic peptide (BNP), atrial natriuretic peptide, endothelin, and high sensitivity C-reactive protein. Wall motion score index was based on a 16-segment model. Abnormal CSE was defined as new or worsening wall motion abnormality at stress, while abnormal sECG was ≥1 mm horizontal/downsloping ST segment depression/elevation (80 mseconds duration). Self-reported outcome data were collected from a mailed Women's Heart Clinic Questionnaire. CE outcomes included all-cause mortality, nonfatal myocardial infarction (MI), heart failure, chest pain hospitalization or development of typical angina (CP), and revascularization (REVASC). Adjusted Cox proportional hazard ratios (HR; 95% confidence intervals) were reported. RESULTS: A total of 366 women (54.4 ± 5.5 years, Framingham risk 6.5% ± 4.4%) completed simultaneous CSE and sECG. Forty-two (11.5%) had abnormal CSE, while sECG was abnormal in 22 (6%) women. Follow-up (4.4 ± 1.2 years) was available in 315/366 (86%) women (78% exercise-CSE, 22% dobutamine-CSE). In those who completed follow-up, CSE was abnormal in 33 women (10.5%) and sECG was abnormal in 21 (6.7%). In 33 women with abnormal CSE, sECG was abnormal in 7 (21.2%) and normal in 26 (79%), p = 0.0004. CE occurred in 27 (8.6%) women: 8 all-cause mortality, 2 nonfatal MI, 13 CP, and 4 REVASC. CE occurred in 21% versus 7% of women with abnormal versus normal CSE, p = 0.014 and 38% versus 6% of women with abnormal versus normal sECG, p < 0.0001. Rest BNP was higher in women with CE versus those without (p = 0.018). Abnormal sECG and abnormal CSE were associated with CE, while only abnormal sECG was an independent predictor of CE (adjusted HR 10.3 [1.9-61.4], p = 0.007). Of the laboratory results, only BNP was associated with CE (adjusted HR 2.9 [1.1-7.3], p = 0.028). CONCLUSIONS: sECG and rest BNP were independent predictors of subsequent CE within 5 years in peri/postmenopausal women at low to intermediate risk of CAD.

A multicenter, prospective study to evaluate the use of contrast stress echocardiography in early menopausal women at risk for coronary artery disease: trial design and baseline findings.

AIMS: This multisite prospective trial, Stress Echocardiography in Menopausal Women At Risk for Coronary Artery Disease (SMART), aimed to evaluate the prognostic value of contrast stress echocardiography (CSE), coronary artery calcification (CAC), and cardiac biomarkers for prediction of cardiovascular events after 2 and 5 years in early menopausal women experiencing chest pain symptoms or risk factors. This report describes the study design, population, and initial test results at study entry. METHODS: From January 2004 through September 2007, 366 early menopausal women (age 54±5 years, Framingham risk score 6.51%±4.4 %, range 1%-27%) referred for stress echocardiography were prospectively enrolled. Image quality was enhanced with an ultrasound contrast agent. Tests for cardiac biomarkers [high-sensitivity C-reactive protein (hsCRP), atrial natriuretic protein (ANP), brain natriuretic protein (BNP), endothelin (ET-1)] and cardiac computed tomography (CT) for CAC were performed. RESULTS: CSE (76% exercise, 24% dobutamine) was abnormal in 42 women (11.5%), and stress electrocardiogram (ECG) was positive in 22 women (6%). Rest BNP correlated weakly with stress wall motion score index (WMSI) (r=0.189, p<0.001). Neither hsCRP, ANP, endothelin, nor CAC correlated with stress WMSI. Predictors of abnormal CSE were body mass index (BMI), diabetes mellitus, family history of premature coronary artery disease (CAD), and positive stress ECG. Twenty-four women underwent clinically indicated coronary angiography (CA); 5 had obstructive (≥50%), 15 had nonobstructive (10%-49%), and 4 had no epicardial CAD. CONCLUSIONS: The SMART trial is designed to assess the prognostic value of CSE in early menopausal women. Independent predictors of positive CSE were BMI, diabetes mellitus, family history of premature CAD, and positive stress ECG. CAC scores and biomarkers (with the exception of rest BNP) were not correlated with CSE results. We await the follow-up data.

Accuracy and precision of three echocardiographic methods for estimating mean pulmonary artery pressure.

BACKGROUND: Pulmonary hypertension is defined as resting mean pulmonary artery pressure (MPAP) ≥ 25 mm Hg. MPAP pressure estimation by right-sided heart catheterization (RHC) is considered the gold standard; however, its invasiveness limits repeated and frequent use. The purpose of this study was to compare the accuracy and precision of three echocardiographic methods for estimating MPAP. METHODS: We prospectively studied 117 patients with simultaneous RHC and echocardiography. MPAP was calculated by three echocardiographic methods: (1) mean gradient method (adding the right ventricular-right atrial mean systolic gradient to the right atrial pressure), (2) Chemla equation (0.61 × systolic pulmonary artery pressure + 2 mm Hg), and (3) Syyed equation (0.65 × systolic pulmonary artery pressure + 0.55 mm Hg). MPAP calculated by these three methods was compared with that obtained invasively by RHC. RESULTS: The mean ± SD of the differences between invasive MPAP and the three echocardiographic methods were -1.6 ± 7.7 mm Hg for the mean gradient method, -3.7 ± 7.4 mm Hg for the Chemla formula, and -3.2 ± 7.6 mm Hg for the Syyed formula. Median absolute differences were 5.5 mm Hg (mean gradient), 5.7 mm Hg (Chemla; P = .45 vs mean gradient), and 6.0 mm Hg (Syyed; P = .23 vs mean gradient). Accuracy (calculated MPAP within 10 mm Hg of RHC-measured MPAP) was 81% (mean gradient), 77% (Chemla), and 76% (Syyed). CONCLUSIONS: Echocardiographic estimation of MPAP by the mean gradient method had similar accuracy and precision compared with the Chemla and Syyed methods. The acceptable accuracy of these methods suggests that they are equally suitable for clinical use.

An alternative echocardiographic method to estimate mean pulmonary artery pressure: diagnostic and clinical implications.

BACKGROUND: The aim of this study was to evaluated an alternative echocardiographic method to calculate mean pulmonary arterial pressure (MPAP). METHODS: One hundred two patients were studied with simultaneous right-heart catheterization (RHC) and echocardiography. MPAP was calculated by adding the right ventricular-right atrial mean systolic gradient to right atrial pressure. RESULTS: The mean difference between MPAP calculated using this method and RHC-derived MPAP was -1.6 mm Hg, less than that of traditional systolic pulmonary arterial pressure (SPAP; -6.4 mm Hg) and MPAP estimated using the pulmonary regurgitation method (-13.9 mm Hg). The median absolute percentage difference of the MPAP calculations relative to RHC was significantly less with this method than with the pulmonary regurgitation method (18% vs 71%; P < .001) and similar to the SPAP method (both 18%; P = .30). CONCLUSION: MPAP calculated using the proposed method is as accurate as SPAP calculation and less variable than previous methods, thus allowing widespread clinical use.

American Society of Echocardiography Consensus Statement on the Clinical Applications of Ultrasonic Contrast Agents in Echocardiography.

UNLABELLED: ACCREDITATION STATEMENT: The American Society of Echocardiography (ASE) is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians. The ASE designates this educational activity for a maximum of 1 AMA PRA Category 1 Credit.trade mark Physicians should only claim credit commensurate with the extent of their participation in the activity. The American Registry of Diagnostic Medical Sonographers and Cardiovascular Credentialing International recognize the ASE's certificates and have agreed to honor the credit hours toward their registry requirements for sonographers. The ASE is committed to resolving all conflict-of-interest issues, and its mandate is to retain only those speakers with financial interests that can be reconciled with the goals and educational integrity of the educational program. Disclosure of faculty and commercial support sponsor relationships, if any, have been indicated. TARGET AUDIENCE: This activity is designed for all cardiovascular physicians, cardiac sonographers, and nurses with a primary interest and knowledge base in the field of echocardiography; in addition, residents, researchers, clinicians, sonographers, and other medical professionals having a specific interest in contrast echocardiography may be included. OBJECTIVES: Upon completing this activity, participants will be able to: 1. Demonstrate an increased knowledge of the applications for contrast echocardiography and their impact on cardiac diagnosis. 2. Differentiate the available ultrasound contrast agents and ultrasound equipment imaging features to optimize their use. 3. Recognize the indications, benefits, and safety of ultrasound contrast agents, acknowledging the recent labeling changes by the US Food and Drug Administration (FDA) regarding contrast agent use and safety information. 4. Identify specific patient populations that represent potential candidates for the use of contrast agents, to enable cost-effective clinical diagnosis. 5. Incorporate effective teamwork strategies for the implementation of contrast agents in the echocardiography laboratory and establish guidelines for contrast use. 6. Use contrast enhancement for endocardial border delineation and left ventricular opacification in rest and stress echocardiography and unique patient care environments in which echocardiographic image acquisition is frequently challenging, including intensive care units (ICUs) and emergency departments. 7. Effectively use contrast echocardiography for the diagnosis of intracardiac and extracardiac abnormalities, including the identification of complications of acute myocardial infarction. 8. Assess the common pitfalls in contrast imaging and use stepwise, guideline-based contrast equipment setup and contrast agent administration techniques to optimize image acquisition.

A stroke of bad luck: left ventricular pacemaker malposition.

Lead wire malposition is thought to be a rare complication of both permanent and temporary pacemaker implantation. The actual incidence and prevalence are unknown because of lack of reporting, which complicates consistency in treatment. Potential safeguards to prevent complications as a result of lead malposition are readily available, effective, and inexpensive, but underused. An 80-year-old white man presented to our institution with right-arm paresthesias and weakness, as well as facial numbness, 4 months after undergoing single-chamber pacemaker placement by an outside hospital because of tachybrady syndrome. Computed tomography scan of the head revealed a recent ischemic stroke. Electrocardiography revealed right bundle-branch block morphology of paced beats. Chest radiography raised the suspicion of lead malposition because of the posterior deflection of the lead wire on the lateral view. Transesophageal echocardiography conclusively demonstrated a pacemaker lead wire that transversed the aortic valve into the left ventricle without the presence of thrombus. The patient underwent successful removal of the device with a transcatheter approach, and a replacement pacemaker was placed for symptomatic bradycardia. It was recently suggested that echocardiography is not able to adequately detect thrombi on lead wires and that all patients with stroke should undergo open heart surgery for device extraction. We think that this does not adequately incorporate the significant comorbidities for some patients in the risk-benefit decision-making processes and that a transcutaneous approach is reasonable for patients without evidence of thrombi who are poor surgical candidates for an open heart procedure. A 12-lead electrocardiogram should be performed on every patient after pacemaker insertion. If right bundle-branch block morphology of paced beats is noted, chest radiography including a lateral view should be ordered. If there is any ambiguity regarding lead placement, echocardiography should be performed for determining lead malposition.

Real-time three-dimensional ultrasound for continuous popliteal blockade: a case report and image description.

Two-dimensional ultrasound guidance has been used as an adjunct for neural blockade. With the development of newer ultrasound technology, three-dimensional ultrasound imaging is now available and may offer improved visualization of anatomic structures and relationships. We describe the successful blockade of the popliteal nerve with three-dimensional ultrasound guidance and image description.

Upper-extremity exercise training in heart failure.

PURPOSE: Aerobic exercise training (ExTR), predominantly performed with lower extremities, has been used to reverse heart failure (HF)-related exercise intolerance. The present study determined the safety and efficacy of upper-extremity exercise in HF subjects because daily activities are performed using both upper and lower extremities and there is little cross-training effects between extremities. METHODS: Seven subjects underwent 36 sessions (40 minutes, 3 times per week for 12 weeks) of upper-extremity ExTR (ARM ExTR) using arm ergometers, the arm function of a NuStep device, and an Airdyne stationary cycle. Exercise intensity and duration during weeks 1 to 4 were gradually increased to achieve a 75% to 85% peak heart rate. Pre- and post-ExTR tests included arm ergometer cardiopulmonary testing with echocardiography and quality of life self-administered surveys. RESULTS: After ARM ExTR test duration increased by 22% (P = .008), respiratory exchange ratio increased by 10% (P = .02), whereas peak oxygen consumption was not improved. Echocardiographic parameters were not altered by ARM ExTR. The total scores of both the Minnesota Living With Heart Failure Questionnaire (P = .02) and the Medical Outcomes Study-36 questionnaire (P = .05) were improved, but the Functional Status Questionnaire scores were not improved. CONCLUSIONS: Although this study was limited in the number of subjects and lacked a control group, results indicate that ARM ExTR is safe and well-tolerated by persons diagnosed with HF, a finding that is relevant for individuals with HF who cannot exercise with lower extremities.

Efficacy and time-efficiency of a "sonographer-driven" contrast echocardiography protocol in a high-volume echocardiography laboratory.

BACKGROUND: Contrast echocardiography (CE) has not gained widespread use despite numerous studies demonstrating its efficacy in the assessment of left ventricular (LV) function. METHODS: We sought to determine whether CE could be used in a high-volume echocardiography laboratory in a clinically effective and time efficient manner. We implemented a protocol with a feasibility phase and an established phase. Cost-benefit analyses were done on the basis of time use. RESULTS: During the feasibility and established phases, data on 119 and 672 patients, respectively, were obtained. After a "sonographer-driven" protocol, contrast studies represented 7% to 8% of the total number of routine transthoracic and stress studies. Stress studies accounted for only 15% of the total number of contrast studies. Obesity was the most common indication for contrast use. LV visualization indices and wall thickening assessment, as evaluated by 2 blinded readers, were significantly improved with CE compared with second harmonic imaging alone. The time to make the decision to use CE and the time taken to administer contrast decreased significantly from the feasibility phase to the established phase (8.3 +/- 5 vs 7.6 +/- 5 min, P <.01, and 13.4 +/- 10 vs 10.2 +/- 5 min, P <.001, respectively). On the basis of time use only, a cost analysis indicated that savings were obtained at a 10-minute reduction in study time. CONCLUSIONS: A "sonographer-driven" CE protocol for LV assessment is feasible in high-volume echocardiography laboratories. It is clinically effective because it significantly improves LV global and regional wall motion visualization. A "sonographer-driven" CE protocol can reduce decision and administration times substantially, thus making CE time-efficient.