Development of a shear ultrasonic spectroscopy technique for the evaluation of viscoelastic fluid properties: Theory and experimental validation

In-situ measurement of viscosity advances the field of rheology, and aides the development of sensing systems for condition and performance monitoring of lubricated mechanisms. Many lubricated mechanisms, such as journal bearings or seals, are characterised by three-layer interfaces; an oil separating two solid (usually metallic) bodies. The viscoelastic study of the lubricating oil in layered systems is possible in-situ by means of ultrasonic reflection (Schirru et al. (2015)). General solutions exist for the reflection of longitudinal plane waves from multi-layered solid-fluid systems. Similar solutions can be applied to plane shear waves. The use of a quarter-wavelength intermediate matching layer improves the sensitivity of the ultrasonic measurement and overcomes problems of acoustic mismatch. This opens the possibility of using reflectance methods to measure engineering (metal-oil) bearing applications that are acoustically mismatched. In this paper, a rigorous mathematical model for wave propagation in a three-layer system is solved for the reflection coefficient modulus and validated using a quarter wavelength ultrasonic viscometer. The model was tested against experimental data for two Newtonian reference fluids, water and hexadecane, and for one non-Newtonian reference fluid, squalene plus polyisoprene (SQL + PIP), measured ultrasonically at frequencies between 5 and 15 MHz. The results are in agreement with the expected viscosity values for the reference fluids. Further, the viscosity measurement is not limited to the resonance frequency, but it is performed over a broad band frequency range. This is important to improve measurement confidence and accurate spectroscopy measurement for the determination of viscoelastic properties.

[New implantable devices for patient management: role and perspectives of remote monitoring of implantable cardioverter-defibrillators]

A large number of studies have demonstrated that remote control of implantable devices (home monitoring, HM) is beneficial for patients, as it allows strict and tailored controls with earlier identification of potential problems, by avoiding unnecessary visits. HM is also beneficial for hospitals, as it progressively reduces the resources necessary for routine controls and contributes to a better management of critical patients. According to current European and Italian guidelines, HM can replace standard ambulatory monitoring, thereby decreasing the number of outpatient visits for each individual patient (it is possible to schedule a comprehensive clinical evaluation at 1 year rather than every 6-8 months, while performing controls at 1 and 3 months by remote transmission). At present, however, reimbursement of HM services is not covered by the National Health System and, as a consequence, cannot be performed as an institutional activity within the hospital. In addition, many critical issues remain to be resolved before the HM system can be fully implemented into daily clinical management, particularly in patients with heart failure at higher risk for sudden cardiac death.

Remote monitoring of CRT-ICD: the multicenter Italian CareLink evaluation--ease of use, acceptance, and organizational implications

PURPOSE

The Medtronic CareLink allows remote implantable device follow-up. In this first European experience with CareLink, we assessed the ease of use of the system, the acceptance, and satisfaction of patients and clinicians.

METHODS

Patients implanted with biventricular defibrillators for more than 6 months received the CareLink monitor and were trained to perform home device interrogation and transmission. Patient and clinician experience and preference were evaluated through specific questionnaires.

RESULTS

Sixty-seven patients were enrolled and were able to perform data transmissions during the 3-month study duration. The overall duration of interrogation procedure was 7 +/- 5 minutes, and frequently the procedure did not require the assistance of a caregiver. Patients reported a general preference for remote versus in-clinic follow-up and described a sense of reassurance created by the remote monitoring capability.In the centers, the review procedure was successful; its mean duration was 5 +/- 2 minutes per transmission and the users indicated that the access and navigation of the review website were easy. At the end of the evaluation, the data available for remote review were judged complete and adequate to provide almost the same standard of care as that offered in traditional in-clinic visit. In general, the remote monitoring was seen as a potential tool to improve the clinical management of patients with device.

CONCLUSIONS

The ease of use, satisfaction, and acceptance of the CareLink Network in European clinical practice appears elevated both for patients and for clinicians.

[Risk stratification for sudden cardiac death: should we juist consider ejection fraction?]

Sudden cardiac arrest is a leading cause of death in industrialized countries. There is solid clinical evidence for implantable cardioverter-defibrillators as the only effective means of preventing sudden cardiac arrest and reducing mortality in high-risk patients. The therapeutic strategy has definitively been validated, but we have not yet identified with the same effectiveness the patients who most likely will benefit from such therapy. Risk stratification of sudden death is therefore one of the major unresolved issues of modern cardiology. Current guidelines identify ejection fraction as the only instrumental parameter for risk stratification of sudden cardiac death. It is strongly consolidated from "old and new" clinical trials that ejection fraction reduction is the real powerful predictor of total mortality and sudden death regardless of its etiology; however it cannot be considered as an indisputable gold standard predictor of risk because it lacks of sensitivity and specificity in the prediction of sudden death. It is reasonable that many factors besides ejection fraction influence patient prognosis; there are different aspects suggesting that a reduction in ejection fraction is a risk factor only in combination with other risk factors. The implantable cardioverter-defibrillator therapy is expensive and associated with possible complications. We therefore need better methods for risk stratification of our patients in order to increase the real cost-effectiveness of current and future treatment options.

Surgical ablation of arrhythmias

The surgical approach was the earliest therapeutic ablation of hyperkinetic arrhythmias. Following the progressive improvements in electrophysiological mapping and operative techniques, new surgical approaches have been developed for the treatment of those arrhythmias related to ectopic phenomena or reentry mechanisms. These procedures have been proven to be highly effective but the associated morbidity and mortality were unacceptably high. More recent and advanced techniques of transcatheter ablation have revolutionized the treatment of these arrhythmias and now represent the treatment of choice in the majority of cases. However, the significant reduction in the operative risk and the improvement in patient outcome with respect to the past, thanks to a better patient selection and to advances in the surgical and myocardial protection techniques, make do that the surgical approach to some forms of arrhythmias is still valid, especially in those cases requiring associated surgery: atrial tachyarrhythmias in patients with congenital heart disease, post-ischemic ventricular tachycardias in patients who necessitate myocardial revascularization, and/or ventricular remodeling and chronic or paroxysmal atrial fibrillation in patients who require cardiac surgery. New techniques such as radiofrequency, microwaves and cryoablation guarantee the creation of linear and transmural lesions with minimum damage to the cardiac structures and appear very interesting as they are surgically simple and associated with shorter procedure times and less complications. The possibility of performing the ablative procedure completely on the epicardial surface may open the way for atrial fibrillation surgery on a totally beating heart and for procedures that are ever less invasive thus enabling treatment of patients without associated surgical indications.