A novel functional calibration method for real-time elbow joint angles estimation with magnetic-inertial sensors

Magnetic-inertial measurement units (MIMUs) are often used to measure the joint angles between two body segments. To obtain anatomically meaningful joint angles, each MIMU must be computationally aligned (i.e., calibrated) with the anatomical rotation axes. In this paper, a novel four-step functional calibration method is presented for the elbow joint, which relies on a two-degrees-of-freedom elbow model. In each step, subjects are asked to perform a simple task involving either one-dimensional motions around some anatomical axes or a static posture. The proposed method was implemented on a fully portable wearable system, which, after calibration, was capable of estimating the elbow joint angles in real time. Fifteen subjects participated in a multi-session experiment that was designed to assess accuracy, repeatability and robustness of the proposed method. When compared against an optical motion capture system (OMCS), the proposed wearable system showed an accuracy of about 4° along each degree of freedom. The proposed calibration method was tested against different MIMU mountings, multiple repetitions and non-strict observance of the calibration protocol and proved to be robust against these factors. Compared to previous works, the proposed method does not require the wearer to maintain specific arm postures while performing the calibration motions, and therefore it is more robust and better suited for real-world applications.

Avoid delivering therapies for nonsustained fast ventricular tachyarrhythmia in patients with implantable cardioverter/defibrillator: the ADVANCE III Trial

INTRODUCTION

The purpose of this investigation is to evaluate whether a prolonged detection interval for life threatening ventricular tachyarrhythmia (VT) is able to reduce therapies (Rx) delivered by an implantable cardioverter/defibrillator (ICD). Until now, only the PREPARE trial demonstrated a reduction of ICD Rx in a cohort of primary prevention patients.

METHODS AND RESULTS

The ADVANCE III study is a prospective, randomized, parallel trial with 2 arms evaluating different intervals to detect (NID), i.e., 18/24 (as currently used) versus 30/40. The primary endpoint is to demonstrate a 20% reduction of ICD Rx (antitachycardia pacing or shocks) delivered to terminate spontaneous VT with a cycle length < or =320 ms in patients with Class I-IIA indication for ICD therapy, regardless of cardiac resynchronization capabilities. The worldwide investigation started in spring 2008 and is expected to be finished in 2011.

CONCLUSIONS

The ADVANCE III trial is the first randomized investigation evaluating the reduction of ICD Rx for fast VT due to a prolongation of NID in a general ICD patient cohort.

Flow dynamics of the St Jude Medical Symmetry aortic connector vein graft anastomosis do not contribute to the risk of acute thrombosis

BACKGROUND

The efficacy of the St Jude Medical Symmetry aortic connector (St Jude Medical, Inc, St Paul, Minn) for coronary artery bypass is currently debated. Potential drawbacks are the biocompatibility of the endoluminal device, the need for graft manipulation during the procedure, and the 90 degrees offset of the vein graft from the ascending aorta, which may induce graft kinking and abnormal fluid dynamics. In this article, a computational approach was designed to investigate the fluid dynamics pattern at the proximal graft.

METHODS

Four models of hand-sewn anastomoses and two models of automated anastomoses were constructed; a finite volume technique was used to simulate realistic graft fluid dynamics, including aortic compliance and proper aortic and graft flow rates. The anastomosis geometry performance was analyzed by calculating time-averaged wall shear stress and the oscillating shear index at the toe and heel regions of the proximal graft.

RESULTS

Time-averaged wall shear stress was significantly lower in the hand-sewn anastomosis models than in the two models that simulated the use of the aortic connector (0.38 +/- 0.07 Pa vs 1.32 +/- 0.4 Pa). Higher oscillating shear index values were calculated in the hand-sewn anastomosis models (0.15 +/- 0.02 Pa vs 0.06 +/- 0.02 Pa).

CONCLUSIONS

Automated anastomosis geometry is associated with less critical fluid dynamics than with conventional hand-sewn anastomosis: the shape of the proximal graft induces more physiological wall shear stresses and less oscillating flow, suggesting a lower risk of atherosclerotic plaque and intimal hyperplasia as compared with conventional anastomosis geometry. Therefore, the reported early thrombosis and late failure of the St Jude Medical aortic connector anastomoses are not related to unfavorable fluid dynamics.