Kristin Imenes

Automatic real-time detection of myocardial ischemia by epicardial accelerometer

OBJECTIVE Myocardial ischemia may be detected with epicardial accelerometers. We developed and tested automated algorithms for real-time detection of myocardial ischemia by accelerometer measurements in both experimental and clinical settings. METHODS In 10 pigs, an accelerometer was fixed to the epicardium in the area perfused by left anterior descending coronary artery. Acceleration and electrocardiogram were simultaneously recorded, and the QRS complex was automatically detected for exact timing of systole. Peak circumferential velocity and displacement were automatically calculated from epicardial acceleration signal within 150 milliseconds after peak R on electrocardiography. Global myocardial function was reduced by esmolol infusion, and regional function was altered by temporary left anterior descending occlusion. Automated ischemia detection analyses were tested in 7 patients during off-pump coronary artery bypass grafting. Left anterior descending coronary artery was occluded for 3 minutes before grafting. In both models, echocardiographic myocardial circumferential strain was used to confirm ischemia. RESULTS Systolic displacement changed most during left anterior descending occlusion. Negative displacement during ischemia was found in pigs (11.5 +/- 2.3 to -1.2 +/- 2.8 mm, P < .01); regional hypokinesia was found in clinical study (12.8 +/- 8.1 to 3.5 +/- 4.4 mm, P < .01). Ischemia was confirmed by echocardiography in both settings. Esmolol infusion induced smaller changes in automated accelerometer measurements than did left anterior descending occlusion (P < .01). CONCLUSIONS Automatic real-time detection of myocardial ischemia with epicardial accelerometer was feasible. Automated ischemia detection analysis may be used for continuous monitoring of myocardial ischemia during cardiac surgery.

MEMS Accelerometer-Based Heart Monitoring System with Myocardial Fixation

The drawbacks of existing post-operative heart monitoring systems create the demand for novel methods of monitoring patients heart activity. The continued advances in the field of micro electromechanical systems (MEMS) make it possible to create a heart monitoring system using commercially available sensors and develop a mission specific package for it. In this paper an early prototype of such a system system is described.

MEMS-based implantable heart monitoring system with integrated pacing function

Miniaturized accelerometer-based implantable heart monitoring systems may increase safety during cardiac surgery. Such systems can provide sustained monitoring compared to imaging techniques. During ischemia, changes in acceleration occur instantly and before changes can be observed by electrocardiography. This may allow earlier detection of adverse events like graft occlusion. Recent designs have been made to meet requirements for postoperative use by easy and safe removal. However, the implantation procedure has been too complicated. The system presented in this paper is a reworked package in which a 3-axis accelerometer is placed inside a stainless steel capsule fabricated by additive manufacturing (3D printing). A needle attached to the package allows for easy implantation. In addition, the metallic capsule makes it possible to use the device as a pacing lead. The system demonstrates easy implantation. Furthermore, in conjunction with a second electrode, pacing and electrical potential sensing functionality is demonstrated.

Implantable MEMS acceleration sensor for heart monitoring recent development and outlook

In this paper a new design for an implantable MEMS acceleration sensor for heart monitoring is described. Based on one of the smallest commercially available accelerometers we have developed a miniaturized system that allows for implantation into the heart muscle and to be used in closed chest application. The paper also assesses the mechanical strength of different cable to substrate bonding methods. As a result the built system is ready for animal experiments which are essential to verify if the presented design is appropriate.

Continuous monitoring of cardiac function by 3-dimensional accelerometers in a closed-chest pig model

OBJECTIVES Cardiac wall motions reflect systolic and diastolic function. We have previously demonstrated the ability of a miniaturized three-axis (3D) accelerometer to monitor left ventricular function in experimental models and in patients. The main aim of this study was to investigate the clinical utility of the method for monitoring the left and right ventricular function during changes in global and regional cardiac function in a postoperative closed-chest situation. METHODS In 13 closed-chest pigs, miniaturized 3D accelerometers were placed on the left ventricle in the apical and basal regions and in the basal region of the right ventricle. An epicardial 3D motion vector was calculated from the acceleration signals in each heart region. Peak systolic velocity along this 3D vector (3D V(sys)) was compared with the positive time derivative of the left and right ventricular pressure and with cardiac index during changes in global LV function (unloading, fluid loading, esmolol, dobutamine) and with ultrasound during regional left ventricular dysfunction (3-min occlusion of the left anterior descending coronary artery). RESULTS Significant and typical changes in accelerometer 3D V(sys) were seen in all heart regions during changes in global cardiac function. 3D V(sys) reflected the left and right ventricular contractility via significant correlations with the positive time derivative of the left and right ventricular pressure, r = 0.86 and r = 0.72, and with cardiac index r = 0.82 and r = 0.73 (all P < 0.001), respectively. The miniaturized accelerometers also detected regional dysfunction, but showed reduced ability to localize ischaemia as the 3D V(sys) in all heart regions showed similar reductions during coronary artery occlusion. CONCLUSIONS Miniaturized 3D accelerometers placed on the heart can assess global and regional function in a closed-chest model. The technique may be used for continuous postoperative monitoring after cardiac surgery.

Thermosonic bonding for ultrasound transducers: Low-temperature metallurgical bonding

A low-temperature bonding process for ultrasound transducers is presented: compatible with poling requirements, manufacturability and reliability. In this work, we demonstrate that a thermosonic bonding process can provide a reliable, metallurgical bond at moderate temperatures, even down to room temperature, with bonding times in the order of seconds. Bonding parameters (temperature, compression force, ultrasonic energy) were optimized by evaluating shear strength on Au stud bump bonded Si chips. Model systems have been bonded, mimicking a complete Electro-Acoustic Module (EAM), including a stack of IC emulator / flex interconnection / interface part of the ultrasound transducer.

Fabrication and assembly of MEMS accelerometer-based heart monitoring device with simplified, one step placement

Abstract An accelerometer-based heart monitoring system has been developed for real-time evaluation of heart wall movement. In this paper, assembly and fabrication of an improved device is presented along with system characterization and test data from an animal experiment. The new device is smaller and has simplified the implantation procedure compared to earlier prototypes. Leakage current recordings were well below those set by the corresponding standards.

Packaging of a multifunctional implantable heart monitoring device

This paper describes recent improvements of a myocardial accelerometer device, which can be used to perform continuous monitoring of heart activity with high specificity and sensitivity. The device is specified to be used for patients undergoing coronary bypass graft surgery. The improved device can reduce the complexity of implantation experienced with the former generation of sensors. A built-in function enabling temporary pacing was also integrated. Besides being an implantable accelerometer sensor, the device can pace the heart and sense the electrical signals when connected to an external pulse generator. Compliance tests for implantable medical device were carried out to prove the essential requirements set by the International Electrotechnical Commission.

Bond strength of conductive Si-Si fusion bonded seals

High temperature silicon direct (fusion) wafer bonding is a process with many application areas. Depending on the application, perfect insulation or zero resistance across the bonded interface is desired, but high bond strength is needed in both cases. Recently, we have presented a hydrophilic bonding process which resulted in ohmic behaviour and negligible electrical resistance of the bonding interface. This paper is an investigation of the bond strength of conductive hydrophilic high-temperature silicon direct wafer bonds. Dicing yield and pull test measurements have been performed. Bonding frames of widths of 100, 200, and 400 μm were fabricated. The measured resistance of chips from boron implanted wafers was 0.35-0.38 Ω, and the resistance of chips from three non-implanted wafers was below 0.68 Ω. The dicing yield was above 89 % for frame widths of 200 μm or wider. Bond strengths of 10.5-13.5 MPa were measured on frames of 400 μm width. There was no significant difference in bond strength between implanted wafers, non-implanted wafers, and wafers with an intentional 60 nm thick SiO2 at the bond interface. The results show that directly bonded silicon bond frames of 200 and 400 μm widths can be conductive and show ohmic behavior while they also have sufficient yield and bond strength for application as device seals in industrial products.

Simulation and analysis of bacterial particle transportation in urinary tract with urethral calculus

The transportation and distribution of living bacteria particles were analyzed in a computational fluid model with the mobile phase of human urine, which resembles the pathogenesis of bacterial urine tract infections with complications of urethral calculi. Interrelated processes contributing to the mass transport and bacteria growth in the urine flow were evaluated. The two-dimensional model was also solved computationally. The results reflected that a urethral calculus could bring about the backward dispersal of bacteriuria in the case of urine tract infection. Furthermore, the shape of urethral stone is an important factor in the biofilm development on its surface. We also designed the conceptual experimental system for in-vitro simulation and further verification, composed of a cell-based lab-on-a-chip and the photomultiplier-tube (PMT)-based bioluminescent detection module.