Orhan Soykan

Development of a novel FRET immunosensor technique

We report on a novel technique to develop an optical immunosensor based on fluorescence resonance energy transfer (FRET). IgG antibodies were labeled with acceptor fluorophores while one of three carrier molecules (protein A, protein G, or F(ab)2 fragment) was labeled with donor fluorophores. The carrier molecule was incubated with the antibody to allow specific binding to the Fc portion. The labeled antibody-protein complex was then exposed to specific and nonspecific antigens, and experiments were designed to determine the in solution response. The paper reports the results of three different donor-acceptor FRET pairs, fluorescein isothiocyanate/tetramethylrhodamine isothiocyanate, Texas Red/Cy5, and Alexa Fluor 546/Alexa Fluor 594. The effects of the fluorophore to protein conjugation ratio (F/P ratio) and acceptor to donor fluorophore ratios between the antibody and protein (A/D ratio) were examined. In the presence of specific antigens, the antibodies underwent a conformational change, resulting in an energy transfer from the donor to the acceptor fluorophore as measured by a change in fluorescence. The non-specific antigens elicited little or no changes. The Alexa Fluor FRET pair demonstrated the largest change in fluorescence, resulting in a 35% change. The F/P and A/D ratio will affect the efficiency of energy transfer, but there exists a suitable range of A/D and F/P ratios for the FRET pairs. The feasibility of the FRET immunosensor technique was established; however, it will be necessary to immobilize the complexes onto optical substrates so that consistent trends can be obtained that would allow calibration plots.

Advances in Medical Devices and Medical Electronics

Medical devices and medical electronics are areas that had little to offer 100 years ago. However, there were three important existing technologies that led to many further developments over the following 100 years. These are the stethoscope, electrocardiography, and X-ray medical imaging. Although these technologies had been described and were available to some extent when the Proceedings of the IEEE pages first appeared, they had yet to achieve the widespread use that they have today. The stethoscope is the oldest of these, and it helped physicians to hear sounds of the body and relate them to functioning and malfunctioning organs. The early use of the stethoscope by physicians was more of an art than a science, but as the Proceedings matured, so did this technology. Engineers were able to make this a more quantitative process by graphically displaying the sounds and ultimately using techniques such as voiceprint analysis to assist the physician in diagnosis and monitoring of treatment. The electrocardiograph had been invented a few years prior to the appearance of the Proceedings, but the apparatus was awkward to use, especially for sick people, and was considered more of an oddity than a viable medical technology 100 years ago. Today, it and devices derived from it such as cardiac patient monitors are important parts of our healthcare system. Similarly, X-rays represented a new technology 100 years ago, but unlike electrocardiography physicians immediately saw the value of this technology and quickly adopted it. Many improvements have been made to the basic technology over the last 100 years culminating in computer tomography and complex image processing. Other devices to create high-quality and 3-D medical images have also been developed in recent years to make medical imaging a very important aspect of clinical care today. Looking to the future is always a difficult task, but it is clear that the electronic health record will play an important role in consolidating the information from various medical devices as well as providing readily available data on patients wherever it might be needed. Future medical devices will need to not only address the problems of diagnostic and therapeutic medicine but also be capable of addressing important societal problems such as worldwide disparities in the availability of medical care, continually rising healthcare costs, and healthcare for travel beyond Earth. The next 100 years promises to be even more exciting than the last from the perspective of medical devices and medical electronics.

Genome-Wide Association of Implantable Cardioverter-Defibrillator Activation With Life-Threatening Arrhythmias

Objectives To identify genetic factors that would be predictive of individuals who require an implantable cardioverter-defibrillator (ICD), we conducted a genome-wide association study among individuals with an ICD who experienced a life-threatening arrhythmia (LTA; cases) vs. those who did not over at least a 3-year period (controls). Background Most individuals that receive implantable cardioverter-defibrillators never experience a life-threatening arrhythmia. Genetic factors may help identify who is most at risk. Methods Patients with an ICD and extended follow-up were recruited from 34 clinical sites with the goal of oversampling those who had experienced LTA, with a cumulative 607 cases and 297 controls included in the analysis. A total of 1,006 Caucasian patients were enrolled during a time period of 13 months. Arrhythmia status of 904 patients could be confirmed and their genomic data were included in the analysis. In this cohort, there were 704 males, 200 females, and the average age was 73.3 years. We genotyped DNA samples using the Illumina Human660 W Genotyping BeadChip and tested for association between genotype at common variants and the phenotype of having an LTA. Results and Conclusions We did not find any associations reaching genome-wide significance, with the strongest association at chromosome 13, rs11856574 at Pu200a=u200a5×10−6. Loci previously implicated in phenotypes such as QT interval (measure of the time between the start of the Q wave and the end of the T wave as measured by electrocardiogram) were not found to be significantly associated with having an LTA. Although powered to detect such associations, we did not find common genetic variants of large effect associated with having a LTA in those of European descent. This indicates that common gene variants cannot be used at this time to guide ICD risk-stratification. Trial Registration ClinicalTrials.gov NCT00664807

Polymorphisms associated with ventricular tachyarrhythmias: rationale, design, and endpoints of the ‘diagnostic data influence on disease management and relation of genomics to ventricular tachyarrhythmias in implantable cardioverter/defibrillator patients (DISCOVERY)’ study

Implantable cardioverter-defibrillator (ICD) therapy is effective in primary and secondary prevention for patients who are at high risk of sudden cardiac death. However, the current risk stratification of patients who may benefit from this therapy is unsatisfactory. Single nucleotide polymorphisms (SNPs) are DNA sequence variations occurring when a single nucleotide in the genome differs among members of a species. A novel concept has emerged being that these common genetic variations might modify the susceptibility of a certain population to specific diseases. Thus, genetic factors may also modulate the risk for arrhythmias and sudden cardiac death, and identification of common variants could help to better identify patients at risk. The DISCOVERY study is an interventional, longitudinal, prospective, multi-centre diagnostic study that will enrol 1287 patients in approximately 80 European centres. In the genetic part of the DISCOVERY study, candidate gene polymorphisms involved in coding of the G-protein subunits will be correlated with the occurrence of ventricular arrhythmias in patients receiving an ICD for primary prevention. Furthermore, in order to search for additional sequence variants contributing to ventricular arrhythmias, a genome-wide association study will be conducted if sufficient a priori evidence can be gathered. In the second part of the study, associations of SNPs with ventricular arrhythmias will be sought and a search for potential new biological arrhythmic pathways will be investigated. As it is a diagnostic study, DISCOVERY will also investigate the impact of long-term device diagnostic data on the management of patients suffering from chronic cardiac disease as well as medical decisions made regarding their treatment.

Solute diffusion through fibrotic tissue formed around protective cage system for implantable devices

This article presents the concept of an implantable cage system that can house and protect implanted biomedical sensing and therapeutic devices in the body. Cylinder-shaped cages made of porous polyvinyl alcohol (PVA) sheets with an 80-µm pore size and/or stainless steel meshes with 0.54-mm openings were implanted subcutaneously in the dorsal region of rats for 5 weeks. Analysis of the explanted cages showed the formation of fibrosis tissue around the cages. PVA cages had fibrotic tissue growing mostly along the outer surface of cages, while stainless steel cages had fibrotic tissue growing into the inside surface of the cage structure, due to the larger porosity of the stainless steel meshes. As the detection of target molecules with short time lags for biosensors and mass transport with low diffusion resistance into and out of certain therapeutic devices are critical for the success of such devices, we examined whether the fibrous tissue formed around the cages were permeable to molecules of our interest. For that purpose, bath diffusion and microfluidic chamber diffusion experiments using solutions containing the target molecules were performed. Diffusion of sodium, potassium and urea through the fibrosis tissue was confirmed, thus suggesting the potential of these cylindrical cages surrounded by fibrosis tissue to successfully encase implantable sensors and therapeutic apparatus.

Signal processing for sensor arrays

Five methods have been developed to process output signals from sensor arrays to improve sensor characteristics. A multielement capacitive force sensor array with nonlinear characteristics and inter-element cross-talk was used to demonstrate and compare the performance of these methods: (1) Variable Threshold, which calculated a threshold value from a histogram of the data to determine whether the output of each element was due to an input or cross-talk; (2) Algebraic Cross-Talk Reduction, which reduced the cross-talk between array elements by solving for the input matrix from the input-output relation of the sensor; (3) 2 x 2 Edge and Shape Detection, which was adapted from image processing techniques and enhanced the resolution of the sensor output; (4) Deconvolution using FFT; and (5) Artificial Neural Network, which was trained to learn the inverse relation of the sensor transfer function. The ability of these methods to reduce the cross-talk seen between sensor elements and more closely estimate the sensor input was studied. nPreprocessing of the sensor output, which consisted of calibration of each element using non-linear curve fitting, was used to compensate for the non-linear, non-uniform sensitivity characteristics of the sensor array elements. Postprocessing compensated for the dependency on the number of excited elements. nA comparative study of eight force sensor arrays using a 200 element test set showed that the simpler signal processing methods, Variable Threshold and 2 x 2 Edge and Shape Detection, performed well only for a limited number of input conditions especially when forces were applied through small objects. In general, neither reduced the error in determining total force by more than 30 percent. The Artificial Neural Network method, the most complicated and computationally intensive method during initial training but simple to implement thereafter, produced superior results for the majority of the input patterns applied to the sensor array, reducing the overall error by 6 to 83 percent. nAll five signal processing techniques reduced the overall errors of the sensor outputs, some more consistently than others. However, when the overall error magnitude was less than 10 percent, only the Artificial Neural Network reduced the error consistently, making it the method of choice. nThe results of this study showed that sensors having outputs with high error values can be converted into sensors with much lower output error using appropriate signal processing methods. Incorporation of such signal processing methods into sensor arrays allows the use of sensors with less than ideal characteristics.

Ventricular evoked response measurements from pacing electrodes

This work presents the results of a study using ventricular electrogram signals to identify the hearts evoked response following an electrical stimulus from a pacing electrode. Acute data were collected in vivo from seven human subjects and analyzed offline. The ability to recognize the evoked response following the pacing pulse was characterized as a function of the parameters of the pacing pulse. Although the characteristics of the evoked response were dependent on the patient, inter-patient data became consistent when the time derivative of the electrocardiogram was considered.

An electronic simulator for testing infant apnea monitors that utilizes realistic physiologic data

An electronic simulator of cardio-respiratory signals for testing and validating infant apnea monitors has been designed, built, tested, and applied. This device can simulate up to four signals that serve as inputs to infant apnea monitors including: (1) transthoracic --_-I__ f-_----__ -electrical impedance, (2) electrocardiogram, and (3) (a 1 chest and abdominal inductance plethysmograph signals. Up to 17 minutes of four channels of actual monitored signals can be stored in ROM and played back in real time to simulate signals coming from sensors on patients.

Long range closed loop telemetry for research

This work presents closed loop, bidirectional telemetry hardware with a telecommunication system to carry data and images for remote control and monitoring of a chronically implanted device. While the uplink of the signals from the implanted unit to the external receiver was achieved via electromagnetic waves, infra-red signals were utilized for downlinking to the implanted device. Telemetry in both directions was capable of maintaining a range more than two and a half meters, although the design was not optimized for data rate. The video and data link with the remote site, which was 15 km away from the implant site, was established using intranet connections utilizing peer-to-peer communications.

Automated piecewise linear modelling of pacing leads

This work presents the development of an automated modeling system to obtain a piece-wise linear electrical model of bradycardia pacing leads. In vivo studies were performed on a canine model under acute conditions, and a computer algorithm was used to determine and verify the model parameters. This iterative algorithm provided a first order electrical model of a type 4058 atrial pacing lead, where the mean point-to-point discrepancy in the time domain was around two percent. This study showed that a piece-wise linear equivalent circuit for the impedance seen by a pacemaker can be determined automatically from acutely collected data.<<ETX>>