Abstract. The design and implementation of software for medical devices is challenging due to their rapidly increasing functionality and the tight coupling of computation, control, and communication. The safetycritical nature and the lack of existing industry standards for verification, make this an ideal domain for exploring applications of formal modeling and analysis. In this study, we use a dual chamber implantable pacemaker as a case study for modeling and verification of control algorithms for medical devices in UPPAAL. We begin with detailed models of the pacemaker, based on the specifications and algorithm descriptions from Boston Scientific. We then define the state space of the closed-loop system based on its heart rate and developed a heart model which can nondeterministically cover the whole state space. For verification, we first specify unsafe regions within the state space and verify the closed-loop system against corresponding safety requirements. As stronger assertions are attempted, the closed-loop unsafe state may result from healthy openloop heart conditions. Such unsafe transitions are investigated with two clinical cases of Pacemaker Mediated Tachycardia and their corresponding correction algorithms in the pacemaker. Along with emerging tools for code generation from UPPAAL models, this effort enables modeldriven design and certification of software for medical devices.
Designing bug-free medical device software is difficult, especially in complex implantable devices that may be used in unanticipated contexts. Safety recalls of pacemakers and implantable cardioverter defibrillators due to firmware problems between 1990 and 2000 affected over 200,000 devices, comprising 41% of the devices recalled and are increasing in frequency. There is currently no formal methodology or open experimental platform to validate and verify the correct operation of medical device software. To this effect, a real-time Virtual Heart Model (VHM) has been developed to model the electrophysiological operation of the functioning (i.e. during normal sinus rhythm) and malfunctioning (i.e. during arrhythmia) heart. We present a methodology to extract timing properties of the heart to construct a timed-automata model. The platform exposes functional and formal interfaces for validation and verification of implantable cardiac devices. We demonstrate the VHM is capable of generating clinically-relevant response to intrinsic (i.e. premature stimuli) and external (i.e. artificial pacemaker) signals for a variety of common arrhythmias. By connecting the VHM with a pacemaker model, we are able to pace and synchronize the heart during the onset of irregular heart rhythms. The VHM has also been implemented on a hardware platform for closed-loop experimentation with existing and virtual medical devices. The VHM allows for exploratory electrophysiology studies for physicians to evaluate their diagnosis and determine the appropriate device therapy. This integrated functional and formal device design approach will potentially help expedite medical device certification for safer operation. Abstract-Designing bug-free medical device software is difficult, especially in complex implantable devices that may be used in unanticipated contexts. Safety recalls of pacemakers and implantable cardioverter defibrillators due to firmware problems between 1990 and 2000 affected over 200,000 devices, comprising 41% of the devices recalled and are increasing in frequency [1]. There is currently no formal methodology or open experimental platform to validate and verify the correct operation of medical device software. To this effect, a real-time Virtual Heart Model (VHM) has been developed to model the electrophysiological operation of the functioning (i.e. during normal sinus rhythm) and malfunctioning (i.e. during arrhythmia) heart. We present a methodology to extract timing properties of the heart to construct a timed-automata model. The platform exposes functional and formal interfaces for validation and verification of implantable cardiac devices. We demonstrate the VHM is capable of generating clinically-relevant response to intrinsic (i.e. premature stimuli) and external (i.e. artificial pacemaker) signals for a variety of common arrhythmias. By connecting the VHM with a pacemaker model, we are able to pace and synchronize the heart during the onset of irregular heart rhythms. The VHM has also been implemented on a hard...
s10009-013-0289-7}, title={Closed-loop verification of medical devices with model abstraction and refinement}, url={http://dx.doi.org/10.1007/ s10009-013-0289-7}, publisher={Springer Berlin Heidelberg}, keywords={Medical devices; Implantable pacemaker; Software verification; Cyberphysical systems; Model abstraction and refinement; CEGAR}, author={ Jiang, Zhihao and Pajic, Miroslav and Alur, Rajeev and Mangharam, Rahul}, pages={1-23}, language={English} } This paper is posted at ScholarlyCommons. AbstractThe design and implementation of software for medical devices is challenging due to the closed-loop interaction with the patient, which is a stochastic physical environment. The safety-critical nature and the lack of existing industry standards for verification, make this an ideal domain for exploring applications of formal modeling and closed-loop analysis. The biggest challenge is that the environment model(s) have to be both complex enough to express the physiological requirements, and general enough to cover all possible inputs to the device. In this effort, we use a dual chamber implantable pacemaker as a case study to demonstrate verification of software specifications of medical devices as timed-automata models in UPPAAL. The pacemaker model is based on the specifications and algorithm descriptions from Boston Scientific. The heart is modeled using timed automata based on the physiology of heart. The model is gradually abstracted with timed simulation to preserve properties. A manual Counter-Example-Guided Abstraction and Refinement (CEGAR) framework has been adapted to refine the heart model when spurious counter-examples are found. To demonstrate the closed-loop nature of the problem and heart model refinement, we investigated two clinical cases of Pacemaker Mediated Tachycardia and verified their corresponding correction algorithms in the pacemaker. Along with our tools for code generation from UPPAAL models, this effort enables modeldriven design and certification of software for medical devices. Computer EngineeringComments @article{vhm_sttt13, year={2013}, issn={1433-2779}, journal={International Journal on Software Tools for Technology Transfer}, doi={10.1007/s10009-013-0289-7}, title={Closed-loop verification of medical devices with model abstraction and refinement}, url={http://dx.doi.org/10.1007/s10009-013-0289-7}, publisher={Springer Berlin Heidelberg}, keywords={Medical devices; Implantable pacemaker; Software verification; Cyber-physical systems; Model abstraction and refinement; CEGAR}, author={ Jiang, Zhihao and Pajic, Miroslav and Alur, Rajeev and Mangharam, Rahul}, pages={1-23}, language={English} } This journal article is available at ScholarlyCommonsAbstract. The design and implementation of software for medical devices is challenging due to the closed-loop interaction with the patient, which is a stochastic physical environment. The safety-critical nature and the lack of existing industry standards for verification, make this an ideal domain for exploring applications of formal modeling ...
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