Safety Assurance of Medical Cyber-Physical Systems using Hybrid Automata: A Case Study on Analgesic Infusion Pump

Interactions between the medical devices and the human body in Medical Cyber Physical Systems (MCPSes) are considered for verifying patient’s safety. The discrete and continuous dynamics of an MCPS require a hybrid approach towards modeling and analysis. In this regard, hybrid automata is used to model analgesic infusion pumps, an exemplary MCPS application. Excursions of unsafe states in this model such as respiratory distress due to drug overdose, are analyzed by hybrid automata reachability analysis. However, given the time delayed dynamics of traditional reachability analysis using Zonotope approximations of states is not feasible. Thus, we propose a zero order hold approximation on the time delayed state variables and perform the reachability analysis on the resulting approximate model. We also provide a bound on the maximum error of the reachability analysis methodology.