Many medical devices must bring together a disparate array of hardware and software components, as well as support a sophisticated, multi-layered Human- Machine Interface (HMI). Persistent Publish/Subscribe (PPS) messaging offers versatile, easy-to-use and reliable messaging that simplifies system design and facilitates HMI implementation. This paper describes PPS messaging in a medical data aggregator and publisher (QNX Medical Demo, or MD) that brings together in a portable demonstration application a blood pressure monitor, spirometer, pulse oximeter, ECG, and insulin pump. PPS also provides messaging to a remote manager, for secure internet communication through the cloud to a records database and a portable tablet.