Medical systems are composed of medical devices and apps which are developed independently by different vendors. A set of communication patterns, based on asynchronous message-passing, has been proposed to loosely integrate medical devices and apps. These patterns guarantee the point-to-point quality of communication service (QoS) by local inspection of messages at its constituent components. These local mechanisms inspect the property of messages to enforce a set of parametrized local QoS properties. Adjusting these parameters to achieve the required point-to-point QoS is non-trivial and depends on the involved components and the underlying network. We use Timed Rebeca, an actor-based formal modeling language, to model such systems and asses their QoS properties by model checking. We model the components of communication patterns as distinct actors. A composite medical system using several instances of patterns is subject to state-space explosion. We propose a reduction technique preserving QoS properties. We prove that our technique is sound and show the applicability of our approach in reducing the state space by modeling a clinical scenario made of several instances of patterns.