Upon undertaking the visionary task of constructing a "digital human" for space physiology, it is prudent to focus on specific questions that might be answered by integrated models. For example, to address cardiovascular alterations risks during space travel, one can benefit from modeling the steady-state and dynamical responses of cardiovascular system variables (heart rate, blood pressure, etc.) following hypothetical perturbations of the system's parameters, such as cardiac electrical state changes. At a multi-system level, one may want to study effects of exercise by incorporating models of skeletal muscle, metabolism, etc. This paper reports on initial efforts to link multiple human system models using an interdisciplinary approach. In this effort, we have connected a medium-fidelity physics-based model of the left and right ventricles of the heart with an existing cardiovascular system simulation (RCVSIM), using the High Level Architecture (HLA) standard for simulation interoperability developed in the Department of Defense (DoD), to produce a Cardiovascular - Ventricular System (CVVS) federated simulation. The combined simulation allows hemodynamic consequences of an arrhythmia to be simulated with modest computational resources in a reasonable time. The paper also reports on extensions to make the simulation suitable for simulating and understanding cardiovascular responses to different exercise regimens.
