Improving In vitro Evaluation Capabilities of Cardiac Assist Devices through a Validated Exercise Simulation

Cardiac assist devices require thorough in vitro evaluation prior to in vivo animal trials, which is often undertaken in mock circulatory loops. To allow for best possible device development, mock circulatory loops need to be able to simulate a variety of patient scenarios. Transition from rest to exercise is one of the most commonly simulated patient scenarios, however, to validate in vitro exercise test beds, baseline data on how the healthy heart and circulatory system responds to exercise is required. Steady state and time response data for heart rate (HR), stroke volume (SV) and cardiac output (CO) was continuously recorded using impedance cardiography in 50 healthy subjects (27 male / 23 female) during exercise on a recumbent exercise ergometer. This data was then used to implement an exercise simulation in a mock circulatory loop and both the steady state and transient results were compared with the mean response of subjects transitioning from rest to 60 W exercise. When transitioning from rest to exercise the time constant (τ) and rise time (t
_r
) for HR, SV and CO were between 10.6-19.3s and 24.7-44.3s respectively for both sexes. No significant differences between the genders were found for τ and t
_r
(p>0.05). Mock circulatory loop results of HR, SV and CO were in good accordance with human data. The present data was used to successfully validate in vitro exercise simulations and may be used to validate in silico numerical simulations of exercise, thus further improving the evaluation capabilities for existing and under development cardiac assist devices.