A Flowthrough Infusion Calorimeter for Measuring Muscle Energetics: Design and Performance

The heat produced during muscle contraction arises from distinct underlying cellular processes. While current calorimeters can measure total muscle heat production, none can allow accurate titration and infusion of chemical drugs to probe the thermodynamic mechanisms that underlie various heart diseases. We have constructed a calorimeter that incorporates an infusion system for exposing muscle samples to time-varying concentrations of pharmacological agents. The design of the instrument is informed by the development and the use of analytical lumped parameter and finite-element models. This new infusion calorimeter uses thermopile-based heat sensors to achieve a noise-equivalent power of 2.6
$\text {nW}\cdot \text {Hz}^{ {-1/2}}$
and a signal-to-noise ratio of up to approximately 1700. We report on the modeling and optimization techniques that were used to inform our design. We characterize the instrument’s performance and demonstrate its utility by exposing muscle to pharmacological interventions that mimic two cardiac disease conditions, acute force impairment and dynamic contracture.