Controlled auxotonic twitch in papillary muscle: a new computer-based control approach

Based on new advancements in digital technology, we developed a PC- and DSP-based measurement and control system for isolated papillary muscle experiments. High flexibility was obtained through a three level control. Length or force was controlled real-time with a sample frequency of 5000 Hz. Muscle length and up to three segment lengths were measured simultaneously and each of these lengths could be chosen as feedback variable. Individual algorithms were implemented for different twitch types. Batches of twitches were organized in experiment protocols. The system included a new twitch type, namely a controlled auxotonic twitch. In this twitch, the muscle acted against a virtual ideal spring, giving a proportional change in developed force and shortening. The value of the virtual spring constant could be set on-line or defined in the experiment protocol. An increasing virtual spring constant represented a smooth transition from isotonic to isometric conditions.