Key Points
- To determine whether a force-length-time relationship accurately characterizes regional left ventricular wall mechanics during auxotonic contractions under varied loading conditions.
- Measured local systolic wall force and segment length in naturally beating canine left ventricles under beta-blockade using auxotonic force gauges and ultrasonic dimension gauges.
- Modulated preload and afterload via acute caval and aortic occlusions to induce wide variations in wall force, segment length, and shortening velocity.
- Wall force plotted against segment length at identical time points post-end-diastole formed consistent, well-defined lines, where a 10% length reduction corresponded to an approximate 50% drop in force at 200 msec.
- At matching length and time points, higher shortening velocity (difference of 0.6 ± 0.1 muscle length/sec, P < 0.001) resulted in only a modest decrease in wall force (difference of 2.23 ± 1.09 g, P ≈ 0.05).
Structured PICO
PPopulationNaturally pumping dog hearts during beta-blockade
IInterventionAcute caval and/or aortic occlusion to alter preload and afterload
OOutcomeForce-length-time (F-L-t) relationship and shortening velocity (-dL/dt) of the left ventricular free wallsurrogate
The force-length-time relationship accurately describes auxotonic contractions in the ventricular wall, with shortening velocity exerting only a modest direct effect on wall force.