Key Points
- Determine the relative contributions of maximal developed pressure and left ventricular volume in modulating the speed of left ventricular relaxation.
- Studied isolated, buffer-perfused, isovolumically beating ferret hearts paced at an 800 ms baseline interbeat interval at 30°C.
- Varied maximal developed pressure independently of volume using seven interbeat intervals (75% to 133% of baseline) via restitution, and varied volume across five levels (80% to 120% of baseline).
- Quantified relaxation speed as the duration of pressure decay from 75% to 25% of maximal developed pressure (T75-25) using multiple linear regression.
- Increases in both maximal developed pressure and left ventricular volume independently prolonged T75-25, with relaxation speed exhibiting 1.45-fold greater sensitivity to pressure than to volume.
- When pressure and volume were modeled together as maximal wall stress, neither parameter nor muscle length independently predicted T75-25, showing relaxation time depends on maximal wall stress alone.
Structured PICO
PPopulationIsolated, buffer-perfused, isovolumically beating ferret hearts
IInterventionVariation of maximal developed pressure (Pdmax) and left ventricular volume (V)
OOutcomeSpeed of left ventricular relaxation quantified as the time period of pressure decay from 75 to 25% Pdmax (T75-25)surrogate
In isolated ferret hearts, the speed of left ventricular relaxation is primarily determined by maximal wall stress, which integrates the effects of maximal developed pressure and left ventricular volume.