Key Points
- This study aims to understand the factors influencing isotonic relaxation in cardiac muscle.
- Studied isotonic relaxation in 12 cat papillary muscles.
- Measured relaxation velocity as a function of preload and afterload loads.
- Analyzed effects of varying initial muscle length and calcium levels on peak relaxation velocity.
- Peak relaxation velocity increased significantly with calcium levels (1.73 ML/s to 2.32 ML/s, p<0.01).
- Caffeine addition also raised peak relaxation velocity (1.67 ML/s to 2.54 ML/s, p<0.01).
- Unique length-velocity trajectories were established despite varying measurement times.
Structured PICO
PPopulation12 cat papillary muscles
IInterventionVarying total load, initial muscle length, increasing Ca++ from 2.5 to 7.5 mM, and addition of 10 mM caffeine
CComparatorBaseline conditions (lower Ca++, no caffeine, different loads/lengths)
OOutcomeIsotonic relaxation velocity (VL)surrogate
In cat papillary muscles, isotonic relaxation velocity is dependent on total load, calcium concentration, and caffeine, but independent of initial muscle length at constant load.