Cardiac energetics and the Fenn effect

Area of Science:

• Cardiovascular Physiology
• Biophysics

Background:

• Cardiac contraction energy output is complex, with activation, work, and load-dependent heat terms.
• Subdivisions of cardiac energy output can be thermodynamically misleading.
• The actin-activated myosin ATPase is the presumed origin of work and load-dependent energy terms.

Purpose of the Study:

• To investigate the load-dependence of cardiac energy output and its relationship to contractility.
• To reconcile existing myothermic and polarographic data with the pressure-volume area (PVA) concept.
• To examine the Fenn effect in cardiac muscle.

Main Methods:

• Phenomenological measurement of cardiac contraction energy components.
• Analysis of enthalpy-load relationships across different species.
• Correlation of cardiac oxygen consumption with ventricular systolic pressure-volume area (PVA).

Main Results:

• Cardiac enthalpy production is significantly load-dependent, indicating a Fenn effect.
• The enthalpy: load relationship shows similar formats across mammalian and amphibian hearts, but scaling is altered by contractility.
• Cardiac oxygen consumption per beat linearly correlates with PVA.
• Cardiac muscle operates at a constant PVA efficiency when basal and activation components are excluded.

Conclusions:

• Cardiac energy output is fundamentally load-dependent, exhibiting a Fenn effect.
• The pressure-volume area (PVA) concept provides a unifying framework for understanding cardiac energy consumption and efficiency.
• Existing myothermic and polarographic data support the PVA model of cardiac energetics.