A structure-function analysis of the left ventricle.

Area of Science:

• Cardiovascular Physiology
• Cardiac Energetics
• Mammalian Heart Function

Background:

• The mammalian left ventricle's structure and function are crucial for systemic circulation.
• Understanding cardiac performance under varying workloads is essential for diagnosing and treating heart conditions.

Purpose of the Study:

• To conduct a structure-function analysis of the mammalian left ventricle.
• To examine the performance of cardiac capillaries, mitochondria, and myofibrils at rest and during heavy exercise.

Main Methods:

• Calculated left ventricular external mechanical work rate using cardiac output and mean arterial blood pressure in sheep and goats.
• Quantified cardiac capillary-tissue geometry and cardiomyocyte ultrastructure via perfusion-fixation.
• Applied an oxygen transport model and a Laplacian model to estimate oxygen consumption and myofibril tension.

Main Results:

• Left ventricular work rate increased from 0.017 W/cm³ at rest to ~0.060 W/cm³ during heavy exercise.
• Oxygen consumption rose from 195 nmol O₂·s⁻¹·cm⁻³ to ~600 nmol O₂·s⁻¹·cm⁻³, remaining predominantly aerobic.
• Mitochondria operated near their functional limits, and myofibrils exhibited reserve tension capacity.

Conclusions:

• The mammalian left ventricle maintains aerobic function and demonstrates reserve capacity during heavy exercise.
• Cardiac mitochondria and myofibrils perform efficiently but near their maximum capabilities under high workload.