Cardiac performance: optimal heart rate for maximal cardiac output

Area of Science:

• Cardiovascular Physiology
• Hemodynamics
• Cardiac Function

Background:

• Understanding the determinants of maximal cardiac output is essential for managing cardiovascular health.
• The interplay between heart rate and stroke volume influences overall cardiac performance.

Purpose of the Study:

• To determine the optimal heart rate for maximal cardiac output under varying conditions of inotropy and blood volume.
• To investigate the relationship between heart rate and stroke volume during cardiac pacing.

Main Methods:

• Anesthetized dogs underwent right atrial pacing to control heart rate.
• Myocardial inotropy was modulated using isoproterenol and propranolol.
• Circulating blood volume was altered via saline infusion.

Main Results:

• A linear inverse relationship was observed between heart rate and stroke volume within the optimal range (SV = k(HR0-HR)).
• Increased inotropy elevated stroke volume equally across heart rates, keeping 'k' constant.
• Blood volume expansion increased stroke volume more at lower heart rates, increasing 'k'.
• Optimal heart rate increased with inotropy but was unaffected by blood volume changes.

Conclusions:

• The optimal heart rate and maximal cardiac output can be accurately predicted from the linear relationship between stroke volume and heart rate.
• Inotropy significantly influences optimal heart rate, while blood volume primarily affects stroke volume magnitude.