Myocardial and ventricular function. Part II: Intact heart

Area of Science:

• Cardiovascular Physiology
• Cardiac Mechanics

Background:

• Cardiac output is influenced by preload, afterload, contractility, and heart rate.
• Ventricular end-diastolic wall stress approximates preload, affecting sarcomere resting length.
• Ventricular function is described by end-diastolic pressure-stroke volume relationships and ejection fraction.

Purpose of the Study:

• To explore factors determining cardiac output and ventricular function.
• To analyze the relationship between preload, afterload, contractility, and cardiac performance.
• To evaluate methods for assessing myocardial contractility.

Main Methods:

• Analysis of preload, afterload, and contractility in isolated cardiac muscle and intact ventricles.
• Examination of pressure-volume relationships and stress-strain relationships.
• Assessment of contractility indexes during isovolumic and ejection phases.

Main Results:

• Stroke volume is inversely related to afterload during ejection.
• Ventricular contraction is characterized as auxotonic due to decreasing afterload.
• Contractility reflects maximum force and rate of shortening, independent of preload/afterload.
• Combined parameters and serial contractions provide the best contractility measurements.

Conclusions:

• No single index fully captures the force-velocity-length relationship of the intact heart.
• Accurate assessment of myocardial contractility necessitates a comprehensive approach.
• Understanding these determinants is crucial for evaluating overall cardiac function.