Frank–Starling law

Starling RAP combined

The Frank–Starling law of the heart, also known as the Frank–Starling mechanism, is a fundamental principle in cardiology that describes the relationship between the stroke volume of the heart and the end-diastolic volume. This law is named after the physiologists Otto Frank and Ernest Starling, who first described the phenomenon in the early 20th century.

Overview

The Frank–Starling law states that the stroke volume of the heart increases in response to an increase in the volume of blood filling the heart (the end-diastolic volume), when all other factors remain constant. This relationship is due to the intrinsic property of cardiac muscle fibers: the more they are stretched during filling, the more forcefully they contract. This mechanism allows the heart to automatically adjust its pumping capacity to accommodate varying volumes of incoming blood.

Mechanism

The mechanism behind the Frank–Starling law involves the sarcomere length-tension relationship in cardiac muscle fibers. When the ventricles fill with more blood, the myocardial fibers are stretched to a greater length. This stretching increases the overlap of actin and myosin filaments within the sarcomere, leading to a more forceful contraction during systole. This ensures that the cardiac output matches the venous return.

Clinical Significance

The Frank–Starling mechanism is crucial for maintaining cardiac output and ensuring efficient circulation. It plays a significant role in various physiological and pathological conditions:

• In heart failure, the Frank–Starling mechanism may be impaired, leading to inadequate cardiac output.
• During exercise, the increased venous return enhances the stroke volume through this mechanism, supporting the increased demand for oxygen and nutrients by the muscles.
• In conditions such as myocardial infarction, the loss of functional myocardium can affect the Frank–Starling relationship, impacting the heart's ability to pump effectively.

Historical Background

The Frank–Starling law was first described by Otto Frank in 1895 and later expanded upon by Ernest Starling in 1914. Their pioneering work laid the foundation for modern understanding of cardiac physiology and has had a lasting impact on the field of medicine.

Related Concepts

• Preload
• Afterload
• Cardiac output
• Ejection fraction
• Venous return
• Myocardial contractility

See Also

• Cardiac cycle
• Heart failure
• Cardiovascular physiology