Preload (cardiology)

An overview of preload in cardiology

Preload in Cardiology

Diagram of the heart during diastole, illustrating preload.

Preload is a term used in cardiology to describe the initial stretching of the cardiac myocytes prior to contraction. It is related to the volume of blood in the ventricles at the end of diastole, just before the heart contracts. This volume is often referred to as the end-diastolic volume (EDV).

Physiological Basis

Preload is influenced by the venous return to the heart and the compliance of the ventricles. The concept of preload is crucial in understanding the Frank-Starling law of the heart, which 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.

Frank-Starling Mechanism

The Frank-Starling mechanism is a fundamental principle that describes how the heart's stroke volume increases with an increase in preload. This mechanism allows the heart to adjust its pumping ability to accommodate varying volumes of incoming blood.

Clinical Significance

Preload is an important factor in the management of various cardiac conditions. It can be affected by factors such as blood volume, venous tone, and ventricular compliance. In clinical practice, preload is often manipulated using medications such as diuretics and vasodilators to optimize cardiac output in patients with heart failure.

Measurement

Preload is not directly measurable, but it can be estimated using parameters such as central venous pressure (CVP) and pulmonary capillary wedge pressure (PCWP). These measurements provide indirect assessments of the volume status and ventricular filling pressures.

Factors Affecting Preload

Several factors can influence preload, including:

• Blood volume: An increase in blood volume, such as from fluid retention, can increase preload.
• Venous return: Factors that enhance venous return, such as increased venous tone or decreased intrathoracic pressure, can increase preload.
• Ventricular compliance: Decreased compliance, as seen in conditions like ventricular hypertrophy, can reduce preload.

Related pages

• Cardiac cycle
• Stroke volume
• Heart failure
• Frank-Starling law of the heart