haemodynamic

Haemodynamics is the branch of physiology that studies the circulation of blood and the forces involved in maintaining tissue perfusion. It encompasses how the heart generates blood flow, how blood moves through vessels, and how factors such as pressure, resistance, and compliance influence circulation. The term is often used interchangeably with hemodynamics in clinical practice.

Flow through the circulatory system follows the principle that flow equals the pressure gradient divided by vascular resistance. Cardiac output, the total blood flow generated by the heart per minute, and mean arterial pressure, a surrogate of systemic perfusion, are key measures. Preload refers to ventricular filling, afterload to the resistance the heart must overcome, and contractility to the intrinsic ability of the myocardium to contract. The relationship among these factors determines stroke volume and tissue perfusion. Microcirculation and venous return also shape dynamic haemodynamics; venous tone and intrathoracic pressure influence preload, while arterial tone sets afterload and systemic vascular resistance.

Measurement and monitoring range from invasive haemodynamic monitoring, such as arterial and central venous pressure lines or pulmonary artery catheter thermodilution, to noninvasive methods including echocardiography and Doppler flow studies. Parameters used include preload indices (central venous pressure, pulmonary capillary wedge pressure), afterload measures (systemic vascular resistance), and indicators of oxygen delivery such as mixed venous oxygen saturation.

Clinically, haemodynamics inform assessment and treatment of shock, heart failure, and perioperative management. Therapies aim to optimize preload, afterload, and contractility to maintain adequate tissue perfusion while avoiding harmful extremes.