Fundamental concepts in cardiovascular physiology

An excellent companion to the study of these concepts can be found at the CCC, courtesy of LITFL:  their Cardiovascular Physiology Overview benefits enormously from flash-animated diagrams. This is merely a brief point-form summary to help the time-poor exam candidate. In fact, those candidates who are poorest can completely omit this vanity topic, as it is has never appeared in the past papers.

Systolic and diastolic blood pressure

• Varies according to site of measurement
• The more distal from the aortic root, the higher the systolic and the lower the diastolic
• Mean arterial pressure is less site-dependent

Mean Arterial Pressure (MAP)

the average arterial pressure during a single cardiac cycle

(more on this elsewhere)

Systemic Vascular Resistance (SVR)

The resistance to blood flow offered by all of the systemic vasculature

(where RAP is right atrial pressure)

Mean Circulatory Filling Pressure (Pmcf or MCFP)

It represents the average filling pressure of the entire circulatory system.

Its major determinant is the tone of veins and venules thoughout the body, as these act the dominant capacitance vessel.

Mean Systemic Filling Pressure (MSFP)

In contrast to the MCFP, this is the mean vascular pressure of the systemic circuit only.

MSFP excludes the right heart and pulmonary circulation.

However, venous "resistance" is usually a minor contributor to venous flow mechanics (there is so little resistance to speak of).

Venous capacitance is regulated by the sympathetic nervous system; noradrenaline is a great venoconstrictor, and most of the time its effect is due to the increased cardiac output resulting from decreased venous capacitance.

Venous return

Under ideal (apneic) conditions, venous return and cardiac output must be equal.

Thus, venous return = cardiac output.

Frank-Starling principle

Preload, Afterload and Contractility