Cardiovascular Physiology

Heart Physiology Definitions:

Stroke volume (SV) = The volume of blood pumped out to the ventricle after one contraction.

Preload = the pressure exerted on the ventricular myocardium by the end diastolic volume (EDV).

As venous return increases, end diastolic volume increases and the ventricular myocytes become more stretched. Remember, more stretch on the muscle results in stronger contraction force. With this stronger contraction force, the stroke volume increases.

Afterload = The resistance pressure that the left ventricle must exceed to push blood forward during systole.

Cardiac Output = The volume of blood ejected by the left ventricle each minute.

CO = SV x HR (heart rate)

Cardiac Cycle:

Atrial Contraction
Isovolumetric phase (i.e. chamber filling time)
Opening Aortic Valve
Ejection phase
Closure of Aortic Valve
Isovolumetric relaxation
Opening Mitral Valve
Filling Phase

For a more indepth discussion on cardiac physiology check out this review by Drs. Chaudhry, Miao and Rehman.

The primary goal of the cardiovascular system is to maintain perfusion. Adequate perfusion is necessary to deliver oxygen and nutrients to all organ systems. The 'cardio' and 'vascular' systems work in concert to accomplish the goal of transporting oxygenated, nutrition laden blood to the cellular networks of the body and subsequently returning deoxygenated, metabolic waste filled blood to the appropriate 'processing organs' (think: lungs, liver, kidneys, spleen) to clean the blood for transport once again.

In order to maintain the goals of circulation in critically ill or injured patients, it's important to know the components of this system and how they work together to keep oxygenation and nutrients continuously delivered for healing. We will first look at cardiovascular physiology, then we will review a few common cardiac and vascular conditions frequently seen in ICU patients.