Advanced Hemodynamics - Orlando Health

Advanced Hemodynamic Monitoring
the needs of the body. For example, an 80 pound elderly woman will need less blood than a 350
pound young, male linebacker. To account for these differences the cardiac index can also be
calculated. The cardiac index (CI) is the cardiac output adjusted for body surface area. The normal
value for this is between 2.5 and 4.2 liters of blood per minute, per square meter of body surface
area. The equation to determine cardiac output is seen below:
Cardiac output = heart rate x stroke volume*
*HR= beats per minute
*Stroke volume= amount of blood ejected from the ventricles in one beat.
Heart Rate
Most non-diseased hearts can tolerate heart rate changes from 40-170 beats per minute. As cardiac
function becomes increasingly compromised this range will become narrower. The heart rate and
the stroke volume should work like a see-saw. If one goes up, the other should go down, and vice
versa. The most common change is related to low stroke volume or increased tissue oxygen
demands which cause the heart rate to increase to compensate for the change. This is termed
compensatory tachycardia.
Stroke Volume
Stroke volume (SV) is the amount of blood ejected from the left ventricle each time the ventricle
contracts. The stroke volume is the difference between end-diastolic volume (EDV), the amount of
blood in the left ventricle at the end of diastole, and end-systolic volume (ESV), the blood volume
in the left ventricle at the end of systole. Normal stroke volume is between 60 and 130 ml/beat. The
equation for SV is seen below:
SV= EDV-ESV
When stroke volume is expressed as a percentage of the end-diastolic volume, it is referred to as the
ejection fraction (EF). A normal left ventricular EF is approximately 55- 70%.
The three main factors that influence the stroke volume are the remaining three components that
determine cardiac performance: preload, afterload, and contractility. These three components are
inter-related. If one is affected, so will it affect one or more of the others.
Preload
The term preload refers to the amount of end-diastolic stretch on the myocardial muscle fibers. This
in turn is determined by the volume of blood filling the ventricle at the end of diastole. In essence,
the greater the filling volume, then the greater the stretch of the myocardial muscle fibers. The more
the myocardial muscle fibers are stretched, the greater the force of the myocardial contraction and
potentially the greater the stroke volume to a physiological limit. Although the stretch of the
myocardial muscle fibers is the most accurate method for determining preload, currently there is not
a way to measure myocardial fiber length. Consequently, it has become the standard to estimate this
value by evaluating the filling volumes using equipment such as central venous pressure monitoring
or pulmonary artery catheter values which will be discussed later. It is clinically acceptable to
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