Hemodynamic Measurement Terminology
There are a number of hemodynamic
terms that you will need to understand in order to properly interpret the hemodynamic
measurements. The following table presents
common values of hemodynamic parameters.
- Afterload: Afterload
describes the resistance that the heart has to overcome, during every beat,
to send blood into the aorta. These resistive forces include vasoactivity
and blood viscosity.
Index (CI): The amount of blood pumped by the heart, per minute, per meter
square of body surface area.
Output (CO): The volume of blood pumped by the heart in one minute.
- Increased cardiac
output may indicate a high circulating volume.
- Decreased cardiac
output indicates a decrease in circulating volume or a decrease in the
strength of ventricular contraction.
Venous Pressure (CVP): CVP readings are used to approximate the Right
Ventricular End Diastolic Pressure (RVEDP). The RVEDP assesses right ventricular
function and general fluid status.
- Low CVP values typically
reflect hypovolemia or decreased venous return.
- High CVP values reflect
overhydration, increased venous return or right sided cardiac failure.
Arterial Pressure (MAP): Reflects changes in the relationship between
cardiac output (CO) and systemic vascular resistance (SVR) and reflects the
arterial pressure in the vessels perfusing the organs.
- A low MAP indicates
decreased blood flow through the organs.
- A high MAP indicates
an increased cardiac workload.
- Preload: is an estimate of end-diastolic pressure in the left ventricle (LVEDP). It reflects the volume of blood returned to the LV just before systole.
- Volume reduction
- Volume increase will
increase preload, mean arterial pressure (MAP) and stroke index (SI).
Artery Pressure (PA Pressure): Blood pressure in the pulmonary artery.
- Increased pulmonary
artery pressure may indicate: a left-to-right cardiac shunt, pulmonary
artery hypertension, COPD or emphysema, pulmonary embolus, pulmonary edema,
left ventricular failure.
Capillary Wedge Pressure (PCWP or PAWP): PCWP pressures are used to approximate
LVEDP (left ventricular end diastolic pressure).
- High PCWP may indicate
left ventricle failure, mitral valve pathology, cardiac insufficiency,
cardiac compression post hemorrhage.
Vascular Resistance (PVR): The measurement of resistance or the impediment
of the pulmonary vascular bed to blood flow.
- An increased PVR or
"Pulmonary Hypertension" is caused by pulmonary vascular disease,
pulmonary embolism, or pulmonary vasculitis, or hypoxia.
- A decreased PVR is
caused by medications such as calcium channel blockers, aminophylline, or
isoproterenol or by the delivery of O2.
Ventricular Pressure (RV Pressure): A direct measurement that indicates
right ventricular function and general fluid status.
- High RV pressure
may indicate: pulmonary hypertension, right ventricle failure, congestive
Index or Stroke Volume Index: (SI or SVI): The amount of blood ejected
from the heart in one cardiac cycle, relative to Body Surface Area (BSA).
It is measured in ml per meter square per beat.
- An increased SVI may
be indicative of early septic shock, hyperthermia, hypervolemia or be caused
by medications such as dopamine, dobutamine, or digitalis.
- A decreased SVI may
be caused by CHF, late septic shock, beta blockers, or an MI.
Volume (SV): The
amount of blood pumped by the heart per cardiac cycle. It is measured in ml/beat.
- A decreased SV may
indicate impaired cardiac contractility or valve dysfunction and may result
in heart failure.
- An increased SV may
be caused by an increase in circulating volume or an increase in inotropy.
Vascular Resistance (SVR): The measurement of resistance or impediment
of the systemic vascular bed to blood flow.
- An increased SVR
can be caused by vasoconstrictors, hypovolemia, or late septic shock.
- A decreased SVR can
be caused by early septic shock, vasodilators, morphine, nitrates, or
is increased if the circulating blood is concentrated and/or if systemic blood
vessels are constricted.
a significant hemorrhage, preload will be increased.