The Importance Of Normal CVP
A normal CVP measurement is an indication that the cardiovascular system is probably functioning properly, especially the heart itself. There can be problems with the heart or other areas in the circulatory system which don't directly affect CVP measurements, and in the normal course of events CVP isn't something that is looked at during most physical examinations.
A normal CVP reading is something you'd want to witness in an intensive care unit; in fact IC is one of the few places such a measurement is usually made. Having said all this, what is CVP anyway, and why is a normal CVP reading important?
Central Venous Pressure - CVP stands for central venous pressure or blood pressure measured at a point just before blood is entering the heart. To measure blood pressure at this location requires an invasive technique, one reason why CVP won't be measured during a routine exam, even if the health of the heart is at issue. To measure CVP, a catheter has to be inserted into a vein and threaded to a particular point near the heart. This is a delicate procedure requiring an experienced practitioner, not only to do the procedure, but to be able to correctly interpret the results of the measurements.
Normal CVP Indicates A Balanced System - A normal CVP measurement basically means that the pressure of blood entering the heart is equal to that leaving the heart. When this pressure is not equal, it means that somewhere in the circulatory system there is either blood loss being experienced or a part of the heart is not pumping efficiently. In the latter case, a failure in the right atrium or ventricle is often to blame. CVP measurements therefore are a good indication of heart failure in progress and are also a good indication as to how well the heart is functioning when a person is in intensive care for whatever reason.
Elasticity And Compliance - Something other than a normal CVP reading can also mean a problem somewhere outside of the heart. Here, basic principles of physics, and to some extent mechanics, come into play. CVP measurements are indicative of what can be called cardiovascular compliance. As blood volume in a vein or artery increases, the vein or artery tends to expand somewhat to accommodate the increased flow. It can only expand so much of course, and when it can expand no further an increase in blood pressure results. Veins are usually much more elastic than are arteries, so can accommodate increased volumes of blood flow without significant changes in blood pressure. Put another way, veins are much more elastic than are arteries.
Compliance is the opposite of elasticity, and is the ability of a blood vessel to return to its initial size (or diameter) once the volume of blood flow and/or the blood pressure is reduced. Just as problems affecting a blood vessel's elasticity or capability to expand can cause problems, so can its compliance or capability to contract.
CVP measurements are determined by many factors so what an abnormal CVP measurement might mean can be difficult at times to fathom. Factors influencing normal CVP range form retraction of skeletal muscles to respiratory activity to the effects of gravity to various medications, to name just four.
Causes Of High And Low CVP - CVP readings will often be higher than normal in the event of heart failure, especially failure on the right side of the heart, decreased cardiac output, or when one is exhaling forcibly. A patient using a ventilator will often have an increase in central venous pressure. CVP readings can be lower than normal when one is inhaling deeply or is in shock. Hypervolemia, or blood loss, is a condition which will commonly result in a lower than normal CVP reading.
If you are ever in an intensive care unit, especially because of a heart problem or following open heart surgery, there's a good chance that one of the monitors the nurses are constantly checking, is measuring your central venous pressure, and hoping for normal CVP readings.