What is Arterial Pressure?
As blood is pumped by the heart it exerts a pressure against the walls of the arteries which conduct it away from the heart to the rest of the body. This is called the arterial pressure, or simply known as blood pressure (BP). From the aorta, the biggest artery, arterial pressure decreases as it travels to smaller arteries, arterioles and capillaries.
Arterial pressure varies from its maximum, or systolic pressure, to its minimum or diastolic pressure. Blood pressure is usually expressed as a ratio, in terms of systolic/diastolic pressures.
How is Arterial Pressure Measured and Monitored?
Arterial pressure may be measured by using non-invasive or by invasive means. Non-invasive methods do not penetrate or invade the skin or any body opening. These are simple and have no complications but are less accurate than invasive measures. Invasive monitoring requires an instrument to pass through skin or body openings. This is very useful in hospital settings where continuous monitoring needs to be done instead of intermittent measurements.
Non-invasive blood pressure measurement may be done by:
- Using a sphygmomanometer – where pressure is reflected by a rise in a column of mercury as a cuff is constricted and slowly released on the left upper arm, covering the brachial artery. The systolic (peak) pressure may be palpated (felt by a finger or two) or heard over a stethoscope. As the pressure decreases the diastolic (trough) is also felt or heard and a ratio is made. Usual BP readings (ex. 120/80) vary depending on age, position, condition of the patients, and many other factors.
This method requires skill from the one doing the measurement, and it is useful in ambulatory settings, clinics and even in the home.
- Oscillometric methods – use electronic devices that can measure pressure with a sensor that detects blood flow and records readings on a monitor. The arm or wrist cuff may be inflated automatically and readings may be done even by an untrained person. These devices are easy to use, especially for repeated measurements, but are not very accurate and have to be calibrated often.
Invasive arterial pressure monitoring is done by inserting a cannula through an artery in the arm, groin or foot to directly measure blood pressure. The cannula is connected to an electronic transducer which can record beat-to-beat pressure changes. Blood pressure monitoring can be done accurately and continuously over long periods. Blood samples can also be obtained directly from the arterial line. This is very advantageous in critical care settings like the intensive care unit, the operating room and whenever intense monitoring is needed.
Some disadvantages to invasive monitoring are bleeding, infection, thrombosis and the need for close supervision by trained personnel.
Significance of Arterial Pressure Monitoring
Arterial BP is one of the vital signs routinely checked and monitored to assess one’s over-all well-being, together with pulse or heart rate, respiratory rate and temperature. Values differ over a wide range, depending on age, physical condition, diseases, body position, recent activity, drugs taken, emotional status, and many other factors.
People with blood pressures consistently or usually exceeding normal values are said to be hypertensive, while those with lower than normal values are hypotensive. BP readings may reflect or indicate the presence of other diseases or conditions such as diabetes, heart disease or bleeding disorders.
In many people BP measurements are done for routine checks of health status in clinics. For some in home care, like the elderly who are hypertensive or suffering from chronic diseases and are kept on maintenance medications, BP monitoring may be done more often to guide therapy. Still, in hospitals and other health institutions arterial pressure monitoring may be required more often for intervention. Depending on the need and practicality, there are different methods available with their own advantages and disadvantages.
Critical Care, “Arterial blood pressure monitoring in overweight critically ill patients: invasive or noninvasive" accessed 12/30/10
MedlinePlus, "Blood Pressure", accessed 12/30/10