Friday, 20 July 2012

- Blood Pressure and Mean Arterial Pressure.

Blood Pressure and Mean Arterial Pressure

Blood pressure (BP) or "arterial blood pressure"  is the pressure exerted by circulating blood upon the walls of blood vessels.

It  is one of the principal vital signs.

During each heartbeat, blood pressure varies between a maximum (systolic) and a minimum (diastolic) pressure.

The blood pressure in the circulation is principally due to the pumping action of the heart. (1)

Differences in mean blood pressure are responsible for blood flow from one location to another in the circulation. The rate of mean blood flow depends on the resistance to flow presented by the blood vessels.

Mean blood pressure decreases as the circulating blood moves away from the heart through arteries and capillaries due to viscous losses of energy.

Mean blood pressure drops over the whole circulation, although most of the fall occurs along the small arteries and arterioles.(2)
Gravity affects blood pressure via hydrostatic forces (e.g., during standing) and valves in veins, breathing, and pumping from contraction of skeletal muscles also influence blood pressure in veins.(1)
The video defines what blood pressure is and shows how it varies in the blood vessels throughout the body. Then it shows what Mean Arterial Pressure is and goes into two different ways to calculate it.

*Mean arterial pressure:

The mean arterial pressure (MAP) is the average over a cardiac cycle and is determined by the cardiac output (CO), systemic vascular resistance (SVR), and central venous pressure (CVP) (3)

MAP = (CO × SVR) + CVP 
Because CVP is usually at or near 0 mmHg, this relationship is often simplified to:
 MAP approx = CO × SVR 
 MAP can be approximately determined from measurements of the systolic pressure  and the diastolic pressure while there is a normal resting heart rate.(3) 
MAP= diastolic BP + 1/3 (Systolic BP - diastolic BP)

  1. Caro, Colin G. (1978). The Mechanics of The Circulation. Oxford [Oxfordshire]: Oxford University Press. 
  2. Klabunde, Richard (2005). Cardiovascular Physiology Concepts. Lippincott Williams & Wilkins. pp. 93–4.
  3. Klabunde, RE (2007). "Cardiovascular Physiology Concepts – Mean Arterial Pressure". Retrieved 2008-09-29.

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