Physiology of Blood Pressure
A major measurement of cardiovascular systems ability to transmit blood through the body is blood pressure (BP). Blood pressure, as many know, contains two numbers the "top" number, and "bottom" number. While many people know of these numbers, few seem to have a good grasp of their meaning. When the heart pumps/contracts, a physiological event called "systole" (sis'tole'ee), it creates a pressure inside the arteries of the body. This pressure wave, felt by the pulse in various locations of the body, pushes blood at a high velocity throughout the body. This initial wave of pressure through the body has to be high in order to propel blood throughout the entire body. Putting this altogether, the systole of the heart creates a high pressure in the major vessels just outside the heart, which is used to drive blood flow throughout the entire body. Likewise, the "systolic pressure" of blood pressure measurement is the higher number and represents the highest pressure achieved by the heart during contraction. Physicians consider 120 mmHg to be "normal" systolic pressure. That being said, normal can have deviations due to a multitude of reasons. After the heart beats, it takes a rest, and allows blood to flow throughout the body and return to the heart. This rest gives the heart muscle time to relax; in addition, the pause taken for rest gives the heart time to prime its pump and allow blood to re–collect inside itself. During this rest period, or "diastole" (die'as'tole'ee), the pressure is usually much lower. Likewise, the "diastolic pressure" is the lower number, and represents the amount of pressure of the system during the heart's resting period. Physicians define a normal diastolic pressure around 80 mmHg. 4 The measure mmHg, or millimeters of Mercury, is a standard measurement for pressure that can be usually explained by most physics teachers (if desired).
Just as CO is a measurement of the heart's average ability to pump blood, Mean Arterial Pressure (MAP) is a measure of an overall average blood pressure. Figure Two demonstrates the calculation of MAP. In general, MAP demonstrates the average pressure within the cardiovascular system. Since a greater proportion of the heart beat is spent in diastole than systole, the ? is applied to the equation to represent this difference. There are three things that can affect the average pressure of the cardiovascular system: Systemic Vascular Resistance (SVR), CO, and volume. Since MAP is an overall measurement for blood pressure, these three factors will be discussed for their implications in high blood pressure (HBP).3
table 12.05.03.02 is available in print form
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