Everyone has a blood pressure, but what does that mean? The pressure in the arteries when the heart contracts (systole) is called systolic blood pressure. This is usually less than 140 millimeters of mercury (mmHg). The pressure in the arteries when the heart is relaxed (diastole) is called diastolic pressure, and this is usually less than 90 mmHg in adults.
Here is another way of looking at blood pressure. Each contraction of the heart causes blood to be pushed (propelled) through the arteries in the form of a pulse wave; thus the flow of blood in the arteries is pulsatile. A wave must have a crest and a trough. The crest is caused when the heart contracts (systole) and is the highest pressure. Systolic blood pressure coincides with the first Korotkoff sounds heard with the stethoscope over the brachial artery at the cubital fossa just below the level of the inflated cuff on the arm. The trough is caused when the heart relaxes (diastole), producing the lowest pressure, or diastolic pressure at which instant all Korotkoff sounds disappear, and no sounds are heard with the stethoscope.
Resistance in the arteries against which the heart must pump is called the total vascular resistance. If the total vascular resistance increases, blood pressure increases. This vascular resistance is increased when the arteries are constricted by disease, aging, drugs, or naturally occurring chemicals in the body such as adrenaline and noradrena-line. Sudden alarming stress, fright, and situations that provoke sudden anxiety may cause secretion of excess adrenaline and noradrenaline, which causes sudden and considerable elevation in systolic blood pressure. In these situations the systolic blood pressure, which may have been 135 mmHg, may shoot up suddenly, and within minutes be 175–200 mmHg.

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