<P> Currently, the RAS is targeted pharmacologically by ACE inhibitors and angiotensin II receptor antagonists . The aldosterone system is directly targeted by spironolactone, an aldosterone antagonist . The fluid retention may be targeted by diuretics; the antihypertensive effect of diuretics is due to its effect on blood volume . Generally, the baroreceptor reflex is not targeted in hypertension because if blocked, individuals may suffer from orthostatic hypotension and fainting . </P> <P> Arterial pressure is most commonly measured via a sphygmomanometer, which historically used the height of a column of mercury to reflect the circulating pressure . The most common automated blood pressure measurement technique is based on the so - called "oscillometric" method . Blood pressure values are generally reported in millimetres of mercury (mmHg), though aneroid and electronic devices do not contain mercury . </P> <P> For each heartbeat, blood pressure varies between systolic and diastolic pressures . Systolic pressure is peak pressure in the arteries, which occurs near the end of the cardiac cycle when the ventricles are contracting . Diastolic pressure is minimum pressure in the arteries, which occurs near the beginning of the cardiac cycle when the ventricles are filled with blood . An example of normal measured values for a resting, healthy adult human is 120 mmHg systolic and 80 mmHg diastolic (written as 120 / 80 mmHg, and spoken as "one - twenty over eighty"). </P> <P> Systolic and diastolic arterial blood pressures are not static but undergo natural variations from one heartbeat to another and throughout the day (in a circadian rhythm). They also change in response to stress, nutritional factors, drugs, disease, exercise, and momentarily from standing up . Sometimes the variations are large . Hypertension refers to arterial pressure being abnormally high, as opposed to hypotension, when it is abnormally low . Along with body temperature, respiratory rate, and pulse rate, blood pressure is one of the four main vital signs routinely monitored by medical professionals and healthcare providers . </P>

A systolic bp value is the pressure when