Blood pressure is a measurement of how much force the blood exerts on the walls of the blood vessels. There are many different events occurring within the body as the heart pumps blood, known collectively as the cardiac cycle, and so blood pressure is measured at different points throughout this cycle. Systolic blood pressure measures the maximum pressure in the arteries during the cardiac cycle, which occurs when the heart contracts, or beats, to pump blood.
Systolic pressure is measured during routine visits to a healthcare provider. It is recorded in mmHg, or millimeters of mercury. Most medical professionals use the ausculatory method of blood pressure measurement. The reading is taken with the patient seated with his or her arm slightly bent and at the same level as the heart.
A cuff is wrapped around the arm an inch (2.54 cm) above the elbow, and a stethoscope placed on the large brachial artery in the arm. The cuff is inflated to about 30 mmHg higher than the patient's last recorded blood pressure, at which point blood flow is negligible. The cuff is then slowly deflated, and the health care provider records the level at which the patient's pulse can first be heard through the stethoscope. This is the systolic blood pressure.
When the pulse is no longer audible, a second number is recorded: the diastolic pressure, or the lowest amount of pressure in the arteries, occurring while the heart is at rest between beats. These two numbers are recorded as the patient's blood pressure: 110/70, for example. The systolic blood pressure reading is the first number, and the diastolic pressure the second. Some medical professionals also use the oscillometric method of measurement, which is similar but uses an electronic pressure sensor to record readings instead of a stethoscope.
Blood pressure is affected by medication, cardiovascular or urological disorders, neurological conditions, and psychological factors such as stress or anger. Even diet and posture can play a role. Because there are so many variables, healthy blood pressure readings can fall anywhere inside a large range. A healthy adult will have systolic blood pressure between 90 and 135 mmHg. Diastolic pressure ranges from 50 to 90 mmHg.
If a patient's systolic reading is consistently higher than 120 mmHg, he or she should consult with a medical professional immediately, particularly if the patient is middle-aged or older. High systolic blood pressure readings are the most accurate means of detecting hypertension, or high blood pressure, in middle-aged and older adults. In many cases, only systolic pressure is high, a condition known as isolated systolic hypertension or ISH. Lowering it to healthy levels can help prevent congestive heart failure and stroke.