Blood pressure monitoring is the repeated measurement of the pressure exerted by circulating blood against the walls of arteries. Blood pressure is usually expressed using two numbers: systolic blood pressure, the pressure during ventricular contraction, and diastolic blood pressure, the pressure during ventricular relaxation. Monitoring can involve measurements taken occasionally in a healthcare setting, repeated measurements at home or continuous or near-continuous measurement using ambulatory equipment. The purpose is to determine a person's blood-pressure pattern rather than relying on a single reading, because blood pressure naturally varies with activity, posture, stress, sleep, illness and other factors.
A conventional blood-pressure measurement uses an inflatable cuff placed around the upper arm and an automated oscillometric device or, in some settings, a manual sphygmomanometer with a stethoscope. The cuff temporarily compresses the brachial artery and is then gradually deflated. Automated devices detect pressure oscillations within the cuff and use algorithms to estimate systolic and diastolic pressure. Manual measurement uses Korotkoff sounds heard through a stethoscope as the cuff pressure falls. Correct cuff size is essential because a cuff that is too small or too large can systematically distort the measurement.
Home blood-pressure monitoring involves taking readings outside a clinic, commonly with a validated upper-arm device. It can provide a more representative picture of usual blood pressure and can help distinguish sustained hypertension from a clinic-related rise known as the white-coat effect. Conversely, some people have normal clinic readings but higher blood pressure in ordinary life, a pattern sometimes called masked hypertension. Home monitoring can also be useful when assessing the effect of lifestyle changes or antihypertensive treatment. Measurements should be taken consistently under appropriate resting conditions to make readings comparable.
Ambulatory blood-pressure monitoring, often abbreviated ABPM, uses a portable device connected to an arm cuff that automatically measures blood pressure at regular intervals over an extended period, commonly including daytime and sleep periods. This provides information about average blood pressure and its variation throughout the day and night. It can identify patterns that are not visible during a short clinical appointment, including differences between waking and sleeping blood pressure. ABPM is particularly useful when clinicians need to confirm whether hypertension is persistent or to investigate discrepancies between clinic and home measurements.
Accurate monitoring depends heavily on technique. Before measurement, the person should generally rest quietly for several minutes, avoid talking during the reading and sit with appropriate back and arm support. The cuff should be placed on bare skin rather than over clothing, with the arm supported approximately at heart level. Recent exercise, caffeine, smoking, anxiety, pain and a full bladder can influence readings. Multiple measurements may be taken and averaged rather than relying on a single value. Consistent technique reduces random variation and makes trends more clinically meaningful.
Blood pressure is not fixed and should not be interpreted as a single permanent characteristic. It changes with posture, physical activity, sleep, emotional state, temperature and disease. Blood pressure also tends to follow circadian patterns, usually declining during sleep in many people. A temporary high reading therefore does not automatically establish chronic hypertension. Conversely, repeatedly normal readings do not necessarily exclude hypertension if measurements are taken under circumstances in which blood pressure is unusually low. Clinical interpretation considers repeated measurements, the measurement method and the person's overall cardiovascular risk.
Blood-pressure monitoring has several purposes beyond diagnosing hypertension. It can help clinicians evaluate whether treatment is adequately controlling blood pressure, identify excessive lowering that might contribute to symptoms, investigate dizziness or suspected hypotension and assess blood-pressure patterns in particular circumstances. In pregnancy, blood-pressure monitoring has additional importance because hypertension can be associated with pregnancy-related disorders. In people with cardiovascular or kidney disease, blood pressure is also an important component of ongoing risk management. The meaning of a measurement therefore depends on the clinical setting and the population in which it was obtained.
Blood pressure is measured in millimetres of mercury, written mmHg, and values are expressed as systolic over diastolic pressure, such as 120/80 mmHg. Thresholds used to define hypertension depend on the guideline, measurement method and clinical context, so a single number should not be interpreted independently of current clinical guidance. Persistent hypertension increases the risk of cardiovascular disease, stroke, kidney disease and other complications, while excessively low pressure can cause inadequate tissue perfusion in some circumstances. Monitoring provides data for clinical decisions, but diagnosis and treatment should be based on appropriate repeated measurements and professional assessment rather than isolated home readings.
