“Blood pressure” generally refers to the pressure blood exerts against blood-vessel walls as it circulates, but often refers to the arterial pressure in the systemic circulation when referred to without context. It can vary under a number of variables, including but not limited to the setting in which the measurement is taken, recent activity and several disease states, but is usually measured at the upper arm and expressed as the maximum (systolic) pressure over minimum (diastolic) pressure in terms of millimeters of mercury (mm Hg). Alongside body temperature, oxygen saturation and the heart and respiratory rates, it is one of the most important of the body’s vital status, usually judged relative to a “normal” adult resting blood pressure of roughly 120/80 mm Hg.
When a disease state causes unusually low blood pressure, the condition is called “hypotension” and the opposite consistently high blood pressure is known as “hypertension”, either disease state having ranges of mild-to-severe causes and onsets that can range from sudden occurrences to chronic conditions. Kidney failure, heart disease, and stroke are among the diseases for which long-term hypertension is a significant risk factor. Western countries display long-term hypotension far less frequently than chronic hypertension, though infrequent monitoring and absence of obvious symptoms result in long-term hypertension often going undetected.
Normal blood pressure ranges for children chart considerably lower than those for adults, often depending on height and with different international reference points based on individual countries’ statistical distributions. Overall, age and sex are just two factors among many that can cause blood pressure to fluctuate even from minute to minute over a 24-hour circadian rhythm, but most individuals generally display the highest readings during afternoons and the lowest readings in the evening. Significantly increased future cardiovascular disease risks have been associated with lack of falling blood pressure at night, causing night-time blood pressure to supersede daytime levels as a predictor of cardiovascular events. Systolic pressure typically rises while diastolic falls as adults age, resulting in generally higher blood pressure among the elderly that charts above normal adult ranges, mostly due to diminished arterial flexibility.
Of course, individual blood pressure will always vary with exercise, strong emotional responses, sleep, digestion, circadian rhythm, and time of day.
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