Exercise also causes vasodilation, or the widening of blood vessels, which increases blood flow and decreases peripheral resistance — which, in healthy people, keeps the diastolic blood pressure from rising during activity. In fact, a diastolic blood pressure increasing greater than 10 mmHg during or after exercise represents an unstable form of hypertension, and may be associated with coronary artery disease, notes Len Kravitz, Ph.D. of the University of New Mexico.

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Modern understanding of the cardiovascular system began with the work of physician William Harvey (1578–1657), who described the circulation of blood in his book "De motu cordis". The English clergyman Stephen Hales made the first published measurement of blood pressure in 1733.[152][153] However, hypertension as a clinical entity came into its own with the invention of the cuff-based sphygmomanometer by Scipione Riva-Rocci in 1896.[154] This allowed easy measurement of systolic pressure in the clinic. In 1905, Nikolai Korotkoff improved the technique by describing the Korotkoff sounds that are heard when the artery is ausculated with a stethoscope while the sphygmomanometer cuff is deflated.[153] This permitted systolic and diastolic pressure to be measured.
Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated.[10] High blood pressure typically does not cause symptoms.[1] Long-term high blood pressure, however, is a major risk factor for coronary artery disease, stroke, heart failure, atrial fibrillation, peripheral vascular disease, vision loss, chronic kidney disease, and dementia.[2][3][4][11]
The cuff is placed around the upper arm and inflated with an air pump to a pressure that blocks the flow of blood in the main artery that travels through the arm. The arm is held at the side of the body at the level of the heart, and the pressure of the cuff is gradually released. As the pressure decreases, a health practitioner listens with a stethoscope over the artery at the front of the elbow or an electronic machine senses the pulsation. The pressure at which the practitioner (or machine) first hears a pulsation from the artery is the systolic pressure (the top number). As the cuff pressure decreases further, the pressure at which the pulsation finally stops is the diastolic pressure (the bottom number).
If your blood pressure remains high for a long period of time, you run the risk of damaging your blood vessels. Your stroke risk rises significantly, too. And because your heart is working harder to push blood through your system, that very valuable muscle can become overworked and grow thicker. An enlarged heart causes further complications, including heart failure. Medications and special implantable pumps can help boost heart function. But if you can manage your blood pressure before it gets too high and puts your heart at risk, you may be able to avoid a lot of complications down the road.
Effective lifestyle modification may lower blood pressure as much as an individual antihypertensive medication. Combinations of two or more lifestyle modifications can achieve even better results.[87] There is considerable evidence that reducing dietary salt intake lowers blood pressure, but whether this translates into a reduction in mortality and cardiovascular disease remains uncertain.[96] Estimated sodium intake ≥6g/day and <3g/day are both associated with high risk of death or major cardiovascular disease, but the association between high sodium intake and adverse outcomes is only observed in people with hypertension.[97] Consequently, in the absence of results from randomized controlled trials, the wisdom of reducing levels of dietary salt intake below 3g/day has been questioned.[96]
The brain requires unobstructed blood flow to nourish its many functions. Very high, sustained blood pressure will eventually cause blood vessels to weaken. Over time these weaken vessels can break, and blood will leak into the brain. The area of the brain that is being fed by these broken vessels start to die, and this will cause a stroke. Additionally, if a blot clot blocks a narrowed artery, blood ceases to flow and a stroke will occur.
High blood pressure is the #2 cause of kidney failure. It accounts for about one-fourth of all cases. High blood pressure can be both a cause of kidney disease and a symptom of kidney disease. When high blood pressure damages your kidneys, they are not able to do all their jobs as well—and one of their jobs is helping your body regulate your blood pressure.
Meschia JF, Bushnell C, Boden-Albala B, et al; American Heart Association Stroke Council; Council on Cardiovascular and Stroke Nursing; Council on Clinical Cardiology; Council on Functional Genomics and Translational Biology; Council on Hypertension.. Guidelines for the primary prevention of stroke: a statement for healthcare professionals from the American Heart Association/American Stroke Association. Stroke. 2014;45(12):3754-3832. PMID: 25355838 www.ncbi.nlm.nih.gov/pubmed/25355838.

Allergic reaction (anaphylaxis): Anaphylactic shock is a sometimes-fatal allergic reaction that can occur in people who are highly sensitive to drugs such as penicillin, to certain foods such as peanuts or to bee or wasp stings. This type of shock is characterized by breathing problems, hives, itching, a swollen throat and a sudden, dramatic fall in blood pressure.