The kidney can respond to changes in blood pressure by increasing or decreasing the amount of urine that is produced. Urine is primarily water that is removed from the blood. When the kidney makes more urine, the amount (volume) of blood that fills the arteries and veins decreases, and this lowers blood pressure. If the kidneys make less urine, the amount of blood that fills the arteries and veins increases and this increases blood pressure. Compared with the other mechanisms for adjusting blood pressure, changes in the production of urine affect blood pressure slowly over hours and days. (The other mechanisms are effective in seconds.)
Many expert groups recommend a slightly higher target of 150/90 mmHg for those over somewhere between 60 and 80 years of age.[99][100][101][105] The JNC-8 and American College of Physicians recommend the target of 150/90 mmHg for those over 60 years of age,[13][106] but some experts within these groups disagree with this recommendation.[107] Some expert groups have also recommended slightly lower targets in those with diabetes[99] or chronic kidney disease with protein loss in the urine,[108] but others recommend the same target as for the general population.[13][103] The issue of what is the best target and whether targets should differ for high risk individuals is unresolved,[109] although some experts propose more intensive blood pressure lowering than advocated in some guidelines.[110]
In hypertensive emergency, there is evidence of direct damage to one or more organs.[27][28] The most affected organs include the brain, kidney, heart and lungs, producing symptoms which may include confusion, drowsiness, chest pain and breathlessness.[26] In hypertensive emergency, the blood pressure must be reduced more rapidly to stop ongoing organ damage,[26] however, there is a lack of randomized controlled trial evidence for this approach.[28]
Kaiser Permanente health plans around the country: Kaiser Foundation Health Plan, Inc., in Northern and Southern California and Hawaii • Kaiser Foundation Health Plan of Colorado • Kaiser Foundation Health Plan of Georgia, Inc., Nine Piedmont Center, 3495 Piedmont Road NE, Atlanta, GA 30305, 404-364-7000 • Kaiser Foundation Health Plan of the Mid-Atlantic States, Inc., in Maryland, Virginia, and Washington, D.C., 2101 E. Jefferson St., Rockville, MD 20852 • Kaiser Foundation Health Plan of the Northwest, 500 NE Multnomah St., Suite 100, Portland, OR 97232 • Kaiser Foundation Health Plan of Washington or Kaiser Foundation Health Plan of Washington Options, Inc., 601 Union St., Suite 3100, Seattle, WA 98101
If your blood pressure is above the normal range for up to 5 readings (taken at different visits), your doctor will likely diagnose you with high blood pressure. Sometimes the doctor may diagnose you after a fewer number of readings, depending on how high above normal your blood pressure is and if you have other medical conditions. Blood pressure tends to be at its highest during exercise, physical work, or stress, and lowest during sleep. Everyone can have a temporary increase in blood pressure at one time or another, which is why it's important to take multiple readings.

There are even more medication types that can lower blood pressure. Some of these are alpha blockers, vasodilators, and central alpha agonists. Your doctor may prescribe these medications if other medications have been ineffective or if you have another condition along with hypertension. Side effects can include fast pulse, palpitations, dizziness, diarrhea, or headaches.
Stress reduction techniques such as biofeedback or transcendental meditation may be considered as an add-on to other treatments to reduce hypertension, but do not have evidence for preventing cardiovascular disease on their own.[125][126][127] Self-monitoring and appointment reminders might support the use of other strategies to improve blood pressure control, but need further evaluation.[128]
^ Jump up to: a b c d e National High Blood Pressure Education Program Working Group on High Blood Pressure in Children and Adolescents (August 2004). "The fourth report on the diagnosis, evaluation, and treatment of high blood pressure in children and adolescents". Pediatrics. 114 (2 Suppl 4th Report): 555–76. doi:10.1542/peds.114.2.S2.555. PMID 15286277. 

Your doctor may diagnose you with high blood pressure when you have consistent systolic readings of 140 mm Hg or higher or diastolic readings of 90 mm Hg or higher. Based on research, your doctor may also consider you to have high blood pressure if you are an adult or child age 13 or older who has consistent systolic readings of 130 to 139 mm Hg or diastolic readings of 80 to 89 mm Hg and you have other cardiovascular risk factors.
^ Expert Panel on Integrated Guidelines for Cardiovascular Health and Risk Reduction in Children and Adolescents, National Heart, Lung, and Blood Institute (Dec 2011). "Expert panel on integrated guidelines for cardiovascular health and risk reduction in children and adolescents: summary report". Pediatrics. 128 Suppl 5: S213–56. doi:10.1542/peds.2009-2107C. PMC 4536582. PMID 22084329.

Unlike high blood pressure symptoms, which are poorly defined and often totally absent, low blood pressure symptoms tend to be more upfront and easily recognizable. The development of symptoms is often a warning sign of a potentially serious underlying disorder. Generally speaking, your blood pressure would need to fall pretty dramatically before symptoms develop.