^ Nagele, Eva; Jeitler, Klaus; Horvath, Karl; Semlitsch, Thomas; Posch, Nicole; Herrmann, Kirsten H.; Grouven, Ulrich; Hermanns, Tatjana; Hemkens, Lars G.; Siebenhofer, Andrea (2014). "Clinical effectiveness of stress-reduction techniques in patients with hypertension". Journal of Hypertension. 32 (10): 1936–44. doi:10.1097/HJH.0000000000000298. ISSN 0263-6352. PMID 25084308.

Sodium is a key part of how the body controls blood pressure levels. The kidneys help balance fluid and sodium levels in the body. They use sodium and potassium to remove excess fluid from the blood. The body gets rid of this excess fluid as urine. When sodium levels in the blood are high, blood vessels retain more fluid. This increases blood pressure against the blood vessel walls.
You are considered to have hypertension if your systolic blood pressure measurements are between 130 and 139 or your diastolic measurement falls between 80 and 89. At this level of blood pressure you may not have any symptoms. When blood pressure reaches 180/120 or higher, a serious condition known as a malignant hypertension or hypertension crisis may occur. This can lead to stroke, kidney damage, heart attacks, or loss of consciousness. If you measure your blood pressure and it is this high, rest a few minutes and measure again. If it remains high, call 911.
Low blood pressure (hypotension) is pressure so low it causes symptoms or signs due to the low flow of blood through the arteries and veins. When the flow of blood is too low to deliver enough oxygen and nutrients to vital organs such as the brain, heart, and kidney, the organs do not function normally and may be temporarily or permanently damaged.
^ Aronow WS, Fleg JL, Pepine CJ, Artinian NT, Bakris G, Brown AS, Ferdinand KC, Ann Forciea M, Frishman WH, Jaigobin C, Kostis JB, Mancia G, Oparil S, Ortiz E, Reisin E, Rich MW, Schocken DD, Weber MA, Wesley DJ, Harrington RA, Bates ER, Bhatt DL, Bridges CR, Eisenberg MJ, Ferrari VA, Fisher JD, Gardner TJ, Gentile F, Gilson MF, Hlatky MA, Jacobs AK, Kaul S, Moliterno DJ, Mukherjee D, Rosenson RS, Stein JH, Weitz HH, Wesley DJ (2011). "ACCF/AHA 2011 expert consensus document on hypertension in the elderly: a report of the American College of Cardiology Foundation Task Force on Clinical Expert Consensus Documents developed in collaboration with the American Academy of Neurology, American Geriatrics Society, American Society for Preventive Cardiology, American Society of Hypertension, American Society of Nephrology, Association of Black Cardiologists, and European Society of Hypertension". J Am Soc Hypertens. 5 (4): 259–352. doi:10.1016/j.jash.2011.06.001. PMID 21771565.
It's tough to get a reading on your average blood pressure if you only measure it at the doctor's office. Buy a home monitoring kit at your local pharmacy. Take two readings a day, morning and night, for a few days. Repeat these steps a few times a year, and share the results with your doctor. Better understanding of your blood pressure is the first step to preventing heart disease and stroke.

Generally, blood pressure tends to be higher if more blood is pumped into the arteries or if the arterioles are narrow and/or stiff. Narrow and/or stiff arterioles, by resisting the flow of blood, increase blood pressure. Arterioles may become narrower when the muscles surrounding them contract. Arterioles may become stiff and narrow when older patients develop atherosclerosis.
Some people have blood vessels that are stiff and lack elasticity, due to vascular disease. When this affects the tiny arteries (arterioles), the arteriolar stiffness causes increased resistance to the flow of blood and high blood pressure. This is most common in people who are also obese, have a lack of physical activity or exercise, have high salt intake, and are older.

Pre-eclampsia is a serious condition of the second half of pregnancy and following delivery characterised by increased blood pressure and the presence of protein in the urine.[23] It occurs in about 5% of pregnancies and is responsible for approximately 16% of all maternal deaths globally.[23] Pre-eclampsia also doubles the risk of death of the baby around the time of birth.[23] Usually there are no symptoms in pre-eclampsia and it is detected by routine screening. When symptoms of pre-eclampsia occur the most common are headache, visual disturbance (often "flashing lights"), vomiting, pain over the stomach, and swelling. Pre-eclampsia can occasionally progress to a life-threatening condition called eclampsia, which is a hypertensive emergency and has several serious complications including vision loss, brain swelling, seizures, kidney failure, pulmonary edema, and disseminated intravascular coagulation (a blood clotting disorder).[23][31]
Low blood pressure is not always a sign of a problem. But if you have symptoms of low blood pressure, your doctor can diagnose the condition and uncover the cause. Symptoms of dizziness and lightheadedness when you stand up from sitting or lying down -- with a decrease in your blood pressure -- may indicate a condition called postural hypotension. A wide range of underlying conditions may also cause your symptoms. It's important to identify the cause of low blood pressure so appropriate treatment can be given.
Beta-blockers cause the heart to slow down and so some of their side effects can be traced to that mechanism of action. Dizziness, weakness, fatigue, and fainting are possible. Beta-blockers also affect the respiratory system, so other side effects include shortness of breath, difficulty breathing, and chest pain. Beta-blockers should not be withdrawn suddenly, as that could result in a heart attack or sudden death.

Health issues may happen; however, when a person's blood pressure suddenly drops and their brain is deprived of an adequate blood supply. The condition may lead to lightheadedness or dizziness. A sudden drop in blood pressure usually happens in a person who has risen from a prone or sitting position to a standing one. When this occurs it is referred to as, 'orthostatic hypotension,' or, 'postural hypotension.' Another type of low blood pressure may happen when a person stands for extended periods of time; it is referred to as, 'neurally mediated hypotension.' 

In the 19th and 20th centuries, before effective pharmacological treatment for hypertension became possible, three treatment modalities were used, all with numerous side-effects: strict sodium restriction (for example the rice diet[152]), sympathectomy (surgical ablation of parts of the sympathetic nervous system), and pyrogen therapy (injection of substances that caused a fever, indirectly reducing blood pressure).[152][158]
To make an official diagnosis of high blood pressure you will need to see your doctor. Often your blood pressure will be checked on at least two different visits, at different times of the day. Your doctor may ask you to keep a blood pressure log for a short time in order to see your overall blood pressure trends. If your blood pressure is consistently over 134/80, your doctor will work with you to determine the best regimen for treating your high blood pressure.
Medicines are available if these changes do not help control your blood pressure within 3 to 6 months. Diuretics help rid your body of water and sodium. ACE inhibitors block the enzyme that raises your blood pressure. Other types of medicines— beta blockers, calcium channel blockers, and other vasodilators—work in different ways, but their overall effect is to help relax and widen your blood vessels and reduce the pressure inside the vessel. [See also the free government publication “Medicines to Help You: High Blood Pressure” (PDF) from the US Food and Drug Administration.]
Blood pressure is given as a reading of two numbers, such as 110/70. The higher number (systolic) is the pressure when the heart beats. The diastolic, or lower number shows the pressure between the heartbeats, while the relaxed heart is refilling with blood. Normal blood pressure readings are lower than 120/80. The cause of most hypertension is unknown. Occasionally, conditions of the kidney or adrenal gland are the cause of high blood pressure.
I just started using high blood pressure medication and purchased a blood pressure meter at age 72. what concerns me is that the BP readings I get have a very wide variance in. I measure every morning as soon as I wake up, while still in bed and prior to having any coffee. I take 3 or 4 readings. I have found that on any given day my reading can vary from 126 to 143 systolic and the diastolic reading from 68 to 87. this wide variance makes it very difficult to track trends. My questions are: is this normal? is my instrument possibly defective? How can my cardiac doctor make a decision to put me on life long medication based on SINGLE reading in his office?
We tend not to think about our blood pressure — it’s a normal function of our heart working regularly. However, when blood pressure stays high over an extended period it means the heart is working harder than it should. Since hypertension usually doesn’t have symptoms, we don’t know what is happening unless we measure it. Accurately measuring blood pressure provides a glimpse into what’s happening inside our bodies without needing expensive diagnostic tests.
Low blood pressure due to nervous system damage (multiple system atrophy with orthostatic hypotension). Also called Shy-Drager syndrome, this rare disorder causes progressive damage to the autonomic nervous system, which controls involuntary functions such as blood pressure, heart rate, breathing and digestion. It's associated with having very high blood pressure while lying down.
The guidelines, from the American Heart Association (AHA) and the American College of Cardiology (ACC), now define high blood pressure as 130 mm Hg or higher for the systolic blood pressure measurement, or 80 mm Hg or higher for the diastolic blood pressure measurement. (Systolic is the top number, and diastolic is the bottom number, in a blood pressure reading.) Previously, high blood pressure was defined as 140 mm Hg or higher for the systolic measurement and 90 or higher for the diastolic measurement.
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.
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