An abnormally fast heart rate (tachycardia) also can cause low blood pressure. The most common example of tachycardia causing low blood pressure is atrial fibrillation (Afib). Atrial fibrillation is a disorder of the heart characterized by rapid and irregular electrical discharges from the muscle of the heart causing the ventricles to contract irregularly and (usually) rapidly. The rapidly contracting ventricles do not have enough time to fill maximally with blood before each contraction, and the amount of blood that is pumped decreases in spite of the faster heart rate. Other abnormally rapid heart rhythms such as ventricular tachycardia also can produce low blood pressure, and sometimes life-threatening shock.
However, sometimes a high reading can occur temporarily and then your numbers will return to normal. If your blood pressure measures at this level, your doctor will likely take a second reading after a few minutes have passed. A second high reading indicates that you’ll need treatment either as soon as possible or immediately depending on whether or not you have any of the symptoms described above.
Vasovagal reaction is a common condition in which a healthy person temporarily develops low blood pressure, slow heart rate, and sometimes fainting. A vasovagal reaction typically is brought on by emotions of fear or pain such as having blood drawn, starting an intravenous infusion, or by gastrointestinal upset. Vasovagal reactions are caused by activity of the involuntary (autonomic) nervous system, especially the vagus nerve, which releases hormones that slow the heart and widen the blood vessels. The vagus nerve also controls digestive tract function and senses activity in the digestive system. Thus, some people can have a vasovagal reaction from straining at a bowel movement or vomiting. 

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]

Hypertension with certain specific additional signs and symptoms may suggest secondary hypertension, i.e. hypertension due to an identifiable cause. For example, Cushing's syndrome frequently causes truncal obesity, glucose intolerance, moon face, a hump of fat behind the neck/shoulder (referred to as a buffalo hump), and purple abdominal stretch marks.[23] Hyperthyroidism frequently causes weight loss with increased appetite, fast heart rate, bulging eyes, and tremor. Renal artery stenosis (RAS) may be associated with a localized abdominal bruit to the left or right of the midline (unilateral RAS), or in both locations (bilateral RAS). Coarctation of the aorta frequently causes a decreased blood pressure in the lower extremities relative to the arms, or delayed or absent femoral arterial pulses. Pheochromocytoma may cause abrupt ("paroxysmal") episodes of hypertension accompanied by headache, palpitations, pale appearance, and excessive sweating.[23]

^ Sacks, F. M.; Svetkey, L. P.; Vollmer, W. M.; Appel, L. J.; Bray, G. A.; Harsha, D.; Obarzanek, E.; Conlin, P. R.; Miller, E. R. (2001-01-04). "Effects on blood pressure of reduced dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) diet. DASH-Sodium Collaborative Research Group". The New England Journal of Medicine. 344 (1): 3–10. doi:10.1056/NEJM200101043440101. ISSN 0028-4793. PMID 11136953.
African-Americans are at greater risk of developing hypertension than people of other races. African-Americans develop high blood pressure earlier in life and have more difficulty achieving blood pressure goals. Some studies suggest that African-Americans may be more sensitive to salt than other races. For those who are genetically prone to salt sensitivity, a small amount (half-teaspoon) of salt can raise blood pressure by 5 mm Hg. Dietary factors and being overweight can also raise blood pressure.
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.'
Making sure your blood pressure numbers are normal is an investment for your future. Putting unnecessary strain on your arteries and your heart can ultimately lead to a heart attack or stroke. Heart disease and strokes are the leading causes of death in the United States. About 1,000 people die every day from complications stemming from 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?
Health care providers measure blood pressure with a sphygmomanometer (sfig-mo-muh-NAH-muh-ter), which has a cuff that's wrapped around the upper arm and pumped up to create pressure. When the cuff is inflated, it squeezes a large artery in the arm, stopping the blood flow for a moment. Blood pressure is measured as air is gradually let out of the cuff, which allows blood to flow through the artery again.

Blood pressure often increases in stages. A person in her thirties may have mild to moderately elevated blood pressure readings. As she ages, blood pressure may continue to slowly rise. If someone develops high blood pressure before the age of 50, the risk of heart attack and stroke is greatly increased. If untreated, high blood pressure can reduce life expectancy by 10 or more years.
Heart attack. Signs of heart attack include mild or severe chest pain or discomfort in the center of the chest or upper abdomen that lasts for more than a few minutes or goes away and comes back. It can feel like pressure, squeezing, fullness, heartburn, or indigestion. There may also be pain down the left arm. Women may also have chest pain and pain down the left arm, but they are more likely to have less typical symptoms, such as shortness of breath, nausea, vomiting, unusual tiredness, and pain in the back, shoulders, or jaw. Read more about the signs and symptoms of a heart attack.
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. 

Blood pressure monitors for use at home can be bought at drug stores, department stores, and other places. Again, these monitors may not always give you a correct reading. You should always compare your machine’s reading with a reading from your doctor’s machine to make sure they are the same. Remember that any measurement above normal should prompt a visit to the doctor, who can then talk with you about the best course of action.
About This Image: Person receiving a blood pressure test. Medical research shows that as we age blood pressure rises slightly to accommodate an increased demand of oxygen and nutrients. It is completely natural for the first number (systolic) to be 100 plus our age. A recent study by a group of UCLA researchers came very close to corroborating Dr. Piette's guide for blood pressure of 100 plus your age for men, subtracting 10 for women, and this is after this rule had been in use for five or more decades. Are we now being taught that Dr. Piette's guide for blood pressure is wrong merely for drug company profit?

*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.

A number of medications contribute to heart disease, including corticosteroids, oral contraceptives, some decongestants, medications that contain caffeine, and many others. In general, it is best to check the label to see if hypertension is one of the side effects of any medications you take, especially if you already have hypertension or if you are at increased risk for it.

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.

The findings mean that an additional 14 percent of U.S. adults, or about 30 million people, will now be diagnosed as having high blood pressure, compared with the number diagnosed before the new guidelines. This will bring the total percentage of U.S. adults with high blood pressure to 46 percent, up from 32 percent previously. [9 New Ways to Keep Your Heart Healthy]
If your blood pressure is elevated, your doctor may request you have more readings over the course of a few days or weeks. A hypertension diagnosis is rarely given after just one reading. Your doctor needs to see evidence of a sustained problem. That’s because your environment can contribute to increased blood pressure, such as the stress you may feel by being at the doctor’s office. Also, blood pressure levels change throughout the day.
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.

Stage 1 and Stage 2 hypertensions require therapy with anti-hypertensive drugs to bring down the blood pressure. Lifestyle modifications are also necessary, but often it is not sufficient for satisfactory control of blood pressure. Hypertension is often asymptomatic in the early course of disease. Symptoms like headache, lightheadedness, palpitations and easy fatigability may occur and chances of them being present increases with increasing blood pressure.

^ Jump up to: a b Kato, Norihiro; Loh, Marie; Takeuchi, Fumihiko; Verweij, Niek; Wang, Xu; Zhang, Weihua; Kelly, Tanika N.; Saleheen, Danish; Lehne, Benjamin (2015-11-01). "Trans-ancestry genome-wide association study identifies 12 genetic loci influencing blood pressure and implicates a role for DNA methylation". Nature Genetics. 47 (11): 1282–93. doi:10.1038/ng.3405. ISSN 1546-1718. PMC 4719169. PMID 26390057.
When blood pressure is measured, there are two numbers for each reading: for example, "120 over 80" is written as 120/80. This is because each heartbeat sends a pressure wave through the bloodstream. The higher number (systolic blood pressure) is the peak of the wave, when your heart contracts (the loud "thump" when you listen to your heartbeat). The lower number (diastolic blood pressure) is the lower "dip" or trough of the wave, when your heart relaxes.