Understanding Blood Pressure Readings
Blood pressure is typically recorded as two numbers, written as a ratio like this:
Read as “117 over 76 millimeters of mercury”
The top number, which is also the higher of the two numbers, measures the pressure in the arteries when the heart beats (when the heart muscle contracts).
The bottom number, which is also the lower of the two numbers, measures the pressure in the arteries between heartbeats (when the heart muscle is resting between beats and refilling with blood).
This chart reflects blood pressure categories defined by the Heart Association.
mm Hg (upper #)
mm Hg (lower #)
|Normal||less than 120||and||less than 80|
|Prehypertension||120 – 139||or||80 – 89|
|High Blood Pressure
(Hypertension) Stage 1
|140 – 159||or||90 – 99|
|High Blood Pressure
(Hypertension) Stage 2
|160 or higher||or||100 or higher|
(Emergency care needed)
|Higher than 180||or||Higher than 110|
* Your doctor should evaluate unusually low blood pressure readings.
How is high blood pressure diagnosed?
Your healthcare providers will want to get an accurate picture of your blood pressure and chart what happens over time. Starting at age 20, the Heart Association recommends a blood pressure screening at your regular healthcare visit or once every 2 years, if your blood pressure is less than 120/80 mm Hg.
Your blood pressure rises with each heartbeat and falls when your heart relaxes between beats. While BP can change from minute to minute with changes in posture, exercise, stress or sleep, it should normally be less than 120/80 mm Hg (less than 120 systolic AND less than 80 diastolic) for an adult age 20 or over..
If your blood pressure reading is higher than normal, your doctor may take several readings over time and/or have you monitor your blood pressure at home before diagnosing you with high blood pressure.
A single high reading does not necessarily mean that you have high blood pressure. However, if readings stay at 140/90 mm Hg or above (systolic 140 or above OR diastolic 90 or above) over time, your doctor will likely want you to begin a treatment program. Such a program almost always includes lifestyle changes and often prescription medication for those with readings of 140/90 or higher.
If, while monitoring your blood pressure, you get a systolic reading of 180 mm Hg or higher OR a diastolic reading of 110 mm HG or higher, wait a couple of minutes and take it again. If the reading is still at or above that level, you should seek immediate emergency medical treatment for a hypertensive crisis. If you can’t access the emergency medical services (EMS), have someone drive you to the hospital right away.
Even if your blood pressure is normal, you should consider making lifestyle modifications to prevent the development of HBP and improve your heart health.
Which number is more important, top (systolic) or bottom (diastolic)?
Typically more attention is given to the top number (the systolic blood pressure) as a major risk factor for cardiovascular disease for people over 50 years old. In most people, systolic blood pressure rises steadily with age due to increasing stiffness of large arteries, long-term build-up of plaque, and increased incidence of cardiac and vascular disease.
What are the Symptoms of High Blood Pressure?
The myth of symptoms
There’s a common misconception that people with high blood pressure, also called HBP or hypertension, will experience symptoms such as nervousness, sweating, difficulty sleeping or facial flushing. The truth is that HBP is largely a symptomless condition. If you ignore your blood pressure because you think symptoms will alert you to the problem, you are taking a dangerous chance with your life. Everybody needs to know their blood pressure numbers, and everyone needs to prevent high blood pressure from developing.
The myth of symptomatic headaches
The best evidence indicates that high blood pressure does not cause headaches except perhaps in the case of hypertensive crisis (systolic/top number higher than 180 OR diastolic/bottom number higher than 110).
In the early 1900s, it was assumed that headaches were more common among people with high blood pressure. However, research into the subject doesn’t support this view. According to one study, people with high blood pressure seem to have significantly fewer headaches than the general population.
In a study published in the journal Neurology, people with higher systolic blood pressure (the top number in blood pressure readings) were up to 40 percent less likely to have headaches compared to those with healthier blood pressure readings. The researchers also looked at another measurement called the pulse pressure, which is the change in blood pressure when the heart contracts. Pulse pressure is calculated by subtracting the bottom number (diastolic reading) from the top number (systolic reading). Those with higher pulse pressure had up to 50 percent fewer headaches. The researchers think that the higher the pulse pressure, the stiffer the blood vessels. The stiffer the blood vessel, the less likely the nerve endings are working properly. If the nerve endings aren’t functioning correctly, the less likely a person will feel pain.
Therefore, headaches or the lack of headaches are not reliable indicators of your blood pressure. Instead, work with your doctor and know your numbers.
The myth of symptomatic nosebleeds
Except with hypertensive crisis, nosebleeds are not a reliable indicator for HBP. In one study, 17 percent of people treated for high blood pressure emergencies at the hospital had nosebleeds. However, 83 percent reported no such symptom. Although it’s also been noted that some people in the early stages of high blood pressure may have more nosebleeds than usual, there are other possible explanations. If your nosebleeds are frequent (more than once a week) or if they are heavy or hard to stop, you should talk to your healthcare professional.
Keep in mind that nosebleeds can be caused by a variety of factors, with the most common one being dry air. The lining of the nose contains many tiny blood vessels that can bleed easily. In a hot climate like the desert Southwest or with heated indoor air, the nasal membranes can dry out and make the nose more susceptible to bleeding. Other causes include vigorously blowing your nose; medical conditions like allergies, colds, sinusitis or a deviated septum; and side effects from some anticoagulant drugs like warfarin (Coumadin®) or aspirin.
Other inconclusively related symptoms
You should not try to evaluate your symptoms in an attempt to self-diagnose high blood pressure. Diagnosis should only be made by a healthcare professional. A variety of symptoms may be indirectly related to HBP but are not always caused by HBP, such as:
- • Blood spots in the eyes
Yes, blood spots in the eyes, or subconjunctival hemorrhage, are more common in people with diabetes or high blood pressure, but neither condition causes the blood spots. Floaters in the eyes are not related to high blood pressure. However, an ophthalmologist may be able to detect damage to the optic nerve caused by untreated HBP.
- • Facial flushing
Facial flushing occurs when blood vessels in the face dilate. The red, burning face can occur unpredictably or in response to certain triggers such as sun exposure, cold weather, spicy foods, wind, hot drinks and skin-care products. Facial flushing can also occur with emotional stress, exposure to heat or hot water, alcohol consumption and exercise, all of which can raise blood pressure temporarily. While facial flushing may occur while your blood pressure is higher than usual, HBP is not the cause of facial flushing.
- • Dizziness
Although it is not caused by HBP, dizziness can be a side effect of some high blood pressure medications. Nonetheless, dizziness should not be ignored, especially if you notice a sudden onset. Sudden dizziness, loss of balance or coordination and trouble walking are all warning signs of a stroke. HBP is one of the leading risk factors for stroke.
The Symptoms of Hypertensive Crisis
As mentioned above, only when blood pressure readings soar to dangerously high levels (systolic of 180 or higher OR diastolic of 110 or higher) may obvious symptoms occur. Blood pressure this high is known as hypertensive crisis, and emergency medical treatment is needed.
In addition to extreme readings, a person in hypertensive crisis may experience:
- • Severe headaches
- • Severe anxiety
- • Shortness of breath
- • Nosebleeds
Low Blood Pressure
To know if you have high or low blood pressure, you need to know what a healthy blood pressure level is. Optimal blood pressure is less than 120/80 mm Hg (systolic pressure is 120 &diastolic pressure is less than 80). Within certain limits, the lower your blood pressure reading is, the better. There is no specific number at which day-to-day blood pressure is considered too low, as long as no symptoms of trouble are present.
If my blood pressure stays around 85/55, do I have a health problem?
As long as you are not experiencing symptoms of low blood pressure, there is no need for concern. Most doctors consider chronically low blood pressure dangerous only if it causes noticeable signs and symptoms, such as:
- • Dizziness or lightheadedness
- • Fainting (called syncope)
- • Dehydration and unusual thirst
Dehydration can sometimes cause blood pressure to drop. However, dehydration does not automatically signal low blood pressure. Fever, vomiting, severe diarrhea, overuse of diuretics and strenuous exercise can all lead to dehydration, a potentially serious condition in which your body loses more water than you take in. Even mild dehydration (a loss of as little as 1 percent to 2 percent of body weight), can cause weakness, dizziness and fatigue.
- • Lack of concentration
- • Blurred vision
- • Nausea
- • Cold, clammy, pale skin
- • Rapid, shallow breathing
- • Fatigue
- • Depression
As long as no symptoms are present, low blood pressure is not a problem. However, if your blood pressure is normally higher or if you are experiencing any of the symptoms listed above, your low pressure may have an underlying cause.
Low blood pressure can occur with:
- • Prolonged bed rest
- • Pregnancy
During the first 24 weeks of pregnancy, it’s common for blood pressure to drop.
- • Decreases in blood volume
A decrease in blood volume can also cause blood pressure to drop. A significant loss of blood from major trauma, dehydration or severe internal bleeding reduces blood volume, leading to a severe drop in blood pressure.
- • Certain medications
A number of drugs can cause low blood pressure, including diuretics and other drugs that treat hypertension; heart medications such as beta blockers; drugs for Parkinson’s disease; tricyclic antidepressants; erectile dysfunction drugs, particularly in combination with nitroglycerine; narcotics and alcohol. Other prescription and over-the-counter drugs may cause low blood pressure when taken in combination with HBP medications.
- • Heart problems
Among the heart conditions that can lead to low blood pressure are an abnormally low heart rate (bradycardia), problems with heart valves, heart attack and heart failure. Your heart may not be able to circulate enough blood to meet your body’s needs.
- • Endocrine problems
Such problems include complications with hormone-producing glands in the body’s endocrine systems; specifically, an under-active thyroid (hypothyroidism), parathyroid disease, adrenal insufficiency (Addison’s disease), low blood sugar and, in some cases, diabetes.
- • Severe infection (septic shock)
Septic shock can occur when bacteria leave the original site of an infection (most often in the lungs, abdomen or urinary tract) and enter the bloodstream. The bacteria then produce toxins that affect blood vessels, leading to a profound and life-threatening decline in blood pressure.
- • 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.
- • Neurally mediated hypotension
Unlike orthostatic hypotension, this disorder causes blood pressure to drop after standing for long periods, leading to symptoms such as dizziness, nausea and fainting. This condition primarily affects young people and occurs because of a miscommunication between the heart and the brain.
- • Nutritional deficiencies
A lack of the essential vitamins B-12 and folic acid can cause anemia, which in turn can lead to low blood pressure.
|Severely low blood pressure can have underlying causes that may:
When to see your healthcare professional
If you experience any dizziness or lightheadedness, it’s a good idea to consult with your healthcare provider. If you have gotten dehydrated, have low blood sugar or have spent too much time in the sun or a hot tub, it is more important to recognize how quickly your blood pressure drops than how low it drops. Keep a record of your symptoms and your activities at the time your symptoms occurred.