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What is blood pressure?
Blood pressure is the force exerted by circulating blood on the walls of blood vessels, and constitutes one of the principal vital signs. Blood pressure is generated by the heart pumping blood into the arteries and is regulated by the response by the arteries to the flow of blood.
What is low blood pressure?
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 permanently damaged.
What is healthy blood pressure?
When the heart beats, it pushes blood through the arteries in the body. The systolic blood pressure measures the pressure generated within the arteries when the heart pumps. The diastolic pressure measures the underlying resting pressure within the artery when the heart is collecting blood and not pumping. Any blood pressure measurement above 120/80 millimeters of mercury is considered elevated.
How is blood pressure generated?
During relaxation of the heart (diastole) the left ventricle of the heart fills with blood returning from the lungs. The left ventricle then contracts and pumps blood into the arteries (systole). The pulse that we can feel when we place our fingers over an artery is caused by the contraction of the left ventricle.
How is blood pressure determined?
Blood pressure is determined by the amount of blood pumped by the left ventricle of the heart into the arteries, and the resistance to the flow of blood caused by the walls of the arteries. Generally, blood pressure tends to be higher if more blood is pumped, or if the arteries are narrow and stiff. Blood pressure tends to be lower if less blood is being pumped, or if the space within the arteries of the body is larger and have less resistance to the flow of blood.
How does the body maintain normal blood pressure?
The body has mechanisms to alter or maintain blood pressure by specialized nerve cells called baroreceptors. These sensors, found in the large arteries closest to your heart, sense blood pressure and then send signals to the heart, the arteries, the veins, and the kidneys that cause them to make changes that regulate blood pressure. The goal is to maintain cardiac output, the amount of blood delivered to organs in the body.
Baroreceptor signals sent to the heart.
Baroreceptor signals sent to the heart can speed up and contract more frequently to eject more blood per minute. This response increases the flow of blood into the arteries and may increase blood pressure.
Baroreceptor signals sent to the veins.
Baroreceptors can signal veins to expand so more blood can be stored in the veins and less blood returns to the heart for pumping into the arteries. As a result, the heart pumps less blood per beat, and blood pressure may decrease. On the other hand, when veins narrow, less blood is stored in the veins, more blood returns to the heart for pumping into the arteries, and blood pressure increases.
Baroreceptor signals sent to the arteries.
When blood pressure is high, the receptors signal the arteries to expand creating less resistance to the flow of blood and decrease blood pressure. When pressure Is low, narrowed arteries create more resistance and raise blood pressure.
Baroreceptor signals sent to the kidneys.
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.)
Is low blood pressure bad for your health?
People who have lower blood pressures have a lower risk of stroke, kidney disease, and heart disease. Athletes, people who exercise regularly, people who maintain ideal body weight, and non-smokers tend to have lower blood pressures. Therefore, low blood pressure is desirable as long as it is not low enough to cause symptoms and potentially damage organs of the body.
What are low blood pressure signs and symptoms?
If low blood pressure is the normal state for a patient, then there will be no symptoms. However, if low blood pressure is symptomatic, then the patient may feel lightheaded and dizzy, unsteadiness as blood flow to the brain is decreased. There may be blurring of vision, weakness, confusion, and nausea. Other organs may be involved causing chest pain, shortness of breath, cool, clammy skin, and passing out or fainting.
What are the causes of low blood pressure?
Conditions that decrease the volume of blood (for example, bleeding, dehydration), reduce cardiac output (for example, heart attack, cardiomyopathy), and decrease the tension in artery walls may cause low blood pressure. Medication side effects can cause low blood pressure, as can spinal cord injuries.
Neurological causes of low blood pressure.
The body requires the central nervous system to be functioning normally to maintain a normal blood pressure. There is a balance between the adrenalin system and the vagus nerve. If there is overstimulation of the vagus nerve, the veins will dilate, not enough blood will return to the heart and blood pressure may fall. Vasovagal syncope is very common and often occurs when a noxious stimulus occurs (fainting at the sight of blood or with pain). Sometimes the vagus nerve is stimulated when a person pushes too hard when urinating or having a bowel movement.
If adrenalin to arteries is blocked, like in a spinal cord injury, the tension in the artery walls is lost and the arteries will dilate, not maintaining blood pressure.
Non-neurological causes of low blood pressure.
Some non-neurologic conditions that can cause low blood pressure include bleeding, dehydration from vomiting and diarrhea or infections, abnormalities in adrenal gland function, and blood loss.
Pregnancy may cause lower blood pressures as part of normal physiology.
Medications may cause of low blood pressure.
Medications may cause low blood pressure. Medicines used to control high blood pressure (angiotensin receptor blockers, beta blockers, calcium channel blockers, alpha-blockers and diuretics or water pills) can work too well and cause symptomatic low blood pressure. Other medications may cause low blood pressure as a side effect. Examples include tricyclic anti-depressants [for example, amitriptyline (Elavil)], Parkinson's medications [for example, levodopa-carbidopa (Sinemet)], and erectile dysfunction therapies [for example, sildenafil (Viagra)].
Alcohol and narcotic pain medications may also cause low blood pressure.
What other conditions cause low blood pressure?
Septicemia is a severe infection in which bacteria (or other infectious organisms such as fungi) enter the blood. Commonly the initial infection may originate in the lungs (as pneumonia), bladder (urinary tract Infection), or in the abdomen (diverticulitis). Untreated, the bacteria enter the bloodstream where they may release toxins and cause life-threatening and profound low blood pressure (septic shock), often with damage to several organs.
What other conditions cause low blood pressure?
Anaphylaxis (anaphylactic shock) is a potentially fatal allergic reaction to medications such as antibiotics, foods like peanuts, bee stings (insect stings), or intravenous contrast dye used in medical studies. The allergic reaction causes the body's immune system to cascade out of control in response to exposure to an allergic substance. However, this situation is not common.
How is low blood pressure diagnosed?
Measuring blood pressure, sometimes in both the lying (supine) and standing positions usually is the first step in diagnosing low blood pressure. In patients with symptomatic low blood pressure, there often is a marked drop in blood pressure upon standing, and patients may even develop lightheadedness and feel as If they are going to pass out. The heart rate may increase as well. Once low blood pressure has been identified its cause needs to be found. Sometimes the causes are readily apparent (for example, trauma with bleeding or a spinal cord Injury, or vasovagal syncope). At other times, the cause may require tests to determine the source of the problem.
How is low blood pressure treated?
Patients with symptoms that are possibly due to low blood pressure should be evaluated by a doctor. Patients who have had a major drop in blood pressure from their usual levels even without the development of symptoms also should be evaluated. Treatment will be based upon the cause of the low blood pressure reading. For example, a person being treated for high blood pressure, may need to have their medications adjusted. Or for a person with dehydration due to vomiting and diarrhea, intravenous fluids may be required.
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