Low Blood Pressure


Low Blood Pressure:

Low blood pressure, or hypotension, occurs when blood pressure during and after each heartbeat is much lower than usual and heart fails to pump enough blood to vital organs (heart, kidney and brain) which is necessary to maintain their normal functioning.

Most normal blood pressures fall in the range of 90/60 millimeters of mercury (mm Hg) to 130/80 mm Hg. Blood pressure lower than this is considered as hypotension. It must be kept in mind that Blood pressure which is lower for one person may be normal for another person. Normal ranges of blood pressure can be seen using Blood pressure chart.

There are three main types of hypotension:

  • Hypotension caused by a sudden loss of blood (shock), infection, or severe allergic reaction
  • Orthostatic hypotension, including postprandial orthostatic hypotension.
  • Neurally mediated hypotension (NMH)

NMH most commonly affects young adults and children. It occurs when a person has been standing for a long time.

Orthostatic hypotension is brought on by a sudden change in body position, most often when shifting from lying down to standing. This type of hypotension usually lasts only a few seconds or minutes. If this type of hypotension occurs after eating a meal, it is called postprandial orthostatic hypotension. This form most commonly affects older adults, those with high blood pressure, and persons with Parkinson’s disease.

What are the causes of low blood pressure?

Conditions that reduce cardiac output (the amount of blood pumped by the heart), decrease the volume of blood, and medications are most common causes for low blood pressure.

  • Moderate or severe bleeding can quickly exhaust an individual’s body of blood, leading to low blood pressure or orthostatic hypotension. Bleeding can be due to surgical complications, or from gastrointestinal abnormalities such as ulcers, tumors, or diverticulosis or trauma. Occasionally, the bleeding may be so severe and rapid (for example, bleeding from a ruptured aortic aneurysm) that it causes shock and death within fews minutes.
  • Dehydration occurs if the patient has prolonged nausea, vomiting, and diarrhea.

Other causes of dehydration are exercise, sweating, fever, and heat exhaustion, or heat stroke. Individuals with mild dehydration may experience only thirst and dry mouth. Moderate to severe dehydration may cause orthostatic hypotension (manifested by lightheadedness, fainting upon standing). Prolonged and severe dehydration lead to shock, , confusion, kidney failure acidosis (too much acid in the blood), coma, and even death if not treated in time.

  • Severe inflammation of body organs, for example, acute pancreatitis can cause hypotension. In acute pancreatitis, fluid leaves the blood vessels to enter the inflamed tissues around the pancreas as well as the abdominal cavity, concentrating blood and reducing its volume.

Causes of low blood pressure due to heart disease

  • Weakened heart muscle cause failure of heart muscle to pump adequate amount of blood. Examples include repeated heart attacks or massive heart attck, medications that are toxic to the heart, viral infections of the muscle of the heart (myocarditis), and diseases of the heart’s valves such as aortic stenosis.

A slow heart rate (bradycardia)leads to decrease amount of blood pumped by the heart. The resting heart rate for a healthy adult is between 60 and 100 beats/minute. Bradycardia occurs when resting heart rates is less than 60 beats/min. It must be noted that bradycardia does not always cause low blood pressure. For example, some highly trained athletes can have resting heart rates in the 40s and 50s (beats per minute) without any symptoms. But in many patients bradycardia can lead to low blood pressure, dizziness, and even fainting. Several common reasons for bradycardia include sick sinus syndrome,heart block, and drug toxicity. Many of these conditions occur in the elderly.

  • Pulmonary embolism is a condition in which a blood clot in a vein (deep vein thrombosis) breaks off and travels to the heart and eventually pulmonary artery (lungs). A large blood clot can block the flow of blood into the left ventricle from the lungs and severely diminish the blood returning to the heart for pumping. Pulmonary embolism is a life-threatening emergency.
  • Pericarditis is an inflammation of the pericardium (membrane surrounding the heart). Pericarditis causes fluid to accumulate within the pericardium and compress the heart, restricting the heart to pump blood.
  • 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. 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 the 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, sometimes even life-threatening shock.

Medications that cause low blood pressure

  • Medications such as calcium channel blockers, beta blockers, and digoxin (Lanoxin) can slow the rate at which the heart contracts and ultimately leading to low blood pressure. Elderly people are especially sensitive to these drugs.
  • Medications for treating high blood pressure (such as ACE inhibitors, angiotensin receptor blockers, beta blockers, calcium channel blockers, and alpha-blockers).
  • Antidepressants, such as amitriptyline ,Parkinson’s disease, such as levodopa-carbidopa (Sinemet), erectile dysfunction (impotence), such as sildenafil (Viagra)
  • Diuretics(water pills) such as hydrochlorothiazide ,furosemide (Lasix)
  •  Alcohol and narcotics.

Other conditions that cause low blood pressure

  • Postural (orthostatic) hypotension is a sudden drop in blood pressure when an individual stands up from a sitting, squatting, or supine position. Gravity causes blood to settle in the veins in the legs when patient stands up so that less blood returns to the heart for pumping, and, as a result, the blood pressure drops. The body normally responds automatically to this by increasing the heart rate and by narrowing the veins to return more blood to the heart. In patients with postural hypotension, this compensating reflex fails to occur, resulting low blood pressure and dizziness. Postural hypotension can occur in persons of all ages but is much more common among the elderly, especially in those on medications for high blood pressure or diuretics. Other causes of postural hypotension include dehydration, adrenal insufficiency, prolonged bed rest, diabetes, alcoholism.
  • Vasovagal reaction is a common condition in which a healthy person temporarily develops low blood pressure, slow heart rate, and sometimes faints. 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. These reactions are caused by activity of the involuntary (autonomic) nervous system, especially the vagus nerve, which releases hormones that slow the heart and dilate the blood vessels.
  • Another form of postural hypotension occurs commonly  in young healthy individuals. After prolonged standing, the individual’s heart rate and blood pressure drop, causing dizziness, nausea, and often fainting. In these individuals, the autonomic nervous system imperfectly responds to prolonged standing by slowing down the heart  and the veins to dilate.
  • Adrenal insufficiency (Addison’s disease) can cause low blood pressure. Addison’s disease is a disorder in which the adrenal glands are destroyed. So adrenal glands fail to produce hormones i.e., cortisol which is necessary to maintain blood pressure and proper function of the heart. Addison’s disease is characterized by weight loss, fatigue, low blood pressure, muscle weakness and darkening of the skin.
  • Micturition syncope is a temporary drop in blood pressure and loss of consciousness after urination. This condition typically occurs in elderly patients and may be due to the release by the autonomic nerves of hormones that lower blood pressure.
  • Anaphylaxis (anaphylactic shock) is a potentially fatal allergic reaction to medications such as penicillin, intravenous iodine, foods such as peanuts, or bee stings (insect stings). In addition to a severe drop in blood pressure, individuals may also experience hives as well as wheezing due to constriction of the airways, and a swollen throat which cause difficulty breathing. The shock is caused by expansion of blood vessels and oozing of water from the blood into the tissues.
  • Septicemia is a severe infection in which bacteria (or other infectious organisms such as fungi) enter the blood. The infection typically originates in the lungs, bladder, or in the abdomen due to diverticulitis or gallstones. The bacteria then enter the blood where they release toxins and cause life-threatening low blood pressure. This condition is called septic shock.

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