Heart And Circulation

Efficiency of the circulation may be impaired by a weakening of the heart's pumping action (heart failure) or irregularity of heartbeat (arrhythmia). In addition, the blood vessels may be narrowed and clogged by fatty deposits (atherosclerosis). This may reduce blood supply to the brain, the extremities (peripheral vascular disease), or to the heart muscle (coronary heart disease), causing angina. These last disorders can be complicated by the formation of clots which may block a blood vessel. In the arteries supplying the heart muscle, this is known as coronary thrombosis, and inside the brain it is the most frequent cause of stroke.

One common circulatory disorder is abnormally high blood pressure (hypertension), in which the pressure of the circulating blood on the vessel walls is increased for reasons not yet fully understood. One factor may be loss of elasticity of the blood vessel walls (arteriosclerosis).

A number of other conditions are caused by temporary alterations to blood vessel size. These include migraine and Raynaud's disease.

Digitalis medicaments

Digitalis is the collective term for a number of naturally occurring substances (also called cardiac glycosides) found in the leaves of herbs of the foxglove family and used for certain heart disorders. The principal medicaments in this group are digoxin and digitoxin. Digoxin is more commonly used because it is shorter-acting and dosage is easier to adjust.

The normal heartbeat results from electrical impulses generated in nerve tissue within the heart. These cause the heart muscle to contract and pump blood. By reducing the passage of electrical impulses in the heart, digitalis makes the heart beat more slowly.

The force with which the heart muscle contracts depends on chemical changes in the muscle. By promoting these chemical changes, digitalis increases the force of muscle contraction each time the heart is stimulated. This compensates for the loss of power that occurs when some of the muscle is damaged following a heart attack. The stronger heartbeat increases the flow of blood to the kidneys. This increases urine production and helps to remove the excess fluid that often accumulates as a result of heart failure.

Digitalis relieves symptoms of heart failure - fatigue, breathlessness, and swelling of the legs - and increases your capacity for exercise. The frequency with which you need to pass urine is also increased initially.

Digitalis medicaments can be toxic and, if blood levels rise too high, may produce symptoms of digitalis poisoning. These include excessive tiredness, confusion, loss of appetite, nausea, vomiting, and diarrhea. If such symptoms occur, it is important to report them to your physician promptly.

Digoxin is normally removed from the body by the kidneys; if kidney function is impaired, the medicament is more likely to accumulate in the body and cause toxic effects. Digitoxin, which is broken down in the liver, is sometimes preferred in such cases. Digitoxin can accumulate after repeated doses, especially if liver function is reduced.

Both digoxin and digitoxin are more toxic when blood potassium levels are low. Potassium deficiency is commonly caused by diuretic medicaments, so that people taking these along with digitalis medicaments need to have the effects of both medicaments and blood potassium levels carefully monitored. Potassium supplements may be required.

Beta blockers

Epinephrine (from the adrenal gland) and similar substances act in part through beta receptors in the body. Beta blockers (also called beta adrenergic blocking agents) prevent the actions of epinephrine-like substances on beta receptors. Used mainly in heart disorders, they are occasionally prescribed for other conditions.

By occupying the beta receptors, beta blockers nullify the stimulating action of norepinephrine. Thus they reduce the force and speed of the heartbeat, prevent the dilation of the airways to the lungs, and prevent the dilation of the blood vessels surrounding the brain and leading to the extremities.

Taken to treat angina, beta blockers reduce the frequency and severity of attacks. As part of the treatment for hypertension, they help to lower blood pressure and thus reduce the risks that are associated with this condition. Beta blockers help to prevent severe attacks of arrhythmia, marked by either irregular or rapid heartbeat.

Because beta blockers affect many parts of the body, they commonly produce minor side effects. By reducing heart rate and air flow to the lungs, they may reduce capacity for strenuous exercise, although this is unlikely to be noticed by somebody whose physical activity was previously limited by heart problems. Many people experience cold hands and feet while taking these medicaments, due to the reduction in blood supply to the limbs. Reduced circulation can also lead to temporary impotence during beta blocker treatment.

The main risk of beta blockers is that of provoking breathing difficulties as a result of their blocking effect on beta receptors in the lungs. Cardio-selective beta blockers, which act principally on the heart, are thought to be less likely than non-cardio-selective ones to cause such problems. But all beta blockers are prescribed with caution for people with asthma, bronchitis, or other forms of respiratory disease.

Beta blockers are not usually prescribed for people who have poor circulation in the limbs, because they reduce the flow of blood and may aggravate such conditions. They are not normally given to people who are subject to heart failure because they may further reduce the force of the heartbeat. Diabetics who need to take beta blockers should be aware that they may notice a change in the warning signs of low blood sugar - in particular, symptoms such as palpitations and tremor may be suppressed.

Beta blockers should not be stopped suddenly after prolonged use; this may provoke a sudden and severe recurrence of symptoms of the original disorder, even a heart attack. Blood pressure may also rise markedly. When the treatment needs to be stopped, it should be withdrawn gradually under medical supervision.

Vasodilators

Vasodilators - medicaments that dilate blood vessels - are commonly prescribed for disorders in which narrowing of the blood vessels leads to reduced blood flow and a consequent lower oxygen supply to parts of the body. Disorders of this type include angina, when a narrowing of the coronary arteries reduces the supply of blood, thereby causing painful spasm. They also include peripheral vascular disease, when blood vessels in the arms and legs cannot supply sufficient blood to the extremities. Vasodilators are also widely used in the treatment of high blood pressure (hypertension) and heart failure.

Several classes of vasodilator medicaments are prescribed, including nitrates, sympatholytics, calcium channel blockers, and ACE (angiotensin-converting enzyme) inhibitors.

Vasodilators widen the blood vessels by relaxing the muscles that surround them. They achieve this either by affecting the action of the muscles directly (nitrates and calcium channel blockers) or by interfering with the nerve signals that govern contraction of the blood vessels (sympatholytics). ACE inhibitors act by blocking enzyme activity in the blood.

In addition to relieving the symptoms of the disorders for which they are taken, vasodilators can have a number of minor adverse effects related to their action on the blood circulation. Flushing and headaches are common at the start of treatment. Dizziness and fainting may also occur as a result of lowered blood pressure. Dilation of the blood vessels can also cause a fluid build up, leading to swelling, particularly of the ankles.

The major risk is that blood pressure may sometimes fall too low. For this reason these medicaments are prescribed with caution for those with unstable blood pressure. It may also be advisable to take the first dose of vasodilator medicaments at a time when you are able to sit or lie down afterward.

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