Impotence, or erectile dysfunction, is the inability to achieve or maintain an erection long enough to engage in sexual intercourse.

Under normal circumstances, when a man is sexually stimulated, his brain sends a message down the spinal cord and into the nerves of the penis. The nerveendings in the penis release chemical messengers, called neurotransmitters, which signal the corpora cavernosa (the two spongy rods of tissue that run thelength of the penis) to relax and fill with blood. As they expand, the corpora cavernosa close off other veins that would normally drain blood from the penis. As the penis becomes engorged with blood, it enlarges and stiffens, causing an erection. Problems with blood vessels, nerves, or tissues of the penis can interfere with an erection.

It is estimated that 10-20 million American men frequently suffer from impotence and that it strikes up to half of all men between the ages of 40 and 70.Doctors used to think that most cases of impotence were psychological in origin, but they now recognize that, at least in older men, physical causes may play a primary role in 60% or more of all cases. In men over 60, the leading cause is atherosclerosis, or narrowing of the arteries, which can restrict the flow of blood to the penis. Injury or disease of the connective tissue, such as may prevent the corpora cavernosa from completely expanding, and damage to the nerves of the penis, from certain types of surgery or neurological conditions such as Parkinson's disease may also cause impotence. Men with diabetes are especially at risk for impotence because of their high risk of both atherosclerosis and a nerve disease called diabetic neuropathy.

Some drugs, including certain types of blood pressure medications, antihistamines, tranquilizers, and antidepressants can interfere with erections. Smoking, excessive alcohol consumption, and illicit drug use may also contribute. In rare cases, low levels of the male hormone testosterone may contribute to erectile failure. Finally, psychological factors, such asstress, guilt, or anxiety, may also play a role, even when theimpotence is primarily due to organic causes.

Years ago, the standard treatment for impotence was an implantable penile prosthesis or long-term psychotherapy. Although physical causes are now more readily diagnosed and treated, individual or marital counseling is stillan effective treatment for impotence when emotional factors play a role.

Injection therapy involves injecting a substance into the penis to enhance blood flow and cause an erection. The Food and Drug Administration (FDA)approved a drug called alprostadil (Caverject) for this purpose in July of 1995. Alprostadil, which relaxes smooth muscle tissue to enhance blood flow into the penis, must be injected shortly before intercourse. Another, similar drug that is sometimes used is papaverine, which has not yet been approved bythe FDA for this use.

In a long-awaited breakthrough, a pill for combating impotence was cleared for marketing by the FDA in March 1998. Called sildenafil citrate (brand name Viagra), the drug boosts levels of a substance called cyclic GMP, which is responsible for widening the blood vessels of the penis. Viagra has been shown to be effective in about 70-80% of men who take it, and it can even work in men with some psychological component to their impotence. Unlike drugs that areinjected into the penis, Viagra causes an erection only when the man is sexually aroused.

Implantable penile prostheses are usually considered a last resort for treating impotence. They are implanted in the corpora cavernosa to make the penis rigid without the need for blood flow. The semirigid type of prosthesis consists of a pair of flexible silicone rods that can be bent up or down. This typeof device has a low failure rate but, unfortunately, it causes the penis toalways be erect, which can be difficult to conceal under clothing.

The inflatable type of device consists of cylinders that are implanted in thecorpora cavernosa, a fluid reservoir implanted in the abdomen, and a pump placed in the scrotum. The man squeezes the pump to move fluid into the cylinders and cause them to become rigid. (He reverses the process by squeezing thepump again.) While these devices allow for intermittent erections, they havea slightly higher malfunction rate than the silicon rods.

Men can return to sexual activity six to eight weeks after implantation surgery. Since implants affect the corpora cavernosa, they permanently take away aman's ability to have a natural erection.

A number of herbs have been promoted for treating impotence. The most widelytouted herbs for this purpose are Coryanthe yohimbe (available by prescription as yohimbine, with the trade name Yocon) and gingko (Gingko biloba), although neither has been conclusively shown to help the condition incontrolled studies. In addition, gingko carries some risk of abnormal bloodclotting and should be avoided by men taking blood thinners such as coumadin.

There is no specific treatment to prevent impotence. Perhaps the most important measure is to maintain general good health and avoid atherosclerosis--by exercising regularly, controlling weight, controlling hypertension and high cholesterol levels, and avoiding smoking. Avoiding excessive alcohol intake mayalso help.

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