Erectile dysfunction

Erectile dysfunction, also known as impotence, is a sexual dysfunction characterized by the inability to develop or maintain an erection of the penis for satisfactory sexual intercourse regardless of the capability of ejaculation. There are various underlying causes, including Type 1 diabetes, many of which are medically reversible.

Due to its personal nature, the subject has been taboo for a long time, and is the stuff of many urban legends. Since the 1930s, folk remedies have been advertised widely for the condition. The introduction of sildenafil (Viagra&reg;) in the 1990s caused a second wave of public attention, propelled in part by heavy advertising.

The Latin term impotentia coeundi describes simple inability to insert the penis into the vagina. It is now mostly replaced by more precise terms.

Medical symptoms
Erectile dysfunction is characterized by the inability to maintain erection. Normal erections during sleep and in the early morning suggest a psychogenic cause, while loss of these erections may signify underlying disease, often cardiovascular in origin. Other things leading to erectile dysfunction are diabetes mellitus (causing neuropathy) or hypogonadism (decreased testosterone levels due to disease affecting the testicles or the pituitary gland).

Medical diagnosis
There are no formal tests to diagnose erectile dysfunction. Some blood tests are generally done to exclude underlying disease, such as diabetes, hypogonadism and prolactinoma.

Duplex ultrasound
Duplex ultrasound is used to evaluate blood flow, venous leak, signs of atherosclerosis, and scarring or calcification of erectile tissue. Injecting prostaglandin, a hormone-like stimulator produced in the body, induces erection. Ultrasound is then used to see vascular dilation and measure penile blood pressure. Measurements are compared to those taken when the penis is flaccid.

Penile nerves function
Tests such as the bulbocavernosus reflex test are used to determine if there is sufficient nerve sensation in the penis. The physician squeezes the glans (head) of the penis, which immediately causes the anus to contract if nerve function is normal. A physician measures the latency between squeeze and contraction by observing the anal sphincter or by feeling it with a gloved finger inserted past the anus. Specific nerve tests are used in patients with suspected nerve damage as a result of diabetes or nerve disease.

Nocturnal penile tumescence (NPT)
It is normal for a man to have five to six erections during sleep, especially during rapid eye movement (REM). Their absence may indicate a problem with nerve function or blood supply in the penis. There are two methods for measuring changes in penile rigidity and circumference during nocturnal erection: snap gauge and strain gauge.

Penile biothesiometry
This test uses electromagnetic vibration to evaluate sensitivity and nerve function in the glans and shaft of the penis. A decreased perception of vibration may indicate nerve damage in the pelvic area, which can lead to impotence.

Pathophysiology
Penile erection is managed by two different mechanisms. The first one is the reflex erection, which is achieved by directly touching the penile shaft. The second is the psychogenic erection, which is achieved by erotic stimuli. The former uses the peripheral nerves and the lower parts of the spinal cord, whereas the latter uses the limbic system of the brain. In both conditions an intact neural system is required for a successful and complete erection. Stimulation of penile shaft by the nervous system leads to the secretion of nitric oxide (NO), which causes the relaxation of smooth muscles of corpora cavernosa (the main erectile tissue of penis), and subsequently penile erection. Additionally, adequate levels of testosterone (produced by the testes) and an intact pituitary gland are required for the development of a healthy male erectile system. As can be understood from the mechanisms of a normal erection, impotence may develop due to hormonal deficiency, disorders of the neural system, lack of adequate penile blood supply or psychological problems.

A few causes of impotence may be iatrogenic (medically caused). Various antihypertensives (medications intended to control high blood pressure) and some drugs that modify central nervous system response may inhibit erection by denying blood supply or by altering nerve activity. Antidepressants, especially SSRIs, can cause impotence as a side effect. Surgical intervention for a number of different conditions may remove anatomical structures necessary to erection, damage nerves, or impair blood supply. Some studies have shown that male circumcision may result in an increased risk of impotence,  while others have found no such effect,  , and another found the opposite. 

Treatment
Treatment depends on the cause. Testosterone supplements may be used for cases with hormonal deficiency. However, usually the cause is lack of adequate penile blood supply as a result of age-dependent damage of inner walls of blood vessels. Previously, medical substances (e.g. apomorphine) were directly injected into the erectile tissue of penile shaft to treat impotence. In some cases refractory to the medical treatment, a penile implant (penile prosthesis) could be advised. After the discovery of orally active agents that increase the efficacy of NO, which dilates the blood vessels of corpora cavernosa, more conservative methods started to be used.

PDE5 Inhibitors
The prescription PDE5 inhibitors sildenafil (Viagra&reg;), vardenafil (Levitra&reg;) and tadalafil (Cialis&reg;) are prescription drugs which are taken orally. They work by blocking the action of PDE5, which causes cGMP to degrade. cGMP causes the smooth muscle of the arteries in the penis to relax, allowing the corpus cavernosum to fill with blood.

PT-141
The experimental drug PT-141 does not act on the vascular system like the former compounds but increases sexual desire and drive in male as well as female. It is applied as a nasal spray PT-141 and works by activation of melanocortin receptors in the brain. It is awaiting FDA approval.

Ginseng
A double-blind study appears to show evidence that ginseng is better than placebo: see the ginseng article for links and more details.

Enzyte
Enzyte is a product that has been advertised by saturation coverage on television channels such as Court-TV. However, the Center for Science in the Public Interest (CSPI) has filed a complaint with the Federal Trade Commission (FTC) about Enzyte for deceptive advertising. It is manufactured by Berkeley Nutritionals, which is alleged to be the subject of an investigation by the Attorney General of Ohio and the defendant in class-action lawsuits.

Enzyte is a supplement that claims to increase the male libido or frequency of erections of the penis. Commercials for Enzyte are shown regularly on television. These commercials feature a man named Bob who never stops smiling, apparently because he had taken Enzyte and improved the size of his sex organs. The commercials are riddled with symbolic phallic imagery, e.g. golf clubs, remarkably tall glasses of iced tea, and a hose spraying barely a trickle of water (carried by someone who doesn't use Enzyte).

The effectiveness of Enzyte is in dispute. Some medical professionals in fact advise against taking Enzyte, saying that it can lead to damage. The Center for Science in the Public Interest have urged the Federal Trade Commission to disallow further television advertising for Enzyte due to a lack of proper studies supporting claims. Enzyte maker Berkeley Premium Nutraceuticals, Inc., is currently under a class action lawsuit for false advertising.

Enzyte is said to contain: Tribulus terrestris; Yohimbe Extract; Niacin; Epimedium; Avena sativa; Zinc Oxide; Maca; Muira Pauma; Ginkgo biloba; L-Arginine; Saw Palmetto. Other ingredients: gelatin, rice bran, oat fiber, magnesium stearate, silicon dioxide.

History
Dr. John R. Brinkley began a fad for finding cures for male impotence during the 1930s. He used the medium of radio to achieve the same kind of advertising boom to treat the same kind of symptoms.

In the 1930s the American radio airwaves were bombarded with such advertising, first from domestic stations and then upon action by the American Medical Association the media blitz was shifted to superpower Mexican border-blasters.

Surgeons began providing inflatable penile implants in the 1970s.

External sources

 * FDA's Consumer Information
 * Erectile Dysfunction Primer
 * Support group for people with permanent impotence or other sexual dysfunction caused by SSRI antidepressants.
 * Erection Web Support group for people with erectile dysfunction and impotence.
 * Enzyte Company website
 * Enzyte investigation reported on CBS-TV news site

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