Erectile dysfunction

Erectile dysfunction (ED, "male impotence") is sexual dysfunction characterized by the inability to develop or maintain an erection of the penis during sexual performance.

A penile erection is the hydraulic effect of blood entering and being retained in sponge-like bodies within the penis. The process is often initiated as a result of sexual arousal, when signals are transmitted from the brain to nerves in the penis. Erectile dysfunction is indicated when an erection is difficult to produce. There are various circulatory causes, including alteration of the voltage-gated potassium channel, as in arsenic poisoning from drinking water. The most important organic causes are cardiovascular disease and diabetes, neurological problems (for example, trauma from prostatectomy surgery), hormonal insufficiencies (hypogonadism) and drug side effects.

Psychological impotence is where erection or penetration fails due to thoughts or feelings (psychological reasons) rather than physical impossibility; this is somewhat less frequent but often can be helped. Notably in psychological impotence, there is a strong response to placebo treatment. Erectile dysfunction, tied closely as it is about ideas of physical well being, can have severe psychological consequences.

Besides treating the underlying causes such as potassium deficiency or arsenic contamination of drinking water, the first line treatment of erectile dysfunction consists of a trial of PDE5 inhibitor drugs (the first of which was sildenafil or Viagra). In some cases, treatment can involve prostaglandin tablets in the urethra, injections into the penis, a penile prosthesis, a penis pump or vascular reconstructive surgery.

The Latin term impotentia coeundi describes simple inability to insert the penis into the vagina. It is now mostly replaced by more precise terms. The study of erectile dysfunction within medicine is covered by andrology, a sub-field within urology.

Signs and symptoms
Erectile dysfunction is characterized by the regular or repeated inability to obtain or maintain an erection. There are several ways that erectile dysfunction is analyzed:


 * Obtaining full erections at some times, such as when asleep (when the mind and psychological issues, if any, are less present), tends to suggest the physical structures are functionally working.
 * Other factors leading to erectile dysfunction are diabetes mellitus (causing neuropathy).

Causes

 * Drugs (anti-depressants (SSRIs) and nicotine are most common)
 * Neurogenic disorders (spinal cord and brain injuries, nerve disorders such as Parkinson's disease, Alzheimer's disease, multiple sclerosis, and stroke )
 * Cavernosal disorders (Peyronie's disease )
 * Psychological causes: performance anxiety, stress, mental disorders (clinical depression, schizophrenia, substance abuse, panic disorder, generalized anxiety disorder, personality disorders or traits ), psychological problems, negative feelings.
 * Surgery (radiation therapy, surgery of the colon, prostate, bladder, or rectum may damage the nerves and blood vessels involved in erection. Prostate and bladder cancer surgery often require removing tissue and nerves surrounding a tumor, which increases the risk for impotence )
 * Ageing. It is four times higher in men in their 60s than in men in their 40s.
 * Kidney failure
 * Diseases such as diabetes and multiple sclerosis (MS). While these two causes have not been proven they’re likely suspects as they cause issues with both the blood flow and nervous systems.
 * Lifestyle: smoking is a key cause of erectile dysfunction. Smoking causes impotence because it promotes arterial narrowing. See also Tobacco and health.

A few causes of impotence may be iatrogenic (medically caused).

Surgical intervention for a number of different conditions may remove anatomical structures necessary to erection, damage nerves, or impair blood supply. Complete removal of the prostate gland or external beam radiotherapy of the gland are common causes of impotence; both are treatments for prostate cancer. 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.

A study in 2002 found that ED can also be associated with bicycling. The number of hours on a bike and/or the pressure on the penis from the saddle of an upright bicycle is directly related to erectile dysfunction.

A recent study suggests an epidemiological association between chronic periodontitis (periodontal inflammation) and erectile dysfunction, similarly to the association between periodontitis and coronary heart diseases, and cerebrovascular diseases. In all the three conditions (erectile dysfunction, coronary heart disease and cerebrovascular diseases), despite the epidemiological association with periodontitis, no causative connection has proved yet.

February 2011: Men who use non-steroidal anti-inflammatory drugs (NSAIDs) 3 times a day for more than 3 months are at a 22 percent increased risk of erectile dysfunction. A link between NSAID use and erectile dysfunction still existed for different age, race, ethnicity, smoker, diabetes, hypertension, high cholesterol, coronary diasease and others health problems. But due to benefit of NSAID, it's too early for men to avoid NSAIDs based solely on the research stated at Journal of Urology.

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 or emotional 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 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. Restriction of blood flow can arise from impaired endothelial function due to the usual causes associated with coronary artery disease, but can also be caused by prolonged exposure to bright light.

Diagnosis
There are no formal tests to diagnose erectile dysfunction. Some blood tests are generally done to exclude underlying disease, such as hypogonadism and prolactinoma. Diabetes is considered a disorder, but is also a risk. Impotence is also related to generally poor physical health, poor dietary habits, obesity, and most specifically cardiovascular disease such as coronary artery disease and peripheral vascular disease.

A useful and simple way to distinguish between physiological and psychological impotence is to determine whether the patient ever has an erection. If never, the problem is likely to be physiological; if sometimes (however rarely), it could be physiological or psychological. The current diagnostic and statistical manual of mental diseases (DSM-IV) has included a listing for impotence.


 * 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.


 * 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.


 * 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. A significant proportion of men who have no sexual dysfunction nonetheless do not have regular nocturnal erections.


 * Penile biothesiometry:This test uses electromagnetic vibration to evaluate sensitivity and nerve function in the glans and shaft of the penis.


 * Dynamic infusion cavernosometry (DICC): technique in which fluid is pumped into the penis at a known rate and pressure. It gives a measurement of the vascular pressure in the corpus cavernosum during an erection.


 * Corpus cavernosometry:Cavernosography measurement of the vascular pressure in the corpus cavernosum. Saline is infused under pressure into the corpus cavernosum with a butterfly needle, and the flow rate needed to maintain an erection indicates the degree of venous leakage. The leaking veins responsible may be visualised by infusing a mixture of saline and x ray contrast medium and performing a cavernosogram.; Digital Subtraction Angiography: In DSA, the images are acquired digitally.


 * Magnetic resonance angiography (MRA): This is similar to magnetic resonance imaging. Magnetic resonance angiography uses magnetic fields and radio waves to provide detailed images of the blood vessels. Doctors may inject a "contrast agent" into the patient's bloodstream that causes vascular tissues to stand out against other tissues. The contrast agent provides for enhanced information regarding blood supply and vascular anomalies.

Treatment
Treatment depends on the cause.

Exercise, particularly aerobic exercise is an effective treatment for erectile dysfunction.

When pharmacological methods fail, a purpose-designed external vacuum pump can be used to attain erection, with a separate compression ring fitted to the penis to maintain it. These pumps should be distinguished from other penis pumps (supplied without compression rings) which, rather than being used for temporary treatment of impotence, are claimed to increase penis length if used frequently, or vibrate as an aid to masturbation. More drastically, inflatable or rigid penile implants may be fitted surgically. Medications carry risk of priapism.

All these mechanical methods are based on simple principles of hydraulics and mechanics and are quite reliable, but have their disadvantages.

Medication
The cyclic nucleotide phosphodiesterases constitute a group of enzymes that catalyze the hydrolysis of the cyclic nucleotides cyclic AMP and cyclic GMP. They exist in different molecular forms and are unevenly distributed throughout the body.
 * Phosphodiesterase type 5 inhibitors

One of the forms of phosphodiesterase is termed PDE5. The prescription PDE5 inhibitors sildenafil (Viagra), vardenafil (Levitra) and tadalafil (Cialis) are prescription drugs which are taken orally. They work by blocking the action of PDE5, which causes cGMP to degrade.

Alprostadil in combination with the permeation enhancer DDAIP has been approved in Canada under the brand name Vitaros as a topical cream first line treatment for erectile dysfunction.
 * Alprostadil

Another treatment regimen is injection therapy. One of the following drugs is injected into the penis: papaverine, phentolamine, and prostaglandin E1.

Surgery
Often, as a last resort if other treatments have failed, the most common procedure is prosthetic implants which involves the insertion of artificial rods into the penis.

Devices
The device helps draw blood into the penis by applying negative pressure. This type of device is sometimes referred to as penis pump and may be used just prior to sexual intercourse. Several types of FDA approved vacuum therapy devices are available with a doctor's prescription.

Alternative medicine
The FDA does not recommend alternative therapies to treat sexual function. There are many different products advertised as "herbal viagra" or "natural" sexual enhancement products, but there are no clinical trials or scientific studies that support the effectiveness of these products for the treatment of erectile dysfunction, and synthetic chemical compounds similar to sildenafil have been found as adulterants in many of these products. The United States Food and Drug Administration has warned consumers that any sexual enhancement product that claims to work as well as prescription products is likely to contain such a contaminant.

History
Dr. John R. Brinkley initiated a boom in male impotence cures in the US in the 1920s and 1930s. His radio programs recommended expensive goat gland implants and "mercurochrome" injections as the path to restored male virility, including operations by surgeon Serge Voronoff.

Modern drug therapy for ED made a significant advance in 1983, when British physiologist Giles Brindley, Ph.D. dropped his trousers and demonstrated to a shocked Urodynamics Society audience his papaverine-induced erection. The drug Brindley injected into his penis was a non-specific vasodilator, an alpha-blocking agent, and the mechanism of action was clearly corporal smooth muscle relaxation. The effect that Brindley discovered established the fundamentals for the later development of specific, safe, orally-effective drug therapies.

Research
Gene therapy is being developed that would allow for weeks or months long effect, supporting erections. This gene therapy involves injection of a transfer gene, calcium-sensitive potassium channel (hMaxi-K), into the penis.
 * Gene therapy

A study done at the Medical College of Georgia has found that venom from the Brazilian wandering spider contains a toxin, called Tx2-6, that causes erections. Scientists believe that combining this toxin with existing medication such as Viagra may lead to an effective treatment for erectile dysfunction.
 * Tx2-6