| Erectile dysfunction (ED) or 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,
such as diabetes, many of which are medically reversible.
The causes of erectile dysfunction may be physiological or psychological.
Psychological impotence can often be helped by almost anything that
the patient believes in; there is a very strong placebo effect.
Due to its embarrassing nature and the shame felt by sufferers,
the subject was taboo for a long time, and is the subject of many
urban legends. Folk remedies have long been advocated, with some
being advertised widely since the 1930s. The introduction of perhaps
the first pharmacologically effective remedy for impotence, sildenafil
(trade name Viagra), in the 1990s caused a wave of public attention,
propelled in part by the news-worthiness of stories about it and
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
an 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 factors
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. 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 is more likely to be psychological.
The current diagnostic and statistical manual of mental diseases
(DSM-IV) has included a listing for impotence.
Clinical tests used to diagnose ED
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.
Penile Angiogram
Invasive test - allows visualization of the circulation in the penis
and is used during the repair of a priapism.
Dynamic Infusion Cavernosometry
(Abbreviated 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. To do this
test, a vasodilator like prostaglandin E-1 is injected to measure
the rate of infusion required to get a rigid erection and to help
find how severe the venous leak is.
Corpus Cavernosometry
Cavernosography is an adjunct to Dynamic Infusion Cavernosometry,
where a contrast material is injected and then it is x-rayed to
visualize any leakage
Digital Subtration Angiography
In DSA, the images are acquired digitally. The computer crates a
mask from lower-contrast x-rays of the same area and digitally isolates
the blood vessels (this is done manually through darkroom masking
with traditional angiography).
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.
Aside from the IV used to introduce the contrast material into the
bloodstream, magnetic resonance angiography is noninvasive and painless
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. Restriction
of blood flow can arise from impaired endothelial function due to
the usual causes associated with coronary artery disease, but can
also include causation by prolonged exposure to bright light or
chronic exposure to high noise levels.
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. Psychiatric medications, especially SSRIs have been
shown to cause erectile dysfunction in patients, both males and
females. Although usually reversible, these sexual side effects
can, in rare cases, last for months or years or permanently after
the drug has been completely withdrawn. This disorder is known as
Post SSRI Sexual Dysfunction.
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.
Excessive alcohol use has long been recognised as one cause of
impotence, leading to the euphemism "brewer's droop,"
or "whiskey dick;" Shakespeare made light of this phenomenon
in Macbeth.
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.
Treatment
Treatment depends on the cause. Testosterone supplements may be
used for cases due to hormonal deficiency. However, the cause is
more usually lack of adequate penile blood supply as a result of
damage to inner walls of blood vessels. This damage is more frequent
in older men, and often associated with disease, in particular diabetes.
Treatments (with the exception of testosterone supplementation,
where effective) work on a temporary basis: they enable an erection
to be attained and maintained long enough for intercourse, but do
not permanently improve the underlying condition.
ED can in many cases be treated by drugs taken orally, injected,
or as penile suppositories. These drugs increase the efficacy of
NO, which dilates the blood vessels of corpora cavernosa. When oral
drugs or suppositories fail, injections (e.g. of apomorphine) into
the erectile tissue of the penile shaft may work.
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. Implants are irreversible and costly.
All these mechanical methods are based on simple principles of
hydraulics and mechanics and are quite reliable, but have their
disadvantages.
In a few cases there is a vascular problem which can be treated
surgically.
PDE5 Inhibitors
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. These multiple forms or
subtypes of phosphodiesterase were initially isolated from rat brain
by Uzunov and Weiss in 1972 and were soon afterward shown to be
selectively inhibited by a variety of drugs in brain and other tissues
(Weiss,1975; Fertel and Weiss, 1976). The potential for selective
phosphodisterase inhibitors to be used as therapeutic agents was
predicted as early as 1977 by Weiss and Hait. This prediction has
now come to pass in a variety of fields, one of which is in the
pharmacologic treatment of erectile dysfunction.
One of the forms of phophodiesterase 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. CGMP specific
phosphodiesterase type 5|cGMP]] causes the smooth muscle of the
arteries in the penis to relax, allowing the corpus cavernosum to
fill with blood.
Vacuum pump
An external vacuum pump will produce an engorged penis with success
approaching 90%; a penis ring will maintain this state, although
it should be removed after not more than 30 minutes. The erection
is not as rigid or hard as a natural erection; drugs or injections,
when they work, may be preferable. Various studies show the degree
of satisfaction of users and their partners to be vary variable,
even when drugs and injections do not work; in one study, about
20% of men who tried a (high-priced) pump decided to proceed to
purchase one. Other studies show higher percentages of satisfied
users.
In some cases frequent use of a vacuum pump can eventually improve
the degree of erection attainable without use of the pump. Claims
of cheap "penis pumps" to permanently increase maximum
penis size should be viewed with caution, however.
Some vacuum pumps, such as Osbon ErecAid, are sold at a higher price
with 100% refund within 90 days to dissatisfied users, with a somewhat
lower price with 50% refund guarantee.[8]This pump is supported
by medical insurance schemes, including the UK's NHS and US Medicare
and private insurers. The better-known pumps sell for prices of
around 200 GBP/400 USD (2006). There is at least one vacuum pump
with rings which sells for around one-fifth of this price.
(Specific devices are mentioned for information only; mention should
not be taken as endorsement).
Dopamine Receptor Agonist
Apomorphine acts mainly on D2-like receptors and is administered
sublingually in the presence of sexual stimulation. Studies have
been inconclusive with efficacy rates ranging from 48-55% to 9-38%.
Currently, the use of apomorphine is limited to pateints with mild
ED.
Inflatable implant
Rigid implant
Surgical treatment of certain cases
Bremelanotide
The experimental drug Bremelanotide (formerly PT-141) does not act
on the vascular system like the former compounds but allegedly increases
sexual desire and drive in males as well as females. It is applied
as a nasal spray. Bremelanotide allegedly works by activating melanocortin
receptors in the brain. It is currently in Phase IIb trials.
hMaxi-K
hMaxi-K is a form of gene therapy using a plasmid vector that expresses
the hSlo gene, that encodes the alpha-subunit of the Maxi-K channel.
It has undergone phase I safety trials.
Ginseng
A double-blind study appears to show evidence that ginseng is better
than placebo:see the ginseng article for more details.
Enzyte
Enzyte is a product that has been advertised by saturation coverage
on television channels such as CourtTV. 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.
Herbal and other alternative treatments
These are generally ineffective when tested blind, but may be useful
for their psychological (placebo) effect: if a good result is expected,
any highly-praised, and often expensive, treatment can be effective.
Reputable drugs can also benefit from the same effect.
Prelox
Prelox is a Proprietary mix/combination of naturally occurring ingredients,
L-arginine aspartate and Pycnogenol. In double blind tests carried
out by Dr. Steven Lamm at New York University School of Medicine,
81.1% of men overall judged Prelox to be effective in improving
their ability to engage in sexual activity.Prelox® for improvement
of erectile function: A review European Bulletin of Drug Research,
Volume 11, No. 3, 2003. Steven Lamm, Frank Schoenlau, Peter Rohdewald
Whilst the supplements should be taken daily, the manufacturers
claim that it brings the spontaneity back into ones' love life;
unlike other products which must be remembered to be taken a fixed
time before sexual activity.
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