Erectile dysfunction (ED) is the inability of a man to achieve or maintain an erection sufficient for his sexual needs or the needs of his partner. Most men experience this at some point in their lives, usually by age 40, and are not psychologically affected by it.
Some men, however, experience chronic, complete erectile dysfunction (impotence), and others, partial or brief erections. Frequent erectile dysfunction can cause emotional and relationship problems, and often leads to diminished self-esteem. Erectile dysfunction has many causes, most of which are treatable, and is not an inevitable consequence of aging.
Incidence and Prevalence
The term "erectile dysfunction" can mean the inability to achieve erection, an inconsistent ability to do so, or the ability to achieve only brief erections. These various definitions make estimating the incidence of erectile dysfunction difficult. According to the National Institutes of Health in 2002, an estimated 15 million to 30 million men in the United States experience chronic erectile dysfunction.
According to the National Ambulatory Medical Care Survey (NAMCS), approximately 22 out of every 1000 men in the United States sought medical attention for ED in 1999.
Incidence of the disorder increases with age. Chronic ED affects about 5% of men in their 40s and 15–25% of men by the age of 65. Transient ED and inadequate erection affect as many as 50% of men between the ages of 40 and 70.
Diseases (e.g., diabetes, kidney disease, alcoholism, atherosclerosis) account for as many as 70% of chronic ED cases and psychological factors (e.g., stress, anxiety, depression) may account for 10–20% of cases. Between 35 and 50% of men with diabetes experience ED.
Anatomy of the Penis
The internal structure of the penis consists of two cylinder-shaped vascular tissue bodies (corpora cavernosa) that run throughout the penis; the urethra (tube for expelling urine and ejaculate); erectile tissue surrounding the urethra; two main arteries; and several veins and nerves. The longest part of the penis is the shaft, at the end of which is the head, or glans penis. The opening at the tip of the glans, which allows for urination and ejaculation, is the meatus.
Physiology of Erection
The physiological process of erection begins in the brain and involves the nervous and vascular systems. Neurotransmitters in the brain (e.g., epinephrine, acetylcholine, nitric oxide) are some of the chemicals that initiate it. Physical or psychological stimulation (arousal) causes nerves to send messages to the vascular system, which results in significant blood flow to the penis. Two arteries in the penis supply blood to erectile tissue and the corpora cavernosa, which become engorged and expand as a result of increased blood flow and pressure.
Because blood must stay in the penis to maintain rigidity, erectile tissue is enclosed by fibrous elastic sheathes (tunicae) that cinch to prevent blood from leaving the penis during erection. When stimulation ends, or following ejaculation, pressure in the penis decreases, blood is released, and the penis resumes its normal shape.
Causes of Impotence
There are many underlying physical and psychological causes of erectile dysfunction. Reduced blood flow to the penis and nerve damage are the most common physical causes. Underlying conditions associated with erectile dysfunction include the following:
- Vascular disease
- Hormone imbalances
- Neurologic conditions
- Pelvic trauma, surgery, radiation therapy
- Peyronie's disease
- Venous leak
- Psychological conditions
- A medical examination may indicate neurological, vascular, or hormonal disease, or Peyronie's disease. History of illness, smoking, drug use, and hypertension can be ascertained with a thorough examination of health history. Laboratory tests are performed to identify the underlying cause.
- Blood Tests and Urinalysis Blood tests can indicate conditions that may interfere with normal erectile function. These tests measure hormone levels, cholesterol, blood sugar, liver and kidney function, and thyroid function. Excess prolactin (hyperprolactinemea) can lower testosterone levels, which can diminish libido. Both of these levels are measured, as well as levels of other sex hormones. If they are persistently low, an endocrinologist (hormone specialist) should be consulted.
- CBC–Complete blood count (CBC) of red cells and white cells is used to evaluate the presence of anemia. A low level of red cells limits the body's utilization of oxygen and can lead to fatigue and general malaise. The level of blood lipids (fats) such as cholesterol and triglycerides may indicate arteriosclerosis, which can reduce blood flow to the penis.
- Liver and kidney function tests–Liver and kidney disease can create horomonal imbalances. Blood tests for liver function involves analysis of enzyme and serum creatinine levels, which are indicators of kidney efficiency.
- Thyroid function tests–Thyroid hormones regulate metabolism and the production of sex hormones; a deficiency may contribute to impotence.
- Urinalysis–Urine is analyzed for protein (albumin), sugar (glucose), and hormone (testosterone) levels that may indicate diabetes mellitus, kidney dysfunction, and testosterone deficiency.
Erectile Function Tests
- Tests that assess erectile function examine the blood vessels, nerves, muscles, and other tissues of the penis and pelvic region.
- Duplex ultrasound–Duplex ultrasound is used to evaluate blood flow, venous leak, signs of artherosclerosis, and scarring or calcification of erectile tissue. Erection is induced by injecting
- prostaglandin, a hormone-like stimulator produced in the body. Ultrasound is then used to see vascular dilation and measure penile blood pressure (which may also be measured with a special cuff). Measurements are compared to those taken when the penis is flaccid.
- Prostate examination–An enlarged prostate, which can be detected with a digital rectal examination (DRE), can interfere with blood flow and nerve impulses in the penis.
- Penile nerve 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). These erections occur about every 90 minutes and last for about 30 minutes. 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.
- Snap gauge involves wrapping three plastic bands of varying strength around the penis. Erectile function is assessed according to which bands break. Strain gauge involves placing special elastic bands at the base and tip of the penis. These bands stretch during erection and register changes in circumference.
- Penile biothesiometry–This test uses electromagnetic vibration to evaluate sensitivity and nerve function in the glands and shaft of the penis. A decreased perception of vibration may indicate nerve damage in the pelvic area, which can lead to impotence.
- Vasoactive injection–When injected into the penis, certain solutions cause erection by dilating blood vessels in erectile tissue. Normally, these injections produce an erection lasting about 20 minutes. During this procedure, penile pressure is measured and x-rays may be taken of the penile blood vessels using a special dye (contrast agent).
A significant number of men develop impotence from psychological causes that can be overcome. When a physiological cause is treated, subsequent self-esteem problems may continue to impair normal function and performance. Qualified therapists (e.g., sex counselors, psychotherapists) work with couples to reduce tension, improve sexual communication, and create realistic expectations for sex, all of which can improve erectile function.
Psychological therapy may be effective in conjunction with medical or surgical treatment. Sex therapists emphasize the need for men and their partners to be motivated and willing to adapt to psychological and behavioral modifications, including those that result from medical or surgical treatment.
Oral medications used to treat erectile dysfunction include selective enzyme inhibitors (e.g., sildenafil [Viagra®], vardenafil HCl [Levitra®], tadalafil [Cialis®]) and yohimbine (Yohimbine®, Yocon®).
Selective enzyme inhibitors are available by prescription and may be taken up to once a day to treat ED. They improve partial erections by inhibiting the enzyme that facilitates their reduction and increase levels of cyclic guanosine monophosphate (cGMP, a chemical factor in metabolism), which causes the smooth muscles of the penis to relax, enabling blood to flow into the corpora cavernosa.
Patients taking nitrate drugs (used to treat chest pain) and those taking alpha-blockers (used to treat high blood pressure and benign prostatic hyperplasia) should not take selective enzyme inhibitors.
Men who have had a heart attack or stroke within the past 6 months and those with certain medical conditions (e.g., uncontrolled high blood pressure, severe low blood pressure or liver disease, unstable angina) that make sexual activity inadvisable should not take Cialis®. Dosages of the drug should be limited in patients with kidney or liver disorders.
Viagra® is absorbed and processed rapidly by the body and is usually taken 30 minutes to 1 hour before intercourse. Results vary depending on the cause of erectile dysfunction, but studies have shown that Viagra is effective in 75% of cases. It helps men with erectile dysfunction associated with diabetes mellitus (57%), spinal cord injuries (83%), and radical prostatectomy (43%).
In clinical studies, Levitra® has been shown to work quickly, provide consistent results, and improve sexual function in most men the first time they take the drug. It also has shown to be effective in men of all ages, in patients with diabetes mellitus, and in men who have undergone radical prostatectomy.
Cialis® has been shown in clinical trials to stay in the body longer than the other selective enzyme inhibitors. It promotes erection within 30 minutes and enhances the ability to achieve erection for up to 36 hours.
Common side effects of selective enzyme inhibitors include headache, reddening of the face and neck (flushing), indigestion, and nasal congestion. Cialis® may cause muscle aches and back pain, which usually resolve on their own within 48 hours.
In October 2007, the Food and Drug Administration (FDA) approved important changes to the drug labeling information for these medications. Selective enzyme inhibitors may be associated with a potential risk for sudden hearing loss, which may be accompanied by ringing in the ears (tinnitus) and dizziness (vertigo). Patients who experience sudden hearing loss in one or both ears while taking these medications for ED should stop taking the drug and contact a health care provider.
Yohimbine improves erections for a small percentage of men. It stimulates the parasympathetic nervous system, which is linked to erection, and may increase libido. It is necessary to take the medication for 6 to 8 weeks before determining whether it will work or not.
Yohimbine has a stimulatory effect and side effects include elevated heart rate and blood pressure, mild dizziness, nervousness, and irritability. Yohimbine's effects have not been studied thoroughly, but some studies suggest that 10% to 20% of men respond to treatment with the drug.
Ease of administration makes oral medication advantageous. Some drugs, however, are suitable for only a relatively small group of men, and in many cases, oral medications may by less effective than other treatments.
Penile implants involve surgical insertion of malleable or inflatable rods or tubes into the penis. A semi-rigid prosthesis is a silicon-covered flexible metal rod. Once inserted, it provides the rigidity necessary for intercourse and can be curved slightly for concealment. It requires the simplest surgical procedure of all the prostheses. Its main disadvantage is that concealment can be difficult with certain types of clothing.
An inflatable penile prosthesis consists of two soft silicone or bioflex (plastic) tubes inserted in the penis, a small reservoir implanted in the abdomen, and a small pump implanted in the scrotum. To produce an erection, a man pumps sterile liquid from the reservoir into the tubes by squeezing the pump in the scrotum.
The tubes act as erectile tissue and expand to form an erection. When the erection is no longer desired, a valve allows the fluid to return to the reservoir. Inflatable prostheses are the most natural feeling of the penile implants and they allow for control of rigidity and size.
The surgical procedure to implant the inflatable prosthesis is slightly more complicated than for a semi-rigid implant. Also, because there are more mechanical parts, there is a higher risk for mechanical failure requiring repair or adjustment.
A self-contained inflatable prosthesis is similar but has fewer parts. It consists of a pair of inflatable tubes in the penis with a pump attached directly to the end of the implant. The reservoir is also located in the shaft of the penis. Its compact design allows for simpler implantation, but because it takes up more space in the penis, there is less room for expansion.
Vascular Reconstructive Surgery
A small percentage of men undergo vascular reconstructive surgery to improve blood flow to the penis. Revascularization involves bypassing blocked veins or arteries by transferring a vein from the leg and attaching it so that it creates a path to the penis that bypasses the area of blockage. Young men with only local arterial blockage are the best candidates for this procedure. It may restore function in 50% to 75% of men.
Venous ligation is performed to prevent venous leak. Problematic veins are bound (ligated) or removed, which allows an adequate amount of blood to remain in the penis. It may improve function in 40% to 50% of men, but some men may experience problems over the long term.
Vascular surgery for erectile dysfunction is rarely performed and is generally considered experimental. Risks include nerve damage and the creation of scar tissue, both of which are causes of impotence. Surgeons experienced with these procedures may be difficult to find.