The neurologic pathways required for erection originate in the cerebral cortex where visual, auditory, and psychic stimuli are processed, and in the pudenal nerve, an afferent nerve that transmits tactile sensations from the genitals to the sacral segments of the spinal cord and cortex. Efferent signals from the spinal cord pass along the pelvic parasympathetic nerves and dilate the corporal vessels. The specific neurotransmitters have not been fully defined; acetylcholine, and perhaps vasoactive intestinal peptide, appears to be important. There are many causes of neurogenic impotence. Anything that disrupts neural pathways or blocks neurochemical transmission will have an adverse effect on erection. Psychologic factors probably interfere with erection by inhibiting corticosacral efferent pathways.
An alprostadil cream that patients apply into the tip of the penis (the urethral meatus, the opening that urine passes through) is currently available in the UK and Europe. It is currently under review by the U.S. Food and Drug Administration (FDA). After application of the cream, an erection occurs within five to 30 minutes, and the erection lasts one to two hours in men who respond to the cream. Doctors recommend that one use the cream for a maximum frequency of two to three times per week and no more frequent than once every 24 hours. It has essentially the same contraindications and side effects as the other formulations of alprostadil. The cream may cause vaginal burning in roughly 4% of partners. Men should not use alprostadil cream for sexual intercourse with women of childbearing potential unless a condom is used. Researchers have performed controlled trial studies to evaluate the safety and effectiveness of this drug. Overall, 52% of men reported improvement in their erections compared to 20% of men receiving placebo. A later analysis demonstrated that 36% of men using the alprostadil cream had a clinically relevant improvement in vaginal penetration ability and 31% clinically relevant improvement in ability to have successful intercourse to ejaculation.
The history can be useful in distinguishing organic from psychogenic impotence (Table 187.1). The patient with organic impotence describes problems with erection that progress over months to years. At first, the patient will have partial erections or seemingly firm erections that become flaccid during intercourse. With time, total erectile failure ensues. Organic impotence is constant and nonselective, meaning it is not better or worse with any specific partner or any type of stimulation.
This point is important – the anticipatory anxiety.  Sports men and women regularly use “mental rehearsal” to help them prepare for a match.  They imagine the shots, the game and perform according to plan when the event arises.  Research has show that musicians mentally practicing their instrument in their mind, use the same brain processes as when playing for real.
Damage to the autonomic pathways innervating the penis may eliminate "psychogenic" erection initiated by the central nervous system. Lesions of the somatic nervous pathways may impair reflexogenic erections and may interrupt tactile sensation needed to maintain psychogenic erections. Spinal cord lesions may produce varying degrees of erectile failure depending on the location and completeness of the lesions. Not only do traumatic lesions affect erectile ability, but disorders leading to peripheral neuropathy may impair neuronal innervation of the penis or of the sensory afferents. The endocrine system itself, particularly the production of androgens, appears to play a role in regulating sexual interest, and may also play a role in erectile function.
The availability of phosphodiesterase-5 (PDE5) inhibitors—sildenafil, vardenafil, tadalafil, and avanafil—has fundamentally altered the medical management of ED. In addition, direct-to-consumer marketing of these agents over the last 15 years has increased the general public’s awareness of ED as a medical condition with underlying causes and effective treatments.
Psychosocial problems are important and may cause erectile dysfunction by themselves or together with other causes of erectile dysfunction, such as diabetes and heart disease. Relationships are complicated and many factors cause tensions, which can affect sexual relations. For some men, these problems can become ongoing and it can help to talk through the issue with a skilled counsellor. It is important to know that the longer erectile dysfunction is left untreated, the greater the effect on relationships. This is another reason why early treatment of erectile dysfunction is important.

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 visualized by infusing a mixture of saline and x-ray contrast medium and performing a cavernosogram.[20] In Digital Subtraction Angiography (DSA), the images are acquired digitally.
The history can be useful in distinguishing organic from psychogenic impotence (Table 187.1). The patient with organic impotence describes problems with erection that progress over months to years. At first, the patient will have partial erections or seemingly firm erections that become flaccid during intercourse. With time, total erectile failure ensues. Organic impotence is constant and nonselective, meaning it is not better or worse with any specific partner or any type of stimulation.
"Data shows the longer you ride, the higher your chance of developing ED in terms of distance per week," Gittens says. If you cycle for exercise or socialization, you don't have to necessarily give it up, just make some modifications. Gittens suggests riding for shorter distances, giving yourself a rest every once in a while, finding a comfortable seat, and getting a bike that’s sized appropriately.
Is your erectile dysfunction due to psychological (stress, relationship problems, etc.) or physical factors? Your doctor may ask if you note erections at night or in the early morning. Men have involuntary erections in the early morning and during REM sleep (a stage in the sleep cycle with rapid eye movements). Men with psychogenic erectile dysfunction (erectile dysfunction due to psychological factors such as stress and anxiety rather than physical factors) usually maintain these involuntary erections. Men with physical causes of erectile dysfunction (for example, atherosclerosis, smoking, and diabetes) usually do not have these involuntary erections. Men with psychogenic erectile dysfunction may relate the onset of problems to a "stressor," such as failed relationship. Your doctor may suggest a test to determine if you have erections during sleep, which may suggest that there may be a psychological cause of the erectile dysfunction.
Currently, placement of a penile prosthesis is the most common surgical procedure performed for erectile dysfunction. Penile prosthesis placement is typically reserved for men who have tried and failed (either from efficacy or tolerability) or have contraindications to other forms of therapy including PDE5 inhibitors, intraurethral alprostadil, and injection therapy.
If you are taking medications (alpha-blockers) for problems with an enlarged prostate, you should discuss your prostate medications with your doctor. Alpha-blockers also can cause lowering of the blood pressure. Thus your doctor will need to carefully watch your blood pressure when you start the PDE5 inhibitor. Common alpha-blockers include doxazosin (Cardura), terazosin (Hytrin), and tamsulosin (Flomax).

Defined as experiencing difficulty having an erection at least 50 percent of the time, about 30 million men in the U.S. suffer from erectile dysfunction (ED), according to the National Institutes of Health. So, if odds are pretty good you’ll experience a failure to launch at some point in your life, take solace in this finding from the University of Adelaide: You can reverse ED by focusing on lifestyle factors, not just popping a blue pill.
Organic Impotence. Diabetes mellitus, thyroid disease, and dysfunction of the pituitary gland or testes can cause impotence, as can certain medications. Other organic causes include arterial ischemia associated with atherosclerosis of the aorta and common iliac arteries, extensive pelvic surgery such as radical prostatectomy, spinal cord injury and other neurologic disorders, and a history of cigarette smoking. Because certain medications can cause impotence, it is recommended that in cases of recent impotence it be determined whether the patient has started on a new drug. The most common offenders are diuretics, antihypertensives, and vasodilators. Alcohol, which sometimes is ignored as a drug, is often a contributor to the problem of impotence.
Impotence: A common problem among men characterized by the consistent inability to sustain an erection sufficient for sexual intercourse or the inability to achieve ejaculation, or both. Impotence can vary. It can involve a total inability to achieve an erection or ejaculation, an inconsistent ability to do so, or a tendency to sustain only very brief erections.
For many men, stopping smoking is an erectile dysfunction remedy, particularly when ED is the result of vascular disease, which occurs when blood supply to the penis becomes restricted because of blockage or narrowing of the arteries. Smoking and even smokeless tobacco can also cause the narrowing of important blood vessels and have the same negative impact. 
Along the same vein as stress, relationship troubles may also be at the root of some men’s erectile problems. Not trusting your partner, fears of birth control failure, or just genuinely not being emotionally attached to a partner could make it hard for a man to have an erection, The Huffington Post reported. Talking about issues within a relationship can help to resolve this problem.

Another potential new treatment consists of penile low-intensity shock wave lithotripsy. This consists of 1500 shocks twice a week for 3–6 weeks. The purpose is to stimulate neovascularisation to the corporal bodies with improvement in penile blood flow and endothelial function. The use of low-intensity shock wave lithotripsy may convert PDE5 inhibitor non-responders to responders.47
While pills for ED are convenient, some men sustain stronger erections by injecting medication directly into the penis. Drugs approved for this purpose work by widening the blood vessels, causing the penis to become engorged with blood. Another option is inserting a medicated pellet into the urethra. The pellet can trigger an erection within 10 minutes.
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