Constriction of the trabecular smooth muscle and helicine arteries induced by sympathetic innervation makes the penis flaccid, with blood pressure in the cavernosal sinuses of the penis near venous pressure. Acetylcholine is thought to decrease sympathetic tone. This may be important in a permissive sense for adequate trabecular smooth muscle relaxation and consequent effective action of other mediators in achieving sufficient inflow of blood into the lacunar spaces. When the trabecular smooth muscle relaxes and helicine arteries dilate in response to parasympathetic stimulation and decreased sympathetic tone, increased blood flow fills the cavernous spaces, increasing the pressure within these spaces so that the penis becomes erect. As the venules are compressed against the tunica albuginea, penile pressure approaches arterial pressure, causing rigidity. Once this state is achieved, arterial inflow is reduced to a level that matches venous outflow.
While studies are limited, it has been shown that male sexual dysfunction can also negatively impact the sexual function of female partners. A study comparing the sexual function of women with partners with erectile dysfunction to those without showed that sexual arousal, lubrication, orgasm, satisfaction, pain and total score were significantly lower in those who had partners with erectile dysfunction. Later in that study, a large proportion of the men with erectile dysfunction underwent treatment. Following treatment, sexual arousal, lubrication, orgasm, satisfaction and pain were all significantly increased. It was concluded that female sexual function is impacted by male erection status, which may improve following treatment of male sexual dysfunction.
More recent estimates suggest that the number of U.S. men with erectile dysfunction may more likely be near 10-20 million. Inclusion of individuals with partial erectile dysfunction increases the estimate to about 30 million. The majority of these individuals will be older than 65 years of age. The prevalence of erectile dysfunction has been found to be associated with age. A prevalence of about 5 percent is observed at age 40, increasing to 15-25 percent at age 65 and older. One-third of older men receiving medical care at a Department of Veterans' Affairs ambulatory clinic admitted to problems with erectile function.
Diabetes is one of the most common causes of ED. Chronically high blood sugar levels can result in nerve damage that affects your body’s ability to translate pleasurable sexual stimulation into an erection. Diabetes can also lead to issues with circulation, which reduces blood flow to the penis and makes it more difficult to keep an erection that is hard enough for intercourse.
ED is often the result of atherosclerosis, and as a result, men with ED frequently have cardiovascular disease. Sexual activity is associated with increased physical exertion, which in some men may increase the risk of having a heart attack (myocardial infarction or MI). The major risk factors associated with cardiovascular disease are age, hypertension, diabetes mellitus, obesity, smoking, abnormal lipid/cholesterol levels in the blood, and lack of exercise. Individuals with three or more of these risk factors are at increased risk for a heart attack during sexual activity. The Princeton Consensus Panel developed guidelines for treating ED in men with cardiovascular disease. Thus, if you have ED and cardiovascular disease (for example, angina or prior heart attack), you should discuss whether or not treatment of ED and sexual activity are appropriate for you.
The Cancer of the Prostate Strategic Urologic Research Endeavor (CaPSURE) study, designed to determine whether an individual man’s sexual outcomes after most common treatments for early-stage prostate cancer could be accurately predicted on the basis of baseline characteristics and treatment plans, found that 2 years after treatment, 177 (35%) of 511 men who underwent prostatectomy reported the ability to attain functional erections suitable for intercourse. 
An initial approach to medical therapy should consider reversible medical problems that may contribute to erectile dysfunction. Included in this should be assessment of the possibility of medication-induced erectile dysfunction with consideration for reduction of polypharmacy and/or substitution of medications with lower probability of inducing erectile dysfunction.
Impotence, or erectile dysfunction, is the inability of a male to attain and keep an erection sufficiently firm to engage in or complete sexual intercourse. Although it is more common in older men, impotence can occur at any age. Impotence is not a normal consequence of aging. About 70% of erectile dysfunction is due to diseases such as diabetes and atherosclerosis, another 10% to 20% is due to psychological factors, and the remaining percentage is related to medications, lifestyle factors, and injury (Source: NIDDK).
In a prospective study from the Prostate Cancer Prevention Trial database, Thompson et al reported that men presenting with ED had a significantly higher chance of developing a cardiovascular event over a 7-year follow-up period.  The hazard ratio was 1.45, which is in the range of risk associated with current smoking or a family history of MI.
Remember what I said before about how it's not you? Okay, sometimes it is you. But it's not that you're not sexy — it's that for men, as well as women, relationship problems (like fighting all the time, or having clashing expectations about where things are going) can severely mess up your sex drive and ability to become aroused. Which makes sense — if you're spending 90 percent of your time together fighting about whether you're going to move in, switching gears to make 10 percent of your time together into a sexy sex party is pretty damned difficult.
Or, perhaps, since it's been only eight months, it might actually scare you a bit. It can be unsettling when someone falls head over heels. It can be hard to trust that kind of enthusiasm, especially if you've been burned by someone who went from hot-and-heavy to suddenly cold. Even if you're crazy about him, you might need to slow things down a little. Or maybe it's harder for you to say than it is for him — and that's why it rubs you wrong.
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A semi-firm penis if correctly handled can give a somewhat pleasant orgasm. I really don't think there is such a thing as an unpleasant orgasm though. I have have ED for two years. It has been than long since I had sex with my wife in her vagina. There has been plenty of oral sex for her. The ED drugs do not work with me. I take injectable Testosterone, and that does not make a big difference. About twice a month I am able to masturbate. Hey I am glad to know it still works. Next week I am going to see urologist number 2. The first one was a jerk and basically wrote me off because of my age. Now I have read about the Viberect device and the NEW pudendal artery (to the penis). There is hope, but in the mean time I will masturbate as often as I can.
It is important to understand that ED is frequently, if not usually, directly related to endothelial dysfunction, and that the release of NO by the vasculature of the penile arteries is directly related to the function of intact, healthy endothelium. In the face of endothelial dysfunction, the process of erection fails to occur in a normal fashion.16
Picture the scene. You get home from the bar with your date. You both decided to leave a little early, after only two drinks, because the chemistry was really there and both of you wanted to cut to the chase and get intimate. To discover each other's bodies. To eat of the fruits of passion. In short, to have sex. You stick the key in the lock, swing the door open, and invite her into your beautiful place. OK, well it might not be exactly beautiful. It might be a bit of a mess, frankly. But you don't let that ruin the moment. You turn around and passionately kiss her. How the two of you make it to your bedroom with some clothing still on is anybody's guess. You jump on the bed and hurriedly strip. God — can't this go any faster, you wonder?
Well, men go through the exact same anxieties, but the difference between men and women is the result is far more obvious in men. The first thing you need to do when you suspect your man is suffering from anxiety-induced erectile dysfunction is to look at him while you're going down on him and say this: "Is there anything you'd really like me to do? I'm willing to do whatever turns you on."
A lot of guys don’t want to admit it, but not being able to get or keep an erection happens more often than you’d think. Guys usually have trouble getting or keeping an erection when they’re nervous, scared or worried about something. They might be worried about how they’ll “perform,” or they could be feeling guilty about having sex. They might be afraid of getting a sexually transmitted disease (STD), or, if they are with a girl, getting their partner pregnant. Drugs (including some anti-depressants) and alcohol can also prevent you from getting and/or maintaining an erection.
Relationship problems can make it difficult for you to get or stay hard when you’re attempting to have sex with the person you’re in a relationship with. However, if you have this problem and you’re in a relationship that doesn’t mean your relationship is necessarily the reason. There are lots of other reasons you might not be able to get or stay hard (see above).
In addition to Viagra, other ED drugs available in the United States include avanafil (Stendra), tadalafil (Cialis) and vardenafil (Levitra). These all improve blood supply to the penis. In combination with sexual stimulation, the drugs can produce an erection sufficient to initiate and complete intercourse. There is also a fast-dissolving form of Levitra, called Staxyn, that you put under your tongue.
Sildenafil is available as oral tablets at doses of 25 mg, 50 mg, and 100 mg. Patients should take sildenafil approximately one hour before sexual activity. In some men, the onset of action of the drug may be as early as 11-20 minutes. It's best for men to take sildenafil on an empty stomach for best results since absorption and effectiveness of sildenafil can be diminished if it is taken shortly after a meal, particularly a meal that is high in fat. Sildenafil and the other PDE5 inhibitors don't cause an immediate erection. Sexual stimulation is necessary for these medications to work.
If you have symptoms of ED, it’s important to check with your doctor before trying any treatments on your own. This is because ED can be a sign of other health problems. For instance, heart disease or high cholesterol could cause ED symptoms. With a diagnosis, your doctor could recommend a number of steps that would likely improve both your heart health and your ED. These steps include lowering your cholesterol, reducing your weight, or taking medications to unclog your blood vessels.