Crossref | PubMed | Google ScholarSee all References Patients with vascular risk factors (diabetes mellitus, hypertension, heart disease, and hyperlipidemia) had significantly decreased peak systolic velocities and increased end-diastolic velocities. Patients with diabetes mellitus had increased end-diastolic velocities and decreased resistive indices, indicating a disorder of venous trapping during erections. Another study examined corpora cavernosal tissue removed at penile prosthesis placement in 21 diabetic men and 42 nondiabetic controls.23x23Saenz de Tejada, I, Goldstein, I, Azadzoi, K, Krane, RJ, and Cohen, RA. Impaired neurogenic and endothelium-mediated relaxation of penile smooth muscle from diabetic men with impotence. N Engl J Med. 1989; 320: 1025–1030
Penile Injection Medication: This is just what it sounds like. Injected at home directly into the penis, the medication alprostadil produces erection by relaxing certain muscles, increasing blood flow into the penis and restricting outflow. Although some sources report an 80 percent success rate, the therapy has disadvantages, such as risks of infection, pain, and scarring—fibrosis—in the penis, and it may also cause priapism. A popular version of this medication is Upjohn Corporation’s Caverject. The MUSE System, by VIVUS, involves the same medicine (a pellet of alprostadil) applied with an eye-dropper-like applicator, directly into the urethra.
 Other treatment options such as penile self-injection therapy, external vacuum pumps and the medicated urethral system for erection are on rare occasions an effective long-term treatment. A very small percentage of men will continue with these treatments as evidenced by a very high drop out rate and a very low refill rate for these treatments. These procedures require extensive planning which interfere with sexual spontaneity and are really not a realistic long-term treatment for young patients with permanent ED. 

Conversely, and of significant clinical importance, is how often patients with ED as their first and sole clinical manifestation suffer from subclinical CAD.17 Previous studies reported a rate of inducible ischaemia by exercise stress testing (EST) in 22% (with a wide range of 5–56%) of ED patients reflecting differences in patient population, risk factors and criteria used for ED and CAD diagnosis. Interestingly, those patients further assessed with coronary angiography had obstructive atherosclerosis in >90% of cases.4,18 In a prospective angiographic study, we documented that 19% of ED patients suffer from clinically silent obstructive CAD.18
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In some cases, however, these drugs may be unsuitable for patients with heart disease. If you are considering one of these drugs and you have heart disease, as many diabetics do, be sure to tell your doctor. In rare cases, the pills may create “priapism,” a prolonged and painful erection lasting six hours or more (although reversible with prompt medical attention).
SOURCES: American Urological Association, "AUA Guideline on the Management of Erectile Dysfunction: Diagnosis and Treatment Recommendations." Barksdale, J. Pharmacotherapy, May 1999; vol 19: pp 573-581. Ferrario, C. Journal of Clinical Hypertension, November/December 2002; vol 4: pp 424-432. Fogari, R. American Journal of Hypertension, January 2001; vol. 14: pp 27-31. Grimm, R. Hypertension, January 1997; vol 29: pp 8-14. Llisteri, J. American Journal of the Medical Sciences, May 2001; vol. 321: pp 336-341. WebMD Medical Reference provided in collaboration with The Cleveland Clinic: "Hypertension: Treatment With ACE Inhibitors."
In an open-label study, 8 patients monitored with a Swan-Ganz catheter were given a total of 40 mg of sildenafil in 4 intravenous transfusions (the equivalent of 1 to 3 times the plasma concentration after an oral dose of 100 mg).62x62Jackson, G, Benjamin, N, Jackson, N, and Allen, MJ. Effects of sildenafil citrate on human hemodynamics. Am J Cardiol. 1999; 83: 13C–20C
Hypertension can affect endothelial function in many ways. It can reduce endothelium-dependent vasodilatation by increasing the vasoconstrictor tone as a result of increased peripheral sympathetic activity.41–43 Another mechanism is hypertension-induced increase in cyclooxygenase activity that leads to an increase in reactive oxygen species; these in turn damage endothelial cells and disrupt their function.44–46 In some cases, endothelial NO synthase (eNOS) gene variations may relate to hypertension-associated endothelial dysfunction.6
Smoking is an independent risk factor for ED. Tobacco smoking causes direct toxicity to endothelial cells, including decreased eNOS activity, increased adhesion expression and impaired regulation of thrombotic factors.6 A meta-analysis of 19 studies by Tengs and Osgood suggested that 40 % of the impotent men studied were current smokers compared with 28 % who had never smoked.49
Erectile dysfunction is a common occurrence in men with diabetes. The incidence of erectile dysfunction increases progressively with age, from 5% in men age 20 to 75% in men over age 65. The cause of erectile dysfunction in men with diabetes is usually related to a decrease in the blood supply to the penis as well as to injury to the nerves that are responsible for the erection mechanism. A decrease in testosterone production has also been identified as the cause in some men with diabetes.