Your doctor may then ask you to undergo some specific tests to evaluate the cause of your erectile problem. Although, in a person with diabetes, the nerve dysfunction is felt to be the main etiological factor, certain basic tests may be carried out to rule out associated causes such as vascular factors, and it is worth having some knowledge about these.
Evaluation of nocturnal penile tumescence (NPT) is one of the earliest tests devised to study erectile dysfunction. The association between sleep and erections was documented as early as 1940 by Halverson.
The primary goal of NPT studies is to distinguish psychogenic causes from organic (vascular, neurogenic, hormonal) causes of impotence. In its sophisticated form, this study involves the use of nocturnal monitoring devices that measure the number of erectile episodes, maximal penile rigidity, tumescence (circumference), and duration of nocturnal erections.
Before the advent of the newer techniques using the rigiscan, physicians used the postage stamp test. Basically, a series of stamps was placed around the base of the penis. If the patient awoke the next morning with the stamps unbroken, this indicated an organic problem. However, if the stamps were broken, this was felt to be a psychological problem. Following the postage stamp test was the development of the snap gauge, a Velcro band placed around the base of the penis that had three colored plastic film elements. Each film ruptured at a specific known force. It took 10 ounces of radial force to rupture the blue tab, 15 ounces to rupture the red tab, and 20 ounces to rupture the clear tab. These snap gauge results were reasonable. However, there was no way to measure rigidity. When the criteria for the snap gauge was carefully examined, it was found that half the men who broke two to three films actually had no rigidity by visual inspection. Because of this, it has lost some favor and it has been mostly supplanted by the rigiscan.
The rigiscan allows us to measure continuous tumescence monitoring, but it also provides rigidity information during the times when the patient is achieving an erection. In addition, it gives detailed information about how often the erections occur, for what period of time, and the rigidity and change in diameter. Rigidity is measured by placing a loop around the base of the penis, which is tightened every thirty seconds with a force of 2.8 Newtons. It records three sessions, and then it is downloaded into a computer. The newest version of the rigiscan uses software that can calculate an entire evening of tumescence and rigidity data into rigidity activity units and tumescence activity units. Several different types of patterns are measured by the rigiscan, including dissociation which is seen with Peyronie's disease. This pattern shows how the base of the penis gets hard and the tip past the areas of the Peyronie's plaque has poor rigidity and tumescence.
Pharmacologic evaluation of the impotent patient consists of testing the erectile response of the penis to an intracavernosally administered vasodilating agent, which causes relaxation of the penile vascular sinusoids and increased blood flow in the cavernous arteries. The resultant engorgement of the corpora results in compression of the subtunical venules and decreases penile venous outflow. Therefore, in order to produce a normal erection, arterial vasodilation, sinusoidal relaxation, and decrease in venous outflow must all occur in response to the vasodilating agent.
In the past, a number of agents have been used for this study, including papaverine (a direct-acting, smooth-muscle relaxant) and phentolamine (an alpha-adrenergic blocking agent). Later, prostaglandin E1 (PGE1), a potent vasodilating agent metabolized locally in the penis was used in many centers.
The technique involves injecting 10ug PGE1 through a 28-gauge needle into the corpus cavernosum. The needle site is compressed manually for at least 5 minutes to prevent hematoma formation. The erectile response is periodically evaluated for both rigidity and duration. In a normal study, a full erection is achieved within 10 to 15 minutes and is defined as one that is firm to palpation and positioned at above 90deg.. The erectile response to the injection should be sustained for at least 15 minutes to complete a normal test.
The pharmacologic test yields important information regarding the vascular status of the penis. The finding of a normal erectile response to the injection rules out the possibility of venous leakage, although some patients (about 20%) with arterial insufficiency may also achieve rigid erection due to an intact veno-occlusive mechanism.
The finding of a normal response to intracavernosal injection in an impotent patient suggests that neurogenic, psychogenic, or hormonal factors may be primarily responsible, but it is difficult to distinguish among these causes. However, a normal pharmacologic screening test makes further evaluation for veno-occlusive dysfunction unnecessary.
An abnormal finding on the pharmacologic test suggests that penile vascular disease (arterial, venous, or sinusoidal) is responsible for impotence.
Although many tests have been suggested and are carried out in very specialized centers, testing for nocturnal penile tumescence (NPT), penile biothesiometry and intracavernosal injections, and their correct interpretation, are sufficient in most cases to point towards the etiological factor(s) leading to erectile dysfunction. And this is especially so for patients with diabetes.
In recent times, one other test has gained prominence in giving a more quantifiable result for vascular anomalies leading to erectile dysfunction.
In 1984, Lue et al introduced the duplex ultrasound for evaluation of male impotence. Notwithstanding the fact that duplex exams evaluate the flow speed and not the arterial flow, they have proved a reliable and reproducible method for the evaluation of penile arterial insufficiency. Duplex ultrasound combined with an intercavernosal injection has pretty much replaced all other tests that are currently available. This single test can evaluate both the early and late stages of an erection, as well as venous leakage.