Penile injection testing

Another method for differentiating between vascular and nonvascular ED involves direct intracorporeal injection of vasodilating chemicals such as PGE1 or papaverine, bimix or trimix. These substances directly dilate healthy penile arteries and sinuses, increasing blood flow to the corpora, resulting in engorgement, rigidity, and full erection. The Combined Intracavernous Injection and Stimulation (CISS) test may also be helpful in diagnosing vascular ED. The patient's self-stimulation in privacy after the injection (by watching an erotic movie with or without masturbation) may yield a better erectile response, especially if the injection elicits partial erection.

Following an intrapenile injection, the development of a rigid erection within 10 - 25 minutes and lasting more than 30 minutes may practically rule out any severe arterial or venous factors. Maintenance of a rigid erection for 30 minutes or more usually denotes the absence of venous leakage, an intact reflexogenic pathway for erections, and the lack of severe disease in the penile arterial system. However, a positive CISS test does not necessarily mean that penile arterial function is completely normal.

In certain cases, when it is suspected that blood has been directed or shunted away from the penile arteries to the arteries of the lower extremities (steal syndrome), the patient is asked to perform knee-bending exercises during erection, without any injections. If a steal or shunt of blood is present, he will lose his erection during these exercises. If the penile arteries are clogged or severely diseased, or if there is abnormal venous leakage, there will not be enough arterial or sinusoidal dilation for an erection to occur, or if an erection does occur in such a case, it will be lost quickly following an intrapenile injection.

In almost all other organic or psychogenic conditions, intracorporeal injections result in normal erections. The idea behind penile injection testing is that the adequacy or inadequacy of arteries and sinuses can be checked while bypassing all the other factors that may affect them. It assesses the integrity of the intrapenile arteries and sinuses and their ability to dilate under the influence of the vasodilating substances injected directly into the corpora. These chemicals are also used to treat patients with ED for whom oral pharmacological therapy is ineffective.