Induction of erection occurs after stimulation of the cavernous and pelvic nerve plexus. Conversely, stimulation of the sympathetic trunk leads to detumescence. The reflex erectile response requires that the sacral reflex arc remain intact. Tactile and sensory signals are received by the somatic sensory pathways and integrate with parasympathetic nuclei within the sacral spinal cord (S2-4) leading to induction of erection via cholinergic signaling. These reflexogenic erections remain intact with upper motor neuron injuries. Psychogenic erections do not require that the sacral reflex arc remain intact. In a cat models, spinal cord removal below L4/L5 led to absence of a reflexogenic erection but stimulation of the medial preoptic area (MPOA) or placement near a female cat in heat led to erection (5,6). Psychogenic erections occur via induction of central pathways traveling from the brain through the sympathetic chain. Non-penile sensory pathways induced by sight, sound, touch and smell travel through the MPOA to the erection centers within the cord T11-L2, and S2-S4 to induce erections (7). When a sacral lower motor neuron injury is present in men, below T12 these types of erections are more likely to occur (8). Spinal cord lesions above T9 are not associated with psychogenic erections (9). Rigidity of erections is less with psychogenic erections because the thoracolumbar sympathetic outflow may contain a decreased concentration of neurons compared to the parasympathetic outflow from the sacral spinal cord.
The FDA recommends that men follow general precautions before taking a medication for ED. Men who are taking medications that contain nitrates, such as nitroglycerin, should NOT use these medications. Taking nitrates with one of these medications can lower blood pressure too much. In addition, men who take tadalafil or vardenfil should use alpha blockers with care and only as instructed by their physician, as they could result in hypotension (abnormally low blood pressure). Experts recommend that men have a complete medical history and physical examination to determine the cause of ED. Men should tell their doctor about all the medications they are taking, including over-the-counter medications.
The first line and by far the most common treatment today is with the prescription drug sildenafil citrate, sold under the brand name Viagra. An estimated 20 million prescriptions for the pill have been filled since it was approved by the FDA in March 1998. It is also the most effective treatment with a success rate of more than 60%. The drug boosts levels of a substance called cyclic GMP, which is responsible for widening the blood vessels of the penis. In clinical studies, Viagra produced headaches in 16% of men who took it, and other side effects included flushing, indigestion, and stuffy nose.
Can’t or don’t want to take ED drugs? The vacuum pump method is the next most common choice among men with erectile dysfunction who pass on pills, says Dr. Bennett. To create an erection, you place a plastic cylinder over the penis and pump the air out of the cylinder to force blood to flow into the penis. An elastic ring that you slide onto the base of your penis holds the erection. This ED treatment device is effective for about 75 percent of men. Side effects include numbness, bruising, and weak ejaculation — and the ring must be removed after 30 minutes.
For best results, men with ED take these pills about an hour or two before having sex. The drugs require normal nerve function to the penis. PDE5 inhibitors improve on normal erectile responses helping blood flow into the penis. Use these drugs as directed. About 7 out of 10 men do well and have better erections. Response rates are lower for Diabetics and cancer patients.