Pathophysiology
As normal erectile function depends on the delicate balance between vasorelaxation and vasoconstriction of the corporal smooth muscle, disruption of this equilibrium can result in
ED. If this critical level of smooth muscle relaxation is not achieved, there vvill be incomplete resistance to the venous outflow of blood from the corpora and full penile tumescence will be compromised. This is described as veno’occlusive dysfunction and can result from deficiency of the various systems that support the normal integrated response for penile erection. Vascular factors: Probably the most frequent causes of organic ED are endothelial dysfunction and disturbance of smooth muscle responsiveness within the corporal tissue of the penis.
Decreased arterial flow and perfusion pressure to the lacunar spaces can result from atherosclerosis, or traumatic arterial occlusive disease, of the hypogastric’Cavernous arterial bed and may also be a contributory factor. Excessive outflow through the subtunical venules may result in incomplete tumescence despite sufficient arterial inflow. This can be caused by insufficient relaxation of the trabecular smooth muscle, which may occur in anxious patients with excessive adrenergic’constrictor tone, through damage to the parasympathetic dilator nerves, or by corporal smooth muscle dysfunction.
Neurological factors: Disorders affecting the sacral spinal cord or the peripheral efferent autonomic fibers to the penis can result in incomplete relaxation of the trabecular smooth
muscle. Also, disruption of the somatic fibers from the penis that transmit sensory stimuli to the thalamus and sensory cortex (via the pudendal nerve) may also result in ED.
Such neurogenic ED can arise from spinal cord injury, multiple sclerosis, peripheral neuropathies (secondary to diabetes), alcoholism, surgical procedures such as radical prostatectomy, or pelvic radiation therapy. Endocrinological factors: Androgens are necessary for normal sexual development but also influence sexual motivation and behavior. Androgens have been shown to influence the activity of nitric oxide synthase (NOS) and smooth muscle relaxation in the corpus cavernosum. Low levels of bioavailable testosterone may result from a wide range of causes, including changes in the sensitivity of the hypothalamic—pituitary—gonadal axis due to aging, primary hypogonadism, hyperprolactinemia, and the use of leutinizing hormonereleasing hormone (LHRH) agonists.
Diabetes is the most common endocrine abnormality associated as a risk factor for ED. ED may eventually develop in 60% of men with diabetes mellitus. The main causes of the associated ED are thouglit to arise from tiie vasculoeenic and neurological sequelae of the diabetes. In particular, endothelial and smooth muscle dysfunction and neurological damage to C fibers have been implicated. As many as 40% of diabetic men are also hypogonadal. ED is also associated with hyperthyroidism. Psychogenic factors: The brain is the most important source of proerectile signaling in response to sexual stimulation. Unpleasant tactile, visual, auditory, and olfactory stimuli will tend to inhibit erection. Unpleasant sexual fantasies, perhaps envisaging embarrassment and rejection due to loss of erection with a partner, and memory of poor past sexual experience or relationship dysfunction, will have a similar effect. If these unpleasant, erectolytic stimuli predominate, there may be inadequate central pro-erectile signaling to provide the degree of sustained cavernosal smooth muscle relaxation required for erection. Penile factors: Peyronie’s disease is associated with ED, although it may coexist with other causal factors. In a recent study, nearly a third of men Avith untreated Peyronie’s disease were found to have ED. Changes in the integrity of the fibroelastic components of the trabeculae may result in reduced compression of the subtunical venules. This may be the result of aging, increased cross’linkage of collagen fibers (induced by non-enzymatic glycosylation and hypoxia), altered collagen synthesis associated with hypercholesterolemia, or by trauma to the penis.
Tags: Anxious Patients, Arterial Flow, Arterial Occlusive Disease, Contributory Factor, Dilator, Endothelial Dysfunction, Frequent Causes, Muscle Relaxation, Neurological Factors, Perfusion Pressure, Peripheral Neuropathies, Pudendal Nerve, Radiation Therapy, Radical Prostatectomy, Sacral Spinal Cord, Sensory Cortex, Sensory Stimuli, Spinal Cord Injury, Tumescence, Venules