Erectile dysfunction (ED) can be classified as organic, psychogenic or mixed. Organic ED is due to physical defects and can be further sub-classified. Psychogenic ED is secondary to psychological factors that are thought to inhibit a man's ability to achieve an erection because of specific stressors. ED often has a mixed component of both organic and psychogenic etiologies.
ED is a common concern for men and their partners, can cause significant depression and anxiety, and can greatly impact quality of life. ED can also lead to a lower level of physical and emotional intimacy resulting in a lower level of satisfaction within a relationship.
Data from various studies has estimated that roughly half of men aged 40-70 years old have some form of erectile dysfunction. It is further estimated that 10% of men aged 30-39 have erectile dysfunction, with prevalence increasing to 59% of men aged 70-79. This extrapolates to over twenty million men in the United States alone with ED.
An understanding of the basic physiology of erections (how erections work) will allow understanding of the causes and treatments of ED. The penis is an organ with paired erection chambers (corpora cavernosa), which are filled with spongy erectile tissue (corporal sinusoids) composed predominantly of smooth muscle. Erection and loss of erection are related primarily to blood flow events regulated by the penile arteries and the erectile bodies. Penile erections are triggered by one of two main mechanisms: direct stimulation of the genitalia or through stimuli coming from the brain (fantasy, smell, sound, etc). Upon stimulation, chemicals are released in the brain that cause signals to pass down the spinal cord and outward through special nerves (nervi erigentes) into the penis. These nerves release another chemical (Nitric Oxide) that causes the aforementioned smooth muscle to relax and blood rushes into the erectile bodies, causing erection. Anxiety or fear can prevent the brain signals from reaching the level required to induce erection. Medical conditions can block the erection arteries or cause scarring of the spongy erection tissue, thereby preventing proper blood flow, or trapping of blood, and limiting the erection.