Advanced Testing for ED

A. Nocturnal Penile Tumescence (NPT) Test

Nocturnal erections occur in healthy males of all ages. Of the nocturnal erections, about 80% occur during REM sleep. The average man has 3-5 episodes of NPT each night, with each episode yielding 30-60 min of erection time. Total NPT time declines with increasing age. NPT has been measured by several methods: stamp test, Snap Gauges, strain gauges, NPTR (_{Rigiscan, Timm Medical Technologies, [Levine and Lenting, 1995]}) sleep lab NPTR and NPT electrobioimpedance (_{NEVA, American Medical Systems, [Knoll and Abrams, 1999]}).

In its classic form, NPT monitoring devices measure the number of erectile episodes, maximal penile rigidity, tumescence (circumference), and duration of the nocturnal erections. These data are recorded in conjunction with electroencephalographic, electro-oculographic, and electromyographic, nasal air flow, and oxygen saturation data, to document REM sleep, the presence or absence of hypoxia, and abnormal limb movement (_{Karacan, 1988}). Because of its expense, sleep lab NPT has been replaced by simpler outpatient devices such as Rigiscan and NEVA. These newer devices have the advantage of electronically recording the number, duration, rigidity, and circumference of penile erections. NPT was originally designed to differentiate psychogenic from organic ED. In the United States, it is now mostly used in medicolegal or complicated cases.

B. Psychological Evaluation

The contemporary definition of psychogenic ED is, "persistent inability to achieve or maintain erection satisfactory for sexual performance which is due to predominantly or exclusively to psychological or interpersonal factors" (_{Lizza and Rosen, 1999}). Therefore, a skillful diagnostic interview is the mainstay of a good psychological evaluation. The diagnostic interview should focus more on the current sexual problem and its immediate causation, partner relationship, and any psychiatric symptoms. Because psychogenic impotence is the result of changes in affect and mood, it usually occurs in a specific pattern. A suggestive history includes sudden onset, selective dysfunction (eg, rigid erection with one partner and poor erection with others, or normal erection during masturbation or fantasy but not during intercourse), and normal pattern of nocturnal erections but abnormal pattern during waking hours. This is often associated with anxiety, guilt, fear, emotional stress, and religious or parental inhibition.