Tests for Erection Problems: What Is Penile Tumescence?

Vigor of Erections in REM Sleep May Reveal Cause of Impotence

A man looks to his erection during nocturnal penile tumescence testing
A man looks to his erection during nocturnal penile tumescence testing. Stephanie Phillips/E+/Getty Images

When erection problems occur, it is important to identify the source of the impotence. One possible evaluation technique is an overnight study of penile tumescence during sleep. What is penile tumescence and how might assessment of it identify a cause of impotence?

What Is Penile Tumescence?

Penile tumescence refers to the hardening and expansion of the penis into an erection. It often occurs in association with REM sleep and may be noted first thing in the morning.

Therefore, an overnight sleep study called a polysomnogram may be used to assess the function of the penis during sleep.

How Does a Penile Tumescence Test Help Identify the Cause of Impotence?

There are various causes of erection problems. Sometimes impotence is due to problems with blood flow or neurologic function. It may also be due to psychological problems, such as stress or performance anxiety. In order to distinguish these various causes, it can be useful to test the "equipment" during sleep, when erections often occur.

Penile tumescence testing monitors the frequency, rigidity, and change in the circumference of the penis during erections that occur REM sleep. An absence of erections may indicates a probable physical cause of the dysfunction.

How Is Nocturnal Penile Tumescence Testing Performed?

When assessment is made during sleep, the measurement is added to a standard sleep study called a polysomnogram.

Strain gauges, most often consisting of metal bands or springy loops, are placed over the base and tip of the flaccid (soft) penis. Normally, when an erection occurs the base circumference will increase up to 1.5 to 2 times the tip conference. Based on sheer differences in size, it is estimated that an increase of 12-15 mm in tip circumference signifies a full erection.

The frequency of these erections can be observed. In addition, pulsations in the penis can be measured. This results in transient increases in circumference that may last up to 1 second. If there is a low frequency of erections, or penile pulsations are not observed, this may reveal a physical cause to the impotence.

It is also possible to assess the strength, vigor, or hardness of an erection. Longitudinal rigidity is measured with something called the buckling pressure. As the name indicates, this is the amount of pressure that needs to be applied by a technician in order for the erection to bend or buckle. This usually requires forces that range from 1000 to 1500 g.

In order to assess the rigidity of the penis, the patient is awakened (most often from REM sleep) and the penis is uncovered and stabilized between the index finger and the thumb. A force gauge is applied to the penis tip and the amount of force applied is gradually increased. In general, this force is increased until the shaft buckles or until the meter reaches 1000 g.

This measurement can usually be completed by a skilled technician in 30 seconds, so that the erection can usually be maintained.

In normal healthy men, the rigidity of an erect penis will range from 750 to 1200 g. It is estimated that rigidity from 500 to 740 g is sufficient for penetration while that less than 500 g would rarely be adequate for sexual performance.

In some cases, a photograph may be used to assess the percentage of a full erection that was achieved.

If you are concerned about the underlying cause of your impotence, speak with your physician about the testing options available to you. In some cases, nocturnal penile tumescence testing may reveal the nature of the dysfunction and lead to optimal treatment options.

Source:

Ware JC, Hirshkowitz M. "Assessment of sleep related erections." In: Kryger MH, et al. Principles and Practice of Sleep Medicine. 4th ed. Philadelphia: WB Saunders, 2005.

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