How does nocturnal penile tumescence check for normal nighttime erections?

Dr. Mehmet Oz, MD
Cardiology (Cardiovascular Disease)
If a man with erectile dysfunction (ED) has an erection during the night, his ED is likely not caused by circulatory or other physical problems. It's more likely related to stress, anxiety, depression, problems in his relationship, or other issues. Problem is, many men have erections at night, but sleep through them, so they don't know they've had them when they wake up. The nocturnal penile tumescence (NPT) test sheds light on this. It's a simple self-administered test. You attach normal postage stamps around your penis, and go to sleep. The stamps are attached to each other, forming a ring around your penis. Do this on three nights. If you wake up each morning, and the stamp seal has been broken, it's a good indicator that you've been having normal nighttime erections. That's good news, really, since ED is often an early warning sign of heart disease. But it does mean you should work with your doctor to figure out what else is happening in your life that may be affecting your ability to have and maintain an erection so you can have a satisfying sex life.
Men typically have three to five erections while sleeping. The Nocturnal penile tumescence (NPT) test determines whether these erections are occurring. If you do not have erections while you sleep, the doctor will look for a health condition or medication that decreases blood flow to the penis or interferes with nerve signals that enable arousal and erection.
If you experience erections in your sleep or upon awakening, your erectile dysfunction (ED) may be caused by stress or depression. The NPT test is done two ways: the strain gauge method and the snap gauge method. The strain gauge method documents changes in circumference when elastic bands on the base and tip of the penis stretch during an erection. The snap gauge method measures erectile function with pressure-sensitive bands that break when an erection occurs.
Whatever the cause of your ED, your doctor can recommend treatment that will help. 

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