The causes of erectile function are many and complex, so it is really difficult to diagnose the cause of impotence. Generally speaking, in the diagnostic process, the doctor will choose a variety of examination methods, one of the more commonly used test is the penile nocturnal penile erection function monitoring, some doctors also referred to it as NPT. Here is a brief introduction to why we need to check the NPT. In order to understand why we need to check the NPT, the first thing we need to know is what is the matter of nocturnal penile erection. The so-called nocturnal erection refers to the spontaneous erection of the penis during sleep. Generally speaking, normal men almost always have an erection at night, and this physiological phenomenon continues from early childhood to old age. After puberty, nocturnal erections occur about 4 to 6 times a night and last for about 150 minutes. In older age, such as 50-60 years old, the frequency and duration of erections decrease, but still last about 60 minutes per night. Nocturnal erections are erections that occur during deep sleep and therefore have little to do with a person’s conscious awareness in the waking state, and are a manifestation of subconscious penile activity. Penile erection is regulated by the center of the brain. Usually, the brain inhibits penile erection during the daytime when the person is conscious, so he or she will not have frequent erections during the daytime for no reason. Only in a special environment and conditions, in a certain libido stimulation, the brain on the erection of the penis from inhibition to promote the role of the penis will be erected. For example, when men and women have sexual contact in an appropriate environment. In some cases, such as in the lack of libido, mental tension, fear, work pressure or mood boredom and other bad emotions, the central nervous system on the erection of the penis will produce a significant inhibition, the penis will be difficult to get an erection and not erect. This is what we usually call psychological impotence. When sleeping at night, this bad psychology will naturally disappear and the inhibitory effect on erection will be lifted. To take advantage of this, the doctor will use an instrument to monitor the erectile function of the penis at night, that is to say, to do a NPT. the result of the NPT will have a certain role in determining whether the impotence is psychological or organic. Generally speaking, most NPT tests are basically normal in psychological impotence. In general, the NPT needs to be measured for three consecutive nights. In this way, the influence of environment and sleep quality on the monitoring results can be greatly excluded.