Penile oxygenation is indeed crucial to maintain good vascular health within the penis. This is why we believe that men have nocturnal erectile activity. These erections occur due to a spontaneous reflex which happens anywhere from 2 to 7 times per night. This will in a sense “exercise” the penile vascular tissue by causing blood vessel dilation, better blood flow, and erection. This process nourishes the penile tissue and prevents collagen from forming. If collagen develops, this results in vascular tissue scarring with subsequent erectile dysfunction. This is the scenario that is believed to occur following penile nerve injury at the time of radical prostate removal for prostate cancer. In an effort to rehabilitate the penis following this surgery and to prevent erectile dysfunction, men are encouraged to take oral medication such as Viagra, Levitra, or Cialis at night to encourage nocturnal erections and/or to use drugs which are instilled into the urethra or injected directly into the penis to stimulate erection.