Does penile tumescence have any relation to sleep architecture?
Since the 1970s, it has been known that nocturnal erections are phenomena of REM sleep. Therefore, the classic hypogonadal teaching that decreased morning erections are caused by low testosterone levels may be related to more than one primary problem. The patient with decreased or absent morning erections may have hypogonadism, but the root cause could lie in abnormal sleep architecture (i.e., sleep disease impairing REM density). One recent 12-week randomized trial evaluated the use of continuous positive airway pressure (CPAP) versus vardenafil versus placebo in a two-by-two factorial study design in 61 men (mean age 55 years; body mass index [BMI] 32kg/m 2 ) with am serum total testosterone levels ≤ 299.9 ng/dL. The CPAP treatment groups showed improvement in, among other parameters, nocturnal erections. The use of CPAP for 6.2 hours per night resulted in a decrease in respiratory events from a mean apnea–hypopnea index (AHI) of 39 events to 14 events per hour in the per-protocol group. Note that CPAP, in this study, improved OSA from the severe range to the mild range, but not into the normal range (AHI < 5 events/hr). One might speculate that even better results would be seen with normalized breathing (AHI < 5 events/hr) at night. Regardless, the authors conclude “these data may convince some men who highly value erectile function to adhere to CPAP therapy.” Other endocrine systems also show a dose–duration response improvement with CPAP. Another inference from these data supports closer historical screening for sleep disease (see question 41) in those patients admitting to decreased or absent morning erections.