At night, something that no-one can explain happens to men of all ages. It usually occurs several times a night, and most men neither realise that it is happening nor have any memory of it the next morning.
Most males who are in reasonable health experience nocturnal erections. During a regular 8-hour sleep, they may have between three and five erectile episodes. These last an average of 10 to 15 minutes each and always arise during the dreaming, or rapid-eye-movement (REM), phase of the sleep cycle.
Men who have some difficulty with their erectile function may find it heartening to know that at night, while they and their worries are fast asleep, their bodies are getting on with the business of having normal erections.
Although most are oblivious to this activity, in rare cases the erections can be problematic, causing the man to wake repeatedly.
While there is no medical explanation for these nocturnal events, some speculate that they are a form of self-maintenance, helping to keep penile tissue bathed in fresh oxygen. With erection, the penis becomes engorged with new blood. This blood brings a fresh supply of oxygen, which keeps the tissue in good condition.
During a night’s slumber, people go through several cycles of REM sleep, in which they experience a range of bodily changes. Although their eyes jerk, their muscles become extremely relaxed and blood flow to the brain is enhanced. At the same time, their heart rate, breathing and blood pressure become irregular and their bowels more active and noisy.
Men commonly wake in the morning from a REM phase with an erection. It used to be thought that this early-morning erection was caused by a full bladder, but now it is viewed as the last of the nocturnal erections. It is thought to be a reflex – known technically as nocturnal penile tumescence, or as a ‘sleep erection’ in infant boys – and was first described in the medical literature in 1940.
By the 1950s, these erections had been linked with REM sleep, and by the 1960s it had been discovered that more than 80 per cent of healthy young men had these erectile episodes during REM sleep.
In the mid-1970s, through a series of studies involving more than 2000 healthy boys and men, researchers documented the existence of sleep-related erections in all healthy males from the age of 3 to 79. Recent detailed research into nocturnal erections and ageing has produced conflicting results. Some studies say that with advancing age there is no change in the number of nightly episodes or in the rigidity of the erections. Others have found a gradual decline in the frequency and duration of tumescence.
Certainly many older men who take Viagra report healthy early-morning erections for two or three mornings after taking the drug.
Because nocturnal erections occur so consistently, doctors believed they could be useful in understanding impotence, and particularly in distinguishing psychological from organic impotence. They based this belief on the assumption that during sleep emotional factors such as fear and anxiety would be neutralised. If this were true, men suffering from psychological impotence should have normal nocturnal erections at such times.
They also assumed that in men with organic impotence, the underlying factors that caused this impotence, such as hormonal imbalance, damaged nerves or inadequate blood circulation, would remain unchanged with sleep and therefore lead to a pattern of abnormal nocturnal erections.
But as they investigated further, they realised they had made yet another assumption. They had assumed that the mechanisms involved in sleep erections were the same as those responsible for sexually stimulated erections.
They began to question all three assumptions. They speculated that different nerve pathways might be responsible for different types of erection. Why, for example, did some men whose impotence resulted from a spinal-cord injury still have normal early-morning erections? They also began considering circulation problems. Some men suffer from a condition known as pelvic steal syndrome. These men can achieve an adequate erection, but the minute they start thrusting or moving their lower body, the blood rushes away from their penis towards the muscles in their buttocks and they lose rigidity. These men often have good, rigid nocturnal erections.
Investigators also found that depression and anxiety could impair nocturnal erections, as could a range of drugs including alcohol, tobacco, antidepressants, narcotics and anticonvulsants. Further, they found that while men with low testosterone could achieve erections if they were erotically stimulated, they did not experience normal nocturnal erections.
But despite the intrinsic weaknesses and limitations of their initial assumption, doctors say nocturnal erections can still provide valuable information for the assessment of impotence. There is no single test that can distinguish organic from psychological impotence, and the advantage of measuring nocturnal erections is that it is noninvasive and relatively inexpensive.
Over the years different ways of measuring nocturnal erections have been devised. In 1980 intrepid researchers used postage stamps. Just prior to sleep, a strip of four stamps was wrapped snugly around the penis, leaving an overlap of half to a full stamp. This overlap was moistened to seal the strip.
Next morning the man inspected the ring to see if it was broken along the perforations. He then repeated this procedure for three consecutive nights. Researchers who devised this method validated it with men watching erotic videos. They placed the stamps in position and then turned on the videos.
According to their reports, the stamps broke apart at 80 to 100 per cent of full erection.
But to the post office’s regret, this method had limitations. Researchers moved on to Velcro bands and snap gauges. Today sophisticated computer technology is used.
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