Thursday, August 13, 2009

Daytime Sleepiness Can Be a Pain

A study in the Aug. 1 issue of the journal Sleep reports that healthy people may be more sensitive to pain if they are sleepy.

study involved 27 healthy, pain-free adults between 18 and 35 years of age. A physical exam, drug screening and lab tests confirmed that they were in good health. An overnight sleep study verified that they didn’t have a sleep disorder such as obstructive sleep apnea.

Participants were grouped as “sleepy” or “non-sleepy” based on the results of a
multiple sleep latency test (MSLT). The 14 people in the sleepy group fell asleep after an average of less than five minutes during the four daytime nap sessions; it took an average of about 13 minutes for the 13 non-sleepy people to fall asleep.

All participants then spent eight hours in bed during a night at a sleep center. The following day another MSLT was conducted. Results show that the healthy, sleepy people remained sleepy even after spending eight hours in bed. They still fell asleep in less than five minutes during MSLT nap sessions.

The day after the eight-hour night in bed also involved two tests for pain sensitivity; tests were conducted at 10:30 a.m. and again at 2:30 p.m. Participants placed their index finger on a radiant heat source; then they withdrew their finger when they felt pain.

For each person a pain threshold was determined; this was the heat intensity that produced a finger withdrawal in less than 21 seconds. Then both index fingers were tested at five different heat intensities.

Sleepy people showed increased pain sensitivity – or “hyperalgesia.” At all five heat intensities they withdrew their finger faster than non-sleepy people. They also had a lower pain threshold than non-sleepy people: 83 degrees versus 90 degrees. People in both groups were more sensitive to pain in the afternoon than in the morning.

Previous studies also have linked sleep and pain sensitivity. A 2007
study in the journal Sleep found that disrupted sleep increases spontaneous pain. A 2006 study in the journal Sleep showed that the loss of four hours of sleep promotes hyperalgesia. In 2000 a study reported that 40 hours of total sleep deprivation increased pain sensitivity.

The authors state that the solution can be simple for healthy, sleepy people: Spend more time in bed each night to get more sleep. But managing sleep can be more complex in people with chronic medical problems. In this case the authors suggest that a medication or cognitive behavioral therapy (CBT) may be needed to increase sleep time.

No comments:

Post a Comment