Even a mild head injury can increase the risk of developing a sleep disorder, according to a study published in Neurology, the scientific journal of the American Academy of Neurology. Israeli and US researchers say these findings highlight the need for improved diagnosis and treatment of sleep disorders in mild traumatic brain injury patients. "As many as 65% of people with mild traumatic brain injury complain of insomnia," said study author Dr. Liat Ayalon of the University of California at San Diego. "This is concerning, since sleeping problems may exacerbate other brain injury symptoms such as headache, emotional distress, and cognitive impairment, making the rehabilitation process much harder." For the study, researchers assessed 42 people who reported to the Sheba Medical Center at Tel Hashomer with complaints of insomnia after mild traumatic brain injury. Those suspected of having a circadian rhythm sleep disorder (CRSD) - a problem with the timing of sleep - underwent scans, sleep studies and had their oral temperature and saliva melatonin measured. The study found 15 of the 42 patients, or 36%, had CRSD. Of those, eight had a delayed sleep-phase syndrome, with problems falling asleep and waking up, and seven people had irregular sleep-wake patterns. "The frequency of sleep disorders in this study is considerably higher than the rate among people attending sleep clinics for insomnia, which is 7% to 10%," said Ayalon. The findings, she said, suggest that sleep disorders involving changes in the timing of sleep may be relatively frequent among brain injury patients. "Misdiagnosis of these patients as insomniac may lead to prescription of medications that help people fall asleep but don't help normalize the sleep-wake cycle," said Ayalon. Since circadian rhythm sleep disorders are often associated with cognitive and psychological problems, she noted, treatment might ultimately lead to improvement in other brain injury related symptoms. Ayalon said further studies are needed to explain the mechanism behind CRSDs in people with brain injury. SLEEP STRENGTHENS MEMORY Meanwhile, sleep not only protects memories from outside interferences; it has also been found to help strengthen them, according to research to be presented presented next week at the American Academy of Neurology's Annual Meeting in Boston. The Harvard Medical School study looked at memory recall with and without interference (competing information). Forty-eight people between 18 and 30 - all of them having normal, healthy sleep routines and not taking medications - took part in the study. Participants were divided into four groups - a wake group without interference, a wake group with interference, a sleep group without interference and a sleep group with interference. All groups were taught the same 20 pairs of words in an initial training session. The wake groups were taught the word pairings at 9 a.m. and then tested on them at 9 p.m. after 12 hours awake. The sleep groups were taught the word pairs at 9 p.m. and tested on them at 9 a.m. after a night of sleep. Just prior to testing, the interference groups were given a second list of word pairs to remember. The first word in each pair was the same on both lists, but the second was different, testing the brain's ability to handle competing information, known as interference. The interference groups were then tested on both lists. The study found that people who slept after learning performed best, successfully recalling more words. Those in the sleep group without interference were able to recall 12% more word pairings from the first list than the wake group without interference. With interference, the recall rate was 44% higher for the sleep group. "This is the first study to show that sleep protects memories from interference," said the study author, neurology Prof. Jeffrey Ellenbogen, Fellow of the American Academy of Neurology. "Perhaps, then, sleep disorders might worsen memory problems seen in dementia." TERROR & WAR HURT LUNGS High concentrations of nitrogen dioxide gas - inhaled for even very brief periods following fires, explosions of military munitions or detonations of terrorist devices - could cause serious lung damage, scientists reported recently at the 233rd national meeting of the American Chemical Society. Dr. Zengfa Gu and colleagues at the Walter Reed Army Institute of Research in Silver Spring, Maryland, reached that conclusion based on experiments with laboratory rats that were exposed to the toxic gas. Gu explained that previous research showed that chronic exposure to low and moderate levels of nitrogen dioxide could damage the lungs. However, there was no clear information on the health risks of brief, high-level exposures. Nitrogen dioxide, a reddish-brown gas with a sharp, biting odor, is most familiar as an air pollutant. Released from the exhaust pipes of automobiles and the burning of fossil fuels, it is an ingredient in photochemical smog. Nitrogen dioxide also is a common indoor air pollutant released from gas ranges and other indoor combustion sources. It can cause nose, eye and more serious health problems. US government industrial health regulations limit workplace exposures to 5 parts per million (ppm). The gas, however, also forms when the heat from fires and explosives makes nitrogen and oxygen in the air combine to form nitrogen dioxide. Gu said information about such brief exposures is important for the military because in battlefield situations, personnel easily can be exposed to high concentrations of nitrogen dioxide. Civilians also could be exposed as a result of terrorist bombings. Similar exposure could occur among civilians trapped in fires before being rescued. "This research is very important," Gu said. "The results tell us that if [one encounters] an environment with high concentrations of inorganic fire gases, serious lung injury may be induced rapidly. So this research provides the scientific background for prevention of inhalation trauma and the treatment of inhalation injury." In their experiments, scientists exposed laboratory rats to varying concentrations of nitrogen dioxide - 100 parts per million, 500 ppm, 1,000 ppm and 2,000 ppm - for five minutes. They monitored effects of nitrogen dioxide during the exposure and examined the lungs afterward. "The experimental data showed that after exposure to high concentrations of nitrogen dioxide for only five minutes, the respiratory function was extremely changed," Gu said. "Breathing rate and depth were sharply inhibited; lung edema was rapidly induced, [and] acute and delayed lung damage occurred." Gu said the research represents the first real-time measurements of breathing changes due to the inhalation of nitrogen dioxide.