Circadian Variations in Body Temperature Linked to Consciousness Level in Brain-Injured Patients

April 19, 2017

MINNEAPOLIS, Minn -- April 19, 2017 -- For people with severe brain injuries, the rhythm of daily fluctuations in body temperature is related to their level of consciousness, according to a study published in the April 19, 2017, online issue of the journal Neurology.

“Our study suggests that the closer the body temperature patterns of a severely brain injured person are to those of a healthy person’s circadian rhythm, the better they scored on tests of recovery from coma, especially when looking at arousal, which is necessary for consciousness,” said Christine Blume, PhD, University of Salzburg, Salzburg, Austria.

In healthy people, daily variations in body temperature closely follow the sleep-wake cycle. Other studies have found that disruptions to the sleep-wake cycle may affect various aspects of health like the immune system and short-term memory. During a normal sleep-wake cycle, the body’s core temperature fluctuates and can drop 1 to 2 degrees during the early morning hours.

For the current study, researchers monitored 18 people with severe brain injuries, those with unresponsive wakefulness syndrome and those in a minimally conscious state. For 1 week, researchers continually monitored the body temperatures of participants with external skin sensors. With that temperature data, they were able to determine the length of the circadian rhythm for each person. Length of temperature cycles of participants ranged from 23.5 to 26.3 hours.

The researchers also evaluated the level of consciousness for each person with the Coma Recovery Scale-Revised, measuring things like response to sound and ability to open eyes with or without stimulation. They found that those who scored better on that scale had body temperature patterns that more closely aligned with a healthy 24-hour rhythm.

“This is the first time an association has been found between circadian variations in body temperature and arousal in brain-injured patients,” said Dr. Blume. “Importantly, arousal is essential for consciousness. Circadian variations are something doctors should keep in mind when diagnosing patients. The time of the day when patients are tested could be crucial. Also, doctors may want to consider creating environments for patients that mimic the light patterns of night and day to help achieve a normal sleep-wake cycle. The hope is that this may help bring a person with a severe brain injury closer to consciousness.”

The researchers tested bright light stimulation on 8 participants for 1 week and found positive effects in 2 patients. Dr. Blume said that larger studies are needed to test the hypothesis that bright light is indeed beneficial for patients.

One limitation of the study was that magnetic resonance imaging data was not available to evaluate the extent of brain damage, especially in the hypothalamus, the portion of the brain where the body clock is located.

Dr. Blume suggests that future studies look at the relationship between body temperature rhythms and other body rhythms like hormone patterns and rest-activity cycles.

SOURCE: American Academy of Neurology

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