Body Temperature, Sleep, and the Circadian Rhythm
An early study published this week in Neurology, a journal of the American Academy of Neurology, showed that brain injury patients have fluctuating body temperatures that are directly related to their level of consciousness.
Dr. Christine Blume, PhD, from the University of Salzburg in Austria led the study. She noted that the findings suggest the circadian rhythm in brain injury patients who were in a coma may have better test scores in recovery if their body temperatures are similar to a healthy person’s. This was noticeable especially regarding arousal, a necessary component of regaining consciousness.
Circadian rhythm, or the biological clock, is a cluster of carrying rhythms in the body’s functions; they are the cycles our body goes through daily, telling us when to eat, sleep, and wake up. This clock regulates many functions in the body, including internal body temperature, which is generally set by the environment, such as darkness or daylight.
Healthy people have body temperature variations that closely correlate with their sleep-wake cycle, with their patterns being controlled by the biological clock. Many studies have indicated that sleep disruption and a chaotic sleep-wake cycle may negatively affect the immune system and short-term memory. In normal cycles, the core temperature in the body fluctuates at regular intervals and can drop 1-2 degrees in the early hours of the morning.
In this recent research, the team analyzed 18 brain injury patients. Some patients had unresponsive wakefulness syndrome and others were in a minimally conscious state. A vegetative state, or unresponsive wakefulness syndrome, is characterized by the patient waking up from a coma by opening his or her eyes and then going back to sleep, but remaining unresponsive. The other group of patients, those in a minimally conscious state, were also in a coma and woke up, but they showed signs of awareness.
Scientists monitored these patients for one week, recording body temperatures with sensors placed on top of the skin. The temperature data allowed researchers to determine the length of each person’s circadian rhythm. The temperature cycles ranged anywhere between 23.5 to 26.3 hours.
Scientists used the Coma Recovery Scale-Revised to evaluate each person’s level of consciousness. This scale measures the ability to open his or her eyes with and without stimulation, as well as how he or she responded to sound. Findings showed that people who had a body temperature pattern that was closely aligned with a 24-hour rhythm had better scores.
Dr. Blume noted that this research, for the first time, makes an association between body temperature in relationship to the circadian rhythm and the arousal in patients who have suffered a brain injury. This is important because arousal is a necessary component of consciousness. Variations in the biological clock should be watched closely by doctors who are diagnosing and treating brain injury patients.
It is important to consider the time of day the patients are tested. Treating providers can consider creating a sleep lab that is similar to the light/dark environment that is necessary to achieve a normal sleep-wake cycle. This type of testing and treatment may bring brain injury patients closer to waking up.
Eight patients received bright light stimulation for a week. Researchers found that two patients had positive responses, and Dr. Blume believes that larger studies will give us a better idea of its efficacy.
MRI data was not available for review of the brain damage at the time of the study, which limited the findings. It would have been helpful to look at the hypothalamus, which is the part of the brain that stores the body’s biological clock.
For future research, Dr. Blume suggests looking at the relationship between other rhythms, like rest-activity cycles, and the body temperature fluctuations.
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