The Body's Themoregulation During SleepHuman beings, as endotherms, are able to thermoregulate, that is, maintain their body temperature. Body temperature is regulated through a balance of heat absorption, production and loss. Human temperature must be maintained within a fairly small range, up or down from the resting temperature of 98.6. Temperatures above 104.9 degrees Fahrenheit or below 92.3 degrees generally cause injury or death. Humans have two zones to regulate, their core temperature and their shell temperature. The temperature of the abdominal, thoracic, and cranial cavities, which contain the vital organs, is called the core temperature. Core temperature is regulated by the brain. The shell temperature includes the temperature of the skin, subcutaneous tissues, and muscles, and it is more affected by external temperature. The core is able to conserve or release heat through the shell. When the core temperature is too high, blood vessels in the skin dilate and heat is lost through their walls. Sweat is also produced, which evaporates and lowers temperature. If a human is too cold, the blood vessels constrict, conserving heat. Blood is preferentially shunted to the internal organs and away from the skin and peripheral structures like limbs. The hypothalamus regulates body temperature between 96.8 and 100.4 degrees Fahrenheit over each 24 hour cycle. During the normal human circadian rhythm, sleep occurs when the core temperature is dropping. Sleep usually begins when the rate of temperature change and body heat loss is maximal. The average adult’s lowest temperature is at about 5 AM, or two hours before waking time. Many mammals lose significant thermal regulatory capacity during sleep. However, most research to date seems to indicate that humans do not have significant difficulty thermoregulating during sleep. In one study, subjects were exposed to a range of temperatures during sleep. Based on animal models, the researchers expected REM sleep to cause difficulty in thermoregulation, but the results showed that there was very little disruption of thermoregulation during REM and other sleep stages. The subjects shivered slightly in cold temperatures during sleep stages 1 and 2. Although skin temperature increased as the subjects were exposed to higher temperatures, their core temperature readings did not change. Other studies have showed different thermoregulatory responses of human subjects, depending on the sleep stage and temperature of the environment. In a different study of adult humans, thermoregulatory efficiency during REM sleep was fairly well maintained. However, thermoregulation was less efficient during Slow Wave Sleep (SWS). When subjected to different environmental temperatures, regulatory processes were affected. An overly warm or cool temperature disturbed sleep. REM sleep decreased, as did SWS to a lesser extent. However, warmth beforehand improved sleep, especially SWS. In depressed patients, sleep is disturbed as well as body temperature rhythms. In these patients, a warm temperature before sleep might be helpful. It does seem that humans maintain thermoregulation during sleep. However, it is possible that ambient temperatures before sleep may have an effect on sleep initiation and quality.
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"O Sleep, rest of all things, mildest of the gods, balm of the soul..." (Iris to Hypnos. Ovid, Metamorphoses) |