The temperature of the tympanic membrane can be less reliable in patients with otitis media. One study reported a temperature difference of 1.2 degrees Celsius (2.16 degrees Fahrenheit) between right and left ears of febrile children using an infrared thermometer. When measurements are made in both ears, differences often are found. However, studies have shown a limited correlation between simultaneous otic temperature (measurement of radiant heat from tympanic membrane and ear canal) and rectal temperature measurements. A tributary of the artery that perfuses the thermoregulatory center perfuses the tympanic membrane, theoretically producing a close approximation to core temperature. The speed and ease with which the tympanic membrane temperature can be measured with an infrared thermometer has made this a frequent anatomic site for measurements. Temperature often is monitored at a peripheral site such as the tympanic membrane, oral cavity or axilla. In contrast to the core temperature, the periphery such as the skin and superficial tissues is influenced by environmental temperatures and seldom is constant. However, access is difficult at these sites, making measurements more invasive and less practical. Temperature recordings from a central site such as rectum, bladder urine, esophagus or blood in a pulmonary artery catheter provide the most accurate readings of core temperature. When the hypothalamic set point is reset at a normal temperature because of a reduction in pyrogen concentration or the use of antipyretics, heat loss occurs by sweating and vasodilation.Ĭore temperature is relatively constant despite fluctuations in the surrounding environment. Shivering increases heat production from muscles but may not be necessary if vasoconstriction sufficiently raises the temperature of the blood supplying the hypothalamus. When the thermoregulatory center is reset at a higher temperature, neurons stimulate vasoconstriction in the extremities and heat is conserved. The body maintains a fairly steady core temperature by balancing heat production from metabolic activity such as in muscle and the liver with loss of heat from the skin and lungs. The body’s thermoregulatory center is in the hypothalamus where neurons receive input from temperature receptors in the skin and from neurons assessing the temperature of blood flow in the hypothalamus. Editor’s note: This is the second of three articles on fever.
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