While absolute temperature is proportional to the average kinetic energy of the random microscopic motions of any materials constituent microscopic particles, in clinical practice temperature is an objective comparative measure of hot or cold.
A fever in man is an abnormally high body temperature. Low core body temperatures (hypothermia) or very high fevers can cause morbidity or mortality. Extremes of environmental temperatures also can cause morbidity and mortality.
Normal body temperature
Many recognise the slightly inaccurate concept that a healthy axillary normal temperature is 37.0 °C (98.6 °F), from Carl Wunderlich. This is based on 25,000 observations and he actually noted a normal range of 36.2 °C to 37.5 °C . The 37.0 °C figure had been arrived at over 30 years earlier by others as well. Considering the equipment available at the time, requiring many minutes of observation, at varying ambient temperatures, and contrasting with today's electronic hospital temperature data bases which are several times that size but also have plenty of inaccurate measures, he did not do too badly.
In healthy adult men and women normal body temperature varies diurnally by about typically 0.5 °C and in females there is variation with the menstrual cycle. Human thermoregulation is within narrow limits for reasons associated with homeostasis and why it has evolved. The temperature depends upon where (and how) it is measured with usual values being:
- oral 33.2–38.2 °C (91.8–100.8 °F)
- axillary 35.5–37.0 °C (95.9–98.6 °F)
- rectal 34.4–37.8 °C (93.9–100.0 °F)
- tympanic membrane 35.4–37.8 °C (95.7–100.0 °F)
Temperature in disease
Fever can be of advantage in the response to some pathogens but has many causes.Even a process as common as sleep deprivation will impact on body temperature and hormone and neurological response or damage can be important quite independent of any inflammatory response to for example cytokines or interferon or a toxin.
Most temperature-related mortality burden is attributable to cold temperatures. However in a city such as Toronto or Stockholm mortality only slightly increases down to temperatures of -20 °C while in London or Madrid mortality increases markedly below 2 °C. So multiple environmental and cultural factors are important and all surveys identify that the typical U shaped curve of mortality increases again beyond 30 °C
- ↑ Wunderlich C. Das Verhalten der Eigenwarme in Krankheiten. Leipzig : Verlag von Otto Wigand. 1870
- ↑ Kelly G. Body temperature variability (Part 1): a review of the history of body temperature and its variability due to site selection, biological rhythms, fitness, and aging. Alternative medicine review : a journal of clinical therapeutic. Dec; 11(4):278-93.
- ↑ Sund-Levander M, Grodzinsky E, Loyd D, Wahren LK. Errors in body temperature assessment related to individual variation, measuring technique and equipment. International journal of nursing practice. Oct; 10(5):216-23.(Link to article – subscription may be required.)
- ↑ Owen JA. Physiology of the menstrual cycle. The American journal of clinical nutrition. 1975 Apr; 28(4):333-8.
- ↑ Craig JV, Lancaster GA, Williamson PR, Smyth RL. Temperature measured at the axilla compared with rectum in children and young people: systematic review. BMJ (Clinical research ed.). Apr 29; 320(7243):1174-8.
- ↑ Sund-Levander M, Forsberg C, Wahren LK. Normal oral, rectal, tympanic and axillary body temperature in adult men and women: a systematic literature review. Scandinavian journal of caring sciences. Jun; 16(2):122-8.
- ↑ Kelly GS. Body temperature variability (Part 2): masking influences of body temperature variability and a review of body temperature variability in disease. Alternative medicine review : a journal of clinical therapeutic. Mar; 12(1):49-62.
- ↑ Gasparrini A, Guo Y, Hashizume M, Lavigne E, Zanobetti A, Schwartz J, Tobias A, Tong S, Rocklöv J, Forsberg B, Leone M, De Sario M, Bell ML, Guo YL, Wu CF, Kan H, Yi SM, de Sousa Zanotti Stagliorio Coelho M, Saldiva PH, Honda Y, Kim H, Armstrong B. Mortality risk attributable to high and low ambient temperature: a multicountry observational study. Lancet. May 20.(Link to article – subscription may be required.)