Temperature Regulation and the Pathogenesis of Fever

ectal thermometer were twice as likely to be febrile on presentation or during hospitalization than
those whose fever had been documented by palpation alone (92% versus 46%; P < .001). [43]
Because the temperature of the rectum, mouth, and tympanic membrane are related but not
identical, it would be useful to have a reliable formula for converting data from one site to that of
another. In a study of healthy young adults, Rabinowitz and associates determined that on average,
rectal readings exceed concurrent oral readings by 0.4° C (0.8° F) and exceed TM readings
(obtained with the IVAC Core) by 0.8° C (1.6° F). [26] However, these relationships were extremely
variable. Their findings concerning the relationship between rectal and oral readings were in
agreement with those of several earlier investigations. [44][45] Their findings with respect to the
relationship between oral and TM readings, however, differed from earlier reports, [19] which had
generally shown TM readings to be higher than simultaneously obtained oral measurements. This
discrepancy most likely reflected the fact that unadjusted-mode TM thermometers—for example,
the IVAC Core—generally give lower readings than adjusted-mode TM thermometers, such as
those used in earlier studies. [30]
Togawa has reported that on average, in a resting healthy adult, the core temperature (pulmonary
artery) is 0.4° C (0.7° F) higher than the oral temperature and 0.2° C (0.4° F) lower than the rectal
temperature—however, again with considerable individual variability. [46] Anagnostakis and
co-workers have concluded in studies comparing rectal and axillary temperatures in infants that
because of a similarly high degree of variability, no standard factor can be developed for converting
axillary to rectal temperatures. [47] Thus, using a temperature reading from one anatomic site to
predict the temperature at another must be done with caution.
Physiologic Variables
Wunderlich and Seguin [48] believed that “old” people have lower body temperatures than younger
persons, and their views in this regard were corroborated by Howell in a report published in Lancet
in 1948. [49] There is also a substantial body of data suggesting that thermoregulation is impaired in
older persons because of various effects of aging on the autonomic nervous system. [50]
Nevertheless, more recent work has not shown lower average core temperatures among healthy
older subjects (mean age, 80.3 years; range, 62 to 99 years) than among healthy younger
subjects. [51] Comparisons of simultaneous oral, axillary, and rectal temperature readings from such
subjects have shown lower average oral and axillary readings in older persons but comparable
average rectal temperatures in older and young subjects.
It has long been known that women exhibit increases in body temperature of about 0.5° C (0.9° F)
at the time of ovulation. [21] Wunderlich and Seguin also maintained that women have slightly higher
normal temperatures than men overall and often show greater and more sudden changes in
temperature. [48] Two more recent studies have corroborated Wunderlich and Seguin’s former but
not latter observation. [8][52]
Body temperature, like most physiologic functions, exhibits circadian rhythmicity that is linked to
the sleep-wake cycle. [53] During normal sleep-wake cycles (i.e., asleep during the night and awake
during the day), the core temperature reaches its zenith in the late afternoon or early evening and
its nadir in the early morning. [8] Adaptation to night-shift work causes a reversal of this pattern.