The following is one in a series of columns illustrating the importance of vital signs to the practice of hospital medicine.
Body temperature is central to the shared human experience. A fever connotes everything from deadly illness to vibrant passion, and its opposite, cold or cooling skin, conjures the specter of mortality. Though life is a fever, the sleep that comes afterward is marked by the departure of its warmth. And, after all, it is a narrow range we inhabit; confusion, unconsciousness, and organ damage set in rapidly as we stray farther and farther from the razor's edge of 37° C. Bodily warmth signifies not merely life, but life's fragility.
Human body temperature must rank as one of the earliest “vital signs” recognized by our ancestors. Being more deeply rooted in the land than their modern descendants, our forebears linked their temperatures to the earth, air and water that defined pre-industrial life.
It was believed that fevers arose directly from the land, born from some vital quality in the air or water itself. The hot or cold winds could easily unbalance the humors in the body, and the stagnant waters of marshlands could throw a patient's delicate physiology out of homeostasis.
In a sense, this was the beginning of environmental medicine, hinging on the observation of fevers among those who inhabited the various climates of Europe, India and China. The term malaria is rooted in the Latin for “bad air,” and the illness was thought to befall those who lived near noxious-smelling swamps and marshes. This was somewhat correct, for many regions of Europe were pestilential hotbeds of Anopheles mosquitos and the Plasmodium organism.
Fevers also taught our medical ancestors the importance of careful observation. The regimented patterns of malarial fevers helped construct the concept of a natural history of disease. Hippocrates described an army of fevers, whose patterns included “semi-tertians, tertians, quartans, quintans, septans, nonans” and noted the severity, time course and prognosis of each.
Fevers are among the most dramatic reminders of core body temperature. But although a physician or parent can diagnose fever in a child by a simple touch of the palm, it was not until the Renaissance that quantifiable measures of body temperature were developed. Such practices were derived from the knowledge that air expands and contracts as it is heated or cooled. When a quantity of water was placed in a long cylinder of glass with a pocket of air sealed in one end, and this tube was then placed in a dish of water, a contraption for approximating temperature could be devised. As the air within expanded or contracted, the air-fluid level seen by an observer rose or fell. The first such devices, known as thermoscopes, were designed by Galileo Galilei (1564—1642) and Santorio Santorio (1561—1636); the latter had the foresight to add a numerical scale to quantify the expansion and contraction of air in the tube.
Santorio's ambitions extended beyond the natural sciences and into the world of medicine. Acknowledging the central place that fever occupies in the natural history of diseases, he designed many of his early thermoscopes for clinical use. When a patient was asked to blow his breath across the closed end of the device, or else place the closed end in the palms or mouth, a vague measure of his body temperature could be assessed. Thus “we can tell if the patient be better or worse,” Santorio assured his readers.
Unfortunately, a thermoscope is also essentially a barometer, much like those that high school students build today in natural science classes. Because the effects of temperature could not be isolated from atmospheric pressure, the thermoscope was naturally limited in its practical utility. Later thermoscopes evolved into the thermometer, which was closed off from the outside atmosphere. Thus the measurement of temperature hinged solely on the properties of the substance within. These early thermometers utilized liquids that, similar to air, expanded with heat and contracted when cold. Candidates for the ideal liquid in the development of thermometers included wine spirits and linseed oil, although mercury soon found its way to the top of the list.
The inventor of the mercury thermometer was Daniel Gabriel Fahrenheit (1686-1736), a glassblower and engineer, as well as the namesake of the Fahrenheit scale. As a major producer of thermometers (among other scientific instruments) in his region, he required a standardized method to calibrate his products. He did this according to 3 points of measurement: The first was a mixture of ice, water and ammonium chloride, which was designated as 0°; the second was a pool of ice water, which was then marked as 32°; and the third was the human body, measured under the armpit or in the mouth, which was thenceforth designated as 96°.
Armpits and mouths are useful in many ways, but their practicality in calibrating thermometers is a dubious practice. Although Fahrenheit was reasonably assured that most subjects' core body temperatures rested at 96°, the matter was not settled. In the 19th century, Carl Wunderlich (1815-1877) trained his scientific skepticism on precisely what constituted an “average” core body temperature. Assembling some 25,000 patients and recording over one million armpit temperatures, he calculated that the average human body temperature should rest at the classic 98.6°F.
This measurement has recently come into doubt, however. More recently (relative to the 19th century), a Harvard study from 1992 declared that the average human body temperature is almost half a degree cooler than Dr. Wunderlich's findings: that is, 98.2°F, with considerable variance according to time of day, gender and perhaps even race. Human beings' lowest temperatures seem to fall at the beginning of the day (around 6 a.m.) and peak in the late afternoon (4 to 6 p.m.). An even newer study has added age as a factor in the variance of human body temperature—in 2005, a Winthrop University Hospital study in Mineola, N.Y., discovered that subjects around the age of 80 had body temperatures considerably lower than younger adults. The study concluded that “older is colder,” finding a single midday mean of subjects to rest at 97.7°F.
Cold temperatures have long been considered hostile to life. Past generations knew that cooler temperatures could preserve many foodstuffs and wines against breakdown and decay. In a fit of genius, Sir Francis Bacon (1561-1626) elected to test this hypothesis during a journey through a winter landscape. While riding in a coach through the snow with the king's physician, Bacon realized that a whole chicken could be preserved all winter by freezing it. He decided to conduct the experiment immediately—he jumped out of the coach, purchased a fowl from a nearby peasant woman, gutted it, and started packing the carcass with snow. As the story goes, the cold was too much for Bacon; he fell ill with pneumonia and died shortly thereafter. There is no mention of whether the chicken was indeed preserved.
However, stories have abounded in history about animals freezing in lakes and ponds, thawing out in spring, and immediately resuming whatever activity they were engaged in before the inconvenient winter set in. Modern accounts have also found a therapeutic use for cold temperatures in human beings. Children have been known to survive harrowing ordeals in sub-freezing temperatures, even long after their hearts have stopped. Upon resuscitation, many such patients have been found to be neurologically healthy, albeit frostbitten.
It is now known that by dropping the core body temperature of patients, in certain scenarios, physicians can utilize the neuroprotective effects of hypothermia to preserve brain tissue. Modern advanced cardiovascular life support courses advocate therapeutic hypothermia for patients who require cardiopulmonary resuscitation after cardiac arrest. Such work has also been undertaken in neonatal encephalopathy, ischemic stroke, traumatic brain injury and neurogenic fever. By decreasing the core body temperature, physicians may decrease metabolic demand for oxygen, interrupt the process of apoptosis in cell death, and even stabilize cell membranes, thus preserving neurons from destruction in critical situations.
In this case, a patient who has scarcely survived a desperate illness may eventually reawaken to a neurologically intact mind. As he recovers, the physician is duly assured that after life's fitful fever, he sleeps well.