A History of Temperature
- V. A. Cyr
- Sep 11, 2024
- 9 min read
Welcome to the discussion of the third vital sign: Temperature. After Blood Pressure and Pulse (and Pulse Oximetry), temperature gives a good idea of what is happening within the body. We have all had to sit at the doctor’s office with a probe under our tongue, waiting for the temperature to register. Or we have all had our foreheads scanned to check our temperature before entering a building during the high times of the COVID-19 pandemic. But why does body temperature matter? How can hypothermia or hyperthermia affect the body? Is having a fever always a bad sign?
Definitions
Temperature is the measurement of hotness or coldness. In medicine, temperature is measured in degrees Celsius (°C) or Centigrade. However, degrees Fahrenheit (°F) are commonly used by laypeople in the United States, as well as in cooking and baking.
Types of Tempratures
Core Temperature
A person’s internal temperature is called the core temperature. The normal range is 36.1°C (97°F) to 37.2°C (99°F), which varies depending on various factors (see below). The core temperature must stay around these limits to ensure the internal organs have the proper temperature to function at their best capacities.
Basal Body Temperature
Basal body temperature is defined as the lowest natural body temperature measured after a period of rest (Steward and Raja, 2023). This is most commonly used to measure fertility (see below).
Skin (“Shell”) Temperature
Skin temperature changes depending on the environment in which the person is found. The skin can feel hot or cold while the core temperature is within normal limits.
Temperature Measurement
Temperature is measured using a thermometer. Many different types of thermometers can be used to measure the different locations of the body. Also, temperatures vary depending on the body’s area being measured. The origin of the thermometer is discussed further below. Here, we will discuss the locations of temperature measurement and the modern versions of the thermometer.
Oral Temperature
Oral temperature is taken inside the mouth, under the tongue. The normal range is 35.7-37.3°C.
Rectal Temperature
Rectal temperature is taken in the rectum via the anus. Although this is invasive and uncomfortable for the patient, it does give the closest measurement to the core temperature. It usually ranges from 36.2-37.7°C, slightly higher than the oral temperature.
Here is an example of a modern oral thermometer (BIOS Medical, n.d.). Less expensive versions are often used to measure rectal temperatures in the hospital, as they can only be used for one patient before being discarded. They are differentiated by the colour of the thermometer (e.g., blue is oral, red is rectal).
Tympanic Temperature
Tympanic temperature in the ear canal gives a similar measurement to oral temperature with a range of 35.8-38°C. The probe is a specific length, so it cannot damage the tympanic membrane (ear drum).
This is an example of a modern tympanic thermometer (First Aid Canada, 2022). These are commonly used with babies and infants.
Axillary Temperature
Axillary temperature is done by pressing the probe into the armpit and tightly closing the patient’s arm to the side of their body. This is one of the less invasive ways to measure temperature, but it yields a lower number than oral temperature, with a range of 35.2-36.8°C. Nurses may resort to this method when a patient is not cooperative with invasive methods (i.e., oral or rectal).
A portable thermometer is used in hospitals and medical clinics (Medex+ Supply, n.d.). The probe is attached to a coiled, stretchable line and used on larger vital signs machines. This can measure oral, axillary (armpit), and rectal temperatures.
Temporal Temperature
Temporal temperature can also be measured on the skin using an infrared thermometer. This is usually done on the patient’s forehead or temporal artery (temple on the face). This method is similar to ancillary temperatures as they measure external (skin) rather than internal temperature.
This modern infrared thermometer measures the temperature on the skin (forehead) (CNWTC, n.d.).
Factors Affecting Temperature
Age
Children’s temperatures are slightly higher than adults. This is why it is essential not to overheat a baby with heavy clothing while they sleep. As adults age (over 60), their temperatures drop slightly. Hence, older people are always cold and like to have the heat on all year round.
Activity
During exercise, the body temperature rises. Research shows that it can temporarily increase to 40°C and self-regulate to normal once the exercise is over (Yousef et al., 2023).
Environment
A healthy person can self-regulate their temperature (homeostasis) to ensure their organs function correctly. Being in a hot environment can cause a person to start sweating. Eccrine glands in the skin excrete sweat to put moisture on the outside of the skin and cool the body down. This is similar to when someone pours water on themselves on a sweltering day. In a cold climate, the body will shiver. The body tries to warm itself up by making the muscles “move” (contract) to produce heat. Think of “warming up” before exercising; the muscles become “warm” and move easier.
Fun Fact: an unclothed person can be exposed to temperatures as low as 12.8°C (55°F) or as high as 54.4°C (130°F) in dry air and maintain an almost constant core temperature (Yousef et al., 2023).
Circadian Rhythm
Circadian rhythm is the changes that occur in a person over 24 hours. The sleep-wake cycle has the most impact on a person’s circadian rhythm. Disturbed sleep, insomnia, working shifts (overnights), and jet lag affect temperature regulation. It is normal to feel cold when you are overtired (This is why you fall asleep so easily when relaxing under a warm blanket!). Throughout the day, the body goes from cooler in the morning to warmer in the evening.
Menstrual Cycle
The menstrual cycle of biologically-born females can affect their body temperature. During ovulation, the temperature increases by 0.25-0.5°C (Coiffard et al., 2021). When using the natural family planning method (for birth control or trying to get pregnant), a woman monitors her basal body temperature. When the temperature is at its highest, this indicates the beginning of the ovulation phase and is when the woman is most fertile.
Origins
Early versions of the modern thermometer were invented around the 16th or 17th century. Galileo invented the first thermoscope, a tool with a bulb on one end and a long water-filled tube. The patient puts their mouth around the bulb, and as the air within it warms up, the water in the tube rises or falls depending on the temperature. However, this instrument lacked accuracy because it was affected by atmospheric pressure. Around 1612, Santorio Santorio calibrated the thermoscope and attempted to measure human temperature (Grodzinsky & Sund Levander, 2019). Although having a calibration to estimate temperature better, it was still an impractical tool and would take a very long time to measure. In 1654, Ferdinand II de Medici produced a thermoscope partially filled with alcohol (Grodzinsky & Sund Levander, 2019). This was the first thermometer to depend on the expansion and contraction of a liquid, which was not affected by barometric pressure.
In the 1700s, Gabriel Fahrenheit created the Fahrenheit temperature scale by choosing the freezing point of water (mixed with salt) as 32°F and the boiling point of water as 212°F (Grodzinsky & Sund Levander, 2019). Fahrenheit then found that the temperature inside a healthy human’s mouth was 96°F (Grodzinsky & Sund Levander, 2019). Fahrenheit created two thermometers: one with alcohol and one with mercury, as he discovered that mercury expanded much more than water. Isaac Newton created his thermometer and barometer to measure the environmental temperature based on Fahrenheit and other’s works.
In 1742, Anders Celsius created a scale known as Celcius, where zero represented the boiling point of water, and 100 was the freezing point of water (Grodzinsky & Sund Levander, 2019). Jean-Pierre Christin later reversed the scale to what is used now (i.e., zero is freezing, and 100 is boiling). In 1743, Christin published the design of a mercury thermometer named the "Thermometer of Lyon,” built by the craftsman Pierre Casati (Grodzinsky & Sund Levander, 2019). Research done by Becquerel and Breschet in 1835 established the mean temperature of a healthy adult to be 37°C (98.6 °F) (Grodzinsky & Sund Levander, 2019). By 1863, John Davy had noted the variations in temperature resulting from exercise, food and drink intake, the influence of external temperature, and the differences in body processes in children (Grodzinsky & Sund Levander, 2019).
Sir Thomas Clifford Allbutt, a British physician, created a better design that many doctors quickly used. His thermometer was 15 centimetres long and had a constriction in the capillary tube that held the mercury at its reading after use (Grodzinsky & Sund Levander, 2019). To calibrate the thermometer, the mercury just needed to be shaken. In addition, the temperature reading was available in just five minutes.
The first non-contact radiometer designed to measure body temperature in the inner ear canal was invented in 1964 by Theodor Benzinger (Grodzinsky & Sund Levander, 2019). Benzinger developed a small radiometer to measure as close as possible to the brain without being invasive. In contrast to the costly thermal systems, this device promised a low-cost and reliable means of measuring temperature close to the brain, but without the invasive contact of thermocouples (i.e., electrodes attached to the hypothalamus) (Grodzinsky & Sund Levander, 2019).
Timeline Throughout History: The Thermometer
Uses in Medicine
Abnormal Temperature Findings
Hypothermia is low (hypo) core body temperature (thermia) below 35°C. This is commonly caused by being exposed to freezing climates. It can also be caused by overdosing on certain medications (e.g., beta-blockers, clonidine, anesthetics). In these cases, it is essential to warm the patient slowly to temperature to ensure they do not become hyperthermic.
Mild hypothermia ranges from 32 to 35°C. Symptoms include nausea, fatigue, shivering, pale-dry skin, hypertension and tachycardia (Duong & Patel, 2024).
Moderate hypothermia is a temperature of 28 to 32°C. Symptoms for this stage are lethargy, cognitive decline, arrhythmias (e.g., atrial fibrillation), hypotension and bradycardia (Duong & Patel, 2024). Shivering ceases at these temperatures, and patients feel warmer than they are. This is why some people undress before succumbing to hypothermia.
Severe hypothermia is a body temperature of less than 28°C. At this point, cerebral (brain) blood flow and all vital signs decrease until the patient becomes unresponsive (Duong & Patel, 2024). If the patient declines into cardiorespiratory failure, they will die.
Symptoms of severe hypothermia (Kraft, 2023).
Hyperthermia, or heat illness, is a high (hyper) core body temperature (thermia) of over 40°C. It can be caused by a scorching climate, reactions to medications, or an insect bite (scorpion sting). Types of hyperthermia are heat rash, edema (swelling), syncope (fainting), cramping (muscle cramps), and exhaustion (extreme fatigue) (Yousef et al., 2023). Just like treating someone with hypothermia, the patient needs to be slowly cooled down to ensure they are still stable. Hypothermia and fever are not the same!
Heat stroke is a severe form of heat illness in which temperatures are over 41°C and can damage vital organs.
Malignant hyperthermia is a hereditary (genetic) disorder in which a person has hyperthermia as a reaction to anesthesia (Watt & McAllister, 2023).
Here are the differences between symptoms of heat exhaustion (left) and heat stroke (right) (National Weather Service, n.d.).
Pyrexia (Fever) is a temperature above the normal range (usually over 38°C). Internal (e.g., infection) or external (e.g., immunization) body factors can cause a fever (Balli et al., 2023). A fever is the immune system’s way of fighting off the unknown factor (e.g., infection or vaccine) in your body. This is why a fever within 24 hours of receiving a vaccine is very common and is not a sign of a complication. Symptoms often depend on the type of infectious agent (i.e., virus, bacterial, etc.).
Hyperpyrexia is a high fever greater than 41°C that occurs in patients with severe infections (Balli et al., 2023).
There are also several types of fevers: continuous, remittent, intermittent, undulant, biphasic, and recurrent.
Here are examples of common causes of each type of fever (AMBOSS, 2023).
I know of nurses who can feel if someone has a fever with the back of their hand. Although this is not an accurate measurement method, it could prompt the nurse to investigate more. What do you think: is temperature important?
– V. A. Cyr
References
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