Instance of using SI - Human body temperature

It is known to all that human is endotherm. which means that human can control the body temperature at a steady level. But what is the normal body temperature of human? Sometimes we will have a fever. But what is the definition of it? In this post we will introduce these. (PS: The main unit in this post is °C, and with K as comment. So u can see how to use SI temperature units correctly.)

Normal human body temperature, also known as normothermia or euthermia, depends upon the place in the body at which the measurement is made, the time of day, as well as the activity level of the person. Nevertheless, commonly mentioned typical values are:

Oral (under the tongue): 36.8 ± 0.4 °C (309.95 ± 0.4 K)

Internal (rectal, vaginal): 37.0 °C (310.15 K)

Different parts of the body have different temperatures. Rectal and vaginal measurements taken directly inside the body cavity are typically slightly higher than oral measurements, and oral measurements are somewhat higher than skin measurements. Other places, such as under the arm or in the ear, produce different typical temperatures. Although some people think of these averages as representing the normal or ideal temperature, a wide range of temperatures has been found in healthy people.

The body temperature of a healthy person varies during the day by about 0.5 °C (0.5 K) with lower temperatures in the morning and higher temperatures in the late afternoon and evening, as the body's needs and activities change. Other circumstances also affect the body's temperature. The core body temperature of an individual tends to have the lowest value in the second half of the sleep cycle; the lowest point, called the nadir, is one of the primary markers for circadian rhythms. The body temperature also changes when a person is hungry, sleepy, or cold.

Methods of measurement

Taking a person's temperature is an initial part of a full clinical examination. There are various types of medical thermometers, as well as sites used for measurement, including:

• In the anus (rectal temperature)
• In the mouth (oral temperature)
• Under the arm (axillary temperature)
• In the ear (tympanic temperature)
• In the vagina (vaginal temperature)
• In the bladder
• On the skin of the forehead over the temporal artery

 The range of a medical thermometer is 35~42 °C, with the accuracy of 0.1 °C.

Variations

Temperature control (thermoregulation) is part of a homeostatic mechanism that keeps the organism at optimum operating temperature, as it affects the rate of chemical reactions. In humans, the average internal temperature is 37.0 °C (310.15 K), though it varies among individuals. However, no person always has exactly the same temperature at every moment of the day. Temperatures cycle regularly up and down through the day, as controlled by the person's circadian rhythm. The lowest temperature occurs about two hours before the person normally wakes up. Additionally, temperatures change according to activities and external factors.

In addition to varying throughout the day, normal body temperature may also differ as much as 0.5 °C (0.5 K) from one day to the next, so that the highest or lowest temperatures on one day will not always exactly match the highest or lowest temperatures on the next day.

Normal human body temperature varies slightly from person to person and by the time of day. Consequently, each type of measurement has a range of normal temperatures. The range for normal human body temperatures, taken orally, is 36.8±0.5 °C (309.95±0.5 K). This means that any oral temperature between 36.3 and 37.3 °C (309.45 and 310.45 K) is likely to be normal. The normal human body temperature is often stated as 36.5~37.5 °C (309.65~310.65 K).

Natural rhythms

Body temperature normally fluctuates over the day, with the lowest levels around 04:00. and the highest in the late afternoon, between 16:00 and 18:00 (assuming the person sleeps at night and stays awake during the day). Therefore, an oral temperature of 37.3 °C (310.45 K) would, strictly speaking, be a normal, healthy temperature in the afternoon but not in the early morning. An individual's body temperature typically changes by about 0.5 °C (0.5 K) between its highest and lowest points each day.

Body temperature is sensitive to many hormones, so women have a temperature rhythm that varies with the menstrual cycle, called a circamensal rhythm. A woman's basal body temperature rises sharply after ovulation, as estrogen production decreases and progesterone increases. Fertility awareness programs use this predictable change to identify when a woman can become pregnant. During the luteal phase of the menstrual cycle, both the lowest and the average temperatures are slightly higher than during other parts of the cycle. However, the amount that the temperature rises during each day is slightly lower than typical, so the highest temperature of the day is not very much higher than usual. Hormonal contraceptives both suppress the circamensal rhythm and raise the typical body temperature by about 0.6 °C (0.6 K).

Temperature also varies with the change of seasons during each year. This pattern is called a circannual rhythm. Studies of seasonal variations have produced inconsistent results. People living in different climates may have different seasonal patterns.

Increased physical fitness increases the amount of daily variation in temperature.

With increased age, both average body temperature and the amount of daily variability in the body temperature tend to decrease. Elderly patients may have a decreased ability to generate body heat during a fever, so even a somewhat elevated temperature can indicate a serious underlying cause in geriatrics.

Measurement methods

Different methods used for measuring temperature produce different results. The temperature reading depends on which part of the body is being measured. The typical daytime temperatures among healthy adults are as follows:

·         Temperature in the anus (rectum/rectal), vagina, or in the ear (otic) is about 37.5 °C (310.65 K)

·         Temperature in the mouth (oral) is about 36.8 °C (309.95 K)

·         Temperature under the arm (axillary) is about 36.5 °C (309.65 K)

Generally, oral, rectal, gut, and core body temperatures, although slightly different, are well-correlated, with oral temperature being the lowest of the four. Oral temperatures are generally about 0.4 °C (0.4 K) lower than rectal temperatures.

Oral temperatures are influenced by drinking, chewing, smoking, and breathing with the mouth open. Cold drinks or food reduce oral temperatures; hot drinks, hot food, chewing, and smoking raise oral temperatures.

Axillary (armpit), tympanic (ear), and other skin-based temperatures correlate relatively poorly with core body temperature. Tympanic measurements run higher than rectal and core body measurements, and axillary temperatures run lower. The body uses the skin as a tool to increase or decrease core body temperature, which affects the temperature of the skin. Skin-based temperatures are more variable than other measurement sites. The peak daily temperature for axillary measurements lags about three hours behind the rest of the body. Skin temperatures are also more influenced by outside factors, such as clothing and air temperature.

Specific temperature concepts

There are some specific temperature concepts when the body temperature is abnormal: fever, hyperpyrexia, hyperthermia, and hypothermia.

Fever:

A temperature setpoint is the level at which the body attempts to maintain its temperature. When the setpoint is raised, the result is a fever. Most fevers are caused by infectious disease and can be lowered, if desired, with antipyretic medications.

An early morning temperature higher than 37.2 °C (> 310.35 K) or a late afternoon temperature higher than 37.7 °C (>310.85 K) is normally considered a fever, assuming that the temperature is elevated due to a change in the hypothalamus's setpoint. Lower thresholds are sometimes appropriate for elderly people. The normal daily temperature variation is typically 0.5 °C (0.5 K), but can be greater among people recovering from a fever.

An organism at optimum temperature is considered afebrile or apyrexic, meaning "without fever". If temperature is raised, but the setpoint is not raised, then the result is hyperthermia.

Hyperpyrexia:

Hyperpyrexia is a fever with an extreme elevation of body temperature greater than or equal to 41.5 °C (314.65 K). Such a high temperature is considered a medical emergency as it may indicate a serious underlying condition or lead to significant side effects. The most common cause is an intracranial hemorrhage. Other possible causes include sepsis, Kawasaki syndrome, neuroleptic malignant syndrome, drug effects, serotonin syndrome, and thyroid storm. Infections are the most common cause of fevers, however as the temperature rises other causes become more common. Infections commonly associated with hyperpyrexia include roseola, rubeola and enteroviral infections. Immediate aggressive cooling to less than 38.9 °C (312.05 K) has been found to improve survival. Hyperpyrexia differs from hyperthermia in that in hyperpyrexia the body's temperature regulation mechanism sets the body temperature above the normal temperature, then generates heat to achieve this temperature, while in hyperthermia the body temperature rises above its set point due to an outside source.

Hyperthermia:

Hyperthermia is an example of a high temperature that is not a fever. It occurs from a number of causes including heatstroke, neuroleptic malignant syndrome, malignant hyperthermia, stimulants such as amphetamines and cocaine, idiosyncratic drug reactions, and serotonin syndrome.

Hypothermia:

In hypothermia, body temperature drops below that required for normal metabolism and bodily functions. In humans, this is usually due to excessive exposure to cold air or water, but it can be deliberately induced as a medical treatment. Symptoms usually appear when the body's core temperature drops by 1~2 °C (1~2 K) below normal temperature.

Here is the temperature classification of human

• Hypothermia:  <35.0 °C (308.15 K)
• Normal: 36.5~37.5 °C (309.65~310.65 K)
• Fever: >37.5 or 38.3 °C (310.65 or 311.45 K)
• Hyperthermia: >37.5 or 38.3 °C (310.65 or 311.45 K)
• Hyperpyrexia: >40.0 or 41.5 °C (313.15 or 314.65 K)

Note: The difference between fever and hyperthermia is the underlying mechanism.
Different sources have different cuts offs for fever,  hyperthermia and hyperpyrexia.

In this post we learned a lot. not only do we knew about the human body temperature, but also we learned about how can we use SI temperature units - K and °C correctly. After reading the post, comment your highest fever temperature in °C and K please. Thank you!