What is Core Temperature? How is it Measured?

7 min read
Nov 22, 2019
Abishek Swaminathen
Abishek SwaminathenN
Medical Content ManagerP
Abishek is the Medical Content Manager of ONiO. A deep love for the life sciences and healthcare, led him to pursue a medical degree. Now in the final year of his bachelor’s, Abishek is extremely passionate about working on the frontiers of healthcare.
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What is Core Temperature? How is it Measured?
Let’s face it. Most of us don’t really think about our body temperature unless we’re having a fever. And even if we do, most of us think that normal body temperature is a static quantity pegged at 36.8°C [98.4°F]. A lot of us are not aware of the fact that our body temperature is always going up and down and even varies from person to person. Over the course of a day, your body temperature fluctuates several times, reflecting the many changes in your body’s state. Different factors like state of consciousness (awake or asleep), physical activity, food intake, stress levels etc impact your body’s temperature and cause tiny upshifts and downshifts. Read ahead to find out what core temperature means and how it’s different to peripheral temperature.

We don’t really need science textbooks to understand that our body works best when it maintains its temperature within a narrow range. From our own experience, we know that when it gets too cold, we try to find a warmer place or put on a jumper. And if it gets a bit too hot, we feel the need to take a dip or turn on the air-conditioning. However, this is not just about feeling comfortable. The reason why we have this preference for a certain “ideal” temperature setting goes much deeper. Our bodies function best within a particular range, that is optimal for enzymatic reactions and metabolic processes. When our body temperature deviates sharply from this range in one direction or the other, it is extremely dangerous and could even result in death.

In a normal state, human body temperature is usually 36.5–37.5 °C [97.7–99.5 °F].

What Is Peripheral Temperature?

When it comes to body temperature, there is more than meets the eye at first glance. The temperature of your body isn’t consistent throughout. The temperature of your body as measured at the level of the surface is different from the temperature at which the innermost structures of your body operate.

Peripheral temperature is the temperature of the body as recorded at the surface-level, i.e on the skin. When we place our hand on someone’s forehead to check if they have a fever, it is their peripheral temperature that we are feeling.

Peripheral body temperature is influenced by exposure to the external environment and by the activity of the autonomic nervous system and the resulting changes in blood flow, under the skin. In a state of sympathetic arousal (i.e during fear, stress or other high-alert states), the blood vessels under the skin constrict (vasoconstriction). This reduces the amount of blood that flows in these blood vessels and therefore, causes a drop in the peripheral temperature. On the other hand, parasympathetic activation results in an increase in the peripheral body temperature.

“Usually, core temperature is 1-2 degrees higher than the temperature at the periphery. At times when the peripheral temperature is increased, due to the adaptive mechanisms described above, the difference between the core and peripheral temperature is at its lowest.”

How Is Peripheral Temperature Measured?

A reading of the peripheral temperature of the body can be obtained from one of these places in the body.

  • Mouth (Oral temperature)
  • Armpit (Axillary temperature)
  • Skin on the forehead (Temporal temperature)

Each of these measurements has its own limitations. For instance, oral temperature readings are influenced by smoking and consumption of hot or cold foods/liquids. So, while these readings might serve their purpose as an indicator of fever or other illness, they aren’t 100% reliable.

What is Core Temperature?

Core temperature (Tc), also referred to as core body temperature, is the temperature of the internal organs, such as the liver, located deep within the body.The human body maintains its core temperature within a very narrow range of 36.5-38.5 ℃ [97.7-101.3 °F]. This is the temperature range that is most conducive for the body’s metabolic processes. The various enzymatic reactions that are vital for survival occur optimally at this temperature.

Usually, core temperature is 1-2 degrees higher than the temperature at the periphery. At times when the peripheral temperature is increased, due to the adaptive mechanisms described above, the difference between the core and peripheral temperature is at its lowest.

Unlike peripheral temperature which undergoes more fluctuations because of close proximity to the external environment, core temperature is maintained relatively constant. When core temperature either drops below the normal lower limit or increases above the upper limit, the body is unable to maintain the integrity of its physiology and it results in serious thermal disorders such as hypothermia or hyperthermia. When the core temperature goes below 33.5 °C [92.3°F] or above 41.5 °C [106.7 °F], the body experiences a rapid decline in normal function causing severe injury to the cells and ultimately resulting in death.

How is Core Temperature Measured?

Core temperature readings can be obtained in a number of ways. Direct measurement of core temperature requires the insertion of a surgical probe and measuring the temperature of the inner organs. However, inserting a probe is an invasive process and is only really feasible in a hospital setting. These are the methods that have traditionally been used to measure/estimate core temperature.

1.Rectal Temperature

Inserting a standard thermometer into the rectum has traditionally been preferred as the most preferable means of measuring core temperature. Usually, readings obtained rectally are about 1°C higher than oral/axillary readings. However, during shock, rectal temperatures fail to accurately correspond to Tc. Another drawback of this method is that it has a protracted response time and falls behind other methods when rapid changes in core temperature need to be picked up.

2. Tympanic Temperature

Using infra-red sensors to measure the temperature of the tympanic membrane of the ear is a commonly used method to calculate Tc. The method is very popular for two reasons. Firstly, the tympanic membrane receives blood from the internal carotid artery, which also supplies blood to the hypothalamus (the brain structure responsible for thermoregulation). Secondly, measuring temperature through the ear is much easier and less invasive, compared to using probes.

However, despite the great promise that this method held, it has recently been proved to be an unreliable method to assess core temperature. The results obtained from this method can be skewed by ear infections or by physical activity. However, this method is still widely used in clinical practice where it is seen as a convenient and reliable option.

3. Oesophageal Temperature

Measuring Tc through oesophageal measurement is preferred because of the location and blood supply of the oesophagus and also because of the high responsiveness of this method. However, with this method, access is the limiting factor. It is difficult to insert the thermistor and the process causes significant discomfort to the subject. Also, it has been shown that readings obtained through this method are not as reliable as those obtained from the pulmonary artery.

4. Urinary Bladder Temperature

This method was thought to be reliable because of the belief that the temperature of the urine corresponds to the body’s core temperature. However, this belief has been shown to be untrue, with the temperature of the urine changing with the rate of urination. So, this method is no longer held to be reliable.

5. Pulmonary Artery Temperature

Pulmonary artery temperature is measured by inserting a catheter. Needless to say, this is not the most convenient and simple means of obtaining a temperature reading. However, pulmonary artery readings are the gold standard for measuring core temperature. They are used in settings where accuracy of the reading is of paramount importance despite the invasiveness of the procedure. Pulmonary artery temperature is considered to be the most accurate representation of Tc because it carries blood directly from the core of the body.

The Future Is Here

Today, we have new technologies that promise to change the way we measure our internal body temperature. With the advent of continuous temperature monitoring, we might no longer have to choose between convenience and accuracy.

The time series data obtained from a continuous temperature monitoring device could have a variety of potential applications, be it in sports research or in monitoring your child’s fever.