Temperature Changes of Nostrils During Breathing
Experiment number : 4344
Goal of experiment
We will observe how the temperature changes around nostrils during inhalation and exhalation.
The primary way air enters the body of a healthy person is the nasal cavity where the incoming air is filtered by the ciliated epithelium, thus getting rid of dust and impurities. From a purely physical point of view, the nasal cavity conchae humidify the air and heat it to a temperature close to the internal temperature of the body before it enters the lungs. Vice versa, when the air leaves the body, it is partially cooled so that the body does not lose a large amount of heat by exhalation. The nasal cavity thus acts as a kind of a heat exchanger.
Nonetheless, at normal room temperature, exhaled air is warmer than inhaled air, and this is what we will visualize with a thermal imaging camera. More precisely, we will not measure the temperature of the air flow directly, rather of the mucous membrane of the nasal cavity, which is warmed (cooled) by the exhaled (inhaled) air.
Thermal imaging camera, a volunteer.
The volunteer is asked to breathe calmly and deeply and the opening of the nostrils is monitored with a thermal imaging camera.
The video below illustrates a successful execution of the experiment. It can be seen that during inhalation (when some air at room temperature enters the nasal cavity), the nostrils cool down, and during exhalation (when the now heated air leaves the body), the nostrils temperature is slightly higher than body temperature.
In this video, the FLIR i7 thermal imaging camera was used. The temperature range of the colour scheme was set in the interval of 34 °C and 40 °C, the emissivity was ε = 0.95.
The described experiment may not work at very high temperatures (e.g. 35 °C and more), when the temperature of the inhaled air is close to the temperature of the human body and therefore the air temperature in the respiratory system.
Because the nasal mucosa is moist, it is measurably cooled not only by the entry of cold air into the nasal cavity, but also by any airflow through the cavity, which accelerates evaporation from the cavity surface (see more in How Airflow Accelerates the Evaporation of Liquids).
The experiment enables cross-curricular interconnection of physics and biology, where the processes ensuring the functioning of the human body are measured and explained from a physical point of view.
Due to the above mentioned cross-curricular connection, in physics class we can also deal with questions that belong to biology – for example why breathing through the nose is better and especially healthier than breathing through the mouth. Students can find the answer, for example, in the theoretical introduction to this experiment – it is clear that when breathing through the mouth, there is no filtering or preheating of the air before it enters the lungs, and likewise, the air is not cooled before it leaves the respiratory system and thus dissipates a large amount of heat from the body.
It should be emphasized that the thermal imaging camera does not measure the temperature of the air itself, but the surface temperature of the inside of the nostrils. For direct measurement of the temperature of inhaled and exhaled air, point temperature sensors can be recommended, but care should be taken when using them, especially if there is direct contact of the nasal mucosa with the sensor.
We must take great precaution when selecting a volunteer! In any case, avoid selecting an “involuntary volunteer” who decides to participate in the experiment under pressure (from a teacher, classmates, etc.). Having a group of classmates watch one’s own nostrils is not exactly an activity that every student would appreciate.
Thermal imaging camera basics – link to PDF
In this experiment, a thermographic measurement is used. The theory of thermography and basic recommendation and procedures that can help you obtain more accurate and undistorted results can be found in Experiments with thermal imaging camera (in Czech only).