Measuring breathing rate
Breathing rate is the number of breaths taken by a person within a specific amount of time, most commonly within 60 seconds. To measure breathing rate, use a watch to time 60 seconds and count the number of breaths taken within the 60 seconds. This is the breathing rate.
The respiratory cycle consists of inspiration (breathing in), expiration (breathing out) and a very short respiratory pause.
In normal adults, the breathing rate is 12–18 breaths per minute. A newborn breathes 60 times per minute. It is always 4–5 times less than heart rate. Slight increase in CO2 content in blood increases breathing rate.
Inspiration and expiration
The respiratory cycle consists of inspiration (breathing in), expiration (breathing out) and a very short respiratory pause. In normal adults, the breathing rate is 12–18 breaths per minute.
Inspiration (or inhalation) is the result of increase in the size of thoracic cavity and this increase is due to the combined action of the ribs and the diaphragm. The ribs are moved upward and outward by the muscles (intercostal muscles) stretched between them, thus enlarging the chest cavity all around.
The diaphragm is a sheet of muscular tissue, which normally remains arched upward like a dome, towards the base of the lungs. On contraction, it falls or flattens from the dome–shaped outline to an almost horizontal plane and thus contributes to the enlargement of the chest cavity lengthwise. As the diaphragm flattens, it presses the organs inside the abdomen and with the abdominal muscles relaxed, the abdominal wall moves outwards. When the thoracic (chest) cavity increases in size, its internal pressure is decreased. The lungs expand and as a result, the pressure inside the lungs is lowered below the atmospheric pressure. The outside air, which is at a greater pressure, rushes in to equalize the pressure.
Expiration (or exhalation) is the result of reverse movements of the ribs and diaphragm. The other set of intercostal muscles contract and pull the ribs down and inward. The diaphragm is relaxed and is moved upwards to its domelike outline as a result of the pressure of the abdominal contents when the muscles in the abdominal wall contract. As a consequence of the above–mentioned movements of ribs and diaphragm, the cavity of the thorax is diminished and the lungs are compressed, forcing the air out into the atmosphere.
The respiratory cycle consists of one inspiration followed by one expiration. The volume of air that enters or leaves during a single respiratory cycle is called the tidal volume. Tidal volume is typically 500 milliliters, meaning that 500 milliliters of air enters during inspiration and the same amount leaves during expiration.