Generality
Respiratory rate is defined as the number of breaths taken by an individual within one minute.
Every single respiratory cycle is composed of a phase of inspiration (a little shorter) and an expiratory phase, in addition to two pauses of which a very short one at the end of inspiration and a longer one (about 1/5 of the total duration of act) at the end of the exhalation.
Normal values
The respiratory rate at rest is 12-16 acts per minute. During strenuous exercise this frequency can reach 35-45 breaths per minute.
Not surprisingly, in increases in heart rate there is a parallel rise in the respiratory rate, with a relationship of about one breath every 4-5 cardiac contractions.
Children and babies
In the newborn and throughout the first year of age, the respiratory rate is about 44 acts per minute; subsequently it decreases progressively, so that at 5 years it is equal to about 20-25 breaths per minute. In the adult, as anticipated, it is around 14 respiratory cycles per minute and increases again, although to a modest extent, in the elderly.
Curiosity
The volume of air entering and leaving the lungs during a single breath at rest is called the tidal volume. Multiplying this data by the respiratory rate, we obtain the so-called minute ventilation; to learn more, see: spirometry.
Causes of impaired respiratory rate
As well as in relation to muscle activity, respiratory rate values can vary according to body size, age, sex, health status, digestive activity, environmental temperature and body position (they decrease in position horizontal).
Higher in women than in men, respiratory rate also increases in febrile states and in abdominal and thoracic conditions that limit the depth of breath.
Tachypnea is defined as an increase in the respiratory rate beyond the physiological limits (> 20 cycles per minute in the adult).
The frequency of breaths also increases in rarefied oxygen environments, such as those typical of high mountains.
Tachypnea and Hyperpnea
In the presence of tachypnea (or polypnea) the breaths become shorter, while in the so-called hyperpnea the acts increase in depth (the two conditions are often - but not necessarily - associated).
In addition to the causes already mentioned, tachypnea can accompany the last months of pregnancy, hyperthyroidism, anemia, heart failure, peritonitis and pain syndromes of the pleura, peritoneum or chest wall (in these cases it represents a mechanism compensatory to the reduced depth of breath, adopted by the patient to protect himself from pain).
Finally, for elements of an emotional nature, during the physical examination many patients have respiratory frequencies higher than the usual ones.
bradypnea
Bradypnea is defined as a decrease in respiratory rate below physiological limits (<12 breaths per minute in adults, <20 / min in 3-12 years, <25 / min in 1-3 years, <30 / min under the age of one).
Absolutely physiological occurrence during sleep, the reduction of the respiratory frequency is typically observed in opioid or alcohol intoxication, in case of brain tumors and in metabolic alkalosis.
