Respiratory Volumes
In breathing, the lungs are neither completely filled with air nor completely emptied. Recording the volume movement of air into and out of the lungs is called spirometry. It is done with the help of a spirometer. Generally, the air in the lungs is divided into four different ‘respiratory volumes’ in man.
- Tidal Volume (TV): It is the volume of air inspired or expired during normal breathing. Its value is approximately 500ml per breath.
- Inspiratory reserve volume (IRV): It is the additional volume of air inspired during forceful inspiration. Its value is 2500-3000ml.
- Expiratory reserve volume (ERV): It is the additional volume of air that expired during forceful expiration. This volume averages 1000-1100ml.
- Residual volume (RV): It is the volume of air remaining in the lung even after forceful expiration. It is about 1100-1200ml.
Lung Volumes And Capacities
The intake of air rich in oxygen present in the environment and the release of air rich in carbon dioxide produced within the body is called breathing. Inspiration is inhaling which means taking in air while expiration is exhaling which is giving out air from the body. Respiration is defined as the oxidation of food to release energy. The organs involved in the process of respiration are called respiratory organs. The various respiratory organs/structures of human beings are as follows:
- External nostrils: These are holes that lead into the nasal chamber of the nasal cavity through the nasal passage.
- Nasal chambers: These are two narrow passages lined by pseudostratified epithelial cells secreting mucus.
- Internal nares: These are the openings of the nasal cavity into the nasopharynx.
- Nasopharynx: It is the part of the pharynx through which only air passes.
- Larynx: aka sound/voice box and helps in sound production. The pharynx opens through the larynx into the trachea.
- Trachea: It divides at the level of the 5th thoracic vertebra into the right and left primary bronchi.
- Bronchi: Each bronchus divides into secondary, tertiary bronchi, and bronchioles which further open into the alveoli.
- Alveoli: These are balloon-like structures helping in the exchange of gases. There are around 300 million alveoli in the two lungs.
- Lungs: These are two in number. Alveoli present within the lungs are the main site of the exchange of gases.
On average, a healthy person breathes 12-16 times per minute. The volume of air involved in breathing movements can be estimated by a Spirometer which helps in the clinical assessment of pulmonary functions.