Inhalation
Inhalation happens when air or other gases enter the lungs.
Inhalation of air
Inhalation of air, as part of the cycle of breathing, is a vital process for all human life. The process is autonomic and does not need conscious control or effort. However, breathing can be consciously controlled or interrupted.Breathing allows oxygen to enter the lungs, from where it can be absorbed into the bloodstream.
Other substances – accidental
Examples of accidental inhalation includes inhalation of water, smoke, food, vomitus and less common foreign substances.Other substances – deliberate
Recreational use
Nitrous oxide has been used recreationally since 1899 for its ability to induce euphoria, hallucinogenic states and relaxation, and is legal in some countries.Helium can be inhaled to give the voice a reedy, duck-like quality, but this can be dangerous as the gas is an asphyxiant and displaces the oxygen needed for normal respiration.
Various illegal gaseous, vapourised or aerosolized recreational drugs exist, and are classed as inhalants.
Medical use
Diagnostic
Various specialized investigations use the inhalation of known substances for diagnostic purposes. Examples include pulmonary function testing and diagnostic radiology.Therapeutic
Gases and other drugs used in anaesthesia include oxygen, nitrous oxide, helium, xenon, volatile anaesthetic agents. Medication for asthma, croup, cystic fibrosis and some other conditions.Mechanism
Inhalation begins with the contraction of the muscles attached to the rib cage; this causes an expansion in the chest cavity. Then takes place the onset of contraction of the thoracic diaphragm, which results in expansion of the intrapleural space and an increase in negative pressure according to Boyle's law. This negative pressure generates airflow because of the pressure difference between the atmosphere and alveolus.The inflow of air into the lungs occurs via the respiratory airways. In health, these airways begin with the nose. It is possible to begin with the mouth, which is the backup breathing system. However, chronic mouth breathing leads to, or is a sign of, illness, and there is no mucus in the mouth to trap unwanted substances unlike the nostrils. They end in the microscopic dead-end sacs always opened, though the diameters of the various sections can be changed by the sympathetic and parasympathetic nervous systems. The alveolar air pressure is therefore always close to atmospheric air pressure at rest, with the pressure gradients that cause air to move in and out of the lungs during breathing rarely exceeding 2–3 kPa.
Other muscles that can be involved in inhalation include: