Inhalation

Inhalation is the process of drawing air or other substances into the lungs through the nose or mouth as part of respiration. Substances that can be inhaled include gases, vapors, aerosols, and particulates.

The air travels down the upper airways, through the trachea and bronchi, to the bronchioles and alveoli where gas exchange occurs. The alveolar-capillary interface allows rapid transfer of many inhaled substances into the blood, while airway tissues may metabolize or react with irritants.

Medical inhalation is used to deliver drugs directly to the lungs. Devices include metered-dose inhalers, dry powder inhalers, soft mist inhalers, and nebulizers. Proper technique and, when needed, spacers, help maximize dose to the lungs.

Deposition and pharmacokinetics: Particle size and humidity influence where a particle deposits. Larger particles settle in the upper airways; smaller particles reach the alveoli. Absorption is rapid due to large surface area and rich blood supply, allowing quick onset of action or systemic exposure.

Exposure and hazards: Inhalation can also involve hazardous exposures in workplaces or environment: smoke, chemical fumes, dust, and pollutants. Acute exposure may cause irritation or chemical injury; chronic exposure is associated with respiratory disease, reduced lung function, and cancer risk depending on agent.

Other uses: Inhalation is also used in anesthesia and research; inhaled anesthetics induce unconsciousness; oxygen therapy is common; inhaled medications for asthma and COPD are standard.