Inhalation is the involuntary process of drawing air into the body to sustain life. Because the respiratory system is constantly exposed to the surrounding atmosphere, it acts as an open gateway for materials to enter the body. This necessary exchange means the inhalation process must contend with both macroscopic foreign objects and invisible, microscopic toxins present in the air.
The Physical Mechanics of Breathing In
The act of breathing air into the lungs, known as inspiration, is driven by muscular contraction that creates a pressure difference. The primary muscle responsible for this is the diaphragm, a large, dome-shaped sheet of muscle situated beneath the lungs. When the diaphragm contracts, it flattens and moves downward toward the abdominal cavity, effectively increasing the vertical volume of the chest space. Simultaneously, the external intercostal muscles located between the ribs contract, pulling the rib cage upward and outward to further expand the thoracic cavity.
This expansion causes the lungs to stretch, increasing their internal volume. This increase in volume leads to a decrease in pressure inside the lungs, causing air to rush in from the atmosphere to equalize the difference. The inhaled air travels through the nose or mouth, down the trachea, and branches into the bronchi, reaching the deepest parts of the respiratory system. This mechanism provides a pathway for harmful substances to bypass the body’s natural defenses.
Hazards of Foreign Object Aspiration
Aspiration is defined as the entry of foreign materials, such as food, liquids, or small objects, into the lower respiratory tract below the level of the vocal cords. This event can lead to two distinct, serious medical concerns: acute airway obstruction or aspiration pneumonia. Acute obstruction, commonly referred to as choking, occurs when a solid object lodges in the larynx or trachea, potentially causing a complete blockage of airflow and rapid asphyxiation. In the case of children, who are particularly vulnerable due to immature swallowing coordination and smaller airways, objects like nuts, seeds, or small toy parts are common culprits.
Aspiration pneumonia involves inhaling stomach contents, oral secretions, or liquids into the bronchial tree and lung tissue. This material can introduce bacteria or cause a severe inflammatory reaction known as pneumonitis. Individuals with difficulty swallowing (dysphagia) or those with impaired consciousness are at higher risk for this complication.
Toxic Risks of Air Pollutant Inhalation
Beyond physical objects, the respiratory system faces a constant threat from invisible, toxic substances that cause chemical damage or systemic harm. One category of concern involves toxic gases, such as carbon monoxide, which displaces oxygen in the bloodstream, leading to suffocation at the cellular level despite continued breathing. Volatile organic compounds (VOCs) are another group of airborne chemicals emitted from household products and industrial sources, which can cause irritation of the eyes, nose, and throat, and may lead to damage in the central nervous system with prolonged exposure. Some VOCs, like formaldehyde, are also recognized as potential human carcinogens.
A major modern health concern involves particulate matter (PM), which is classified by size, with PM10 and PM2.5 being the most relevant to lung health. PM2.5 refers to fine particles less than 2.5 micrometers in diameter, which is small enough to travel deep into the lung’s gas-exchange regions and even cross into the bloodstream. The size of the particle determines where it lodges, with larger PM10 particles generally depositing in the upper airways, causing irritation. The chemical makeup of these particles, which can include metals and organic compounds from sources like wildfire smoke or vehicle exhaust, can trigger inflammatory responses and oxidative stress in the lung tissue.
Chronic inhalation of these microscopic pollutants is linked to the development and exacerbation of respiratory and cardiovascular diseases. Long-term exposure to PM2.5 is associated with the onset of chronic obstructive pulmonary disease (COPD), reduced lung function growth in children, and increased risk of lung cancer. The inflammatory signals initiated in the lungs can also affect the heart, increasing the risk of heart attacks and abnormal heart rhythms.