Respiration

"Breathe in through nose, out through mouth. Wax on, wax off. Don't forget to breathe, very important."
--Myagi (The Karate Kid)

Discussion about placing masks over one's nose and mouth to prevent the inhalation of airborne pathogens must be grounded in basic understanding of breathing and respiration. In grade school and high school science class, we learn that respiration is a central process of life. To produce energy, organizations take in oxygen and glucose, and release carbon dioxide and water.

Humans obtain oxygen by inhaling air. Ambient air contains approximately 21% oxygen by volume--more than enough for respiratory function under normal conditions. When we inhale, muscular contraction in the chest area causes the thoracic cavity to expand. Expansion causes air pressure inside the lungs to decrease, which permits outside air to be sucked through the nose and/or mouth down the esophagus and into the lungs. 

Millions of tiny air sacs in the lungs connected to small blood vessels provide a medium for exchange, trading oxygen from the air for carbon dioxide in the blood. Water from surrounding tissue is also partially vaporized in the air sacs.

When we exhale, the chest area muscles work in the opposite direction and expand. The thoracic cavity contracts, causing air pressure inside the lungs to increase, thereby expelling air back out through the esophagus, nose, and mouth into the air. The 'spent' air includes the respiratory bi-products of carbon dioxide and water in addition to leftover oxygen from the inhaled air that did not take part in the exchange.

Several factors influence respiratory efficiency. Chronic physiological conditions related to the blood (e.g., low hemoglobin) or to the lungs (e.g., COPD) can reduce capacity for respiratory exchange. 

Physical exertion can also challenge respiratory capacity, as exertion increases demand for oxygen and produces more carbon dioxide for disposal. To compensate, the cardiopulmonary system ramps up through heavier, more frequent breathing and higher heart rates.

The external environment influences respiratory efficiency as well. Smoke-filled air, for instance, carries less oxygen and more particulate matter, both of which can impair respiratory exchange.

Basic concepts about respiration pertain to the masking context--something we'll discuss in a future post.