Citation:

Pleil, J., M. Davis, AND C. Matty. The physics of human breathing: flow, timing, volume and pressure parameters for normal, on-demand, and ventilator respiration. Journal of Breath Research. Institute of Physics Publishing, Bristol, Uk, 15(4):NA, (2021). https://doi.org/10.1088/1752-7163/ac2589

Impact/Purpose:

This article is an overview of the physics of human breathing, including parameters for normal breathing and breathing under special circumstances, such as artificial atmospheres and medical interventions to provide oxygen needed by cells and tissues.  Although humans have evolved to breathe 1-atmosphere with 21% O2, the human systems biology is adaptable to the immediate environment (altitude, pressure, CO2). Humans can quickly adapt to small changes in external conditions or O2 demand unconsciously and can also consciously modify breathing for singing, swimming, breath holding, and coughing.  Technology has been developed to protect humans from inhaling contaminants in the air, to provide adequate air flow and concentrations for flight, travel, and sport activities, and for medical supplementation of O2 within the construct of normal breathing for trauma or disease intervention. Although much of contemporary breathing research involves the chemistry and metabolism of breathing, the physics of breathing described herein is also an important factor in preservation of human life. This article has long term importance of helping readers understand the physics of breathing and issues that may arise when normal breathing is compromised, requiring intervention. This article will be of interest to the breath community, health specialists, the general public, and local communities.

Description:

Normal breathing for healthy humans is taken for granted; it occurs without conscious effort using ambient (1-atmosphere) pressure with 21% oxygen concentration.  The body automatically adjusts for stress, exercise, altitude, and mild disease by increasing volume and frequency of breathing.   Longer term adaptations for exercise and altitude include increases in red blood cell counts and higher concentrations of capillaries in muscle tissue.  When more challenging external environmental conditions or pulmonary illnesses exceed the capability for these adaptations, the human system requires technology to maintain sufficient ventilation to preserve life. On the environmental side there are two conditions to be addressed:  toxicity of the surrounding atmosphere, and changes in external pressure and oxygen concentration.  On the medical side, mechanisms for assisting breathing include oxygen supplementation at ambient pressure, positive pressure/flow without additional oxygen, or a combination of both.  This overview describes the various technologies applied to maintaining a safe breathing environment.  Topics for environmental intervention include filter-based and flowing air-supply masks for toxic environments (occupational and laboratory protection), and on-demand gas supply systems for firefighters, underwater (SCUBA), and altitude (high performance aircraft, spacecraft) applications.  The topics for medical intervention include nasal cannula, continuous positive airway pressure (CPAP), and medical ventilators.  The primary purpose of this article is to provide a basic understanding of normal human breathing and the adaptation of breathing in different environments using available technologies. 

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