Normal Breathing Pattern (Normal Respiration Cycle)

Modern physiology textbooks suggest the following parameters of the normal breathing pattern (normal respiration) at rest for healthy subjects:
- inhalation is 1.5-2 s
- exhalation is 1.5-2 s
- automatic pause of almost no breathing is 2 s
- tidal volume (the depth of inhalation) is 500-600 ml
- breathing frequency (or Rf - respiratory frequency or respiratory rate) is 10-12 breaths/min.

The international physiological norm for the breathing rate at rest is 6 L/min (for a 70-kg man). Normal stress-free breath holding time after usual exhalation (that correlates with body-oxygen content) is 40 s. References for medical textbooks that provide these values are below.

Normal respiration cycle chart

This chart shows 4 breathing cycles of the normal respiration pattern for normal subjects:
inhalation (the upward lines), exhalation (the downward lines) and automatic pause
(the almost horizontal lines) accompanied by relaxation of all breathing muscles.

Features of the normal breathing pattern

Apart from numbers, there are many important qualities of normal respiration. If you have healthy friends or relatives, you can easily observe that their breathing is slow, regular, nasal only, diaphragmatic, invisible and inaudible (no panting, no wheezing, no sighing, no yawning, no sneezing, no coughing, no deep inhalations or exhalations). They take small inhalations and then relax for the exhalation. The exhalation is followed by an automatic pause (or period of no breathing) of about 2 s. The normal body oxygen level is about 40 s for the medical norm and 60 s for the Buteyko norm.

Most of the job of inhalation (up to 80-90%) is done by the diaphragm, the main breathing muscle. Exhalation is passive and is accompanied by the relaxation of all breathing muscles. These parameters of the normal respiration cycle were established about 100 years ago. Published medical articles found that in the 1920-1930's, normal subjects were breathing even less air at rest than the medical norm (6 L of air per minute). You can find these 1920-1930's studies on this page devoted to Hyperventilation: Present in Over 90% of Normal People with 24 medical publications.

Reference pages: Breathing norms and medical facts:
- Breathing norms: Parameters, graph, and description of the normal breathing pattern
- 6 breathing myths: Myths and superstitions about breathing and body oxygenation (prevalence: over 90%)
- Hyperventilation: Definitions of hyperventilation: their advantages and weak points
- Hyperventilation syndrome: Western scientific evidence about prevalence of chronic hyperventilation in patients with chronic conditions (37 medical studies)
- Normal minute ventilation: Small and slow breathing at rest is enjoyed by healthy subjects (14 studies)
- Hyperventilation prevalence: Present in over 90% of normal people (24 medical studies)
- HV and hypoxia: How and why deep breathing reduces oxygenation of cells and tissues of all vital organs
- Body-oxygen test (CP test) : How to measure your own breathing and body oxygenation (two in one) using a simple DIY test
- Body oxygen in healthy: Results for the body-oxygen test for healthy people (27 medical studies)
- Body oxygen in sick : Results for the body-oxygen test for sick people (14 medical studies)
- Buteyko Table of Health Zones: Clinical description and ranges for breathing zones: from the critically ill (severely sick) up to super healthy people with maximum possible body oxygenation
- Morning hyperventilation: Why people feel worse and critically ill people are most likely to die during early morning hours

References: pages about CO2 effect:
- Vasodilation: CO2 expands arteries and arterioles facilitating perfusion (or blood supply) to all vital organs
- The Bohr effect: How and why oxygen is released by red blood cells in tissues
- Cell oxygen levels: How alveolar CO2 influences oxygen transport
- Oxygen transport: O2 transport is controlled by vasoconstriction-vasodilation and the Bohr effects, both of which rely on CO2
- Free radical generation: Reactive oxygen species are produced within cells due to anaerobic cell respiration caused by cell hypoxia
- Inflammatory response: Chronic inflammation in fueled by the hypoxia-inducible factor 1, while normal breathing reduces and eliminates inflammation
- Nerve stabilization: People remain calm due to calmative or sedative effects of carbon dioxide in neurons or nerve cells
- Muscle relaxation: Relaxation of muscle cells is normal at high CO2, while hypocapnia causes muscular tension, poor posture and, sometimes, aggression and violence
- Bronchodilation: Dilation of airways (bronchi and bronchioles) is caused by carbon dioxide, and their constriction by hypocapnia (low CO2)
- Blood pH: Regulation of blood pH due to breathing and regulation of other bodily fluids
- CO2: lung damage: Elevated carbon dioxide prevents lung injury and promotes healing of lung tissues
- CO2: Topical carbon dioxide can heal skin and tissues
- Synthesis of glutamine in the brain, CO2 fixation, and other chemical reactions
- Deep breathing myth: Ignorant and naive people promote the idea that deep breathing and breathing more air at rest is beneficial for health
- Breathing control: How is our breathing regulated? Why hypocapnia makes breathing uneven, irregular and erratic.

Medical textbooks references

Ganong W, Review of medical physiology; 15-th ed., 1995, Prentice Hall Int., London.

Guyton A, Physiology of the human body; 6-th ed., 1984, Suanders College Publ., Philadelphia.

McArdle W, Katch F, Katch V, Essentials of exercise physiology (Second edition); Lippincott, Williams and Wilkins, London 2000.

Straub N, Section V, The Respiratory System, in Physiology, editors. R Berne & M Levy, 4-th edition, Mosby, St. Louis, 1998.

Summary of values useful in pulmonary physiology: man. In the Section: Respiration and Circulation, ed. by P Altman & D Dittmer, 1971, Bethesda, Maryland (Federation of American Societies for Experimental Biology).

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