Hypocapnia (Hypocarbia): Definition, Symptoms and Treatment
Definition of hypocapnia (hypocarbia)
Hypocapnia (hypocapnea, also known as hypocarbia) is defined as a deficiency of carbon dioxide in the arterial blood. Most medical sources define hypocapnia as less than 35 mm Hg for partial CO2 pressure in the arterial blood. The arterial CO2 value for normal breathing at rest is 40 mm Hg (or about 5.3% CO2 partial pressure at sea level).
Another term "alveolar hypocapnia" describes low CO2 levels in the alveoli of the lungs. Severe alveolar hypocapnia generally leads arterial hypocapnia, which causes respiratory alkalosis. (People with lung conditions often have arterial hypercapnia (elevated CO2) caused by alveolar hypocapnia since alveolar hypocapnia immediately causes bronchospasm.) These studies (see the Table below) show that alveolar hypocapnia is very common for many chronic diseases. Most of these patients (with heart disease, diabetes, cancer, and so forth) have arterial hypocarbia as well. Furthermore, this Table also identifies the cause of hypocapnia.
Minute ventilation rates (chronic diseases)
click below for abstracts
|Normal breathing||6 L/min||-||Medical textbooks|
|Healthy Subjects||6-7 L/min||>400||Results of 14 studies|
|Heart disease||15 (±4) L/min||22||Dimopoulou et al, 2001|
|Heart disease||16 (±2) L/min||11||Johnson et al, 2000|
|Heart disease||12 (±3) L/min||132||Fanfulla et al, 1998|
|Heart disease||15 (±4) L/min||55||Clark et al, 1997|
|Heart disease||13 (±4) L/min||15||Banning et al, 1995|
|Heart disease||15 (±4) L/min||88||Clark et al, 1995|
|Heart disease||14 (±2) L/min||30||Buller et al, 1990|
|Heart disease||16 (±6) L/min||20||Elborn et al, 1990|
|Pulm hypertension||12 (±2) L/min||11||D'Alonzo et al, 1987|
|Cancer||12 (±2) L/min||40||Travers et al, 2008|
|Diabetes||12-17 L/min||26||Bottini et al, 2003|
|Diabetes||15 (±2) L/min||45||Tantucci et al, 2001|
|Diabetes||12 (±2) L/min||8||Mancini et al, 1999|
|Diabetes||10-20 L/min||28||Tantucci et al, 1997|
|Diabetes||13 (±2) L/min||20||Tantucci et al, 1996|
|Asthma||13 (±2) L/min||16||Chalupa et al, 2004|
|Asthma||15 L/min||8||Johnson et al, 1995|
|Asthma||14 (±6) L/min||39||Bowler et al, 1998|
|Asthma||13 (±4) L/min||17||Kassabian et al, 1982|
|Asthma||12 L/min||101||McFadden & Lyons, 1968|
|COPD||14 (±2) L/min||12||Palange et al, 2001|
|COPD||12 (±2) L/min||10||Sinderby et al, 2001|
|COPD||14 L/min||3||Stulbarg et al, 2001|
|Sleep apnea||15 (±3) L/min||20||Radwan et al, 2001|
|Liver cirrhosis||11-18 L/min||24||Epstein et al, 1998|
|Hyperthyroidism||15 (±1) L/min||42||Kahaly, 1998|
|Cystic fibrosis||15 L/min||15||Fauroux et al, 2006|
|Cystic fibrosis||10 L/min||11||Browning et al, 1990|
|Cystic fibrosis*||10 L/min||10||Ward et al, 1999|
|CF and diabetes*||10 L/min||7||Ward et al, 1999|
|Cystic fibrosis||16 L/min||7||Dodd et al, 2006|
|Cystic fibrosis||18 L/min||9||McKone et al, 2005|
|Cystic fibrosis*||13 (±2) L/min||10||Bell et al, 1996|
|Cystic fibrosis||11-14 L/min||6||Tepper et al, 1983|
|Epilepsy||13 L/min||12||Esquivel et al, 1991|
|CHV||13 (±2) L/min||134||Han et al, 1997|
|Panic disorder||12 (±5) L/min||12||Pain et al, 1991|
|Bipolar disorder||11 (±2) L/min||16||MacKinnon et al, 2007|
|Dystrophia myotonica||16 (±4) L/min||12||Clague et al, 1994|
What causes hypocapnia
Hypocarbia is caused by chronic hyperventilation (or an automatic deep breathing pattern) leading to alveolar hypocapnia (lack of CO2), and if there is no ventilation-perfusion mismatch, to arterial CO2 deficiency. Normal breathing is imperceptible or unperceivable, since it is small and light (10-12 breaths/min, 500 ml for tidal volume, and 6 L/min for minute ventilation at rest for a 70-kg person). In contrast, hypocapnic patients and even most normal subjects breathe over 10 L/min and have over 18 breaths/min for respiratory frequency.
Among lifestyle factors that cause hyperventilation and hypocarbia are physical exercise with mouth breathing, meals (eating and especially overeating), stress, anxiety, overheating, attempts to breathe deeply, deep breathing exercises (except slow ones, like Pranayama), supine sleep and being in the horizontal position, poor posture and many other factors (see Causes of Hyperventilation web page).
Symptoms of hypocarbia
Since hypocapnia is based on chronic hyperventilation, its symptoms are the same as the symptoms of hyperventilation. They are very wide and range from chronic coughing and nasal congestion, to constipation, coughing and muscle cramps. Among other common symptoms of hypocapnia are bronchospasm, cold extremities, mouth breathing, exacerbations of asthma, angina pain, and many others.
The key pathological effect of both, alveolar and arterial hypocapnia is reduced levels of oxygen in body cells (tissue hypoxia), This promotes virtually all chronic diseases. These and other physiological effects associated with low CO2 and low oxygen levels in body cells, with numerous medical studies, are provided below (in CO2-related links). More information about symptoms of hypocapnia can be found here: symptoms of hyperventilation.
Severe hypocarbia: the most common cause/factor of mortality in the severely sick
The majority of terminally sick people die in conditions of severe hypocapnia due to heavy and fast breathing. Separate web pages of this site have numerous studies that show that terminally sick patients with cancer, cystic fibrosis, HIV, and other conditions have up to 30-40 breaths per minute or more at rest.
Respiratory alkalosis, the result of heavy breathing in the sick, is the most common acid-base abnormality observed in patients who are critically ill. It is common for those with numerous diseases, including cancer, cardiovascular disease, diabetes, HIV-AIDS, asthma, COPD, and many other conditions.
This YouTube Video explains the details and provides many quotes from medical studies - Hypocapnia, Respiratory Alkalosis: Key Causes of Deaths in the Most Sick.
Treatment of hypocapnia
Since hypocapnia is based on overbreathing, successful treatment of hypocarbia is based on addressing the cause: chronic hyperventilation. Therefore, treatment of hypocapnia is the same as treatment of hyperventilation. Note that based on impressive clinical evidence (CO2 measurements in thousands of healthy and sick people), leading Soviet physiologist Dr. KP Buteyko and about 150 medical doctors (Buteyko breathing practitioners) suggested a different definition of hypocapnia: less than 6.5% CO2. According to Dr. Buteyko, treatment of hypocapnia should be based on achievement of this goal: 6.5% CO2 or about 46 mm Hg for alveolar CO2 pressure.
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.
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