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Hypocapnia (Hypocarbia): Definition, Symptoms and Treatment

Definition of hypocapnia (hypocarbia)

Carbon dioxide molecule 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)

Condition Minute
Number of
All references or
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

Note that advanced stages of asthma can lead to lung destruction, ventilation-perfusion mismatch,
and arterial hypercapnia causing further reduction in body oxygen levels.

What causes hypocapnia

Dark and lighter cloudsHypocarbia 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

People with mouth breathingSince 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

Medical people smilingSince 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.

Go to Hyperventilation Symptoms

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