Hypocapnia: Definition, Causes, 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 that causes to 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 (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 ventilation	Number of people	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

What causes hypocapnia

Dark and lighter clouds Hypocarbia is caused by chronic hyperventilation (or 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 breathing Since hypocapnia is based on chronic hyperventilation, its symptoms are the same as 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) that 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 (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

Majority of terminally sick people die in conditions of severe hypocapnia due to heavy and fast breathing. Separate web pages of this site has numerous studies that showed 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 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 smiling 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 huge 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 Web Pages: Breathing norms, Medical Graphs and Tables about Breathing Rates (Minute Ventilation) and Body Oxygen in Healthy, Normal and Sick People
Breathing norms Parameters, graph, and description of the normal breathing pattern
6 breathing myths 6 myths about breathing and body oxygenation (prevalence: over 90%)
Hyperventilation Definitions of hyperventilation: their advantages and weak points
Hyperventilation Syndrome in the Sick. Table 1. Western scientific evidence about prevalence of CHV (chronic hyperventilation) in patients with various chronic conditions (34 medical studies)
Normal Minute Ventilation in Healthy Subjects: Easy and Light Breathing (14 Studies)
Hyperventilation Prevalence Present in Over 90% of Normal People (24 medical publications)
HV and hypoxia How and why deep breathing reduces oxygenation of cells and tissues of all vital organs
Body oxygen test How to measure your own breathing and body oxygenation (a simple DIY test)
Body oxygen in healthy Table 4. CP (body oxygen level) in healthy people (27 medical studies)
Body oxygen in sick Table 5. CP (body oxygen level) in sick people (14 medical studies)
Buteyko Table of Health Zones with clinical description of most common zones
Morning HV Morning hyperventilation effect or how and why critically ill people are most likely to die during early morning hours

References: CO2 Effects Web Pages
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 and oxygen transport are controlled by alveolar CO2 and breathing
Oxygen Transport depends on breathing and these two effects (Vasoconstriction-Vasodilation and the Bohr effect) are parts of two diagrams that summarize influences of hypocapnia (low CO2 content in the blood and cells) on circulation and O2 delivery
Free Radical Generation takes place due to anaerobic cell respiration caused by cell hypoxia. Hence, antioxidant defenses of the human body are also regulated by CO2 and breathing
Inflammatory Response is controlled by breathing since hypoxia leads to or intensifies chronic inflammation through over-expression of the hypoxia-inducible factor 1, while normal breathing reduces these processes
Nerve stabilization takes place due to calmative or sedative effects of carbon dioxide in neurons or nerve cells
Muscle relaxation or relaxation of muscle cells is normal at high CO2, while hypocapnia causes muscular tension, poor posture and, sometimes, aggression and violence
Brochodilation - dilation of airways (bronchi and bronchioles) by carbon dioxide, and their constriction due to hypocapnia
Blood pH regulation and regulation of other bodily fluids
CO2: Lung Damage Healer: Elevated carbon dioxide prevents injury and promotes healing of lung tissues
CO2: Skin and Tissue Healer
Synthesis of Glutamine in the Brain, CO2 fixation, and other chemical reactions
CO2 myth "CO2 is a toxic waste gas" myth
Breathing control How is our breathing regulated? Why hypocapnia makes breathing uneven and erratic

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