How CO2 (carbon dioxide) Influences Blood pH and Causes Respiratory Alkalosis
Blood pH is tightly regulated by a system of buffers that
continuously maintain it in a normal range of 7.35 to 7.45 (slightly
alkaline). Blood pH drop below 7 can lead to a coma and even death due
to severe acidosis. This causes depression of the central nervous
system. High blood pH (above 7.45) is called alkalosis. Severe
alkalosis (when blood pH is more than 8) can also lead to death, as it
often happens during last days or hours of life in the chronically and
terminally ill.
Carbon dioxide plays one of the central roles in this blood pH
abnormality. Note, however, that tissue hypoxia due to criticlaly low
carbon dioxide level in the alveoli is usually the main
life-threatening factor in the severely sick. As we discussed before,
CO2 is crucial for vasodilation and the Bohr effect.
If you click on the picture (on the right), you can watch the video clip "How do we breathe when we die". This GoogleVideo clip summarizes numerous epidemiological stuides related to ineffective breathing in the severely sick and critically ill people. The video clip will open in a new window.
The main conclusion that relates to breathing in the severely sick is that their breathing is very fast and deep, while oxygenation of cells is critical. This is the reason why regardless of the health condition critically ill patients are often provided with pure oxygen. You can read all these medical abstracts on the web page How do we breathe when we die?
The main mechanisms for blood pH maintainance and control are:
- Carbonic Acid-Bicarbonate Buffer System
- Protein Buffer System
- Phosphate Buffer System
- Elimination of Hydrogen Ions via Kidneys
Many people believe that if you eat certain foods, it can cause your blood to become more alkaline or acidic. Medical research studies have clearly shown that breathing and blood carbon dioxide and bicarbonate ions levels are more significant factors in blood pH control. Alveolar hyperventilation that is common in the sick reduces cell oxygenation, increases resting blood lactate levels, intensifies production of free radicals due to tissue hypoxia (cells are deprived of oxygen), causes diabetic ketoacidosis in the genetically predisposed patients, and suppresses the immune system and main blood pH buffer systems of the human organism.
Changes in carbon dioxide and breathing cause immediate and long-term effects of blood pH. They are not necessary the same. The immediate effects are simple: higher CO2 content causes blood acidification and pH decrease, while reduced carbon dioxide levels increase blood pH often causing death in the critically ill (see a review of medical studies below). Long term effects depend on the direction of change (moving closer to normal breathing or not), genetic factors, existing pathologies, diet, physical exercise, thermoregulation, and many other parameters.
CO2 gas, when dissolved in blood, is the second largest group of negative ions of blood plasma. Hence, breathing directly affects blood pH. In its turn, blood pH is tightly monitored within a very narrow range (from about 7.3 to 7.5) by the group of nerve cells located in the medulla oblongata in order to have normal body biochemistry. The same nerve cells control breathing by through several independent mechanisms, including peripheral and central CO2 and O2 chemoreceptors.
It is not a surprise that even mildly sick patients suffer from blood pH abnormalities due to breathing since they breathe about 2-3 times more than the medical norm. For review of 34 medical studies click here (the Table with minute ventilation data).
Hence, arterial CO2, carbon dioxide, through several indepedent biochemical mechanisms can influence blood pH and causes respiratory alkalosis in patients with chronic diseases
Dr. K. P. Buteyko and his colleagues also found that CO2 controls and regulates composition and properties of many all other bodily fluids, including secretions of the stomach, composition and properties of saliva and mucus, pH of the urine. For example, for most people, in conditions of hyperventilation, stomach and urinary pH become too low (too acidic) promoting development of gastritis and ulcers, or urinary stones.