Part 3: Breathing Chemistry
BREATHING CHEMISTRY (internal respiration)
Many people believe that good breathing is about moving as much oxygen (O2) as possible into the blood, while simultaneously eliminating (excreting) as much carbon dioxide (CO2) as possible from the blood, through “the right” breathing mechanics. This view is both uninformed and simplistic. Yes, O2 delivery to body cells is essential, of course, but the best way to accomplish this is not so obvious. And yes, excretion of excessive CO2 is critical, but not all of it, only some of it. Contrary to the belief of many, CO2 is a precious body substance and its ever presence is required not only for health but for life itself.
External respiration (breathing mechanics) is regulated from breath to breath by chemo-regulatory reflexes located in the brainstem. These reflexes are regulated based on pH of arterial blood plasma (pHa) and cerebrospinal fluid, CO2 concentration in blood plasma (PaCO2) and cerebrospinal fluid, and by O2 concentration in arterial blood plasma (PaO2). These reflexes operate breathing through the diaphragm and the internal intercostal muscles while at rest. This is one reason why if chest breathing predominates, based on an unconsciously learned breathing habit (where “feeling in control” may take precedence over allowing for the reflexes), that diaphragmatic training can be so fundamentally important, i.e., clients may learn to prefer mechanics that are consistent with good chemistry.
Acid-base balance is about pH regulation, i.e., hydrogen ion concentration (pH = power of hydrogen).
An aqueous (water) solution is neutral when the pH is 7.0. Solutions with a pH of less than 7.0 are acidic
and solutions with a pH of higher than 7.0 are alkaline. The body keeps blood plasma within very tight
limits of pH, optimally 7.38-7.40, but generally within a range of 7.35-7.45. Hence, as pH drops blood
plasma becomes less alkaline (not acidic) and when it rises it becomes more alkaline. Values of less than
7.35 mean acidemia and values above 7.45 mean alkalemia.
Overbreathing, which is the most common form of learned dysfunctional breathing, leads to a CO2 deficit (hypocapnia) resulting in respiratory alkalosis (pH higher than 7.45). Underbreathing, which is unusual, leads to excessive accumulation of CO2 (hypercapnia) resulting in respiratory acidosis (pH lower than 7.35). Both conditions can result in profound physiological changes responsible for a wide range of
symptoms and deficits, short term and long term. Low arterial CO2 concentrations, however, may not necessarily be the result of a dysfunctional habit, but rather a compensatory response to some other physiological compromise, e.g., lactic acidosis during anaerobic exercise, or cardiac insufficiency in patients with heart conditions.
The Henderson-Hasselbalch (H-H) equation describes pH regulation of blood plasma and other extracellular fluids, as follows (simplified format):
pH = [HCO3-] ÷ PaCO2, OR [H+] = PaCO2 ÷ [HCO3-]
where, [HCO3-] = bicarbonate ion concentration
where, [H+] = hydrogen ion concentration
where, PaCO2 = arterial CO2 concentration (partial pressure arterial CO2)
where pH is the reciprocal of hydrogen ion concentration
Bicarbonates are regulated by the kidneys and the PCO2 concentration by breathing. The kidneys are very slow to act, and don’t even begin to compensate for changes in pH for at least eight hours and may take up to five days to make its full contribution toward normalizing pH. Breathing on the other hand can immediately effect pH level, within seconds, positively by the action of reflex mechanisms and positively OR negatively by learned breathing habits. It is here where the psychology of breathing can make its grand entry into physiology through its role in the regulation of the H-H equation. Consider the following rewrite of the equation: Acid-base physiology = kidney function ÷ breathing behavior.
Breathing mechanics, controlled by brainstem reflexes (external respiration), normally regulate the pH of extracellular body fluids, including blood plasma, cerebrospinal fluid, interstitial fluid (that surround all cells in the body), and lymph. But, learned breathing habits can get in the way of these reflexes leading to insidious and generally unidentified outcomes by both practitioners and their clients.
About 98.5% of oxygen diffused into the blood of the pulmonary capillaries surrounding the alveoli of the lungs, is carried in the blood by hemoglobin in red blood cells. Hemoglobin delivers its oxygen based on blood plasma O2 concentration (PaO2) as per the oxyhemoglobin dissociation curve. As PaO2 drops in busy tissues hemoglobin begins to deliver its oxygen. The CO2 concentration and the pH of cytosol in red blood cells significantly affect when and where hemoglobin will deliver its oxygen (Bohr Effect). If a tissue is busy at work it will generate more CO2 which diffuses into the red blood cell. The presence of more CO2 and the reduced pH of the cytosol (CO2 forms H2CO3, carbonic acid) reduces hemoglobin’s affinity for oxygen (changes its conformation), leading to an earlier distribution of its oxygen as per the Bohr effect (that is, releasing oxygen at higher levels of PaO2). Very importantly, also resulting from increased CO2 concentration and a lower pH of cytosol in red blood cells, hemoglobin will release nitric oxide (NO), a powerful vasodilator, providing for increased blood flow and volume in busy tissues that require more oxygen and glucose.
Brainstem reflex mechanisms regulate breathing mechanics (external respiration) such that the correct CO2 concentration is maintained in the alveoli of the lungs (where gas exchange takes place). This ensures that blood moving through the pulmonary capillary network returns to systemic circulation with a CO2 concentration that balances the H-H equation, thus keeping pH within normal limits. Thus, when
one intentionally ventilates by taking large breaths, slow or fast, diaphragmatically or in the chest, PaCO2 concentration can drop and drive up pH toward respiratory alkalosis. The result is vascular constriction and unfriendly hemoglobin (where O2 and NO are more sparingly released), and thus a radically reduced oxygen and glucose supply to body tissues in need, e.g., to the brain and to the heart.
Written by Dr. Peter Litchfield
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