Tissue Oxygenation and CFS



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Oxygen Delivery Overview
Carbon Dioxide, pH and Breathing Technique
     CO2, HCO3- and pH
     The Bohr Effect
     Hypocapnia - Too Low Blood CO2 Levels
     Hypercapnia - Too High Blood CO2 Levels
Inefficient Oxygen Perfusion
     Introduction
     Porphyrins and Heme Production
     Methylation
     Cardiac Insufficiency and ASBAs
     2,3-BiPhosphoGlycerate (2,3-BPG)
     Reduction in Oxygen-Permeability of Capillaries
     Methemoglobinemia - Oxidised Hemoglobin, Free Radicals & Peroxynitrite
     Lipofuscin
     Carbon Monoxide
     Hydrogen Sulphide (H2S)
Dr Paul Cheney's Theory on Oxygen Toxicity and PFOs
Dr Paul Cheney's Theory on Low CO2 Levels
Markers of Low Oxygenation
Supplemental Oxygen
O2 Concentrators - General
O2 Concentrators - Maintenance Schedule
Bitmos Oxy 6000 Review




Oxygen Delivery Overview:

Before we look at some of the potential problems associated with oxygenation in CFS patients, let us first briefly remind ourselves how Oxygen (O2) is delivered to the tissues and how Carbon Dioxide (CO2) is removed from the tissues.

http://en.wikipedia.org/wiki/Red_blood_cell

The purpose of breathing is to absorb oxygen into the blood and expel carbon dioxide and other gaseous waste products from the blood, in accordance with requirements.

Under normal circumstances, the air we breathe in contains 0.04% CO2 and the air we breathe out contains 4% CO2. Normally, in each breath only 10% of the alveolar gas is replaced in each breath (including both O2 and CO2). The percentage of O2 exhaled from each breath depends on your oxygen consumption (VO2) and metabolic rate.

Oxygen is required by all the cells of the body in the process of respiration, where carbon-containing sugar chains and other storage compounds are 'burnt' using O2, involving a complex cycle of mitochondrial co-factors, resulting in the production of water and CO2.

Oxygen is absorbed in the lungs, where it is transported around the body in the arterial blood, until it arrives at the capillaries, the very thin and permeable blood vessels which form a 'web' or 'matrix' around the tissues they supply. The capillaries at the tissues and the alveoli in the lungs both provide a enormous surface area where diffusion and absorption can occur.

http://en.wikipedia.org/wiki/Capillaries

The capillaries supply nutrients and oxygen to the target cells, nutrients coming from the blood plasma and the oxygen coming from the Red Blood Cells. The capillary blood removes/absorbing waste products and Carbon Dioxide (from respiration). The CO2 is then transported in the venous bloodstream to the lungs where it diffuses and is expelled from the body. Breathing of course does not occur only when blood has completed a complete circuit around the body (!) but happens continously, with this exchange occuring continuously.

RBCs have one main purpose which is gaseous exchange. RBCs also perform secondary functions including:

RBCs are anucleate when mature, meaning that they do not have a cell nucleus unlike other bodiliy cells. RBCs have an average life span of 100-120 days, after which time they are 'eaten' by Macrophages, a type of White Blood Cell. The blood stream is able to absorb and transport large quantities of gases by having a high concentration of Red Blood Cells. The concentration of RBCs may vary depending on the partial pressure of oxygen one is habitually used to breathing (e.g. altitude).

The Hemoglobin protein molecule in a RBC is comprised of 4 Heme molecules bound together. Each Heme molecule is able to accommodate one O2 or CO2 molecule. Heme is a type of metalloprotein containing a Ferrous Iron (Fe2+) in the centre of a carbon ring. Of course not all Hemoglobin molecules in the RBCs in the blood are fully saturated with gases. The extent of saturation and diffusion is dependent on the partial pressures of the gases at the exchange point and also the relative affinity of the gas-Hemoglobin bond inside the RBC. A number of factors may affect the strength of the Hemoglobin bond with the O2, including pH and 2,3-BPG concentration. The general trend across all the RBCs in the blood is described by the Oxygen-Hemoglobin Dissociation Curve.

http://en.wikipedia.org/wiki/Oxygen-haemoglobin_dissociation_curve

www.ventworld.com/resources/oxydisso/dissoc.html

The Oxygen-Hemoglobin Dissociation Curve is described by % O2 Saturation on the y-axis (SaO2 %) and Partial Pressure of O2 in mmHg on the x-axis (PaO2). It is not a linear relationship, of course, and forms a S-curve or Sigmoid-curve pattern. Each person will have a slightly different curve, which can be conceptualised by either a shift to the left or a shift to the right of the 'Satndard' curve.

The midpoint of the curve, the point of 50% O2 saturation, is used for reference purposes, and is the partial pressure of O2 necessary to produce that degree of O2 saturation in the RBCs. 50% saturation is of course not something to aim for but is just a useful point on the graph to use to compare Oxygen-Hemoglobin DIssociation Curves.

When describing the degree of saturation of Hemoglobin, the following terms are generally used.

Hemoglobin bound to CO2 loses its affinity to O2, described by the Bohr effect, shifting the O2-Hemoglobin-Dissociation Curve to the right. The Hemoglobin bond to CO2 is reversible.

Most of the O2 in the blood is carried in the Hemoglobin of the Red Blood Cells (RBCs or Erythrocytes), with a small amount dissolved in the blood plasma. Conversely, most of the CO2 is dissolved in the blood plasma in the form of bicarbonate (HCO3-), with only a small amount of CO2 molecules actually dissolved in the blood plasma or bound to the Hemoglobin of the RBCs. Most of the Hemoglobin in the venous blood is therefore deoxygenated and is not bound to any gases, but instead bound to H+ ions from the blood (once the O2 has been squeezed out at the capillary sites). These H+ ions are released into the blood plasma once the RBCs arrive at the lungs, when they are substituted at the hemoglobin bindings sites with O2. H+ ions bind most readiliy to DeoxyHemoglobin (containing no O2).

H+ ions bind with great affinity to Hemoglobin, especially DeoxyHemoglobin (in the venous blood). DeoxyHemoglobin bound to H+ has a slightly reduced affinity for O2, in the same way that Carbaminoglobin (CO2-bound Hemoglobin) has a reduced affinity for O2 also. With greater H+ ion concentrations, or lower blood pHs, Hemoglobin binds more readily to H+ and subsequently has slightly reduced affinity to O2. This similarly shifts the O2-Hb-Dissoc. Curve to the right. Higher CO2 blood levels result in a lower pH or increased H+ ion concentration too.

http://en.wikipedia.org/wiki/Hemoglobin

www.nda.ox.ac.uk/wfsa/html/u13/u1312_02.htm

There are a number of factors that control how much oxygen is absorbed by the cells and tissues of the body. Some of these are examined in subsequent sections of this page.

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Carbon Dioxide, pH and Breathing Technique:

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