Oxygen cascade

Editor's Notes

• #3: ATP,the coenzyme that supplies energy to all active metabolic processes.
• #6: Deoxygenated venous blood becomes oxygenated on the pulmonary capillaries after diffusion down a concentration gradient across the alveolar capillary membrane.
• #8: When dealing with the gas mixture,each gas contribute seperatly to the total gas pressure k/a partial pressure of the individual gas. And the partial pressure of the gas is directly propotional to its concemtration. Haemoglobin saturation is determined by the partial pressure of oxygen. When these values are graphed they produce the Oxygen Disassociation Curve piO2= Fio2 8 BAROMETRIC PRESSURE Barometric pressure at mt everest =253 mmHg
• #9: In alveoli the inspired gases are mixed with residual alveolar gas from previous breath.o2 is taken up and co2 is added.the final alveolar 02 tension can be estimated by pA02=PI02-pac02/RQ piO2= Fio2 * BAROMETRIC PRESSURE (760-47)0.21=150mm Hg
• #10: The factors that determine the precise value of alveolar PO2 are (1) the PO2 of atmospheric air, (2) the rate of alveolar ventilation, and (3) the rate of total body oxygen consumption piO2= Fio2 * BAROMETRIC PRESSURE 0.21 *(760-47) –(40/0.8) 1000mmHg
• #11: Within the lung, oxygen diffuses from the alveoli into the pulmonary capillaries, driven by the gradient between the partial pressure of oxygen in the alveolar space and that in the deoxygenated pulmonary capillary blood. O2 moves across the alveolar membranes into the pulmonary capillaries by passive diffusion , across the alveolar-capillary membrane, through the plasma and across the erythrocyte membrane and binds to Hb.
• #12: Within the lung, oxygen diffuses from the alveoli into the pulmonary capillaries, driven by the gradient between the partial pressure of oxygen in the alveolar space and that in the deoxygenated pulmonary capillary blood. O2 moves across the alveolar membranes into the pulmonary capillaries by passive diffusion , across the alveolar-capillary membrane, through the plasma and across the erythrocyte membrane and binds to Hb.
• #13: A layer of fluid lining the alveolus and containing surfactant that reduces the surface tension of the alveolar fluid. The alveolar epithelium composed of thin epithelial cells. An epithelial basement membrane. A thin interstitial space between the alveolar epithelium and the capillary membrane. A capillary basement membrane that in many places fuses with the alveolar epithelial basement membrane. The capillary endothelial membrane.
• #14: Transit time for blood is ~ 0.75 sec (time blood remains in the lungs capillary). EQUILIBRIUM TIME –> Normally ~0.25 sec(1/3rd of total transit time) is required for Oxygen as well as Carbon Dioxide diffusion. Rest 0.50 sec is the safety margin (which helps in diffusion during exercise, high altitude or impaired diffusion) Rate of gas diffusion = Diffusion coefficient X Pressure gradient x Surface area of the membrane /Thickness of the membrane any factor that increases the thickness (eg. Fibrosis, oedema fluid) can  interfere significantly with normal respiratory exchange of gases. Greater the surface area  greater is the rate of diffusion. The large capillary surface area in alveoli and the 0.4 to 0.5 micrometer thickness of the alveolar-capillary membrane greatly facilitate )2 diffusion.  The volume of gas transfer across the alveolar-capillary membrane per unit time is
• #16: – Henry’s Law the amount of gas dissolved in a liquid will be directly proportional to the partial pressure of the gas in the liquid-gas interface” As long as the PO2 in the gas phase is higher than the PO2 in the liquid phase, there will be a net diffusion of O2 into the blood .
• #17: Respiratory Unit is composed of a respiratory bronchiole, alveolar ducts, atria, and alveoli.
• #18: The Alveolar–arterial gradient is a measure of the difference between the alveolar concentration (A) and the arterial (a) concentration of oxygen. most common mechanism of hypoxemia is increased A-a gradient which depends on right to left shunt (directly propotional),v/q mismatch,mixed venous o2 tension (incersely propotional)
• #21: Which states that the concentration of any gas in solution is propotional to its partial pressure.
• #22: At a normal PaO2 of 100 mm Hg, however, the Hb saturation (SaO2) is only about 97% due to the following three normal physiologic shunts •Thebesian venous drainage into the left atrium •Bronchial venous drainage into pulmonary veins •Alveoli that are under ventilated, also referred to as dead space ventilation Thus, the amount of arterial oxygen in the preceding equation must be adjusted to 97 percent: 
• #25: It is the percentage expression of no of oxygen binding site occupied out of maximum no of a binding site available.
• #26: At pH 7.4, temp 37, po2 50% is at 27 mmhg
• #27: A small drop is systemic capillaries po2 can result in release of large amount of oxygen from the metabolically active cells
• #32: The high co2 content of venous capillary blood by decreasing hemoglobin affinity for o2 facilitates the release of o2 to tissues. Conversely the lower co2 content in pulmonary capillaries increases hemoglobin affinity for 02 again, facilitating 02 uptake from alveoli.
• #38: DO2 decreases in response to: Low blood oxygenation that can be caused by Low PaO2 Low SaO2 Low hemoglobin concentration Low cardiac output DO2 increases in response to: Increased blood oxygenation caused by Increased PaO2 Increased SaO2 Increased hemoglobin concentration Increased cardiac output
• #39: The Critical DO2 •The DO2 at which the VO2 becomes supply-dependent is called the critical oxygen delivery (critical DO2). It is the lowest DO2 that is capable of fully supporting aerobic metabolism . • It is identified by the bend in the DO2–VO2 curve . • Despite the ability to identify the anaerobic threshold, the critical DO2 has limited clinical value. • First, the critical DO2 has varied widely in studies of critically ill patient, and it is not possible to predict the critical DO2 in any individual patient in the ICU. •Second, the DO2–VO2 curve can be curvilinear (i.e., without a single transition point from constant to changing VO2) , and in these cases, it is not possible to identify a critical DO2.
• #43: This means that only 25% of the oxygen delivered to the systemic capillaries is taken up into the tissues. The DO2–VO2 Relationship • As O2 delivery (DO2) begins to decrease below normal, the O2 uptake (VO2) initially remains constant, indicating that the O2 extraction (O2ER) is increasing as the DO2 decreases. Further decreases in DO2 eventually leads to a point where the VO2 begins to decrease. • The transition from a constant to a varying VO2 occurs when the O2 extraction increases to a maximum level of 50% to 60% (O2ER = 0.5 to 0.6). Once the O2ER is maximal, further decreases in DO2 will result in equivalent decreases in VO2 because the O2ER is fixed and cannot increase further. • When this occurs, the VO2 is referred to as being supply-dependent, and the rate of aerobic metabolism is limited by the supply of oxygen. This condition is known as dysoxia . • As aerobic metabolism (VO2) begins to decrease, the oxidative production of high energy phosphates (ATP) begins to decline, resulting in impaired cell function and eventual cell death.
• #48: With further reduction in delivery of oxygen critical point is reached where oxygen consumption becomes directly propotional to oxygen delivery
• #49: .