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25 Cards in this Set
- Front
- Back
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How is carbon dioxide transported in blood?
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Dissolved in blood. Transported to the lungs.
(10% is bound to hemoglobin) |
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What is atmospheric pressure assumed to be?
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760 mmHg
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Partial pressure formula
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Pgas = Patm x fgas = 760 x mole fraction <sub>gas</sub>
Mole fraction of a gas = moles of a gas/ total moles |
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What is the alveolar-arterial gradient (A-a gradient?)
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The difference between the partial pressure of oxygen in the alveoli and arterial circulation.
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Equation for Partial Pressure of Oxygen in the Alveoli
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P<sub>A</sub>O2 = (Patm - Ph20) x fiO2 - P<sub>a</sub>CO2/R
Patm = atmospheric pressure Ph20 = partial pressure of water fiO2 = fraction of inspired oxygen P<sub>a</sub>CO2 = partial pressure of arterial carbon dioxide R = metabolic respiratory quotient. Ratio of exhaled CO2 to inhaled oxygen. |
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What is R normally?
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0.8
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What is the normal alveolar arterial gradient?
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2.5 + 0.21 * age in years
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What are five factors that cause hypoxia?
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1) High altitude
2) Hypoventilation 3) Ventilation-Perfusion mismatch (V/Q) 4) Shunt 5) Disorders of hemoglobin |
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How does high altitude cause hypoxia?
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Atmospheric pressure is reduced, so there is decreased partial pressure of oxygen. A-a gradient is normal.
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What does hypoventilation result in?
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Decreased P<sub>A</sub>O2 because alveolar oxygen isn't being replenished.
May result from decreased alveolar ventilation and/or increased dead space ventilation. |
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Where is V/Q highest? Lowest?
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Highest in upper lung zones (even though there is less ventilation and perfusion); Lowest in lower lung zones
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What is diffusion block?
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Increased distance between the alveoli and capillaries. May be due to a thickened membrane or fluid in the alveoli
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What is a shunt?
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Occurs when some venous blood doesn't oxygenate when traversing the capillaries because it doesn't come into contact with functioning alveoli. The oxygen poor blood mixes with blood that was exposed to functioning alveoli. Results in INCREASED A-a gradient.
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what are the two types of shunt?
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Anatomic shunt: blood bypasses the alveoli (eg intracardiac shunt)
Physiologic (intrapulmonary): When blood passes through the lungs but comes into contact with alveoli that don't participate in oxygenation (may be collapsed or filled with fluid) |
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Two examples of disorders of hemoglobin causing hypoxia
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1) Carbon monoxide poisoning
2) Severe anemia |
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What does partial pressure of arterial carbon dioxide depend on?
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VCO2
PaCO2 = k_________________ VE (1 – VD/VT) VCO2 = production of CO2 VE = minute ventilation (tidal volume * respiratory rate) VD/VT is dead space ventilation |
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Causes of Increased carbon dioxide production
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Sepsis (Kussmail respiration)
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Causes of Increased dead space ventilation
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Emphysema, PE, Acute Respiratory Distress Syndrome
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Oxygen carrying capacity equation
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CaO2 = 1.34 * Hb * Saturation + 0.003 *PO2
Hb in g/dl Saturation is a fraction PO2 = partial pressure of O2 in blood |
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What is the
A) Steep B) Plateau phases in the oxy/hemoglobin dissociation curve? |
A) Steep phase: between 20-50 mmHg, small rises in PO2 will result in dramatic rise in oxygen sat of Hb
2) Plateau phase (>60), oxygen saturation of Hb increases relatively little with increasing partial pressure of O2 |
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How does CO poisoning affect the Oxy/Hb dissociation curve?
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depresses it by decreasing the number of Hb binding sites available
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Delivery of oxygen equation
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DO2 = C<sub>a</sub>O2 * Cardiac output
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What is normal Delivery of oxygen (DO2)?
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approximately 1 l/min
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What causes right shifts in the oxygen/hemoglobin dissociation curve?
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1) Acidemia
2) Hypercapnea 3) Hyperthermia 4) Increasing 2,3 DPG |
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A shift to the _____ has the effect of increasing release of oxygen from hemoglobin (facilitates unloading in the tissues)
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right
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