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25 Cards in this Set

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How is carbon dioxide transported in blood?
Dissolved in blood. Transported to the lungs.

(10% is bound to hemoglobin)
What is atmospheric pressure assumed to be?
760 mmHg
Partial pressure formula
Pgas = Patm x fgas = 760 x mole fraction <sub>gas</sub>


Mole fraction of a gas = moles of a gas/ total moles
What is the alveolar-arterial gradient (A-a gradient?)
The difference between the partial pressure of oxygen in the alveoli and arterial circulation.
Equation for Partial Pressure of Oxygen in the Alveoli
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.
What is R normally?
0.8
What is the normal alveolar arterial gradient?
2.5 + 0.21 * age in years
What are five factors that cause hypoxia?
1) High altitude
2) Hypoventilation
3) Ventilation-Perfusion mismatch (V/Q)
4) Shunt
5) Disorders of hemoglobin
How does high altitude cause hypoxia?
Atmospheric pressure is reduced, so there is decreased partial pressure of oxygen. A-a gradient is normal.
What does hypoventilation result in?
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.
Where is V/Q highest? Lowest?
Highest in upper lung zones (even though there is less ventilation and perfusion); Lowest in lower lung zones
What is diffusion block?
Increased distance between the alveoli and capillaries. May be due to a thickened membrane or fluid in the alveoli
What is a shunt?
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.
what are the two types of shunt?
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)
Two examples of disorders of hemoglobin causing hypoxia
1) Carbon monoxide poisoning

2) Severe anemia
What does partial pressure of arterial carbon dioxide depend on?
VCO2
PaCO2 = k_________________
VE (1 – VD/VT)

VCO2 = production of CO2
VE = minute ventilation (tidal volume * respiratory rate)
VD/VT is dead space ventilation
Causes of Increased carbon dioxide production
Sepsis (Kussmail respiration)
Causes of Increased dead space ventilation
Emphysema, PE, Acute Respiratory Distress Syndrome
Oxygen carrying capacity equation
CaO2 = 1.34 * Hb * Saturation + 0.003 *PO2

Hb in g/dl
Saturation is a fraction
PO2 = partial pressure of O2 in blood
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
How does CO poisoning affect the Oxy/Hb dissociation curve?
depresses it by decreasing the number of Hb binding sites available
Delivery of oxygen equation
DO2 = C<sub>a</sub>O2 * Cardiac output
What is normal Delivery of oxygen (DO2)?
approximately 1 l/min
What causes right shifts in the oxygen/hemoglobin dissociation curve?
1) Acidemia
2) Hypercapnea
3) Hyperthermia
4) Increasing 2,3 DPG
A shift to the _____ has the effect of increasing release of oxygen from hemoglobin (facilitates unloading in the tissues)
right