RESPIRATORY: 599 - 600 Flashcards
Characterize the normal pulmonary circulation system in terms of resistance, pressure, and compliance.
Low resistance
Low pressure
High compliance
What is hypoxic vasoconstriction?
A decrease in PAO2 shifts blood away from poorly ventilated regions of lung to well-ventilated regions of lung
What is the major complication of pulmonary hypertension?
Cor pulmonale and subsequent right sided heart failure (JVD, edema, hepatomegaly)
Describe perfusion limited gas exchange.
Gas equilibrates early along the length of the capillary (i.e. maximal gas exchange).
Diffusion can only be increased if blood flow itself is increased.
Describe diffusion limited gas exchange.
Gas does not equilibrate by the time blood reaches the end of the capillary (i.e. less than maximal gas exchange).
What gases are perfusion limited?
O2 (normal health), CO2, N2O
What gases are diffusion limited?
O2 (in cases of emphysema, fibrosis), CO
What is the equation for the volume of a gas that will diffuse across a membrane?
Vgas = A/T x Dk(P1 - P2)
where V = volume, A = area, T = thickness, Dk = diffusion constant, P1 - P2 = difference in partial pressures
What happens to the diffusion membrane in emphysema?
Decrease in area
What happens to the diffusion membrane in pulmonary fibrosis?
Increase in thickness
How do we relate pulmonary vascular resistance to pressure and flow?
General equation: delta P = Q x R so R = delta P / Q
where delta P = pressure difference, Q = flow, R = resistance
So in this case: PVR = (P pulmonary artery - P left atrium) / cardiac output
What is the equation for calculating resistance based on all of its components?
R = 8nl / (πr^4)
where n = viscosity of blood, l = vessel length, r = vessel radius
What is the alveolar gas equation?
PAO2 = PIO2 - PaCO2/R
where PAO2 = alveolar PO2, PIOS = PO2 in inspired air, PaCO2 = arterial PCO2, R = respiratory quotient = CO2 produced/O2 consumed
What is a normal value for PIO2?
150
What is a normal value for the respiratory quotient?
0.8
What is the A-a gradient?
PAO2 - PaO2
What is a normal value for A-a gradient?
10-15 mm Hg
When do we see an increased A-a gradient?
In cases of hypoxemia
What can cause an increased A-a gradient?
Shunting, V/Q mismatch, fibrosis (from limited diffusion)
What are the three types of oxygen deprivation?
- Hypoxemia - decrease in PaO2 (in oxygen getting to the blood)
- Hypoxia - decreased O2 delivery to tissue
- Ischemia - loss of blood flow
How can we break up the causes of hypoxemia?
Normal A-a gradient vs. Increased A-a gradient
When do we see hypoxemia with a normal A-a gradient?
High altitude or hypoventilation
What are 4 causes of hypoxia?
- Decreased cardiac output
- Hypoxemia
- Anemia
- CO poisoning
What are 2 causes of ischemia?
- Impeded arterial flow
2. Decreased venous drainage
