Resp - Physio (Pulmonary circulation & related concepts) Flashcards
Pg. 599-601 in First Aid 2014 Sections include: -Pulmonary circulation -Pulmonary vascular resistance -Alveolar gas equation -Oxygen deprivation -V/Q mismatch -CO2 transport -Response to high altitude -Response to exercise
What kind of resistance and compliance does the pulmonary circulation normally have?
Normally a low-resistance, high-compliance system.
Compare the effects of PO2 and PCO2 on pulmonary and systemic circulation.
PO2 and PCO2 exert opposite effects on pulmonary and systemic circulation.
What effect does a decrease in PAO2 have on the lungs, and why?
A decrease in PAO2 causes a hypoxic vasoconstriction that shifts blood away from poorly ventilation regions of lung to well-ventilated regions of lung.
What are the 2 types of gas exchange?
(1) Perfusion limited (2) Diffusion limited
Describe perfusion limited gas exchange. Include gases involved and gas equilibration.
Perfusion limited - O2 (normal health), CO2, N2O. Gas equilibrates early along the length of the capillary. Diffusion can be increased only if blood flow increases.
Describe diffusion limited gas exchange. Include gases involved and gas equilibration.
Diffusion limited - O2 (emphysema, fibrosis), CO. Gas does not equilibrate by the time blood reaches the end of the capillary.
How can diffusion be increased in perfusion limited gas exchange?
Diffusion can be increased only if blood flow increases.
What cardiac condition can be caused by pulmonary hypertension? What are 3 symptoms that characterize this?
A consequence of pulmonary hypertension is cor pulmonale and subsequent right ventricular failure (jugular venous distention, edema, hepatomegaly)
What is the equation for Diffusion?
Diffusion: Vgas = A/T x Dk(P1 - P2) where A = area, T = thickness, and Dk(P1 - P2) ~ difference in partial pressures
What effect do emphysema and pulmonary fibrosis have on the factors in the Diffusion equation?
A (area) decreased in emphysema, T (thickness) increased in pulmonary fibrosis
Draw graphs comparing Perfusion limited versus Diffusion limited. Make the axes partial pressure of gas in pulmonary capillary blood (Pa) versus Length along pulmonary capillary. Label the partial pressure of gas in alveolar air (PA).
See p. 599 in First Aid 2014 for two graphs on left
Draw a graph of Oxygen in the following conditions: Normal, Exercise, and Fibrosis. Make the axes partial pressure of gas in pulmonary capillary blood (Pa) versus Length along pulmonary capillary. Label the partial pressure of gas in alveolar air (PA).
See p. 599 in First Aid 2014 for graph on right
What is the equation for Pulmonary vascular resistance (PVR)?
PVR = (P pulm artery - P L atrium) / Cardiac output, P pulm artery = pressure in pulmonary artery & P L atrium = pulmonary wedge pressure
What is the relationship between pressure, flow, and resistance?
Remember: Pressure differential = Q x R, so R = Pressure differential / Q
What is the equation for Resistance?
R = 8nl/(pi)r^4, where n = viscosity of blood, l = vessel length, & r = vessel radius
What is the alveolar gas equation?
PAO2 = PIO2 - (PaCO2) / R = 150 - (PaCO2) / 0.8, where PAO2 = alveolar PO2 (mmHg), PIO2 = PO2 in inspired air (mmHg), PaCO2 = arterial PCO2 (mmHg), and R = respiratory quotient = CO2 produced / O2 consumed
What is the respiratory quotient?
R = respiratory quotient = CO2 produced / O2 consumed
What value is the A-a gradient?
A-a gradient = PAO2 - PaO2 = 10-15 mmHg
In what context may A-a gradient increase? What are 3 examples of causes leading to this context?
Increased A-a gradient may occur in hypoxemia; causes include shunting, V/Q mismatch, fibrosis (impairs diffusion)
What defines hypoxemia?
Hypoxemia (low PaO2)
What are 2 classifications of hypoxemia? Give examples of each.
(1) Normal A-a gradient - High altitude, Hypoventilation (2) High A-a gradient - V/Q mismatch, Diffusion limitation, Right-to-left shunt
What defines hypoxia?
Hypoxia (low O2 delivery to tissues)
What are 4 settings in which Hypoxia occurs?
Low cardiac output, Hypoxemia, Anemia, CO poisoning
What defines ischemia?
Ischemia (loss of blood flow)
What are 2 settings in which Ischemia occurs?
Impeded arterial flow, Decreased venous drainage
What is ideal for adequate gas exchange?
Ideally, ventilation is matched to perfusion (i.e., V/Q = 1) in order for adequate gas exchange.
What are the 2 major lung zones? What is their V/Q? What is wasted in each zone?
Lung zones: (1) Apex of the lung - V/Q = 3 (wasted ventilation) (2) Base of the lung - V/Q = 0.6 (wasted perfusion)
What are 3 forms of oxygen deprivation?
(1) Hypoxemia (low PaO2) (2) Hypoxia (low O2 delivery to tissue) (3) Ischemia (loss of blood flow)
How does ventilation and perfusion compare at the base versus the apex of the lung?
Both ventilation and perfusion are greater at the base of the lung than at the apex of the lung.
What happens to V/Q during exercise, and why?
With exercise (high cardiac output), there is vasodilation of apical capillaries, resulting in a V/Q ratio that approaches 1.
Where in the lung do organisms that thrive in high O2 flourish? Give an example.
Certain organisms that thrive in high O2 (e.g., TB) flourish in the apex
What causes V/Q to approach 0? In this case, what effect does 100% O2 have?
V/Q –> 0 = airway obstruction (shunt). In shunt, 100% O2 does not improve PO2.
What causes V/Q to approach infinity? In this case, what effect does 100% O2 have?
V/Q –> infinity = blood flow obstruction (physiologic dead space). Assuming < 100% dead space, 100% O2 improves PO2.
What is the order of pressures associated with Zone 1?
Zone 1: PA > Pa > PV
What is the order of pressures associated with Zone 2?
Zone 2: Pa > PA > PV
What is the order of pressures associated with Zone 3?
Zone 3: Pa > PV > PA
Explain the V/Q in Zone 1 (apex) versus Zone 3 (base).
Zone 1: decreased V / very decreased Q –> increased V / Q; Zone 3: increased V / very increased Q –> decreased V/ Q
Draw the lung and label its zones, depicting the magnitude of different pressures.
See p. 600 in First Aid 2014 for visual at bottom of page
What are the 3 forms in which CO2 is transported from tissues to lungs? Give the percentages of each.
CO2 is transported from tissues to the lungs in 3 forms: (1) HCO3- (90%) (2) Carbaminohemoglobin or HbCO2 (5%). CO2 bound to Hb at N-terminus of globin (not heme). CO2 binding favors taut form (O2 unloaded). (3) Dissolved CO2 (5%)
In Carbaminohemoglobin or HbCO2, where is the CO2 bound? What does CO2 binding favor?
Carbaminohemoglobin or HbCO2 (5%). CO2 bound to Hb at N-terminus of globin (not heme). CO2 binding favors taut form (O2 unloaded).
What chemical reaction does oxygenation promote in the lungs? What effect does this have? Name the effect and describe it.
In the lungs, oxygenation of Hb promotes dissociation of H+ from Hb. This shifts equilibrium toward CO2 formation; therefore, CO2 is released from RBCs (Haldane effect)
What happens in the peripheral tissue with regard to Hb and O2, and why? What is the name of this effect?
In peripheral tissue, high H+ from tissue metabolism shifts curve to right, unloading O2 (Bohr effect).
How is the majority of blood CO2 carried, and where?
Majority of blood CO2 is carried as HCO3- in the plasma.
Draw a diagram depicting the creation of 3 forms of CO2 by which CO2 in transported from tissues to lungs.
See p. 601 in First Aid 2014 for visual
What changes occur to blood gases in response to high altitude, and why?
Low atmospheric oxygen –> Low PaO2 –> increased ventilation –> low PaCO2
How is ventilation affected by high altitude?
Chronic increase in ventilation.
How is erythropoietin affected by high altitude? What effect(s) does this have?
Increased erythropoietin –> increased hematocrit and Hb (chronic hypoxia)
How does 2,3-BPG change in response to high altitude? What effect does this have?
Increase 2,3-BPG (binds to Hb so that Hb releases more O2)
What is an example of a cellular change that occurs in response to high altitude?
Cellular changes (increased mitochondria)
What does renal system do in response to high altitude, and why?
Increased renal excretion of HCO3- (e.g., can augment by use of acetazolamide) to compensate for the respiratory alkalosis
What is the response to high altitude by pulmonary vasculature? What result does it cause?
Chronic hypoxic pulmonary vasoconstriction results in RVH.
What is the response to exercise in terms of production and consumption of gases?
Increased CO2 production, Increased O2 consumption
How is the ventilation rate changed in response to exercise, and why?
Increased ventilation rate to meet O2 demand.
How is V/Q ratio affected in response to exercise?
V/Q ratio from apex to base becomes more uniform
How is pulmonary blood flow changed in response to exercise, and why?
Increased pulmonary blood flow due to increased cardiac output
How is the pH changed in response to exercise, and in what context?
Decreased pH during strenuous exercise (secondary to lactic acidosis)
What is the response to exercise in terms of arterial and venous blood gases?
No change in PaO2 and PaCO2, but increased in venous CO2 content and decreased in venous O2 content
