pulmonary circulation Flashcards
Normally, pulmonary circulation is a ____ (high/low) resistance, ____ (high/low) compliance system.
Low, high
Within the lungs, a decrease in PAO2 causes what process to occur within the vasculature in the area?
Hypoxic vasoconstriction
Within the lungs, hypoxic vasoconstriction serves what physiologic function?
• It shifts blood away from the poorly ventilated areas of the lung to those that are well ventilated
Name the perfusion-limited gases.
Oxygen (normal health), carbon dioxide, nitrous oxide
Under perfusion-limited conditions, where along the length of the pulmonary capillary do the partial pressures of a gas equilibrate?
Early (gas exchange is not limited by its ability to cross the membrane, only by the supply of blood)
A patient becomes hypoxic from a massive hemorrhage. Under these perfusion-limited conditions, how can pulmonary gas exchange be increased?
By increasing blood flow
Name the diffusion-limited gases.
• Oxygen (emphysema, fibrosis), carbon monoxide
Under what two conditions is oxygen a diffusion-limited gas?
Emphysema and fibrosis
Under diffusion-limited conditions, where along the length of the pulmonary capillary does the gas equilibrate?
It does not equilibrate (the characteristics of the gas cause it to diffuse slowly across the alveolar membrane)
A patient with untreated pulmonary hypertension presents with jugular venous distention, edema, and hepatomegaly. What caused this?
The patient is showing signs of cor pulmonale (right heart failure), a complication of pulmonary hypertension
What is the equation for diffusion of a gas across a membrane?
Vgas = A/T × Dk(P1 - P2), where A = area, T = thickness, DkP1 - P2) = difference in partial pressures
A patient has emphysema. Which variable is affected by his disease in the equation for gas diffusion, and how? (See image.)
The area of membranes available for gas transfer (A) is decreased in emphysema, causing a decrease in diffusion
In the equation for gas diffusion, which variable is affected by pulmonary fibrosis, and how?
Thickness of the alveolar membrane is increased in pulmonary fibrosis, causing a decrease in diffusion
How is pulmonary vascular resistance calculated?
PVR = pressure in the pulmonary artery - pressure in the left atrium)/cardiac output
How is left atrial pressure measured?
It is approximated by pulmonary wedge pressure
How do you measure pulmonary vascular resistance using flow and the difference in pressure across it?
R = ΔP/Q, where R is resistance, P is pressure, Q is flow
Pulmonary vascular resistance is ____ (directly/inversely) related to vessel length and ____ (directly/inversely) related to vessel radius.
Directly; inversely—R = (8ηl)/(πr4), where η = viscosity of blood, l = vessel length, and r = vessel radius
A patient’s cardiac output is 5 L/min. Ppulm artery is 10 mmHg, & PL atrium is 5 mmHg. What is the pulmonary vascular resistance?
PVR = (Ppulm artery - PL atrium)/cardiac output = ([10 mmHg - 5 mmHg])/5 L/min) = 1 (mmHg × min)/L
Matt’s pulmonary vascular resistance is 2 (mmHg × min)/L. If Ppulm artery is 20 mmHg and PL atrium is 8 mmHg, find the cardiac output.
CO = 6 L/min, as PVR = (Ppulm artery - PL atrium)/cardiac output = 2 (mmHg × min)/L = ([20 mmHg - 8 mmHg])/cardiac output)
Define the variables of the full alveolar gas equation: PAO2= PIO2 - PaCO2/R.
PAO2 = alveolar PO2, PIO2 = PO2 in inspired air, PaCO2 = arterial PCO2, R = respiratory quotient = CO2 produced/O2 consumed
How can the alveolar gas equation be simplified and approximated (assuming that the patient is breathing ambient air)?
PAO2 = 150 - (PaCO2/0.8)
By using the alveolar gas equation, what important measure of pulmonary function can be determined?
The alveolar-arterial gradient
What is the normal alveolar-arterial gradient?
10–15 mmHg
Explain why the alveolar-arterial gradient might be elevated. What three pathologic processes can cause this?
V/Q mismatches, diffusion limitations (fibrosis), and shunting (a rise in the A-a gradient may occur in hypoxemia)
A patient has a respiratory quotient (R) of 1.0. What does this tell you about current metabolic state?
The respiratory quotient (R) is a ratio of carbon dioxide produced to oxygen consumed
A patient breathes air with a PO2 of 100 mmHg. PaCO2 is 30 mmHg. With a respiratory quotient of 0.6, what is alveolar O2?
50 mmHg, as PAO2 = PIO2 - PaCO2/R = 100 mmHg - (30 mmHg/0.6)
A patient’s alveolar PO2 is 100 mmHg. Air PO2 is 150 mmHg. Assuming a respiratory quotient of 0.8, what is their arterial CO2?
40 mmHg, as = PAO2 = PlCO2 - PaCO2/R = 100 mmHg = 150 mmHg - (× mmHg/0.8)
Name five processes that can lead to hypoxemia (decreased arterial oxygen).
High altitude, hypoventilation, ventilation/perfusion ratio mismatches, diffusion limitations, and right-to-left shunting
Which two processes lead to hypoxemia with a normal A-a gradient?
High altitude and hypoventilation (e.g., opioid use)
Which three processes can lead to hypoxemia with an increased A-a gradient?
Ventilation/perfusion ratio mismatches, diffusion limitation, and right-to-left shunting
Name four processes that can lead to hypoxia (decreased oxygen delivery to tissue).
Decreased cardiac output, hypoxemia, anemia, and carbon monoxide poisoning
Name two processes that can lead to ischemia (loss of blood flow).
Impeded arterial flow and reduced venous drainage
What is the difference between hypoxemia and hypoxia?
Hypoxemia is decreased arterial partial pressure of oxygen, whereas hypoxia is decreased oxygen delivery to tissue
A patient appears sedated and is breathing slowly after a painful surgical procedure. What is his likely A-a gradient?
The A-a gradient would be normal (he was likely given too much pain control with opioids, causing sedation and hypoventilation)
A hiker is weak after rapidly ascending a mountain. What is his likely A-a gradient?
The A-a gradient would be normal in cases of hypoxemia caused by high altitudes
A patient is found to have a diffusion limitation in his lungs. How is his likely A-a gradient affected?
It is increased
A patient develops a pulmonary embolus. What is his likely A-a gradient?
This is a case of V/Q mismatch, which would cause an increased A-a gradient
A patient is found to have a right-to-left shunt. How is his likely A-a gradient affected?
It is increased
A patient has tuberculosis. This and other microorganisms that thrive in high-oxygen environments flourish in which part of the lungs?
The apex
A woman chokes and aspirates a peanut. What is her ventilation/perfusion ratio likely to be?
Approaching 0, as airway obstruction creates a blood flow shunt which isn’t part of gas exchange (0 = “oirway” obstruction)
A child chokes on a peanut. This airway obstruction leads to perfusion with no ventilation within an area of the lungs. What is this called?
A shunt
A man suffers a pulmonary embolus. What is his ventilation/perfusion ratio likely to be?
Approaching ∞, as the pulmonary embolus is a blood flow obstruction, causing physiologic dead space (∞ = blood flow obstruction)
Which zone of the lung is associated with wasted ventilation?
Zone 1
Which zone of the lung is associated with wasted perfusion?
Zone 3
In a hypoxic patient due to ____ (dead space/shunting), 100% oxygen does not improve the partial pressure of oxygen in the blood.
Shunting
In a hypoxic patient due to ____ (dead space/shunting), 100% oxygen does improve the partial pressure of oxygen in the blood.
Dead space (assuming the dead space is
What is the ideal ventilation/perfusion ratio for gas exchange?
1:1
Within what part of the lung does ventilation/perfusion equal approximately 3?
The apex of the lung
In the apex of the lung, there is wasted ____ (perfusion/ventilation).
Ventilation
Within what part of the lung does ventilation/perfusion equal approximately 0.6?
The base of the lung
Is ventilation greater at the base of the lung or the apex of the lung?
The base of the lung
Is perfusion greater at the base of the lung or the apex of the lung?
The base of the lung
A patient exercises. The vasodilation of the apical capillaries of the lung results in what change to the ventilation/perfusion ratio?
The ventilation/perfusion ratio approaches 1, maximizing gas exchange to meet the metabolic demands of exercise
Once inside a red blood cell, carbon dioxide combines with which molecule to eventually become bicarbonate?
Water
What enzyme catalyzes the conversion of carbon dioxide and water into carbonic acid?
Carbonic anhydrase
Within a red blood cell, the carbonic acid formed from the combination of carbon dioxide and water dissociates into what two compounds?
Hydrogen and bicarbonate ions
What is the fate of the bicarbonate that results from the deprotonation of carbonic acid within a red blood cell?
It gets exchanged out of the red blood cell for a chloride molecule that enters the red blood cell
In the lungs, the oxygenation of hemoglobin promotes what?
The dissociation of a proton from hemoglobin and therefore a decrease in pH, which favors formation of carbon dioxide from bicarbonate
Name the effect in which oxygenation of hemoglobin in the lungs promotes H+ dissociation, causing CO2 release from RBCs.
The Haldane effect
A woman has lactic acidosis. How will this pH reduction in the peripheral tissues relative to the lungs shift the oxygen dissociation curve?
It will shift it to the right, favoring dissociation of oxygen from hemoglobin
In peripheral tissue, the right shift of the oxygen dissociation curve causes oxygen unloading. What is this effect called?
The Bohr effect
A hiker goes up to high altitudes for an afternoon. What happens to his ventilation, PaO2, and PaCO2?
PaO2 and PaCO2 decrease, as ventilation is increased
A patient has been living high in the mountains for years. What happens to his erythropoietin levels?
In response to high altitude, erythropoietin levels are increased, as are hematocrit and hemoglobin
A hiker ascends a mountain. What happens to his level of 2,3-bisphosphoglycerate?
In response to high altitude, the 2,3-BPG level increases
What substance binds to hemoglobin so that hemoglobin releases more oxygen as a physiologic response to high altitude?
2,3-bisphosphoglycerate
A hiker climbs up a tall mountain. What cellular change occurs in response to this?
An increase in the number of mitochondria occurs in response to high altitude
A man ascends a mountain. Increased renal excretion of what substance occurs in response?
Bicarbonate
The increased renal excretion of bicarbonate that is seen in response to high altitude compensates for what?
The respiratory alkalosis that occurs as a result of increased ventilation
The increased renal excretion of bicarbonate that is seen in response to high altitude can be augmented using what?
Acetazolamide
A man decides to live in the mountains for several years. In response, chronic hypoxic pulmonary vasoconstriction results in what condition?
Right ventricular hypertrophy
A man undergoes an exercise test. What happens to carbon dioxide production in his muscles? Oxygen consumption? Rate of ventilation?
They are all increased
A man undergoes an exercise test. What happens to the ventilation/perfusion ratio?
It becomes more uniform from apex to base
A woman undergoes an exercise test. What happens to pulmonary blood flow?
It increases due to increased cardiac output
A personal trainer undergoes strenuous exercise. How does the pH of the body change?
pH decreases during strenuous exercise due to lactic acidosis
PaO2 and PaCO2 ____ (increase/decrease/stay the same) in response to exercise.
Stay the same
When a patient exercises, the venous CO2 content ____ (increases/decreases), whereas venous O2 content ____ (increases/decreases).
Increases, decreases
