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Questions and Answers
What is the typical normal value for anatomic dead space in mL?
Which situation indicates that physiologic dead space may be greater than anatomic dead space?
What does the equation $V_D = V_T \times \frac{P_{aCO_2} - P_{ECO_2}}{P_{aCO_2}}$ calculate?
How is minute ventilation calculated?
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What is the effect of increased alveolar ventilation on arteriolar Pco2?
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What is the formula for calculating alveolar ventilation?
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What is the normal respiratory rate range for a healthy adult in breaths per minute?
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The apex of a healthy lung primarily contributes to which of the following?
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What happens to the V/Q ratio in the lungs during exercise?
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What physiological change occurs in response to strenuous exercise regarding pulmonary resistance?
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How does the venous CO2 content change in response to exercise?
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What type of acid-base disturbance is initially caused by ascent to high altitude?
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What effect does living at high altitude have on erythropoietin synthesis?
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What is the primary respiratory response to decreased PaO2 at high altitude?
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What is the effect of carbonic anhydrase inhibitors on acute respiratory alkalosis due to high altitude?
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What happens to the number of mitochondria in response to living at high altitude?
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What is the primary reason for fetal hemoglobin (HbF) having a higher O2 binding affinity compared to adult hemoglobin (HbA)?
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What is the equation used to calculate the O2 content of blood?
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What form of hemoglobin is primarily found in the lungs?
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What is the P50 value related to in the oxygen-hemoglobin dissociation curve?
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What does the sigmoidal shape of the oxygen-hemoglobin dissociation curve indicate?
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In what scenario is SaO2 typically normal despite decreased hemoglobin levels?
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What physiological state characterizes the taut form of hemoglobin?
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What is the average concentration of hemoglobin in blood?
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What change occurs in hemoglobin concentration during polycythemia?
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What effect does decreased O2 binding to hemoglobin have?
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How is the majority of CO2 transported in the blood?
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What initiates the synthesis of erythropoietin (EPO) in the kidneys?
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In which lung zone is blood flow highest?
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Which process buffers H+ ions in red blood cells?
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During oxygenation of hemoglobin in the lungs, what happens to H+ ions?
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What is a consequence of right-to-left shunts?
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In the lungs, what occurs when HCO3- enters red blood cells?
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What characterizes the pulmonary circulation under normal conditions?
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What is the normal average value for the ventilation/perfusion (V/Q) ratio?
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In which zone of the lung is the ventilation/perfusion (V/Q) ratio lowest?
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What type of V/Q mismatch occurs due to an airway obstruction?
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What condition leads to a V/Q ratio of infinity (∞)?
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Does 100% O2 improve PaO2 in V/Q mismatch due to pulmonary embolus?
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Study Notes
Pulmonary Physiology
- Tuberculosis often occurs in the apex of the lung
- Exercise causes vasodilation of apical capillaries in the lung, which leads to a V/Q ratio closer to 1
- Exercise increases O2 consumption and ventilation rate to meet O2 demand
- Exercise makes the V/Q ratio from apex to base more even
- Exercise increases pulmonary blood flow, due to increased cardiac output
- Exercise decreases pulmonary resistance
- Strenuous exercise leads to decreased pH due to lactic acidosis
- Exercise does not cause a change in PaCO2 or PaO2
- Exercise increases venous CO2 content and decreases venous O2 content
- Decreased atmospheric oxygen (e.g., high altitude) decreases PaO2
- Decreased PaO2 (e.g., high altitude) increases ventilation
- Increased ventilation (e.g., high altitude) decreases PaCO2
- High altitude causes initial respiratory alkalosis and hypoxia, which can cause acute altitude sickness
- High altitude leads to a chronic increase in ventilation
- Respiratory alkalosis due to high altitude can be treated with carbonic anhydrase inhibitors
- Living at high altitude causes chronic hypoxia, which increases erythropoietin synthesis and leads to polycythemia
- High altitude causes an increase in 2,3-BPG and intracellular changes like increased mitochondria
- Respiratory alkalosis causes increased functional residual capacity (FRC) and total lung capacity (TLC)
- FRC can be measured with helium dilution or body plethysmography
- Anatomic dead space is typically 150 mL
- Physiologic dead space includes anatomic and alveolar dead space
- Alveolar dead space is greatest in the apex of a healthy lung
- Physiologic dead space is the total volume of inspired air that does not participate in gas exchange
- Physiologic dead space is equal to anatomic dead space in healthy lungs
- Physiologic dead space can be greater than the anatomic dead space in certain conditions, suggesting a V/Q mismatch
- Pathologic dead space occurs when part of the respiratory zone is ventilated but not perfused
- Physiologic dead space can be calculated using the equation: [V_D = V_T \times \frac{P_{aCO_2} \space - \space P_{ECO_2} }{P_{aCO_2} }]
- Minute ventilation is the total volume of gas entering the lungs per minute
- Alveolar ventilation is the volume of gas reaching the alveoli per minute, accounting for physiologic dead space
- Minute ventilation can be calculated as Minute Ventilation (VE) = VT × RR
- Alveolar ventilation can be calculated as Alveolar Ventilation (VA) = (VT - VD) × RR
- Normal respiratory rate for a healthy adult is 12-20 breaths/min
- Arterial and alveolar Pco2 is determined by alveolar ventilation if CO2 production is constant
- Increased alveolar ventilation decreases arteriolar and alveolar Pco2
- Decreased alveolar ventilation increases arteriolar and alveolar Pco2
- Methemoglobinemia can be caused by exposure to certain chemicals (e.g., benzocaine, dapsone)
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Methemoglobinemia is associated with:
- Decreased SaO2 (typically to 85%)
- Decreased O2 content
- Normal PaO2
- Decreased PaCO2
- Most adult hemoglobin is composed of 2 α and 2 β subunits, known as HbA
- Fetal hemoglobin (HbF) has a much higher O2 binding affinity than adult hemoglobin (HbA)
- HbF has a higher O2 binding affinity to drive O2 diffusion across the placenta from mother to fetus
- HbF has decreased affinity for 2,3-BPG, leading to its increased O2 binding affinity
- Hemoglobin exists in two forms: taut (deoxygenated) and relaxed (oxygenated)
- Taut form has a low affinity for O2
- Relaxed form has a high affinity for O2
- Taut form is found in most tissues (where O2 is released from hemoglobin)
- Relaxed form is found in the lungs (where O2 binds to hemoglobin)
- 1 gram of hemoglobin can bind 1.34 mL of O2
- Normal hemoglobin concentration in blood is ~15 g/dL
- O2-binding capacity of blood is 20.1 mL O2 / 100 mL blood
- O2 content of blood can be calculated as O2 content = (1.34 × Hb × SaO2) + (0.003 × PaO2)
- Anemia causes decreased hemoglobin concentration, which leads to decreased O2 content but normal SaO2 and PaO2
- O2 delivery to tissues can be calculated as O2 delivery = CO × O2 content of blood
- Sigmoidal shape of the oxygen-hemoglobin dissociation curve is due to positive cooperativity
- One myoglobin molecule can bind one O2 molecule
- P50 of the oxygen-Hb dissociation curve is the Po2 at which hemoglobin is 50% saturated
- Oxygen-Hb dissociation curve is roughly flat between 60 and 100 mmHg Po2
- Oxygen-myoglobin dissociation curve is normal, not sigmoidal
- Anemia decreases hemoglobin concentration
- Polycythemia increases hemoglobin concentration, O2 content with normal SaO2 and PaO2
- Erythropoietin (EPO) is a hormone synthesized in the kidneys in response to hypoxia
- Hypoxia causes decreased O2 delivery to the kidneys, which increases hypoxia-inducible factor 1α production, stimulating EPO synthesis
- Hypoxia-inducible factor 1α acts in renal fibroblasts to synthesize erythropoietin mRNA
- EPO causes differentiation of proerythroblasts, which become mature erythrocytes
- Deoxygenated hemoglobin can act as a buffer for H+ ions
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CO2 is transported in the blood in three forms:
- Dissolved CO2 (5%)
- Carbaminohemoglobin (HbCO2) (25%)
- Bicarbonate (HCO3-) (70%)
- CO2 binds to hemoglobin at the N-terminus of globin
- Decreased O2 binding to hemoglobin causes increased affinity for CO2 and H+ (Haldane effect)
- Increased O2 binding to hemoglobin causes decreased affinity for CO2 (Haldane effect)
- In red blood cells (in plasma), CO2 combines with H2O via carbonic anhydrase, forming H2CO3
- H+ in red blood cells from H2CO3 is buffered by deoxyhemoglobin
- HCO3- in red blood cells* is transported into the plasma in exchange for Cl-
- HCO3- in the plasma is carried to the lungs in venous blood
- Oxygenation of hemoglobin in the lungs promotes H+ release from its buffering sites
- HCO3- enters the red blood cells in the lungs in exchange for Cl-
- H2CO3 in the red blood cell is reconverted to CO2 and H2O and expired
- Cl--HCO3- exchange across the RBC membrane is mediated by band 3 protein
- Pulmonary circulation is characterized by low resistance and high compliance
- Decreased PAO2 causes hypoxic vasoconstriction, shunting blood away from poorly ventilated areas
- Fetal pulmonary vascular resistance is very high due to generalized hypoxic vasoconstriction
- Hypoxia causes vasoconstriction in pulmonary circulation
- Hypercapnia causes vasoconstriction in pulmonary circulation
- Hypoxia causes vasodilation in systemic circulation
- Hypercapnia causes vasodilation in systemic circulation
- Blood flow (Q) is lowest in zone 1 (apex) of the lung
- Blood flow (Q) is highest in zone 3 (base) of the lung
- Pressure relationships in zone 1: PA ≥ Pa > Pv
- Pressure relationships in zone 2: Pa > PA > Pv
- Pressure relationships in zone 3: Pa > Pv > PA
- Zone 1 has high alveolar pressure that can compress capillaries and reduce blood flow
- Zone 2 blood flow is driven by the difference between arteriolar and alveolar pressure
- Zone 3 blood flow is driven by the difference between arteriolar and venous pressure
- Right-to-left shunts cause hypoxemia, as cardiac output is not delivered to the lungs
- Hypoxemia due to right-to-left shunt cannot be corrected with high O2 gas
- Left-to-right shunts do not cause hypoxemia
- V/Q ratio is the ratio of alveolar ventilation to pulmonary blood flow
- Normal average V/Q ratio is 0.8
- Alveolar ventilation (V) is lowest in zone 1 (apex) of the lung
- Alveolar ventilation (V) is highest in zone 3 (base) of the lung
- Ventilation and perfusion are greater at the base than the apex
- V/Q ratio is highest in zone 1 (apex) of the lung
- V/Q ratio is lowest in zone 3 (base) of the lung
- V/Q ratio is normally 3 at the apex indicating wasted ventilation
- V/Q ratio is normally 0.6 at the base indicating wasted perfusion
- Ideal V/Q ratio for gas exchange is 1 (ventilation matches perfusion)
- Blood flow obstruction creates a V/Q ratio of ∞ (dead space)
- Airway obstruction creates a V/Q ratio of 0 (shunt)
- Dead space is ventilation of lung regions that are not perfused (V/Q = ∞)
- Shunting is perfusion of lung regions that are not ventilated (V/Q = 0)
- Pulmonary embolus causes dead space V/Q mismatch
- Airway obstruction causes shunt V/Q mismatch
- 100% O2 improves PaO2 in dead space V/Q mismatch if less than 100% dead space
- 100% O2 does not improve PaO2 in shunt V/Q mismatch
- High O2 organisms (e.g., M. tuberculosis) flourish in the apex of the lung
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Description
Test your knowledge on pulmonary physiology and the effects of exercise and high altitude on lung function. This quiz covers topics such as V/Q ratios, oxygen consumption, and the body's response to different environmental conditions. Challenge yourself to see how well you understand these crucial concepts.
