Compliance — MCQs
On this page
A 68-year-old man with both severe COPD (emphysema) and newly diagnosed idiopathic pulmonary fibrosis presents with worsening dyspnea. His pressure-volume curve shows a complex pattern with features of both diseases. Static compliance measured at mid-lung volumes is 120 mL/cm H2O. His pulmonologist must decide on optimal management. Synthesizing the pathophysiology of both conditions, what represents the most significant clinical challenge in managing his combined disease?
A 42-year-old woman with systemic sclerosis develops both pulmonary fibrosis and chest wall restriction from skin thickening. Her measured total respiratory system compliance is 30 mL/cm H2O. Testing with complete paralysis and positive pressure ventilation shows isolated lung compliance of 50 mL/cm H2O. She is being considered for immunosuppressive therapy versus supportive care. Evaluate which intervention would provide the greatest improvement in her respiratory mechanics.
A 58-year-old man with end-stage pulmonary fibrosis is being evaluated for lung transplantation. His current static compliance is 25 mL/cm H2O (normal: 200 mL/cm H2O). He also has mild obesity (BMI 32) and ankylosing spondylitis affecting chest wall mobility. Post-transplant, assuming successful bilateral lung transplant with normal donor lungs, what would be the expected change in his total respiratory system compliance?
A research study compares two patients with different lung pathologies but identical functional residual capacity (FRC) of 3.0 L. Patient A has pulmonary fibrosis with FRC above the steep portion of the compliance curve. Patient B has emphysema with FRC on the flat upper portion of the curve. Both attempt to inhale the same tidal volume. Analyzing their work of breathing, which statement best characterizes the difference?
A 32-year-old woman develops acute respiratory distress syndrome (ARDS) following sepsis. She is mechanically ventilated with tidal volume 450 mL and plateau pressure 35 cm H2O (PEEP 10 cm H2O). Her static compliance is calculated as 18 mL/cm H2O. The team considers changing ventilator settings. Analyzing her respiratory mechanics, what change would most effectively improve compliance while minimizing ventilator-induced lung injury?
A 55-year-old woman with idiopathic pulmonary fibrosis and a 40-year-old man with severe emphysema both have the same total lung capacity of 4.5 L on pulmonary function testing. However, their pressure-volume curves show opposite patterns. During inspiration from FRC, which patient requires greater change in pleural pressure to achieve the same tidal volume, and why?
A 70-year-old man with severe kyphoscoliosis presents with chronic dyspnea. Pulmonary function testing shows reduced total lung capacity and functional residual capacity. His lung tissue biopsy is normal, but respiratory muscle strength testing shows normal values. Analysis of his pressure-volume curve shows a normal curve for lung tissue alone, but decreased total respiratory system compliance. What explains his respiratory mechanics?
A premature infant born at 28 weeks gestation develops respiratory distress syndrome. Arterial blood gas shows pH 7.25, PaCO2 55 mmHg, PaO2 50 mmHg on 60% FiO2. Chest X-ray reveals ground-glass opacities. Surfactant therapy is administered. Which mechanism best explains the improvement in lung mechanics following treatment?
A 45-year-old woman presents with progressive dyspnea and dry cough over 6 months. Chest CT shows bilateral interstitial infiltrates. Pulmonary function tests reveal FEV1/FVC ratio of 0.85, reduced total lung capacity, and a steep pressure-volume curve shifted downward and to the right. What is the primary mechanical change in her lungs?
A 65-year-old man with COPD undergoes pulmonary function testing. His FEV1 is 65% predicted, and spirometry shows an obstructive pattern. A pressure-volume loop demonstrates reduced elastic recoil with increased total lung capacity. When comparing his lungs to a healthy individual, what physiological change best explains his altered compliance?
Compliance US Medical PG Practice Questions and MCQs
Question 1: A 68-year-old man with both severe COPD (emphysema) and newly diagnosed idiopathic pulmonary fibrosis presents with worsening dyspnea. His pressure-volume curve shows a complex pattern with features of both diseases. Static compliance measured at mid-lung volumes is 120 mL/cm H2O. His pulmonologist must decide on optimal management. Synthesizing the pathophysiology of both conditions, what represents the most significant clinical challenge in managing his combined disease?
- A. Pulmonary rehabilitation cannot address the opposing mechanical derangements
- B. The increased compliance from emphysema completely negates decreased compliance from fibrosis
- C. The opposing effects on compliance create a pseudonormal total respiratory compliance masking disease severity (Correct Answer)
- D. Emphysema treatment with bronchodilators will worsen fibrosis progression
- E. Oxygen therapy beneficial for COPD will accelerate fibrotic changes
Explanation: ***The opposing effects on compliance create a pseudonormal total respiratory compliance masking disease severity*** - In **Combined Pulmonary Fibrosis and Emphysema (CPFE)**, the **increased lung compliance** from upper-lobe emphysema is offset by the **decreased compliance** from lower-lobe fibrosis. - This results in a **pseudonormalization** of lung volumes (like FVC and TLC) and compliance measurements, which can lead to a significant **underestimation of disease severity** during clinical assessment. *Pulmonary rehabilitation cannot address the opposing mechanical derangements* - While mechanical derangements are complex, **pulmonary rehabilitation** remains a cornerstone of management to improve functional capacity and reduce dyspnea in both conditions. - The challenge is not that rehabilitation is ineffective, but rather the **physiological monitoring** and objective assessment of progress are hampered by masked lung volumes. *The increased compliance from emphysema completely negates decreased compliance from fibrosis* - The two forces do not perfectly negate each other; rather, they coexist to produce a **paradoxical physiological profile** where static measurements appear mid-range while gas exchange is severely impaired. - Patients often exhibit a **disproportionate reduction in DLCO** (diffusion capacity) despite relatively preserved lung volumes, indicating the negation is only superficial and numerical. *Emphysema treatment with bronchodilators will worsen fibrosis progression* - There is no clinical evidence suggesting that **bronchodilators** (beta-agonists or anticholinergics) used for COPD/emphysema accelerate the **pathological scarring** seen in idiopathic pulmonary fibrosis. - Bronchodilators primarily target **airway smooth muscle** and do not interfere with the fibroblastic pathways driving interstitial lung disease. *Oxygen therapy beneficial for COPD will accelerate fibrotic changes* - **Long-term oxygen therapy (LTOT)** is used to treat chronic hypoxemia in both COPD and fibrosis and does not cause or accelerate **lung remodeling** or fibrosis. - While high concentrations of inspired oxygen (FiO2) can cause **oxidative stress**, the flow rates used for clinical management do not contribute to the progression of pulmonary fibrosis.
Question 2: A 42-year-old woman with systemic sclerosis develops both pulmonary fibrosis and chest wall restriction from skin thickening. Her measured total respiratory system compliance is 30 mL/cm H2O. Testing with complete paralysis and positive pressure ventilation shows isolated lung compliance of 50 mL/cm H2O. She is being considered for immunosuppressive therapy versus supportive care. Evaluate which intervention would provide the greatest improvement in her respiratory mechanics.
- A. Supportive care only, as both components contribute equally and irreversibly
- B. Combined therapy targeting lung disease with chest wall mobilization (Correct Answer)
- C. Aggressive immunosuppression targeting both lung and skin disease
- D. Lung-directed therapy only, as it contributes more to total compliance reduction
- E. Chest wall-directed physical therapy, as it is the primary limiting factor
Explanation: ***Combined therapy targeting lung disease with chest wall mobilization*** - The total respiratory compliance (Ct) is calculated using the formula **1/Ct = 1/Clung + 1/Cchest wall**; here, 1/30 = 1/50 + 1/Ccw, which calculates the **chest wall compliance** as 75 mL/cm H2O. - Both the lungs (50 mL/cm H2O) and chest wall (75 mL/cm H2O) are significantly below the **normal value of ~200 mL/cm H2O**, meaning both require intervention for meaningful improvement. *Supportive care only, as both components contribute equally and irreversibly* - While both contribute, they are not strictly equal (50 vs 75), and **systemic sclerosis**-associated lung/skin disease may respond to modern therapeutic interventions. - Labeling these as **irreversible** ignores potential benefits from immunosuppression in the active inflammatory stages of **interstitial lung disease**. *Aggressive immunosuppression targeting both lung and skin disease* - While immunosuppression addresses the underlying **pathophysiology**, it may not provide immediate mechanical relief for fixed **chest wall restriction**. - Effective management often requires adding **physical therapy** and mobilization to address the extrinsic mechanical constraint caused by **scleroderma skin thickening**. *Lung-directed therapy only, as it contributes more to total compliance reduction* - Although lung compliance (50) is lower than chest wall compliance (75), ignoring the **chest wall component** neglects a significant portion of the patient's **work of breathing**. - Solely treating the lung disease will not bypass the **extrinsic restriction** imposed by the tight skin and musculoskeletal changes. *Chest wall-directed physical therapy, as it is the primary limiting factor* - The calculations show that **lung compliance** is actually more severely reduced (50) than chest wall compliance (75). - Focusing only on the **chest wall** would leave the primary cause of the **restrictive ventilatory defect** (pulmonary fibrosis) unaddressed.
Question 3: A 58-year-old man with end-stage pulmonary fibrosis is being evaluated for lung transplantation. His current static compliance is 25 mL/cm H2O (normal: 200 mL/cm H2O). He also has mild obesity (BMI 32) and ankylosing spondylitis affecting chest wall mobility. Post-transplant, assuming successful bilateral lung transplant with normal donor lungs, what would be the expected change in his total respiratory system compliance?
- A. Improved lung compliance but worsened chest wall compliance from surgery
- B. Worse compliance initially due to transplant rejection and denervation
- C. Return to completely normal respiratory compliance matching healthy individuals
- D. Improved but still reduced compliance due to persistent chest wall restriction (Correct Answer)
- E. No significant change because the primary problem is muscular weakness
Explanation: ***Improved but still reduced compliance due to persistent chest wall restriction*** - Total respiratory system compliance follows the formula **1/C_total = 1/C_lungs + 1/C_chest_wall**, meaning the total compliance is limited by the stiffest component. - While the lung transplant corrects the **pulmonary fibrosis**, the patient's **obesity** and **ankylosing spondylitis** cause extrinsic restriction that maintains a low **chest wall compliance**. *Improved lung compliance but worsened chest wall compliance from surgery* - Although surgical trauma can temporarily affect chest wall dynamics, the **ankylosing spondylitis** is the primary chronic factor limiting chest wall expansion here. - The logic is flawed because the improvement in **lung compliance** from the donor lungs far outweighs any minor surgical stiffness in the long term. *Worse compliance initially due to transplant rejection and denervation* - **Denervation** typically leads to loss of the cough reflex but does not significantly alter the mechanical **elasticity** or compliance of the lung tissue itself. - Acute rejection would decrease compliance, but the question asks for the "expected" outcome of a **successful bilateral transplant**. *Return to completely normal respiratory compliance matching healthy individuals* - Total compliance cannot return to normal because the **chest wall** remains stiff due to the patient's underlying skeletal and adipose conditions. - Even with perfect donor lungs, the **extrapulmonary restriction** means the total system compliance will remain below the normal **200 mL/cm H2O**. *No significant change because the primary problem is muscular weakness* - The patient's primary problem in the lungs was **pulmonary fibrosis**, which is a mechanical parenchymal issue, not purely muscular weakness. - Total compliance will definitely show a **significant increase** from the baseline of 25 mL/cm H2O because the severely stiff fibrotic lungs have been replaced.
Question 4: A research study compares two patients with different lung pathologies but identical functional residual capacity (FRC) of 3.0 L. Patient A has pulmonary fibrosis with FRC above the steep portion of the compliance curve. Patient B has emphysema with FRC on the flat upper portion of the curve. Both attempt to inhale the same tidal volume. Analyzing their work of breathing, which statement best characterizes the difference?
- A. Patient B does less work because emphysematous lungs are more compliant
- B. Patient A does less work because fibrotic lungs have increased elastic recoil assisting inspiration
- C. Patient A does more elastic work; Patient B does more resistive work
- D. Patient B does more elastic work due to hyperinflation beyond optimal compliance (Correct Answer)
- E. Both do equal work because FRC and tidal volumes are identical
Explanation: ***Patient B does more elastic work due to hyperinflation beyond optimal compliance*** - In **emphysema**, although the lung itself is more compliant, operating on the **flat upper portion** of the pressure-volume curve means that very high pressures are required to increase volume further. - **Hyperinflation** causes the patient to breathe at high lung volumes where the **chest wall compliance** also decreases, significantly increasing the **elastic work of breathing**. *Patient B does less work because emphysematous lungs are more compliant* - While **static compliance** is higher in emphysema, the patient's position on the **asymptotic portion** of the curve makes the **dynamic work** much higher for each breath. - This ignore the **obstructive pathology** and the mechanical disadvantage of a flattened **diaphragm** that increases total work. *Patient A does less work because fibrotic lungs have increased elastic recoil assisting inspiration* - **Increased elastic recoil** in fibrosis actually **opposes inspiration**, making it harder to expand the lungs and increasing work. - Fibrotic lungs have **decreased compliance** across all volumes, necessitating greater **transpulmonary pressure** for a given tidal volume. *Patient A does more elastic work; Patient B does more resistive work* - While Patient B does have increased **resistive work** due to airway collapse, this option ignores the massive increase in **elastic work** occurring at the top of the compliance curve. - Patient B's work is elevated by both **resistive** and **elastic** components due to the loss of **radial traction** and hyperinflation respectively. *Both do equal work because FRC and tidal volumes are identical* - Work of breathing depends on the **slope of the pressure-volume curve** (compliance) at the specific starting volume, not just the volume itself. - Identical **Functional Residual Capacity (FRC)** does not equate to identical **respiratory mechanics** when the underlying lung pathologies are opposites like fibrosis and emphysema.
Question 5: A 32-year-old woman develops acute respiratory distress syndrome (ARDS) following sepsis. She is mechanically ventilated with tidal volume 450 mL and plateau pressure 35 cm H2O (PEEP 10 cm H2O). Her static compliance is calculated as 18 mL/cm H2O. The team considers changing ventilator settings. Analyzing her respiratory mechanics, what change would most effectively improve compliance while minimizing ventilator-induced lung injury?
- A. Switch to pressure-control mode with same plateau pressure
- B. Increase respiratory rate while maintaining current tidal volume
- C. Increase tidal volume to 600 mL to recruit more alveoli
- D. Decrease PEEP to 5 cm H2O to reduce plateau pressure
- E. Increase PEEP to 15 cm H2O to prevent alveolar collapse (Correct Answer)
Explanation: ***Increase PEEP to 15 cm H2O to prevent alveolar collapse*** - In **ARDS**, low compliance is driven by **atelectrauma** and alveolar flooding; increasing **PEEP** recruits collapsed alveoli, shifting the lung to a more compliant part of the **pressure-volume curve**. - Targeted recruitment through higher **PEEP** reduces **biotrauma** and cyclic opening/closing of units, effectively improving **static compliance** in a "recruitable" lung. *Switch to pressure-control mode with same plateau pressure* - Transitioning to **pressure-control ventilation (PCV)** provides a decelerating flow profile but does not inherently change the **static compliance** of the lung tissue. - Without adjusting the **distending pressure** or recruiting new alveoli, the underlying mechanical properties and risk of **lung injury** remain similar. *Increase respiratory rate while maintaining current tidal volume* - Increasing the **respiratory rate** helps manage **hypercapnia** but does not improve the **static compliance** of the respiratory system. - This strategy does not address **alveolar recruitment** and may lead to **auto-PEEP** if expiratory time is insufficient. *Increase tidal volume to 600 mL to recruit more alveoli* - This would likely cause **volutrauma** and further increase the **plateau pressure** beyond the safe limit of 30 cm H2O, worsening lung injury. - High **tidal volumes** in ARDS are associated with increased mortality due to **overdistension** of the "baby lung." *Decrease PEEP to 5 cm H2O to reduce plateau pressure* - While this might lower the **plateau pressure**, it would lead to widespread **alveolar de-recruitment** and worsens oxygenation. - Decreasing **PEEP** in ARDS often results in a further drop in **compliance** due to the loss of functional lung volume (atelectasis).
Question 6: A 55-year-old woman with idiopathic pulmonary fibrosis and a 40-year-old man with severe emphysema both have the same total lung capacity of 4.5 L on pulmonary function testing. However, their pressure-volume curves show opposite patterns. During inspiration from FRC, which patient requires greater change in pleural pressure to achieve the same tidal volume, and why?
- A. The fibrosis patient, because increased surface tension prevents alveolar expansion
- B. The emphysema patient, because increased airway resistance requires more driving pressure
- C. The emphysema patient, because decreased elastic recoil requires more negative pressure to inflate
- D. The fibrosis patient, because decreased compliance requires greater pressure change for the same volume (Correct Answer)
- E. Both require the same pressure because they have equal total lung capacity
Explanation: ***The fibrosis patient, because decreased compliance requires greater pressure change for the same volume*** - **Inspiration** requires overcoming the stiff lung parenchyma in **idiopathic pulmonary fibrosis**, where **lung compliance** is significantly decreased. - Applying the formula **Compliance = ΔV / ΔP**, a low compliance means a much larger change in **intrapleural pressure (ΔP)** is needed to generate the same **tidal volume (ΔV)**. *The fibrosis patient, because increased surface tension prevents alveolar expansion* - While **stiffness** is present, fibrosis is primarily due to **collagen deposition** in the interstitium rather than a primary defect in **surfactant** or surface tension. - Increasing pressure is required to stretch the **fibrotic tissue**, not necessarily to overcome surface tension at the air-liquid interface. *The emphysema patient, because increased airway resistance requires more driving pressure* - While **emphysema** involves increased airway resistance due to **dynamic compression**, this refers to flow and would not explain why it would require *more* pressure than a stiff lung for volume expansion. - In inspiration, the primary factor determining the pressure-volume relationship is **static compliance**, which is actually high in emphysema. *The emphysema patient, because decreased elastic recoil requires more negative pressure to inflate* - **Decreased elastic recoil** actually means the lungs are more **compliant** (floppy) and easier to distend with very little pressure. - An emphysema patient requires a **smaller** change in transpulmonary pressure to achieve the same volume compared to a healthy or stiff lung. *Both require the same pressure because they have equal total lung capacity* - **Total Lung Capacity (TLC)** is a measurement of volume, whereas the work of breathing depends on the **slope** of the pressure-volume curve, known as **compliance**. - Two patients can reach the same maximal volume but follow entirely different **mechanical paths** to get there based on the health of their elastic fibers.
Question 7: A 70-year-old man with severe kyphoscoliosis presents with chronic dyspnea. Pulmonary function testing shows reduced total lung capacity and functional residual capacity. His lung tissue biopsy is normal, but respiratory muscle strength testing shows normal values. Analysis of his pressure-volume curve shows a normal curve for lung tissue alone, but decreased total respiratory system compliance. What explains his respiratory mechanics?
- A. Primary decrease in lung compliance from parenchymal disease
- B. Combined decrease in lung and chest wall compliance
- C. Respiratory muscle weakness reducing lung volumes
- D. Increased lung compliance with normal chest wall compliance
- E. Primary decrease in chest wall compliance from skeletal deformity (Correct Answer)
Explanation: ***Primary decrease in chest wall compliance from skeletal deformity*** - In patients with **kyphoscoliosis**, the structural **skeletal deformity** stiffens the thoracic cage, leading to a significant **reduction in chest wall compliance**. - This is confirmed by the **normal lung biopsy** and the pressure-volume curve showing **normal lung compliance** but **decreased total respiratory system compliance** (1/Ctotal = 1/Clung + 1/Cchest wall). *Primary decrease in lung compliance from parenchymal disease* - This would typically be seen in **interstitial lung diseases** or fibrosis, but the patient's **lung biopsy is normal** and the lung-only pressure-volume curve is normal. - The pathology here is **extrapulmonary (chest wall)** rather than involving the **lung parenchyma** itself. *Combined decrease in lung and chest wall compliance* - While long-term severe kyphoscoliosis might eventually cause atelectasis, the question explicitly states that the **lung tissue biopsy is normal** and the curve for **lung tissue alone is normal**. - Therefore, the restrictive defect is isolated to the mechanical limitations of the **stiff chest wall**. *Respiratory muscle weakness reducing lung volumes* - This is ruled out because the patient's **respiratory muscle strength testing** showed **normal values**. - Conditions like **Myasthenia Gravis** or **ALS** would cause weakness, but here the issue is a **mechanical/structural resistance** rather than a lack of force. *Increased lung compliance with normal chest wall compliance* - **Increased lung compliance** is a hallmark of **emphysema/COPD**, which would present with increased, not decreased, total lung capacity (TLC). - Kyphoscoliosis presents as a **restrictive lung disease** pattern, characterized by **reduced TLC** and **decreased compliance** of the respiratory system.
Question 8: A premature infant born at 28 weeks gestation develops respiratory distress syndrome. Arterial blood gas shows pH 7.25, PaCO2 55 mmHg, PaO2 50 mmHg on 60% FiO2. Chest X-ray reveals ground-glass opacities. Surfactant therapy is administered. Which mechanism best explains the improvement in lung mechanics following treatment?
- A. Decreased alveolar surface tension increasing compliance (Correct Answer)
- B. Bronchodilation decreasing airway resistance
- C. Strengthened alveolar walls increasing elastic fibers
- D. Increased pulmonary blood flow improving V/Q matching
- E. Increased elastic recoil decreasing compliance
Explanation: ***Decreased alveolar surface tension increasing compliance*** - Exogenous **surfactant** lowers the surface tension at the air-liquid interface of the **alveoli**, preventing them from collapsing at low lung volumes. - By decreasing **surface tension**, the pressure required to expand the lungs is reduced, which directly increases **lung compliance** and decreases the **work of breathing**. *Bronchodilation decreasing airway resistance* - Surfactant acts on the **alveolar surface**, not on the smooth muscle of the bronchioles, so it does not cause **bronchodilation**. - **Respiratory Distress Syndrome (RDS)** is primarily a restrictive disease of the lung parenchyma rather than an obstructive disease of the **airways**. *Strengthened alveolar walls increasing elastic fibers* - Surfactant is a **phospholipid-protein complex** (primarily dipalmitoylphosphatidylcholine) that acts as a detergent; it does not structurally alter **elastic fibers**. - Improvement in lung mechanics is due to **functional changes** in surface forces rather than immediate anatomical changes to the **alveolar walls**. *Increased pulmonary blood flow improving V/Q matching* - While oxygenation improves, the primary mechanism of surfactant is mechanical; any change in **pulmonary blood flow** is a secondary effect of improved **alveolar ventilation**. - Improved **V/Q matching** occurs because previously collapsed alveoli are recruited, but the "best" explanation for the mechanical change is decreased **surface tension**. *Increased elastic recoil decreasing compliance* - Increased **elastic recoil** would make the lungs harder to inflate, which is the opposite of the effect desired in **RDS** treatment. - Surfactant actually facilitates lung expansion by reducing the inward **collapsing pressure** (P = 2T/r) predicted by **Laplace's Law**.
Question 9: A 45-year-old woman presents with progressive dyspnea and dry cough over 6 months. Chest CT shows bilateral interstitial infiltrates. Pulmonary function tests reveal FEV1/FVC ratio of 0.85, reduced total lung capacity, and a steep pressure-volume curve shifted downward and to the right. What is the primary mechanical change in her lungs?
- A. Increased lung compliance with normal chest wall compliance
- B. Normal lung compliance with decreased chest wall compliance
- C. Decreased lung and increased chest wall compliance
- D. Increased lung and chest wall compliance
- E. Decreased lung compliance with normal chest wall compliance (Correct Answer)
Explanation: ***Decreased lung compliance with normal chest wall compliance*** - Pulmonary fibrosis presents with a **restrictive pattern**, characterized by an increased **FEV1/FVC ratio** and a significant reduction in **Total Lung Capacity (TLC)**. - The downward and rightward shift of the **pressure-volume curve** demonstrates that the lungs are stiffer, meaning lower **lung compliance** is required to generate the same volume expansion. *Increased lung compliance with normal chest wall compliance* - This mechanical profile is characteristic of **emphysema**, where the loss of elastic tissue makes the lungs excessively distensible. - In obstructive diseases like emphysema, the **FEV1/FVC ratio** is decreased, and lung volumes are typically increased, not decreased. *Normal lung compliance with decreased chest wall compliance* - This scenario is seen in **extrapulmonary restrictive disorders** such as **obesity**, kyphoscoliosis, or neuromuscular diseases. - While the chest wall restricts expansion, the **lung parenchyma** itself remains healthy and retains its normal elasticity and compliance. *Decreased lung and increased chest wall compliance* - This combination is clinically rare; **increased chest wall compliance** is generally seen in specific pediatric populations (infants) due to a highly pliable rib cage. - In this patient, the **interstitial infiltrates** confirm that the pathology is intrapulmonary, specifically affecting the lung tissue's elastic properties. *Increased lung and chest wall compliance* - Increased compliance in both compartments would result in an extremely high **TLC** and a curve shifted upward and to the left. - This is the opposite of the clinical findings in **restrictive lung disease**, which mandates higher pressures to inflate "stiff" lungs.
Question 10: A 65-year-old man with COPD undergoes pulmonary function testing. His FEV1 is 65% predicted, and spirometry shows an obstructive pattern. A pressure-volume loop demonstrates reduced elastic recoil with increased total lung capacity. When comparing his lungs to a healthy individual, what physiological change best explains his altered compliance?
- A. Increased alveolar surface tension from surfactant deficiency
- B. Increased collagen deposition in interstitial spaces
- C. Bronchial smooth muscle hypertrophy
- D. Destruction of elastic tissue in alveolar walls (Correct Answer)
- E. Pulmonary vascular remodeling
Explanation: ***Destruction of elastic tissue in alveolar walls*** - In **COPD/emphysema**, the degradation of **elastin fibers** by proteases leads to loss of structural integrity and **increased lung compliance**. - Reduced **elastic recoil** means the lungs are more distensible (easily inflated) but fail to collapse efficiently during expiration, causing **air trapping** and increased **Total Lung Capacity (TLC)**. *Increased alveolar surface tension from surfactant deficiency* - **Surfactant deficiency** (typical of **Neonatal Respiratory Distress Syndrome**) increases surface tension, which **decreases compliance** and causes alveolar collapse. - High surface tension makes the lungs stiff and difficult to inflate, which is the opposite of the physiology seen in this **obstructive** case. *Increased collagen deposition in interstitial spaces* - **Interstitial lung diseases** (fibrosis) involve the deposition of **collagen**, which results in stiff lungs and **decreased compliance**. - This pathology presents with a **restrictive pattern** on spirometry, characterized by reduced **TLC**, unlike the increased volumes seen in emphysema. *Bronchial smooth muscle hypertrophy* - This is a hallmark of **Asthma** and **Chronic Bronchitis**, which increases **airway resistance** during expiration rather than changing the elastic properties of the lung parenchyma. - While it contributes to an **obstructive pattern**, it does not explain the specific pressure-volume loop change of **reduced elastic recoil**. *Pulmonary vascular remodeling* - This process involves thickening of the pulmonary arteries and is associated with **pulmonary hypertension**, not primary changes in lung compliance. - While common in advanced COPD, it affects the **circulatory resistance** of the lungs rather than the **elasticity** of the alveolar units.
Question 11: A 57-year-old man comes to the physician because of a 2-year history of fatigue, worsening shortness of breath, and a productive cough for 2 years. He has smoked 1 pack of cigarettes daily for the past 40 years. Examination shows pursed-lip breathing and an increased anteroposterior chest diameter. There is diffuse wheezing bilaterally and breath sounds are distant. Which of the following parameters is most likely to be decreased in this patient?
- A. Thickness of small airways
- B. Work of breathing
- C. Lung elastic recoil (Correct Answer)
- D. Lower airway resistance
- E. Pulmonary vascular pressure
Explanation: ***Lung elastic recoil*** - The patient's presentation (long smoking history, dyspnea, pursed-lip breathing, increased AP diameter, distant breath sounds, and wheezing) is classic for **emphysema**, a form of **COPD**. - Emphysema involves the destruction of **alveolar walls** and **elastic fibers**, leading to a significant decrease in the lung's ability to passively recoil during expiration. *Thickness of small airways* - In COPD, particularly chronic bronchitis, there is often **inflammation and thickening of the small airways** due to goblet cell hyperplasia and mucus gland hypertrophy, increasing their thickness, not decreasing it. - This thickening contributes to increased airway resistance. *Work of breathing* - The **destruction of elastic recoil** in emphysema means the patient must actively use accessory muscles to exhale, significantly **increasing the work of breathing**, which is evident from pursed-lip breathing. - Patients with COPD expend much more energy to breathe than healthy individuals. *Lower airway resistance* - Emphysema, while characterized by alveolar destruction, also has an obstructive component due to **airway collapse during expiration** (loss of radial traction) and potential inflammation/mucus, which leads to **increased lower airway resistance**, not decreased resistance. - This increased resistance contributes to air trapping and wheezing. *Pulmonary vascular pressure* - Chronic hypoxia resulting from severe COPD can lead to **pulmonary vasoconstriction** and remodeling of the pulmonary arteries, causing **pulmonary hypertension** and an increase in pulmonary vascular pressure. - This is a common complication in advanced COPD, not a decreased parameter.
Question 12: A 51-year-old man comes to the physician because of progressive shortness of breath, exercise intolerance, and cough for the past 6 months. He is no longer able to climb a full flight of stairs without resting and uses 3 pillows to sleep at night. He has a history of using cocaine in his 30s but has not used any illicit drugs for the past 20 years. His pulse is 99/min, respiratory rate is 21/min, and blood pressure is 95/60 mm Hg. Crackles are heard in both lower lung fields. An x-ray of the chest shows an enlarged cardiac silhouette with bilateral fluffy infiltrates and thickening of the interlobar fissures. Which of the following findings is most likely in this patient?
- A. Increased carbon dioxide production
- B. Decreased pulmonary vascular resistance
- C. Increased residual volume
- D. Decreased lung compliance (Correct Answer)
- E. Decreased forced expiratory volume
Explanation: ***Decreased lung compliance*** - The patient's symptoms (shortness of breath, orthopnea, crackles) and X-ray findings (enlarged cardiac silhouette, bilateral fluffy infiltrates, interlobar fissure thickening) are classic for **congestive heart failure (CHF)** leading to pulmonary edema. - In CHF, fluid accumulation in the lungs makes them stiffer and harder to inflate, resulting in **decreased lung compliance**. *Increased carbon dioxide production* - While exercise increases carbon dioxide production, the patient's severe **exercise intolerance** suggests he is not performing activity sufficient to cause a significant increase in CO2 production as a primary pathological finding. - Furthermore, this is not a direct consequence of the underlying cardiac pathology described. *Decreased pulmonary vascular resistance* - **Decreased pulmonary vascular resistance** is typically seen in conditions like pulmonary hypertension treated with vasodilators or in some forms of pulmonary shunting, which is the opposite of what would be expected in heart failure with pulmonary congestion. - In heart failure, increased pressures in the left atrium can lead to **increased pulmonary venous and capillary pressures**, often resulting in increased pulmonary vascular resistance over time. *Increased residual volume* - **Increased residual volume** is characteristic of obstructive lung diseases (e.g., emphysema, asthma) due to air trapping. - Pulmonary edema and congestion, as seen in heart failure, cause restrictive physiology and would typically lead to **decreased lung volumes**, including residual volume, due to compression of alveoli by fluid. *Decreased forced expiratory volume* - While heart failure can lead to some airflow limitation due to airway compression from interstitial edema, a **decreased forced expiratory volume (FEV1)** is primarily a hallmark of obstructive lung diseases like COPD or asthma. - The dominant physiological change in this patient's presentation is **restrictive lung disease** due to pulmonary edema, not obstructive.
Practice by Chapter
Definition of lung compliance
Practice Questions
Static vs dynamic compliance
Practice Questions
Pressure-volume curves
Practice Questions
Surfactant function and synthesis
Practice Questions
Surface tension effects on compliance
Practice Questions
Elastic recoil of lung tissue
Practice Questions
Chest wall compliance
Practice Questions
Combined respiratory system compliance
Practice Questions
Altered compliance in disease states
Practice Questions
Restrictive lung disease mechanics
Practice Questions
Obstructive lung disease effects
Practice Questions
Compliance measurement techniques
Practice Questions
Age-related changes in compliance
Practice Questions
Want unlimited practice?
Get full access to all questions, explanations, and performance tracking.
Start For Free