Respiratory System — MCQs

Respiratory System Indian Medical PG Practice Questions and MCQs

Question 721: Which of the following describes the chloride ion exchange in red blood cells, where bicarbonate ions are exchanged for chloride ions to maintain electrical neutrality?

A. Root effect
B. Chloride shift (Correct Answer)
C. Bohr effect
D. Haldane effect

Explanation: ***Chloride shift***- This is the term for the exchange of a **bicarbonate ion** ($ ext{HCO}_3^-$) moving out of the red blood cell for a **chloride ion** ($ ext{Cl}^-$) moving into the cell to maintain **electrical neutrality**. - It is essential for the efficient transport of **carbon dioxide** ($ ext{CO}_2$) from peripheral tissues to the lungs in the form of dissolved bicarbonate. *Haldane effect* - Describes the process where the unloading of **oxygen** in peripheral tissues increases the affinity of hemoglobin for **carbon dioxide** ($ ext{CO}_2$) and $ ext{H}^+$ (and vice versa in the lungs). - It primarily relates to the interaction between $ ext{O}_2$ saturation and $ ext{CO}_2$ binding, not the ion exchange itself. *Root effect* - This effect describes the decrease in the **oxygen carrying capacity** of hemoglobin caused by a drop in pH, often seen in fish. - It is a specialized form of the **Bohr effect**, but specifically refers to the non-sigmoidal shape of the $ ext{O}_2$-Hb curve at low pH. *Bohr effect* - This phenomenon explains that an increase in $ ext{PCO}_2$ or a decrease in pH (more **acidity**) shifts the oxygen-hemoglobin dissociation curve to the **right**. - This shift promotes the release of **oxygen** from hemoglobin to active tissues where $ ext{CO}_2$ production is high.

Question 722: A 45-year-old man undergoes spirometry testing. His results show FEV1 2.8 L (70% predicted), FVC 5.0 L (100% predicted), and FEV1/FVC ratio of 0.56. He has a 20-pack-year smoking history. What is the underlying pathophysiological mechanism for his reduced FEV1/FVC ratio?

A. Reduced lung compliance from interstitial fibrosis
B. Bronchial smooth muscle hypertrophy without change in airway resistance
C. Decreased alveolar surface area from emphysematous destruction
D. Increased airway resistance from small airway obstruction and loss of elastic recoil (Correct Answer)

Explanation: ***Increased airway resistance from small airway obstruction and loss of elastic recoil*** - The spirometry results (FEV1/FVC ratio < 0.70, specifically 0.56 in this case) define an **obstructive lung pattern**, characterized by difficulty exhaling air rapidly. - In **COPD** (highly likely given 20-pack-year smoking history), the reduced FEV1/FVC ratio results from **two key mechanisms**: (1) **Small airway obstruction** from inflammation, mucus plugging, and smooth muscle hypertrophy causing increased airway resistance, and (2) **Loss of elastic recoil** from emphysematous destruction of alveolar walls, leading to dynamic airway collapse during expiration. - This combination produces the characteristic obstructive pattern with prolonged expiratory phase. *Reduced lung compliance from interstitial fibrosis* - Reduced compliance is characteristic of **restrictive lung diseases** (e.g., pulmonary fibrosis, interstitial lung disease) where lungs become stiff. - This would cause **reduced FVC** with normal or increased FEV1/FVC ratio (>0.70), not the obstructive pattern seen here. - This patient's FVC is 100% predicted, ruling out restriction. *Bronchial smooth muscle hypertrophy without change in airway resistance* - While smooth muscle hypertrophy does occur in chronic airway diseases, it **increases** airway resistance rather than having no effect. - This option incorrectly suggests hypertrophy doesn't affect resistance, making it physiologically inaccurate. *Decreased alveolar surface area from emphysematous destruction* - Emphysematous destruction does decrease alveolar surface area, but this primarily impairs **gas exchange (diffusion capacity/DLCO)**, not spirometric flow rates. - The reduced FEV1/FVC ratio results from **loss of elastic recoil** causing airway collapse, not from surface area reduction per se. - Surface area loss is a structural consequence of emphysema; the functional consequence affecting spirometry is loss of radial traction on airways.

Question 723: Surface tension of the fluid lining the alveoli increases during:

A. Inspiration
B. Standing
C. Expiration (Correct Answer)
D. Supine

Explanation: ***Expiration*** - During expiration, the alveoli **decrease in size** and the alveolar radius becomes smaller. - As the surface area contracts, surfactant molecules become **compressed** and less effective at reducing surface tension. - According to the **Law of Laplace** (P = 2T/r), with a smaller radius and increased surface tension, alveoli would tend to collapse—surfactant normally prevents this, but surface tension is **highest at end-expiration**. - This physiological increase in surface tension during expiration is why **surfactant is critical** to prevent alveolar collapse, especially in premature infants with respiratory distress syndrome. *Incorrect: Inspiration* - During inspiration, alveoli **expand** and increase in radius. - Surfactant's unique property is that it **lowers surface tension more effectively** when spread over a larger surface area. - This dynamic behavior of surfactant ensures that surface tension actually **decreases during inspiration**, facilitating alveolar expansion and reducing the work of breathing. *Incorrect: Standing* - Standing affects the **distribution of ventilation and perfusion** (V/Q ratio) due to gravitational effects on blood flow and lung mechanics. - It does **not directly alter** the surface tension of the alveolar fluid lining on a molecular level. - Regional differences may occur, but there is no consistent, predictable increase in overall surface tension with standing. *Incorrect: Supine* - The supine position redistributes lung volumes and may cause some **airway closure** in dependent regions. - While functional residual capacity (FRC) may decrease slightly, this does **not cause a specific increase** in alveolar surface tension. - Effects on surface tension are indirect and not the primary physiological change with postural alterations.

Question 724: Effect of pulmonary embolism on graph of V/Q?

A. Decreased V/Q ratio approaching zero
B. Increased V/Q ratio approaching infinity (dead space) (Correct Answer)
C. Normal V/Q ratio
D. Increased perfusion (Q) and decreased ventilation (V)

Explanation: ***Increased V/Q ratio approaching infinity (dead space)*** - In pulmonary embolism, an embolus obstructs a pulmonary artery, leading to a significant reduction or complete cessation of **perfusion (Q)** to the downstream lung tissue, while **ventilation (V)** remains unaffected. - This creates a V/Q mismatch where the ratio V/Q becomes very high, approaching infinity. This ventilated but unperfused lung region is known as **physiological dead space**. *Decreased V/Q ratio approaching zero* - A decreased V/Q ratio occurs when ventilation is impaired relative to perfusion (V<Q), a condition known as a **shunt**. - This is characteristic of conditions like **pneumonia**, **pulmonary edema**, or **atelectasis**, where alveoli are filled with fluid or collapsed but still receive blood flow. *Normal V/Q ratio* - Pulmonary embolism is a classic cause of a severe **V/Q mismatch**, specifically creating high V/Q units; therefore, the ratio in the affected area is not normal. - A normal V/Q ratio (approximately 0.8) implies well-matched ventilation and perfusion, which is the state PE directly disrupts. *Increased perfusion (Q) and decreased ventilation (V)* - This describes the opposite of what occurs in pulmonary embolism, where the primary problem is a **decrease in perfusion (Q)** due to the arterial blockage. - Increased perfusion with decreased ventilation would result in a **low V/Q ratio (shunt)**, not the high V/Q dead space seen in PE.

Question 725: Which of the following is correct about the flow volume curve shown below? (Recent NEET Pattern 2016-17)

A. A= Emphysema, B= Upper airway obstruction, C= Pulmonary fibrosis
B. A= Extraparenchymal restrictive lung disease, B= upper airway obstruction, C= Pulmonary fibrosis
C. A= Emphysema, B= Extraparenchymal restrictive lung disease, C= Pulmonary fibrosis
D. A= Emphysema, B= Upper airway obstruction, C= Extraparenchymal restrictive lung disease (Correct Answer)

Explanation: ***Correct Answer: A= Emphysema, B= Upper airway obstruction, C= Extraparenchymal restrictive lung disease*** - Curve **A** shows a reduced expiratory flow rate, especially in later expiration, and an increased residual volume, consistent with **emphysema** due to loss of elastic recoil. - Curve **B** shows a plateauing of both inspiratory and expiratory limbs, characteristic of a **fixed upper airway obstruction**. - Curve **C** shows a shift to the left with reduced lung volumes but preserved or increased flow rates, typical of **extraparenchymal restrictive lung disease**. *Incorrect: A= Emphysema, B= Upper airway obstruction, C= Pulmonary fibrosis* - While A and B are correctly identified, C is incorrectly identified as pulmonary fibrosis. **Pulmonary fibrosis** is an *intraparenchymal* restrictive lung disease, which would show a proportionate reduction in both flow and volume, similar to C but typically with less preserved flow rates at lower volumes. - Extraparenchymal restrictive lung disease (like chest wall restriction or neuromuscular disease) reduces lung volumes but the airways themselves are usually healthy, leading to strong expiratory efforts for the reduced volume. *Incorrect: A= Extraparenchymal restrictive lung disease, B= upper airway obstruction, C= Pulmonary fibrosis* - Curve **A** is clearly indicative of an obstructive pattern with a significantly prolonged and reduced expiratory flow, not extraparenchymal restrictive disease. - Curve **C** is restrictive, but the specific pattern aligns better with extraparenchymal restrictive disease rather than pulmonary fibrosis (an intraparenchymal restrictive disease). *Incorrect: A= Emphysema, B= Extraparenchymal restrictive lung disease, C= Pulmonary fibrosis* - Curve **B** shows a characteristic **fixed obstruction pattern** (plateauing), which is seen in upper airway obstruction, not extraparenchymal restrictive lung disease. - Curve **C** is restrictive, but as noted, the pattern here is more consistent with extraparenchymal restriction than pulmonary fibrosis.

Question 726: Which flow volume curve recording is shown below?

A. Parenchymal obstructive airway disease
B. Fixed intrathoracic obstruction (Correct Answer)
C. Variable extrathoracic obstruction
D. Variable intrathoracic obstruction

Explanation: ***Fixed intrathoracic obstruction*** - The flow-volume loop shows **flattening of both inspiratory and expiratory limbs** equally. This indicates a fixed obstruction within the intrathoracic airways, affecting airflow during both phases regardless of transmural pressure changes. - Examples include **tracheal stenosis** or **tumors** within the main bronchi, which permanently narrow the airway. *Parenchymal obstructive airway disease* - This condition (e.g., asthma, COPD) would typically show a **decreased peak expiratory flow** and a "scooped out" appearance of the expiratory limb, while the inspiratory limb is often preserved or only mildly affected. - The obstruction is primarily within the **smaller airways** and can vary with lung volume. *Variable extrathoracic obstruction* - This would result in a flattened inspiratory limb but a relatively normal expiratory limb because the **negative inspiratory pressure collapses the airway lumen** during inspiration, while positive expiratory pressure often helps to open it. - Examples include vocal cord dysfunction or goiter compressing the trachea **outside the chest cavity**. *Variable intrathoracic obstruction* - This would primarily affect the **expiratory limb**, causing flattening, as the positive intrathoracic pressure during exhalation tends to narrow the already compromised airway. The inspiratory limb would be less affected. - Conditions like **tracheomalacia** within the chest cavity can cause this, where the airway collapses during exhalation.

Question 727: Which flow volume curve recording is shown below?

A. Parenchymal obstructive airway disease
B. Restrictive defect
C. Variable extrathoracic obstruction (Correct Answer)
D. Variable intrathoracic obstruction

Explanation: ***Variable extrathoracic obstruction*** - This flow-volume loop shows a **flattening** of the **inspiratory limb** (I), while the expiratory limb (E) remains relatively normal. - Variable extrathoracic obstructions, such as vocal cord dysfunction or laryngeal edema, predominantly affect airflow during inspiration because the extrathoracic airway pressure becomes more negative than atmospheric pressure during inspiration, leading to airway narrowing. *Parenchymal obstructive airway disease* - Characterized by a **diminished expiratory flow** and a **scooped-out appearance** of the expiratory limb on the flow-volume loop. - The inspiratory limb is usually well preserved, which is not seen here as the inspiratory limb is significantly affected. *Restrictive defect* - Presents as a **miniature version of a normal flow-volume loop**, indicating reduced lung volumes, but usually with preserved flow rates for the given lung volume. - Both inspiratory and expiratory flows would be proportionally reduced, unlike the isolated inspiratory flattening shown. *Variable intrathoracic obstruction* - This typically causes a **flattening or reduction in the expiratory limb** of the flow-volume loop, with a relatively normal inspiratory limb. - During forced expiration, the positive intrathoracic pressure compresses the compromised intrathoracic airway, leading to obstruction.

Question 728: Which of the following areas of nitrogen washout test indicate closing volume?

A. 1
B. 2
C. 3
D. 4 (Correct Answer)

Explanation: ***4*** - Area 4 represents the **closing volume**. This is the point where the **small airways in the dependent parts of the lungs close**, leading to a sharp increase in the nitrogen concentration in the exhaled gas. - This sharp increase occurs because air from the upper regions of the lungs, which are better ventilated, continues to empty, and this air has a higher concentration of nitrogen as the patient was initially breathing 100% oxygen. *1* - Area 1 is known as the **anatomical dead space**, representing the initial part of exhalation consisting entirely of gas from the conducting airways (which has a near-zero nitrogen concentration). - This phase reflects the emptying of gas that did not participate in gas exchange, thus showing very low nitrogen levels as it's primarily the 100% oxygen inhaled for the test. *2* - Area 2, or the **alveolar washout phase**, shows a rapid increase in nitrogen concentration as exhaled gas now includes a mixture of dead space air and alveolar air. - This phase reflects the emptying of alveoli from different regions of the lung, but not yet the effect of airway closure. *3* - Area 3 is the **alveolar plateau**, where the nitrogen concentration remains relatively stable, indicating uniform emptying from the remaining open alveoli. - This plateau phase shows the mixing of gases from various lung units, with a steady increase in nitrogen as the oxygen washes out.

Question 729: Which statement related to lung compliance shown in the image below is correct:

A. A = Emphysema, B = Fibrosis (Correct Answer)
B. A = Fibrosis, B = Emphysema
C. A = Fibrosis, B = Alveolar Proteinosis
D. A = Alveolar Proteinosis, B = Fibrosis

Explanation: ***A = Emphysema, B = Fibrosis*** - Curve A shows **higher lung volume for a given pressure, indicating increased compliance**, which is characteristic of **emphysema** due to destruction of elastic tissue in alveolar walls. - Curve B shows **lower lung volume for a given pressure, indicating decreased compliance**, which is characteristic of **fibrosis** due to increased stiffness and reduced distensibility of lung tissue. *A = Fibrosis, B = Emphysema* - This is incorrect because the curves are reversed. **Fibrosis causes decreased compliance** (curve would be positioned lower like B, not higher like A), while **emphysema causes increased compliance** (curve would be positioned higher like A, not lower like B). *A = Fibrosis, B = Alveolar Proteinosis* - This is incorrect because **alveolar proteinosis causes decreased lung compliance** similar to fibrosis. Both conditions would show curves in the lower position. Curve A clearly demonstrates **increased compliance**, which does not match either condition. *A = Alveolar Proteinosis, B = Fibrosis* - This is incorrect because **alveolar proteinosis results in decreased lung compliance** due to accumulation of surfactant-like material in alveoli. It would correspond to a lower compliance curve, not the increased compliance shown in curve A. While **fibrosis correctly matches decreased compliance** (curve B), alveolar proteinosis cannot be curve A.

Question 730: The baseline oxyhemoglobin dissociation curve is depicted in blue color. Shift of curve to which side indicates Bohr effect?

A. Green (shift to left)
B. Red (shift to right) (Correct Answer)
C. Blue (no shift)
D. None of these

Explanation: ***Red (shift to right)*** - The **Bohr effect** describes the rightward shift of the oxyhemoglobin dissociation curve caused by increased **CO2** and decreased **pH** (acidosis). - This rightward shift indicates **decreased oxygen affinity**, allowing hemoglobin to release oxygen more readily to metabolically active tissues that produce CO2 and acid. - This is represented by the **red curve** in the image. *Green (shift to left)* - A **left shift** indicates **increased oxygen affinity**, meaning hemoglobin holds onto oxygen more tightly and releases it less readily. - This occurs with **decreased CO2**, **increased pH** (alkalosis), **decreased temperature**, and **decreased 2,3-BPG**. - These are **opposite conditions** to the Bohr effect. *Blue (no shift)* - The **blue curve** represents the baseline oxyhemoglobin dissociation curve with no shift. - The Bohr effect specifically refers to a **curve shift** (rightward with increased CO2/decreased pH), not the baseline position. - Therefore, blue does not represent the Bohr effect. *None of these* - The **red curve** (rightward shift) accurately represents the Bohr effect, making this option incorrect. - The Bohr effect is a well-established concept with a **characteristic rightward shift** when CO2 increases or pH decreases.

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