Respiratory System Practice Questions

Q: The diffusion capacity of the lung is decreased in all of the following conditions except?

Goodpasture's syndrome. **Explanation:** The **Diffusion Capacity of the Lung for Carbon Monoxide (DLCO)** measures the ability of the lungs to transfer gas from the inhaled air to the red blood cells in the pulmonary capillaries. It depends on the surface area available for exchange, the thickness of the alveolar-capillary membrane, and the hemoglobin volume. **Why Goodpasture’s Syndrome is the Correct Answer:** In **Goodpasture’s Syndrome**, there is acute pulmonary hemorrhage. The presence of free hemoglobin (RBCs) within the alveoli binds to the carbon monoxide used during the DLCO test. This leads to an **increase in DLCO** rather than a decrease. This is a classic "exception" frequently tested in exams. **Analysis of Incorrect Options:** * **Interstitial Lung Disease (ILD):** DLCO is **decreased** due to the thickening and fibrosis of the alveolar-capillary membrane, which increases the diffusion distance. * **Pneumocystis jirovecii Pneumonia (PJP):** This infection causes significant inflammation and "foamy" exudates in the alveoli, increasing the barrier thickness and **decreasing** DLCO. In fact, a low DLCO is a highly sensitive screening marker for PJP in HIV patients. * **Primary Pulmonary Hypertension:** DLCO is **decreased** because of structural changes in the pulmonary vasculature (obliteration of capillaries), which reduces the effective surface area and capillary blood volume available for gas exchange. **High-Yield Clinical Pearls for NEET-PG:** * **Increased DLCO:** Seen in Pulmonary hemorrhage (Goodpasture’s), Polycythemia, Left-to-right shunts, and Exercise. * **Decreased DLCO:** Seen in Emphysema (loss of surface area), ILD (thickened membrane), Anemia (low Hb), and Pulmonary Embolism. * **Asthma vs. COPD:** DLCO is usually **normal or increased in Asthma**, but **decreased in Emphysema**. This is a key physiological differentiator.

Q: Shift of the oxygen dissociation curve to the right occurs in which of the following conditions?

Acidosis. **Explanation:** The Oxygen Dissociation Curve (ODC) represents the relationship between the partial pressure of oxygen ($PO_2$) and the percentage saturation of hemoglobin ($SaO_2$). A **shift to the right** indicates a decreased affinity of hemoglobin for oxygen, meaning oxygen is more easily released to the tissues. **Why Acidosis is the Correct Answer:** Acidosis (decreased pH) causes a rightward shift through the **Bohr Effect**. When $H^+$ ions increase, they bind to specific amino acid residues in hemoglobin, stabilizing the "Tense" (T) state. This conformational change reduces hemoglobin's affinity for oxygen, facilitating its unloading in metabolically active tissues where lactic acid or $CO_2$ levels are high. **Analysis of Options:** While the question asks for "which condition," it is important to note that **technically, all four options (A, B, C, and D) cause a rightward shift.** In the context of NEET-PG, if this appears as a single-choice question, **Acidosis** or **Increased $PCO_2$** are often prioritized as primary physiological drivers. However, if this were a "multiple correct" style or if "All of the above" were an option, it would be more accurate. * **B, C, and D:** Increased 2,3-DPG, increased temperature, and increased $PCO_2$ all stabilize the T-state of hemoglobin and shift the curve to the right. **High-Yield NEET-PG Pearls:** * **Mnemonic for Right Shift (CADET, face Right!):** **C**O2 increase, **A**cidosis, **D**PG (2,3-DPG) increase, **E**xercise, **T**emperature increase. * **Left Shift:** Occurs in Alkalosis, decreased temp, decreased 2,3-DPG, and presence of **HbF (Fetal Hemoglobin)** or **Carbon Monoxide (CO)**. * **P50 Value:** The $PO_2$ at which Hb is 50% saturated. A right shift **increases** the P50 (normal is ~26.7 mmHg).

Q: Oxygen dissociation curve shifts to the right in all the following conditions except:

Blood transfusion. The **Oxygen Dissociation Curve (ODC)** represents the relationship between the partial pressure of oxygen ($PO_2$) and the percentage saturation of hemoglobin. A **shift to the right** indicates a decreased affinity of hemoglobin for oxygen, facilitating oxygen unloading to tissues. ### Why "Blood Transfusion" is the Correct Answer: Stored blood undergoes a depletion of **2,3-Bisphosphoglycerate (2,3-BPG)** over time. 2,3-BPG is essential for stabilizing the "T" (Tense) state of hemoglobin, which promotes oxygen release. When a patient receives a transfusion of stored blood, the low levels of 2,3-BPG cause the curve to **shift to the left** (increased affinity), meaning the hemoglobin holds onto oxygen more tightly. ### Explanation of Incorrect Options (Conditions that shift the curve to the Right): * **Diabetic Ketoacidosis (DKA):** This condition involves metabolic **acidosis** (decreased pH). According to the **Bohr Effect**, an increase in $H^+$ ions stabilizes the T-state of hemoglobin, shifting the curve to the right. * **High Altitude:** Hypoxia at high altitudes stimulates an increase in **2,3-BPG production** within RBCs to compensate for lower atmospheric $PO_2$, shifting the curve to the right to enhance tissue oxygenation. * **Anaemia:** In chronic anaemia, there is a compensatory **increase in 2,3-BPG** levels to ensure that the limited amount of hemoglobin available can efficiently deliver oxygen to the tissues. ### NEET-PG High-Yield Pearls: * **Mnemonic for Right Shift (CADET, face Right!):** **C**O2 increase, **A**cidosis, **D**PG (2,3-BPG) increase, **E**xercise, **T**emperature increase. * **P50 Value:** The $PO_2$ at which hemoglobin is 50% saturated. A **Right shift increases the P50**, while a Left shift decreases it. * **Fetal Hemoglobin (HbF):** Always causes a **Left shift** because it has a poor binding affinity for 2,3-BPG, ensuring it can take oxygen from maternal blood.

Q: What is the alveolar ventilation for a person with a vital capacity of 500 mL, a respiratory rate of 14/min, a tidal volume of 500 mL, and a dead space of 150 mL?

4900 mL. ### Explanation **1. Understanding the Correct Answer (C: 4900 mL)** Alveolar ventilation ($\dot{V}_A$) is the volume of fresh air that reaches the gas-exchange units (alveoli) per minute. Unlike Minute Ventilation, it accounts for the **Anatomical Dead Space** ($V_D$), which is the air that remains in the conducting airways and does not participate in gas exchange. The formula for Alveolar Ventilation is: $$\dot{V}_A = (\text{Tidal Volume} - \text{Dead Space}) \times \text{Respiratory Rate}$$ **Calculation:** * Tidal Volume ($V_T$) = 500 mL * Dead Space ($V_D$) = 150 mL * Respiratory Rate ($RR$) = 14/min * $\dot{V}_A = (500 - 150) \times 14$ * $\dot{V}_A = 350 \times 14 = \mathbf{4900\ mL/min}$ **2. Analysis of Incorrect Options** * **A (2500 mL):** This is a distractor value with no physiological basis in this context. * **B (3500 mL):** This represents the total volume of air reaching the alveoli in one minute if the respiratory rate were 10/min, or simply $350 \times 10$. * **D (6000 mL):** This represents the **Minute Ventilation** ($\dot{V}_E = V_T \times RR$), which is $500 \times 12$ (using a standard rate) or $500 \times 14 = 7000$ mL. It incorrectly ignores the dead space. **3. Clinical Pearls & High-Yield Facts** * **Vital Capacity (VC):** In this question, VC is a "distractor." It is the maximum volume of air a person can exhale after maximum inhalation and is not used to calculate ventilation. * **Dead Space:** In a healthy adult, anatomical dead space is approximately **2 mL/kg** of ideal body weight (roughly 150 mL). * **Efficiency:** Increasing the **depth** of breathing (Tidal Volume) is more effective at increasing alveolar ventilation than increasing the **rate** of breathing, because the dead space is constant for every breath. * **Physiological Dead Space:** This equals Anatomical Dead Space + Alveolar Dead Space (wasted ventilation in non-perfused alveoli). In healthy individuals, they are nearly equal.

Q: Which of the following compounds is elevated in bronchial asthma?

Leukotrienes. **Explanation:** **Bronchial Asthma** is a chronic inflammatory airway disease characterized by reversible airway obstruction, mucus hypersecretion, and bronchial hyperresponsiveness. The underlying pathophysiology involves a Type I Hypersensitivity reaction. **Why Leukotrienes are correct:** In asthma, the activation of mast cells and eosinophils leads to the metabolism of arachidonic acid via the **5-Lipoxygenase (5-LOX) pathway**. This results in the production of **Cysteinyl Leukotrienes (LTC4, LTD4, and LTE4)**, formerly known as the *Slow-Reacting Substance of Anaphylaxis (SRS-A)*. These compounds are potent bronchoconstrictors (1000x more potent than histamine), increase vascular permeability, and stimulate mucus secretion, making them central to asthma pathogenesis. **Why the other options are incorrect:** * **PGI2 (Prostacyclin):** Produced via the Cyclooxygenase (COX) pathway, it is a potent vasodilator and inhibitor of platelet aggregation. It does not play a primary role in the bronchoconstriction seen in asthma. * **PGH2:** This is an unstable intermediate in the COX pathway that is rapidly converted into various prostaglandins or thromboxanes; it is not a specific marker for asthma. * **Thromboxane (TXA2):** Primarily involved in platelet aggregation and vasoconstriction. While it has minor bronchoconstrictor effects, it is not the hallmark mediator elevated in asthma compared to leukotrienes. **High-Yield Clinical Pearls for NEET-PG:** * **Zileuton:** A drug that inhibits the 5-Lipoxygenase enzyme. * **Montelukast/Zafirlukast:** Selective antagonists of the **CysLT1 receptor**, used as maintenance therapy in asthma. * **Aspirin-Exacerbated Respiratory Disease (AERD):** Occurs because Aspirin blocks the COX pathway, shunting arachidonic acid toward the LOX pathway, leading to an overproduction of leukotrienes. * **Charcot-Leyden Crystals:** Found in the sputum of asthmatics, derived from eosinophil lysophospholipase.

Q: Which muscles are involved in quiet expiration?

Neither diaphragm nor intercostal muscles. **Explanation:** The correct answer is **D. Neither diaphragm nor intercostal muscles.** **1. Underlying Medical Concept:** In respiratory physiology, **quiet expiration** (eupnea) is a purely **passive process**. It does not require active muscle contraction. Instead, it relies on the **elastic recoil** of the lungs and the chest wall. When the muscles of inspiration (diaphragm and external intercostals) relax, the intra-thoracic volume decreases, and the intra-alveolar pressure rises above atmospheric pressure, causing air to flow out of the lungs. **2. Why the other options are incorrect:** * **A & B (Diaphragm and Intercostal muscles):** These are the primary muscles of **quiet inspiration**. The diaphragm is the most important muscle, responsible for about 75% of the air movement during quiet breathing. * **C (Both):** This is incorrect because, while these muscles are active during the *inspiratory* phase, they are inhibited/relaxing during quiet expiration. **3. NEET-PG Clinical Pearls & High-Yield Facts:** * **Forced Expiration:** Unlike quiet expiration, forced expiration (e.g., coughing, sneezing, or exercise) is an **active process**. The primary muscles involved are the **abdominal muscles** (rectus abdominis, obliques) and the **internal intercostal muscles**. * **Accessory Muscles of Inspiration:** These include the sternocleidomastoid and scalene muscles, which are recruited during respiratory distress. * **Compliance:** The ease with which the lungs expand is called compliance. A loss of elastic recoil (as seen in **Emphysema**) makes even quiet expiration difficult, often requiring the use of accessory muscles. * **Key Rule:** Inspiration is always active; Expiration is passive at rest but active during exertion.

Q: Which of the following is NOT decreased in infiltrative lung disease?

Alveolar-arterial difference in PaO2. **Explanation:** Infiltrative lung diseases (such as Idiopathic Pulmonary Fibrosis or Sarcoidosis) are classic examples of **Restrictive Lung Diseases**. The fundamental pathology involves the deposition of fibrous tissue in the alveolar walls, making the lungs "stiff" and difficult to expand. **Why Option B is the Correct Answer:** The **Alveolar-arterial (A-a) gradient** is the difference between the partial pressure of oxygen in the alveoli ($PAO_2$) and the arterial blood ($PaO_2$). In infiltrative diseases, the thickened alveolar-capillary membrane creates a diffusion barrier. This impairs oxygen transfer, leading to a lower $PaO_2$ relative to $PAO_2$. Consequently, the **A-a gradient is INCREASED**, not decreased. **Why the other options are incorrect:** * **A & C (Vital Capacity and Total Lung Capacity):** In restrictive disease, the lungs cannot expand fully due to increased elastic recoil. This leads to a reduction in all lung volumes and capacities, including TLC, VC, and FRC. * **D (Lung Compliance):** Compliance is the change in volume per unit change in pressure ($C = \Delta V / \Delta P$). Because the lungs are stiff (fibrotic), they require much higher pressure to achieve a small change in volume. Therefore, **lung compliance is decreased**. **High-Yield Clinical Pearls for NEET-PG:** * **FEV1/FVC Ratio:** In restrictive lung disease, both FEV1 and FVC decrease, but the ratio remains **normal or is increased** (unlike obstructive disease where it decreases). * **Diffusion Capacity (DLCO):** This is characteristically **decreased** in infiltrative diseases due to the thickened interstitium. * **Radiology:** Look for "honeycombing" or "ground-glass opacities" on HRCT, which are hallmarks of advanced infiltrative disease.

Question 1

When the respiratory muscles are relaxed, the lungs are at which of the following volumes?

Accepted Answer

Functional residual capacity (FRC)

Answer

Expiratory reserve volume (ERV)

Answer

Residual volume (RV)

Answer

Inspiratory reserve volume (IRV)

Question 2

Which of the following pulmonary function changes are typically seen in an untreated patient with acute bronchial asthma?

Accepted Answer

Decreased forced vital capacity (FVC)

Answer

Increased peak expiratory flow

Answer

Decreased total lung capacity (TLC)

Answer

Increased residual volume (RV)

Question 3

The diffusion capacity of the lung is decreased in all of the following conditions except?

Accepted Answer

Goodpasture's syndrome

Answer

Interstitial lung disease

Answer

Pneumocystis jirovecii pneumonia

Answer

Primary pulmonary hypertension

Question 4

Shift of the oxygen dissociation curve to the right occurs in which of the following conditions?

Accepted Answer

Acidosis

Answer

2,3-DPG

Answer

Increased temperature

Answer

Increased Pco2

Question 5

Oxygen dissociation curve shifts to the right in all the following conditions except:

Accepted Answer

Blood transfusion

Answer

Diabetic ketoacidosis

Answer

High altitude

Answer

Anaemia

Question 6

What is the alveolar ventilation for a person with a vital capacity of 500 mL, a respiratory rate of 14/min, a tidal volume of 500 mL, and a dead space of 150 mL?

Accepted Answer

4900 mL

Answer

2500 mL

Answer

3500 mL

Answer

6000 mL

Question 7

Which of the following compounds is elevated in bronchial asthma?

Accepted Answer

Leukotrienes

Answer

PGI2

Answer

PGH2

Answer

Thromboxane

Question 8

Which muscles are involved in quiet expiration?

Accepted Answer

Neither diaphragm nor intercostal muscles

Answer

Diaphragm

Answer

Intercostal muscles

Answer

Both diaphragm and intercostal muscles

Question 9

Which of the following is NOT decreased in infiltrative lung disease?

Accepted Answer

Alveolar-arterial difference in PaO2

Answer

Vital capacity

Answer

Total lung capacity

Answer

Lung compliance

Question 10

Carotid body receptors are stimulated when there is:

Accepted Answer

Decreased O2 tension

Answer

Increased O2 tension

Answer

Decreased CO2 tension

Answer

Increased heart rate

Respiratory System — MCQs

Respiratory System — MCQs

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