Respiratory System Practice Questions

Q: If FEV1 is 1.3 L and FVC is 3.1 L in an adult man, what pattern is suggested?

Obstructive lung disease. **Explanation:** The diagnosis of ventilatory defects is primarily based on the **FEV1/FVC ratio** (Tiffeneau-Pinelli index). 1. **Why Option C is Correct:** In this case, the FEV1/FVC ratio is **1.3 / 3.1 = 0.41 (or 41%)**. In a healthy adult, the normal ratio is approximately **0.70 to 0.80 (70-80%)**. A ratio **below 0.70** is the hallmark of **Obstructive Lung Disease** (e.g., Asthma, COPD). In obstructive diseases, airway resistance increases, making it difficult to exhale air rapidly, which disproportionately reduces the FEV1 compared to the FVC. 2. **Why Other Options are Incorrect:** * **Option A (Normal):** A normal pattern requires an FEV1/FVC ratio > 0.70 and an FVC within the predicted normal range. Here, the ratio is significantly reduced. * **Option B (Restrictive):** In restrictive lung diseases (e.g., Pulmonary Fibrosis), both FEV1 and FVC decrease proportionately. Consequently, the FEV1/FVC ratio remains **normal or is even increased** (> 0.80), because the primary issue is lung expansion, not airway obstruction. **High-Yield NEET-PG Pearls:** * **Obstructive Pattern:** ↓FEV1, ↓FVC, **↓↓Ratio ( 0.8)**, ↓TLC. * **FEV1** is the most sensitive parameter for monitoring obstructive diseases. * **Flow-Volume Loops:** Obstructive disease shows a "scooped-out" appearance; Restrictive disease shows a "miniature" but normal-shaped loop.

Q: What is the oxygen-carrying capacity of an 18-year-old male with a hemoglobin of 14 g/dL?

18. **Explanation:** The oxygen-carrying capacity of blood refers to the maximum amount of oxygen that can be carried by hemoglobin (Hb) in a given volume of blood. **The Calculation:** 1. **Hüfner's Constant:** Each gram of hemoglobin can bind approximately **1.34 mL** of oxygen when fully saturated. 2. **Formula:** Oxygen-carrying capacity = Hemoglobin (g/dL) × 1.34 mL O₂/g. 3. **Application:** 14 g/dL × 1.34 ≈ **18.76 mL/dL**. Rounding to the nearest whole number provided in the options, **18** is the most accurate answer. **Analysis of Options:** * **Option A (14):** This is simply the hemoglobin value. It does not account for the binding constant. * **Option B (16):** This value would correspond to a lower hemoglobin level (approx. 12 g/dL). * **Option D (22):** This value would be seen in polycythemia or an individual with a much higher hemoglobin concentration (approx. 16.5 g/dL). **Clinical Pearls for NEET-PG:** * **Dissolved Oxygen:** In addition to Hb-bound oxygen, 0.003 mL of O₂ is dissolved in every 100 mL of plasma per mmHg of $PaO_2$. This is usually negligible (approx. 0.3 mL/dL) but becomes vital in hyperbaric oxygen therapy. * **Total Oxygen Content:** The sum of bound oxygen and dissolved oxygen. * **Shift to the Right:** Factors like increased $CO_2$, $H^+$ (decreased pH), Temperature, and 2,3-BPG decrease Hb affinity for $O_2$, facilitating unloading at tissues (Bohr Effect). * **Normal Range:** For a healthy adult male, the average oxygen-carrying capacity is roughly 20 mL/dL (assuming Hb of 15 g/dL).

Q: Which of the following is a feature of the Hering-Breuer reflex?

All of the above. The **Hering-Breuer Inflation Reflex** is a protective mechanism triggered by the over-inflation of the lungs. When tidal volume exceeds approximately 1.5 liters (in adults), stretch receptors in the smooth muscles of the bronchi and bronchioles are activated. ### **Mechanism and Explanation** 1. **Respiratory Effect (Option A):** Impulses travel via the **Vagus nerve (CN X)** to the solitary tract nucleus (NTS) in the medulla. This inhibits the dorsal respiratory group (DRG) and the apneustic center, prematurely terminating inspiration. This results in a shorter inspiratory phase, leading to **rapid, shallow breathing** (tachypnea) to prevent alveolar over-distension. 2. **Cardiovascular Effects (Options B & C):** The reflex involves "Vagal cross-talk." Stimulation of the vagal afferents from the lungs leads to a concomitant increase in parasympathetic outflow to the heart and a decrease in sympathetic tone. This results in: * **Bradycardia:** Due to increased vagal (parasympathetic) discharge to the SA node. * **Hypotension:** Due to systemic vasodilation and decreased cardiac output. Since the reflex triggers all three physiological responses, **Option D (All of the above)** is the correct answer. ### **High-Yield Clinical Pearls for NEET-PG** * **Receptors:** Slowly Adapting Stretch Receptors (SARs). * **Afferent Pathway:** Vagus Nerve. * **Physiological Role:** In neonates, it is active during normal tidal breathing. In adults, it is mainly a protective mechanism during exercise or high-volume states. * **Hering-Breuer Deflation Reflex:** A separate reflex where lung deflation triggers a shorter expiratory phase to increase respiratory rate (preventing lung collapse).

Q: Surfactant is primarily composed of which of the following substances?

Phospholipids. **Explanation:** **1. Why Phospholipids are Correct:** Pulmonary surfactant is a surface-active lipoprotein complex secreted by **Type II alveolar epithelial cells**. Its primary function is to reduce surface tension at the air-liquid interface of the alveoli, preventing alveolar collapse (atelectasis) during expiration. Chemically, surfactant is composed of approximately **90% lipids** and 10% proteins. Among the lipids, **phospholipids** are the most abundant. Specifically, **Dipalmitoylphosphatidylcholine (DPPC)**, also known as Lecithin, is the single most important component responsible for reducing surface tension. **2. Why Other Options are Incorrect:** * **A & D (Fibrin and Fibrinogen):** These are proteins involved in the blood coagulation cascade. Their presence in the alveoli is pathological (e.g., in Acute Respiratory Distress Syndrome or Hyaline Membrane Disease), where they form "hyaline membranes" that impair gas exchange, but they are not physiological components of surfactant. * **B (Mucoprotein):** While mucus (containing mucoglycoproteins) lines the upper conducting airways to trap particles, it is not a primary constituent of the surfactant found in the distal alveoli. **3. NEET-PG High-Yield Clinical Pearls:** * **L/S Ratio:** The Lecithin/Sphingomyelin ratio in amniotic fluid is used to assess fetal lung maturity. A ratio **> 2:1** usually indicates mature lungs. * **Surfactant Proteins:** There are four types (SP-A, B, C, D). **SP-B and SP-C** are essential for the hydrophobic properties and spreading of surfactant. * **Clinical Correlation:** Deficiency of surfactant in premature infants leads to **Infant Respiratory Distress Syndrome (IRDS)**. * **Storage:** Surfactant is stored in intracellular organelles of Type II pneumocytes called **Lamellar bodies**.

Q: A 25-year-old male cigarette smoker has a history of respiratory infections and has also been found to have hematuria. A high value for diffusing capacity is noted during pulmonary function testing. This finding is consistent with which of the following disorders?

Intrapulmonary hemorrhage. **Explanation:** The **Diffusing Capacity of the Lung for Carbon Monoxide (DLCO)** measures the ability of the lungs to transfer gas from inhaled air to the red blood cells (RBCs) in pulmonary capillaries. It is dependent on the surface area of the blood-gas barrier, the thickness of the membrane, and the **total volume of hemoglobin** available in the pulmonary capillaries to bind CO. **Why Intrapulmonary Hemorrhage is Correct:** In conditions like Goodpasture syndrome (suggested here by the triad of smoking, respiratory symptoms, and hematuria/nephritis), blood accumulates within the alveoli. This **extravasated hemoglobin** in the alveolar spaces binds to the inhaled carbon monoxide during the test. Since there is more hemoglobin available to "soak up" the CO than in a healthy lung, the calculated DLCO value becomes **pathologically elevated.** **Analysis of Incorrect Options:** * **Anemia:** Decreases DLCO because there is less hemoglobin available in the capillaries to bind CO. * **Emphysema:** Decreases DLCO due to the destruction of alveolar walls, which reduces the total surface area available for gas exchange. * **Cystic Fibrosis:** Generally decreases DLCO due to mucus plugging, airway obstruction, and eventual fibrosis/scarring of the gas-exchange surface. **NEET-PG High-Yield Pearls:** * **Increased DLCO is rare.** Key causes include: **Intrapulmonary hemorrhage**, Polycythemia, Left-to-right shunts, and Exercise (due to increased capillary recruitment). * **Decreased DLCO** is seen in: Emphysema (only obstructive disease with low DLCO), Interstitial Lung Disease (fibrosis), Anemia, and Pulmonary Embolism. * **Goodpasture Syndrome:** Characterized by anti-GBM antibodies attacking the lungs (hemoptysis) and kidneys (hematuria). Smoking is a known trigger for the pulmonary manifestations.

Q: Specific lung compliance is decreased in all of the following conditions EXCEPT:

Chronic bronchitis. **Explanation:** **Specific Lung Compliance** is defined as compliance per unit lung volume (Compliance/FRC). It is used to standardize compliance across different lung sizes, ensuring that a child and an adult have comparable values. **Why Chronic Bronchitis is the Correct Answer:** In **Chronic Bronchitis**, the primary pathology involves airway inflammation and excessive mucus production rather than significant destruction of the lung parenchyma or changes in elastic recoil. Therefore, **lung compliance remains relatively normal**. In contrast, in Emphysema (the other component of COPD), compliance increases due to the loss of elastic fibers. Since compliance is not decreased in chronic bronchitis, it is the correct "Except" choice. **Why the Other Options are Incorrect:** * **Pulmonary Fibrosis:** This is a restrictive lung disease where the lungs become "stiff" due to excess collagen deposition. This significantly **decreases** compliance. * **Decreased Surfactant:** Surfactant reduces surface tension. A deficiency (e.g., NRDS) increases surface tension, making the alveoli prone to collapse and **decreasing** compliance. * **Pulmonary Congestion:** The presence of excess fluid/blood in the interstitium increases lung stiffness and interferes with alveolar expansion, thereby **decreasing** compliance. **High-Yield Clinical Pearls for NEET-PG:** * **Compliance (C) = ΔV / ΔP.** It is the measure of "distensibility." * **Increased Compliance:** Seen in **Emphysema** (loss of elastic recoil) and **Aging**. * **Decreased Compliance:** Remember the mnemonic **"SCAR"**: **S**urfactant deficiency, **C**ongestion (edema), **A**telectasis, and **R**estrictive lung diseases (Fibrosis). * Specific compliance is a more accurate measure than total compliance when comparing individuals with different lung volumes (e.g., after a pneumonectomy).

Q: What is the normal partial pressure of carbon dioxide in arterial blood?

40 mm Hg. **Explanation:** The partial pressure of carbon dioxide in arterial blood (**PaCO₂**) is a critical physiological parameter regulated by the balance between metabolic CO₂ production and alveolar ventilation. 1. **Why Option A is Correct:** In a healthy adult at sea level, the normal range for PaCO₂ is **35–45 mm Hg**, with **40 mm Hg** being the standard physiological mean. This value ensures that the blood pH remains within the narrow range of 7.35–7.45. The peripheral and central chemoreceptors are exquisitely sensitive to changes in PaCO₂, adjusting the rate and depth of respiration to maintain this steady state. 2. **Why Other Options are Incorrect:** * **Option B (37 mm Hg):** While within the normal range (35–45), it is not the standard "textbook" value used for physiological calculations or the mean arterial reference. * **Option C (45 mm Hg):** This represents the upper limit of normal arterial CO₂. However, 45 mm Hg is specifically the classic value for **mixed venous blood (PvCO₂)** as it returns to the lungs from the tissues. * **Option D (60 mm Hg):** This indicates significant **hypercapnia** (respiratory acidosis), often seen in Type 2 respiratory failure or severe hypoventilation. **High-Yield Clinical Pearls for NEET-PG:** * **P(A-a)O₂ Gradient:** While we focus on CO₂, remember that the Alveolar-arterial oxygen gradient is a key tool to differentiate causes of hypoxia. * **CO₂ Transport:** Most CO₂ (approx. 70%) is transported as **bicarbonate (HCO₃⁻)**, 23% as carbaminohemoglobin, and 7% dissolved in plasma. * **Haldane Effect:** Deoxygenation of blood increases its ability to carry CO₂; this occurs in systemic tissues. * **Control of Breathing:** The **central chemoreceptors** in the medulla are primarily stimulated by changes in H⁺ concentration derived from PaCO₂, making CO₂ the primary drive for respiration in healthy individuals.

Q: What is the partial pressure for carbon dioxide in the inspired air?

0.3 mm Hg. ### Explanation The partial pressure of a gas in a mixture is determined by its fractional concentration and the total barometric pressure ($P_{gas} = F_{gas} \times P_{total}$). **1. Why Option A is Correct:** At sea level, the total atmospheric pressure is **760 mm Hg**. Carbon dioxide ($CO_2$) makes up approximately **0.04%** of the dry atmospheric air. * **Calculation:** $0.0004 \times 760 \text{ mm Hg} \approx \mathbf{0.3 \text{ mm Hg}}$. This negligible concentration ensures a steep diffusion gradient between the pulmonary capillary blood ($PCO_2 \approx 46 \text{ mm Hg}$) and the alveoli, facilitating efficient $CO_2$ elimination. **2. Analysis of Incorrect Options:** * **Option B (158 mm Hg):** This is the partial pressure of **Oxygen ($PO_2$)** in inspired (atmospheric) air. It is calculated as $21\%$ of $760 \text{ mm Hg}$ ($0.21 \times 760$). * **Option C (100 mm Hg):** This represents the normal **Alveolar partial pressure of Oxygen ($PAO_2$)**. It is lower than inspired air due to the addition of water vapor and the constant diffusion of $O_2$ into the blood. * **Option D (32 mm Hg):** This is the approximate partial pressure of $CO_2$ in **expired air**. It is higher than inspired air because it includes $CO_2$ cleared from the alveoli, but lower than alveolar $CO_2$ ($40 \text{ mm Hg}$) due to mixing with dead space air. **High-Yield Clinical Pearls for NEET-PG:** * **Humidification:** As air enters the respiratory tract, it is saturated with water vapor ($PH_2O = 47 \text{ mm Hg}$). This dilutes the $PO_2$ from $158 \text{ mm Hg}$ (dry air) to **$149 \text{ mm Hg}$** (humidified tracheal air). * **Alveolar $PCO_2$:** Is typically maintained at **$40 \text{ mm Hg}$**. * **Diffusion Gradient:** $CO_2$ is **20 times more soluble** than $O_2$, allowing it to diffuse rapidly across the respiratory membrane despite a much smaller pressure gradient ($6 \text{ mm Hg}$ for $CO_2$ vs. $60 \text{ mm Hg}$ for $O_2$).

Question 1

A normal subject makes an inspiratory effort against a closed airway. What would you expect to occur?

Accepted Answer

Pressure inside the pulmonary capillaries falls

Answer

Tension in the diaphragm decreases

Answer

The internal intercostal muscles become active

Answer

Intrapleural pressure increases (becomes less negative)

Question 2

If FEV1 is 1.3 L and FVC is 3.1 L in an adult man, what pattern is suggested?

Accepted Answer

Obstructive lung disease

Answer

Normal lung function

Answer

Restrictive lung disease

Answer

None of the above

Question 3

What is the oxygen-carrying capacity of an 18-year-old male with a hemoglobin of 14 g/dL?

Accepted Answer

18

Answer

14

Answer

16

Answer

22

Question 4

Which of the following is a feature of the Hering-Breuer reflex?

Accepted Answer

All of the above

Answer

Rapid shallow breathing

Answer

Bradycardia

Answer

Hypotension

Question 5

Surfactant is primarily composed of which of the following substances?

Accepted Answer

Phospholipids

Answer

Fibrin

Answer

Mucoprotein

Answer

Fibrinogen

Question 6

Which of the following parameters shifts the O2 dissociation curve to the right?

Accepted Answer

Anemia

Answer

Carbon monoxide poisoning

Answer

Anoxic hypoxia

Answer

Increase in fetal hemoglobin

Question 7

A 25-year-old male cigarette smoker has a history of respiratory infections and has also been found to have hematuria. A high value for diffusing capacity is noted during pulmonary function testing. This finding is consistent with which of the following disorders?

Accepted Answer

Intrapulmonary hemorrhage

Answer

Anemia

Answer

Cystic fibrosis

Answer

Emphysema

Question 8

Specific lung compliance is decreased in all of the following conditions EXCEPT:

Accepted Answer

Chronic bronchitis

Answer

Pulmonary congestion

Answer

Pulmonary fibrosis

Answer

Decreased surfactant

Question 9

What is the normal partial pressure of carbon dioxide in arterial blood?

Accepted Answer

40 mm Hg

Answer

37 mm Hg

Answer

45 mm Hg

Answer

60 mm Hg

Question 10

What is the partial pressure for carbon dioxide in the inspired air?

Accepted Answer

0.3 mm Hg

Answer

158 mm Hg

Answer

100 mm Hg

Answer

32 mm Hg

Respiratory System — MCQs

Respiratory System — MCQs

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