Respiratory System — MCQs

Respiratory System Indian Medical PG Practice Questions and MCQs

Question 471: Which of the following is NOT true about COPD?

A. Reduced FEV1
B. Increased Residual Volume
C. Decreased Diffusion capacity (DLco) (Correct Answer)
D. Decreased Maximal Expiratory Flow Rate (MEFR)

Explanation: **Explanation:** The key to answering this question lies in distinguishing between the two main components of COPD: **Chronic Bronchitis** and **Emphysema**. While both involve airway obstruction, their physiological profiles differ regarding gas exchange. **Why Option C is the Correct Answer (The "NOT True" statement):** Decreased Diffusion Capacity (DLco) is a hallmark of **Emphysema** (due to alveolar wall destruction reducing the surface area for gas exchange). However, in **Chronic Bronchitis**, the DLco is typically **normal** because the alveolar-capillary membrane remains intact. Since the term "COPD" encompasses both, and DLco is not universally decreased across all COPD phenotypes, it is the most nuanced "incorrect" general statement compared to the definitive obstructive patterns seen in the other options. **Analysis of Incorrect Options:** * **A. Reduced FEV1:** This is the gold standard for diagnosing any obstructive lung disease. Increased airway resistance leads to a significant drop in the Forced Expiratory Volume in 1 second. * **B. Increased Residual Volume (RV):** Due to "air trapping" and loss of elastic recoil, patients cannot fully exhale, leading to an increase in RV and Total Lung Capacity (TLC). * **D. Decreased MEFR:** Obstruction and premature airway closure during expiration characteristically reduce the flow rates (MEFR/PEFR). **NEET-PG High-Yield Pearls:** * **Gold Standard Diagnosis:** FEV1/FVC ratio < 0.70 post-bronchodilator. * **Pink Puffers (Emphysema):** High compliance, low DLco, severe dyspnea. * **Blue Bloaters (Chronic Bronchitis):** Normal compliance, normal DLco, cyanosis, and edema. * **Flow-Volume Loop:** Shows a characteristic "scooped-out" appearance in the expiratory limb.

Question 472: Tachycardia is caused by hypoxia due to which of the following mechanisms?

A. Reflexly through peripheral chemoreceptors
B. Diffuse vasodilation
C. Through the central chemoreceptor
D. Secondarily after hyperventilation (Correct Answer)

Explanation: **Explanation:** The cardiovascular response to hypoxia is complex because it involves both direct and indirect (reflex) pathways. While it may seem intuitive that hypoxia directly stimulates the heart, the primary cause of tachycardia in a conscious human is actually **secondary to hyperventilation.** 1. **Why Option D is Correct:** When hypoxia occurs, peripheral chemoreceptors (carotid and aortic bodies) are stimulated, leading to an increase in rate and depth of respiration (**hyperventilation**). This hyperventilation triggers two main mechanisms that cause tachycardia: * **Hering-Breuer Reflex (Lung Inflation Reflex):** Increased lung stretch inhibits the vagal (parasympathetic) center in the medulla, leading to a rise in heart rate. * **Hypocapnia:** Hyperventilation washes out $CO_2$. Low $PCO_2$ inhibits the cardioinhibitory center, further increasing the heart rate. 2. **Why Other Options are Incorrect:** * **Option A:** Direct stimulation of peripheral chemoreceptors (if ventilation is controlled/fixed) actually causes **bradycardia** and vasoconstriction. The tachycardia seen clinically is a result of the respiratory override. * **Option B:** While hypoxia causes local vasodilation in systemic tissues, this is a peripheral vascular effect and not the primary mechanism for the initial tachycardic response. * **Option C:** Central chemoreceptors respond primarily to changes in $H^+$ and $PCO_2$ in the brain ECF, not to hypoxia. In fact, severe hypoxia can depress the central nervous system. **High-Yield Clinical Pearls for NEET-PG:** * **Direct effect of Hypoxia:** Bradycardia (seen in isolated chemoreceptor stimulation). * **Indirect/Reflex effect of Hypoxia:** Tachycardia (due to lung stretch and decreased vagal tone). * **Key Concept:** In a conscious, spontaneously breathing individual, the **indirect effect (tachycardia)** always overrides the direct effect. * **Clinical Correlation:** This is why patients with acute respiratory distress or high-altitude sickness present with tachycardia.

Question 473: Which of the following is used to measure the resistance in small airways?

A. Vital capacity
B. FEV1
C. Maximum mid expiratory flow rate (Correct Answer)
D. Closing volume

Explanation: ### Explanation **Correct Answer: C. Maximum Mid Expiratory Flow Rate (MMEFR / FEF 25-75%)** The **Maximum Mid Expiratory Flow Rate (MMEFR)**, also known as **FEF 25-75%**, represents the average flow rate during the middle half of a forced expiration. Unlike FEV1, which is effort-dependent and reflects large airway patency, MMEFR is **effort-independent** and highly sensitive to the status of the **small airways** (bronchioles <2mm in diameter). In early obstructive lung diseases (like early COPD or asthma), the small airways are the first to be affected—a region often called the "silent zone." MMEFR is the most sensitive indicator for detecting obstruction in these peripheral airways. **Why other options are incorrect:** * **A. Vital Capacity (VC):** This is a static lung volume representing the maximum amount of air a person can expel from the lungs after maximum inhalation. It measures lung capacity/size but does not provide information about airway resistance or flow rates. * **B. FEV1:** Forced Expiratory Volume in 1 second primarily reflects resistance in the **large, central airways**. It is the gold standard for diagnosing and monitoring obstructive diseases but is less sensitive than MMEFR for early small airway disease. * **C. Closing Volume:** This is the volume remaining in the lungs at the point when small airways in the lower (dependent) zones of the lung begin to close during expiration. While it *relates* to small airway stability, it is used to detect early small airway closure rather than measuring flow resistance. **High-Yield Clinical Pearls for NEET-PG:** * **Small Airway Disease:** Often referred to as the "Silent Zone" because it contributes only 10-20% of total airway resistance; significant damage can occur before FEV1 becomes abnormal. * **Most sensitive test for early obstruction:** MMEFR (FEF 25-75%). * **Effort Independence:** The middle part of the flow-volume loop is determined by the elastic recoil of the lungs and is not affected by how hard the patient tries to exhale.

Question 474: What is the normal pulmonary capillary pressure?

A. 5 mm Hg
B. 10 mm Hg (Correct Answer)
C. 20 mm Hg
D. 32 mm Hg

Explanation: **Explanation:** The pulmonary circulation is a **low-pressure, low-resistance system** compared to the systemic circulation. The normal mean pulmonary capillary pressure is approximately **10 mm Hg** (ranging between 7–12 mm Hg). This low pressure is physiological necessity to prevent the filtration of fluid into the alveoli, ensuring efficient gas exchange. **Why 10 mm Hg is correct:** In the lungs, the Starling forces are balanced such that the capillary hydrostatic pressure (10 mm Hg) is significantly lower than the plasma colloid osmotic pressure (~28 mm Hg). This "safety factor" keeps the alveoli dry by favoring the absorption of fluid into the interstitium/capillaries rather than filtration into the air spaces. **Analysis of Incorrect Options:** * **A (5 mm Hg):** This is closer to the normal **Left Atrial Pressure** (mean ~2–5 mm Hg). While low, it does not represent the pressure within the capillary bed itself. * **C (20 mm Hg):** This value is too high for a normal capillary. A mean pulmonary capillary pressure above 18–20 mm Hg typically indicates pulmonary venous congestion or early **pulmonary edema**. * **D (32 mm Hg):** This is the average hydrostatic pressure at the arterial end of a **systemic capillary**. If pulmonary capillary pressure reached this level, massive pulmonary edema would occur instantly. **High-Yield NEET-PG Pearls:** * **Mean Pulmonary Artery Pressure (mPAP):** Normal is ~15 mm Hg. Pulmonary hypertension is defined as mPAP >20 mm Hg at rest. * **West Zones of the Lung:** Pulmonary capillary pressure varies by position; it is lowest at the apex (Zone 1) and highest at the base (Zone 3) due to gravity. * **PCWP (Pulmonary Capillary Wedge Pressure):** Measured via a Swan-Ganz catheter, it is a clinical surrogate for left atrial pressure and pulmonary capillary pressure. Normal is 6–12 mm Hg.

Question 475: In an asthmatic patient, which of the following pulmonary functions would show the greater improvement on inhaling a bronchodilator?

A. Tidal volume
B. FEV1 (Correct Answer)
C. FEF 25%-75%
D. FVC

Explanation: ### Explanation **Correct Option: B (FEV1)** **Underlying Medical Concept:** Asthma is a reversible obstructive airway disease. The hallmark of obstruction is a reduction in expiratory flow rates, most notably the **Forced Expiratory Volume in 1 second (FEV1)**. In clinical practice, the "Reversibility Test" is used to diagnose asthma. A significant improvement in FEV1 (typically defined as an increase of **>12% and >200 mL**) after inhaling a short-acting beta-2 agonist (SABA) is the gold standard for confirming reversible airway obstruction. While other parameters may improve, FEV1 is the most reliable, standardized, and clinically significant marker for assessing the immediate response to bronchodilators. **Analysis of Incorrect Options:** * **A. Tidal Volume:** This is the volume of air moved during normal quiet breathing. While it may feel easier to breathe after a bronchodilator, tidal volume is not a sensitive or specific measure of airway obstruction or bronchodilator response. * **C. FEF 25%-75%:** This measures the flow rate during the middle half of expiration and is a sensitive marker for **small airway disease**. While it may show improvement, it is highly variable and less reproducible than FEV1, making it a secondary measure. * **D. FVC (Forced Vital Capacity):** FVC represents the total volume of air exhaled. In pure asthma, FVC is often normal or only slightly reduced due to air trapping. While it may increase slightly as air trapping resolves, the change is less dramatic and less diagnostic than the change in FEV1. **High-Yield Clinical Pearls for NEET-PG:** * **Tiffeneau Index:** The FEV1/FVC ratio is **decreased (<70%)** in obstructive lung diseases (Asthma, COPD) but **normal or increased** in restrictive diseases. * **Reversibility:** A post-bronchodilator improvement in FEV1 of >12% is the classic diagnostic criterion for Asthma. * **Flow-Volume Loop:** In asthma, the expiratory limb shows a characteristic **"scooped-out"** appearance due to airway obstruction.

Question 476: Select the best statement regarding the respiratory centers.

A. The normal rhythmic pattern of breathing originates from neurons in the dorsal respiratory group.
B. During quiet breathing, expiratory neurons are inhibited.
C. The apneustic center promotes inspiration.
D. The pneumotaxic center can override the function of the inspiratory centers. (Correct Answer)

Explanation: ### Explanation **1. Why Option D is Correct:** The **pneumotaxic center**, located in the upper pons (nucleus parabrachialis), acts as a "switch-off" point for inspiration. Its primary function is to limit the duration of inspiration by inhibiting the dorsal respiratory group (DRG). By controlling the "filling phase" of the lungs, it indirectly increases the respiratory rate. In extreme cases, strong pneumotaxic signals can override the inspiratory drive, making breathing shallow and rapid. **2. Why Other Options are Incorrect:** * **Option A:** While the DRG was historically thought to be the primary pacemaker, current evidence shows that the **Pre-Bötzinger complex** (located in the Ventral Respiratory Group) is the actual pacemaker responsible for generating the normal rhythmic pattern of breathing. * **Option B:** During quiet breathing, expiration is a **passive process** resulting from the elastic recoil of the lungs. Expiratory neurons are not necessarily "inhibited"; rather, they are simply **inactive**. They only become active during forceful or active expiration. * **Option C:** The **apneustic center** (lower pons) does promote inspiration by prolonging the firing of the DRG (causing "apneusis"). However, its role is physiological secondary to the pneumotaxic center, and it is normally inhibited by the pneumotaxic center and vagal afferents. **3. High-Yield Clinical Pearls for NEET-PG:** * **Location Summary:** DRG and VRG are in the **Medulla**; Pneumotaxic and Apneustic centers are in the **Pons**. * **Hering-Breuer Reflex:** Inflation of the lungs triggers stretch receptors that send signals via the **Vagus nerve** to inhibit the DRG, preventing over-inflation (similar to the pneumotaxic center's function). * **Lesion Effects:** A lesion above the pons with vagi intact results in normal breathing. A lesion at the mid-pons level with vagi cut results in **Apneustic breathing** (prolonged inspiratory gasps).

Question 477: What is the Haldane effect?

A. Effect of 2,3-BPG
B. Dissociation of CO2 on oxygenation (Correct Answer)
C. Dissociation of O2 on addition of CO2
D. Chloride shift

Explanation: ### Explanation The **Haldane Effect** describes the phenomenon where the oxygenation of hemoglobin in the lungs promotes the dissociation (release) of carbon dioxide from the blood. **Why Option B is Correct:** The underlying mechanism is based on the fact that **deoxygenated hemoglobin (deoxy-Hb)** has a higher affinity for $CO_2$ and acts as a better buffer for $H^+$ ions than oxyhemoglobin. 1. In the lungs, $O_2$ binds to hemoglobin, making it more acidic. 2. This acidity reduces its ability to carry $CO_2$ as carbamino compounds and releases $H^+$ ions. 3. These $H^+$ ions react with bicarbonate ($HCO_3^-$) to form $H_2CO_3$, which dissociates into $CO_2$ and $H_2O$, allowing $CO_2$ to be exhaled. Essentially, **oxygenation promotes $CO_2$ unloading.** **Analysis of Incorrect Options:** * **Option A:** 2,3-BPG decreases hemoglobin's affinity for oxygen, shifting the Oxygen-Hemoglobin Dissociation Curve (ODC) to the right. * **Option C:** This describes the **Bohr Effect**, which is the inverse of the Haldane effect. It states that increased $CO_2$ (and acidity) promotes the release of $O_2$ to the tissues. * **Option D:** **Chloride Shift (Hamburger Phenomenon)** refers to the exchange of $Cl^-$ and $HCO_3^-$ across the RBC membrane to maintain electrical neutrality during $CO_2$ transport. **High-Yield Clinical Pearls for NEET-PG:** * **Haldane Effect** occurs in the **Lungs** ($CO_2$ release). * **Bohr Effect** occurs in the **Tissues** ($O_2$ release). * The Haldane effect is quantitatively more important in $CO_2$ transport than the Bohr effect is in $O_2$ transport. * **Mnemonic:** **H**aldane = **H**emoglobin (Oxygenation) affects $CO_2$. **B**ohr = **B**lood $CO_2$ affects $O_2$.

Question 478: At which gestational age does surfactant production in the lungs begin?

A. 28 weeks (Correct Answer)
B. 32 weeks
C. 34 weeks
D. 36 weeks

Explanation: **Explanation:** **Correct Option: A (28 weeks)** Surfactant is a surface-active lipoprotein complex secreted by **Type II pneumocytes**. While surfactant synthesis begins as early as 20–24 weeks of gestation, it only reaches physiologically significant levels and begins to be secreted into the alveolar spaces around **28 weeks**. This timing is crucial as it marks the threshold where the fetal lungs gain the functional capacity to prevent alveolar collapse (atelectasis) upon expiration, significantly improving the chances of extrauterine survival. **Analysis of Incorrect Options:** * **B (32 weeks):** While surfactant levels continue to rise, this is an intermediate stage. It is not the "beginning" of functional production. * **C (34 weeks):** This is the clinical milestone where surfactant levels are usually sufficient to prevent **Respiratory Distress Syndrome (RDS)**. Most clinicians consider 34 weeks the "safe" zone where antenatal steroids are no longer routinely required. * **D (36 weeks):** By this time, the lungs are considered mature. The L/S ratio (Lecithin/Sphingomyelin) typically exceeds 2:1, indicating full pulmonary maturity. **High-Yield Clinical Pearls for NEET-PG:** * **Composition:** Surfactant is 90% lipids and 10% proteins. The most abundant phospholipid is **Dipalmitoylphosphatidylcholine (DPPC)** or Lecithin. * **Key Protein:** **Surfactant Protein B (SP-B)** is the most important for reducing surface tension. * **Stimulant:** **Glucocorticoids** (Cortisol) accelerate surfactant synthesis by stimulating Type II pneumocytes. This is why Betamethasone/Dexamethasone is given in preterm labor. * **Inhibitor:** **Hyperinsulinemia** (seen in infants of diabetic mothers) inhibits surfactant production, increasing the risk of RDS even in near-term babies.

Question 479: What is the characteristic of type-II respiratory failure?

A. Low PaO2 and low PaCO2
B. Low PaO2 and normal PaCO2
C. Normal PaO2 and high PaCO2
D. Low PaO2 and high PaCO2 (Correct Answer)

Explanation: ### Explanation Respiratory failure is clinically defined as the inability of the respiratory system to maintain adequate gas exchange. It is categorized into two main types based on arterial blood gas (ABG) patterns: **1. Why Option D is Correct:** **Type-II Respiratory Failure (Ventilatory Failure)** is characterized by **Hypoxemia (Low $PaO_2$) AND Hypercapnia (High $PaCO_2$)**. The underlying mechanism is **alveolar hypoventilation**. Since the lungs are failing to "pump" air out effectively, carbon dioxide accumulates in the blood ($PaCO_2 > 45 \text{ mmHg}$). Because $CO_2$ displaces oxygen in the alveoli (as per the Alveolar Gas Equation), the $PaO_2$ subsequently drops ($PaO_2 < 60 \text{ mmHg}$). Common causes include COPD, neuromuscular disorders (e.g., Guillain-Barré syndrome), and central respiratory depression (e.g., opioid overdose). **2. Analysis of Incorrect Options:** * **Option A & B:** These describe **Type-I Respiratory Failure (Hypoxemic Failure)**. In Type-I, there is low $PaO_2$ but the $PaCO_2$ is either **low** (due to compensatory hyperventilation) or **normal**. This is typically caused by V/Q mismatch or diffusion defects (e.g., Pneumonia, Pulmonary Edema, ARDS). * **Option C:** This is physiologically unlikely in acute respiratory failure. If $PaCO_2$ is significantly elevated due to hypoventilation, $PaO_2$ will inevitably fall unless the patient is on supplemental oxygen. **3. High-Yield Clinical Pearls for NEET-PG:** * **The A-a Gradient:** In Type-II failure caused by extrapulmonary issues (e.g., drug overdose), the **Alveolar-arterial (A-a) gradient is Normal**. If the cause is intrinsic lung disease (e.g., COPD), the A-a gradient is **Increased**. * **Type-III Failure:** Refers to perioperative respiratory failure (atelectasis). * **Type-IV Failure:** Refers to respiratory failure due to shock (hypoperfusion of respiratory muscles). * **Gold Standard Diagnosis:** Arterial Blood Gas (ABG) analysis is essential to differentiate between Type-I and Type-II.

Question 480: A 64-year-old woman presents with complaints of dyspnea and orthopnea. She is a lifelong non-smoker. Her pulmonary function testing is as follows. What is the most probable diagnosis?

A. Combined Obstructive - Restrictive Lung disease (Correct Answer)
B. Mild Obstructive Lung Disease
C. Moderate Obstructive Lung Disease
D. Restrictive Lung Disease

Explanation: ***Combined Obstructive - Restrictive Lung disease*** - **FEV1/FVC ratio < 70%** indicates obstructive pattern while **reduced TLC < 80% predicted** and **decreased FVC** suggest restrictive component. - This pattern occurs in conditions like **COPD with pulmonary fibrosis** or **bronchiectasis with scarring**, combining airway obstruction with lung volume reduction. *Mild Obstructive Lung Disease* - Would show **FEV1/FVC < 70%** with **normal or increased TLC** due to air trapping, not the reduced lung volumes seen here. - **FEV1 would be 60-80% predicted** in mild obstruction, but restrictive changes would be absent. *Moderate Obstructive Lung Disease* - Characterized by **FEV1 40-60% predicted** with **FEV1/FVC < 70%** but **preserved or increased TLC**. - The **reduced TLC and restrictive pattern** observed here contradicts pure obstructive pathophysiology. *Restrictive Lung Disease* - Would show **normal or increased FEV1/FVC ratio (>70%)** with **reduced TLC and FVC** due to lung stiffness. - The **obstructive component (FEV1/FVC < 70%)** present in this case rules out pure restrictive disease.

Practice by Chapter

Mechanics of Breathing

Practice Questions

Pulmonary Ventilation

Practice Questions

Pulmonary Circulation

Practice Questions

Gas Exchange in the Lungs

Practice Questions

Oxygen and Carbon Dioxide Transport

Practice Questions

Control of Breathing

Practice Questions

Respiratory Adjustments in Health and Disease

Practice Questions

High Altitude Physiology

Practice Questions

Diving Physiology

Practice Questions

Respiratory Function Tests

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free