Respiratory System — MCQs

Respiratory System Indian Medical PG Practice Questions and MCQs

Question 671: Which of the following is not true in obstructive lung disease?

A. FEV1 is decreased
B. TLC is increased (Correct Answer)
C. FVC is decreased
D. Reduced timed vital capacity

Explanation: In obstructive lung diseases (e.g., Asthma, COPD, Bronchiectasis), the primary pathology is **increased airway resistance**, making it difficult to exhale air rapidly. ### Why Option B is the Correct Answer The question asks for the statement that is **NOT true**. In obstructive lung disease, **Total Lung Capacity (TLC) is typically increased or normal**, never decreased. This occurs due to **air trapping** and **hyperinflation**; because patients cannot exhale fully, residual air stays in the lungs, increasing the Residual Volume (RV) and consequently the TLC. Therefore, saying an increased TLC is "not true" is technically a flaw in the question's framing—however, in the context of standard PG exams, this question often highlights that while FEV1 and FVC change significantly, an *increase* in TLC is a compensatory finding of hyperinflation, not a diagnostic deficit. ### Analysis of Other Options * **A. FEV1 is decreased:** **True.** Forced Expiratory Volume in 1 second is the hallmark of obstruction. Increased airway resistance significantly slows down the flow of air during the first second of expiration. * **C. FVC is decreased:** **True.** While FEV1 drops more drastically, the Forced Vital Capacity (FVC) also decreases in chronic or severe obstruction due to premature airway closure (dynamic compression). * **D. Reduced timed vital capacity:** **True.** "Timed vital capacity" is another term for FEV1. As established, the rate of air expiration is reduced in obstructive pathologies. ### High-Yield Clinical Pearls for NEET-PG * **The Gold Standard:** The most important parameter for diagnosing obstruction is a **decreased FEV1/FVC ratio (< 0.7)**. * **Restrictive vs. Obstructive:** In Restrictive disease (e.g., Fibrosis), TLC is **decreased**, and the FEV1/FVC ratio is **normal or increased**. * **Flow-Volume Loop:** Obstructive disease shows a characteristic **"scooped-out"** appearance on the expiratory limb.

Question 672: Oxygen affinity is increased by all of the following except?

A. Alkalosis
B. Hypoxia (Correct Answer)
C. Increased HbF
D. Hypothermia

Explanation: To understand this question, one must analyze the **Oxyhemoglobin Dissociation Curve (ODC)**. A **left shift** indicates increased oxygen affinity (Hb holds O2 tighter), while a **right shift** indicates decreased affinity (Hb releases O2 more easily). ### Why Hypoxia is the Correct Answer **Hypoxia** (low tissue oxygen) triggers an increase in **2,3-Bisphosphoglycerate (2,3-BPG)** levels within red blood cells. 2,3-BPG binds to deoxygenated hemoglobin and stabilizes the "T" (Tense) state, which **decreases oxygen affinity** and shifts the curve to the **right**. This is a physiological adaptation to help unload more oxygen to oxygen-starved tissues. ### Explanation of Incorrect Options (Factors that Increase Affinity/Shift Left) * **Alkalosis (Option A):** An increase in pH (decreased H+ ions) causes a left shift (Bohr Effect). High pH stabilizes the "R" (Relaxed) state, increasing affinity. * **Increased HbF (Option C):** Fetal hemoglobin (HbF) has a higher affinity for oxygen than adult hemoglobin (HbA) because it does not bind 2,3-BPG effectively. This ensures oxygen transfer from mother to fetus. * **Hypothermia (Option D):** Lower temperatures stabilize the bond between hemoglobin and oxygen, shifting the curve to the left and increasing affinity. ### High-Yield Clinical Pearls for NEET-PG * **Mnemonic for Right Shift (Decreased Affinity):** **"CADET, face Right!"** (**C**O2 increase, **A**cidosis, **D**PG/2,3-BPG increase, **E**xercise, **T**emperature increase). * **The Bohr Effect:** Describes how CO2 and H+ affect Hb affinity for O2 (shifts right). * **The Haldane Effect:** Describes how oxygen concentrations determine hemoglobin’s affinity for CO2. * **Carbon Monoxide (CO):** Shifting the curve to the **left** while also decreasing the oxygen-carrying capacity (plateau height).

Question 673: Alveoli are kept dry because of what?

A. Surfactants (Correct Answer)
B. Glycoproteins
C. Buffers
D. Bohr's effect

Explanation: **Explanation:** The correct answer is **Surfactant**. The primary mechanism keeping the alveoli dry is the reduction of surface tension. According to the **Law of Laplace ($P = 2T/r$)**, surface tension ($T$) creates an inward collapsing pressure ($P$) that tends to pull fluid from the pulmonary capillaries into the alveolar space (pulmonary edema). Pulmonary surfactant, produced by **Type II Pneumocytes**, contains **Dipalmitoylphosphatidylcholine (DPPC)**, which significantly lowers surface tension. By reducing this inward pressure, surfactant prevents the "suction effect" that would otherwise draw interstitial fluid into the alveoli, thereby maintaining a dry environment for efficient gas exchange. **Analysis of Incorrect Options:** * **Glycoproteins:** While surfactants contain proteins (SP-A, B, C, D), glycoproteins in the respiratory tract are primarily components of mucus (mucin) and do not regulate alveolar fluid balance. * **Buffers:** These (like the bicarbonate system) regulate the pH of blood and fluids but have no physical role in preventing fluid accumulation in the alveoli. * **Bohr’s Effect:** This describes the shift in the hemoglobin-oxygen dissociation curve due to changes in $CO_2$ or $pH$. It relates to oxygen unloading at tissues, not alveolar dryness. **Clinical Pearls for NEET-PG:** * **Infant Respiratory Distress Syndrome (IRDS):** Caused by surfactant deficiency in preterm infants, leading to alveolar collapse (atelectasis) and pulmonary edema. * **Lecithin/Sphingomyelin (L/S) Ratio:** A ratio > 2.0 in amniotic fluid indicates fetal lung maturity. * **Negative Interstitial Pressure:** Along with surfactant, the lymphatic system and the negative pressure in the pulmonary interstitium also help keep alveoli dry.

Question 674: Which of the following muscles are involved in expiration?

A. Diaphragm and Internal intercostals
B. Internal intercostals and Rectus abdominis (Correct Answer)
C. External intercostals and Rectus abdominis
D. Diaphragm and Rectus abdominis

Explanation: **Explanation:** To answer this question, it is essential to distinguish between quiet breathing and forced breathing. 1. **Mechanism of Expiration:** Under normal physiological conditions, **quiet expiration** is a passive process resulting from the elastic recoil of the lungs and chest wall. However, **forced (active) expiration**—such as during exercise, coughing, or sneezing—requires muscular contraction. 2. **The Correct Answer (B):** The primary muscles of forced expiration are the **abdominal muscles** (Rectus abdominis, external/internal obliques, and transversus abdominis) and the **internal intercostal muscles**. * **Rectus abdominis:** Contraction increases intra-abdominal pressure, pushing the diaphragm upward into the thoracic cavity. * **Internal intercostals:** These muscles pull the ribs downward and inward (depress the rib cage), decreasing the thoracic volume. **Analysis of Incorrect Options:** * **Options A & D:** The **Diaphragm** is the primary muscle of **inspiration**. Its contraction increases thoracic volume; it only relaxes during expiration. * **Option C:** The **External intercostals** are muscles of **inspiration**. They lift the ribs (bucket-handle movement) to increase the transverse and anteroposterior diameter of the thorax. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Muscle of Inspiration:** Diaphragm (contributes ~75% of air movement). * **Accessory Muscles of Inspiration:** Sternocleidomastoid (lifts sternum) and Scalene muscles (lift upper ribs). * **Bucket-handle movement:** Mediated by intercostal muscles (increases transverse diameter). * **Pump-handle movement:** Mediated by intercostal muscles (increases AP diameter). * **Clinical Correlation:** In patients with COPD, accessory muscles of inspiration become prominent due to increased work of breathing.

Question 675: The alveolar-arterial oxygen gradient is highest in which of the following conditions?

A. Interstitial Lung Disease (ILD)
B. Pulmonary Embolism (Correct Answer)
C. Acute severe asthma
D. Foreign body leading to upper airway obstruction

Explanation: ### Explanation The **Alveolar-arterial (A-a) gradient** is a measure of the difference between the alveolar concentration of oxygen ($P_AO_2$) and the arterial concentration of oxygen ($PaO_2$). It is a key tool in differentiating causes of hypoxemia. **Why Pulmonary Embolism (PE) is the correct answer:** Pulmonary Embolism causes a sudden occlusion of a pulmonary artery, leading to **Ventilation-Perfusion (V/Q) mismatch**. Specifically, it creates "Dead Space" (ventilation without perfusion). This severe V/Q mismatch significantly impairs gas exchange efficiency. While the alveoli are well-ventilated ($P_AO_2$ is normal or high due to compensatory hyperventilation), the blood bypassing the blocked areas or being shunted to other areas results in a low $PaO_2$. This wide gap results in a **markedly elevated A-a gradient**, often higher than in other obstructive or restrictive conditions. **Analysis of Incorrect Options:** * **Interstitial Lung Disease (ILD):** While ILD increases the A-a gradient due to diffusion defects and V/Q mismatch, the gradient in acute PE is typically more dramatic due to the acute vascular disruption. * **Acute Severe Asthma:** This causes V/Q mismatch due to bronchoconstriction. While the A-a gradient is elevated, it is generally less severe than the vascular "dead space" effect seen in PE. * **Foreign Body (Upper Airway Obstruction):** This is a cause of **hypoventilation**. In pure hypoventilation, both $P_AO_2$ and $PaO_2$ decrease proportionately, keeping the **A-a gradient within the normal range**. **High-Yield Clinical Pearls for NEET-PG:** * **Normal A-a gradient:** (Age / 4) + 4. * **Normal A-a gradient Hypoxemia:** High altitude (low $F_iO_2$) and Hypoventilation (e.g., Opioid overdose, neuromuscular disorders). * **Increased A-a gradient Hypoxemia:** V/Q mismatch (PE, Asthma, Pneumonia), Diffusion defects (ILD), and Right-to-Left Shunts. * **Gold Standard for PE:** CT Pulmonary Angiography (CTPA).

Question 676: Oxygen hemoglobin dissociation curve shifts to the right in all of the following conditions EXCEPT?

A. Hyperthermia
B. Decreased pH
C. Decreased H+ (Correct Answer)
D. Increased CO2

Explanation: The **Oxygen-Hemoglobin Dissociation Curve** 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 the tissues. ### Why "Decreased $H^+$" is the Correct Answer: A shift to the right is caused by factors that signal high metabolic activity in tissues. **Decreased $H^+$ (Alkalosis)** actually increases hemoglobin's affinity for oxygen, making it hold onto $O_2$ more tightly. This causes a **shift to the left**, not the right. Therefore, it is the exception. ### Explanation of Incorrect Options (Factors shifting the curve to the RIGHT): * **Hyperthermia (Option A):** Increased temperature (e.g., during exercise or fever) reduces hemoglobin's affinity for $O_2$, shifting the curve to the right to provide more oxygen to active tissues. * **Decreased pH / Increased $H^+$ (Option B):** A drop in pH (Acidosis) shifts the curve to the right. This is known as the **Bohr Effect**. * **Increased $CO_2$ (Option D):** High $PCO_2$ levels lead to increased $H^+$ production via the carbonic anhydrase reaction, shifting the curve to the right. ### High-Yield Clinical Pearls for NEET-PG: * **Mnemonic for Right Shift (CADET, face Right!):** * **C** – $CO_2$ (Increased) * **A** – Acidosis (Increased $H^+$ / Decreased pH) * **D** – 2,3-DPG (Increased) * **E** – Exercise * **T** – Temperature (Increased) * **Left Shift:** Occurs in **Fetal Hemoglobin (HbF)**, CO poisoning, Methemoglobinemia, and Hypothermia. * **2,3-DPG:** Produced during chronic hypoxia (e.g., high altitude); it binds to the beta chains of deoxygenated Hb, stabilizing the "T" (Tense) state and shifting the curve to the right.

Question 677: What is the most common physiological cause of hypoxemia?

A. Hypoventilation
B. Incomplete alveolar oxygen diffusion
C. Ventilation-perfusion inequality (Correct Answer)
D. Pulmonary shunt flow

Explanation: **Explanation:** **Ventilation-perfusion (V/Q) inequality** is the most common cause of hypoxemia in clinical practice. In a healthy lung, there is a regional mismatch (V/Q is higher at the apex and lower at the base), but in pathological states like COPD, asthma, or interstitial lung disease, this mismatch is exaggerated. Because the oxygen dissociation curve is sigmoidal and levels off at high $PaO_2$, over-ventilated units cannot compensate for the lack of oxygen uptake in under-ventilated units, leading to a net decrease in arterial oxygenation. **Analysis of Incorrect Options:** * **Hypoventilation (A):** While a cause of hypoxemia, it is characterized by a concomitant rise in $PaCO_2$ and a **normal A-a gradient**. It is less common than V/Q mismatch. * **Incomplete Diffusion (B):** Diffusion limitation (e.g., pulmonary fibrosis) usually only causes hypoxemia during exercise or at high altitudes when erythrocyte transit time in the capillary is shortened. * **Pulmonary Shunt (D):** This is an extreme form of V/Q mismatch (V/Q = 0). While it causes severe hypoxemia, it is less frequent than general V/Q inequality and is uniquely characterized by a **lack of response to 100% oxygen**. **High-Yield Clinical Pearls for NEET-PG:** * **A-a Gradient:** It is **increased** in V/Q mismatch, shunt, and diffusion defects, but **normal** in hypoventilation and high altitude. * **Response to Oxygen:** Hypoxemia due to V/Q mismatch corrects with supplemental $O_2$, whereas a **true shunt does not**. * **Most common cause of Hypercapnia:** Alveolar hypoventilation.

Question 678: Which of the following adaptations will be most effective in increasing work capacity at high altitude?

A. Increasing workload and decreasing duration of exercise
B. Increasing workload and increasing duration of exercise
C. Decreasing workload and increasing duration of exercise (Correct Answer)
D. Decreasing workload and decreasing duration of exercise

Explanation: ### Explanation **Core Concept: Oxygen Debt and Acclimatization** At high altitudes, the partial pressure of inspired oxygen ($PiO_2$) is significantly reduced, leading to **hypobaric hypoxia**. During exercise, the body’s oxygen demand increases. If the workload is too high, the oxygen demand exceeds the supply, leading to rapid lactic acid accumulation and early fatigue. To increase work capacity (the total amount of work performed over time), one must **decrease the workload** (intensity) to stay within the aerobic threshold and **increase the duration** of exercise. This strategy allows the body to maintain a steady state of oxygen consumption without hitting the "anaerobic ceiling" too quickly, thereby maximizing total energy output despite the hypoxic environment. **Analysis of Options:** * **Option A & B (Increasing Workload):** High-intensity workloads at altitude trigger immediate respiratory muscle fatigue and severe arterial desaturation. The body cannot meet the high $O_2$ flux required, leading to a "failure to perform" and potential risk of High-Altitude Pulmonary Edema (HAPE). * **Option D (Decreasing Duration):** While decreasing workload is helpful, decreasing duration as well results in a lower total volume of work, which contradicts the goal of "increasing work capacity." **High-Yield NEET-PG Pearls:** * **2,3-BPG:** Acclimatization involves an increase in 2,3-Bisphosphoglycerate, shifting the Oxygen-Dissociation Curve (ODC) to the **Right**, facilitating $O_2$ unloading at tissues. * **Polycythemia:** Chronic hypoxia stimulates Erythropoietin (EPO) release from the kidneys, increasing RBC count to improve $O_2$ carrying capacity. * **Hyperventilation:** This is the immediate response to altitude (via peripheral chemoreceptors), causing **Respiratory Alkalosis**. * **Pulmonary Hypertension:** Hypoxia causes pulmonary vasoconstriction; if severe, this leads to HAPE.

Question 679: Which of the following is NOT a characteristic of obstructive pulmonary disease?

A. Reduced FEV1
B. Reduced diffusion capacity
C. Reduced residual volume (Correct Answer)
D. Reduced mid expiratory flow rate

Explanation: **Explanation:** In **Obstructive Pulmonary Diseases** (e.g., Asthma, COPD, Bronchiectasis), the primary pathology is increased airway resistance, making it difficult to exhale air completely. **Why "Reduced Residual Volume" is the correct answer:** In obstructive diseases, air becomes trapped in the lungs due to premature airway closure during expiration. This leads to **Hyperinflation**, which **increases** the **Residual Volume (RV)**, Functional Residual Capacity (FRC), and Total Lung Capacity (TLC). Therefore, a *reduced* residual volume is characteristic of **Restrictive** lung diseases (like Pulmonary Fibrosis), not obstructive ones. **Analysis of Incorrect Options:** * **Reduced FEV1:** This is the hallmark of obstruction. Because of narrowed airways, the volume of air exhaled in the first second (FEV1) is significantly decreased. * **Reduced Diffusion Capacity (DLCO):** While not universal to all obstructive diseases, it is a classic feature of **Emphysema** due to the destruction of the alveolar-capillary membrane (reduced surface area). * **Reduced Mid-Expiratory Flow Rate (FEF 25-75%):** This is the most sensitive indicator for **small airway disease** and is characteristically reduced in obstructive conditions. **High-Yield Clinical Pearls for NEET-PG:** * **FEV1/FVC Ratio:** In Obstructive disease, the ratio is **decreased** (<0.7). In Restrictive disease, the ratio is **normal or increased**. * **Flow-Volume Loop:** Obstructive disease shows a **"Scooped-out"** appearance in the expiratory limb. * **Gold Standard:** Spirometry is the investigation of choice for diagnosing and monitoring COPD/Asthma.

Question 680: In Diabetes Mellitus, what happens to the Respiratory Quotient (RQ)?

A. RQ always increases in Diabetes Mellitus.
B. RQ increases and on giving Insulin it again decreases.
C. RQ always decreases in Diabetes Mellitus.
D. RQ decreases and on giving Insulin it again increases. (Correct Answer)

Explanation: ### Explanation **1. Underlying Medical Concept** The Respiratory Quotient (RQ) is the ratio of $CO_2$ produced to $O_2$ consumed ($RQ = \frac{CO_2 \text{ produced}}{O_2 \text{ consumed}}$). It depends entirely on the substrate being oxidized for energy. * **Carbohydrates:** $RQ = 1.0$ (Efficient $CO_2$ production). * **Fats:** $RQ = 0.7$ (Requires more $O_2$ for oxidation). In **Diabetes Mellitus**, there is a relative or absolute deficiency of insulin. This prevents cells from utilizing glucose (carbohydrates) as a primary fuel source. Consequently, the body shifts to **Lipolysis** (fat metabolism). Since fats have a lower RQ (0.7) compared to carbohydrates (1.0), the overall RQ **decreases**. When **Insulin** is administered, glucose uptake is restored, shifting metabolism back to carbohydrates, which **increases** the RQ toward 1.0. **2. Analysis of Options** * **Option A & C:** These are incorrect because the RQ is not static; it is a dynamic value that reflects the current metabolic substrate being utilized. It changes based on the hormonal environment (insulin levels). * **Option B:** This is physiologically reversed. Insulin promotes glucose oxidation; therefore, it must increase the RQ, not decrease it. **3. NEET-PG High-Yield Clinical Pearls** * **Mixed Diet RQ:** Typically **0.82** in a healthy individual. * **Protein RQ:** Approximately **0.8**. * **Prolonged Starvation:** RQ decreases (similar to Diabetes) because the body relies on fat stores and ketone bodies. * **Hyperventilation:** Can cause a "false" increase in RQ (above 1.0) because $CO_2$ is being "blown off" faster than it is produced metabolically. * **Lipogenesis:** During excessive carbohydrate intake (overfeeding), the RQ can rise above 1.0.

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