Respiratory System Practice Questions

Q: Which of the following statements is true regarding asthma?

Increased FRC and increased residual volume. **Explanation:** Asthma is a chronic inflammatory **obstructive lung disease** characterized by reversible airway narrowing. The pathophysiology revolves around **air trapping** and **hyperinflation**. **1. Why Option B is Correct:** During an asthma attack, bronchoconstriction and mucus plugging lead to premature closure of the small airways during expiration. This prevents the lungs from emptying completely, a phenomenon known as **air trapping**. * **Residual Volume (RV):** The volume of air remaining in the lungs after maximal expiration increases because air is trapped behind closed airways. * **Functional Residual Capacity (FRC):** Since FRC is the sum of RV and Expiratory Reserve Volume (ERV), an increase in RV leads to a compensatory increase in FRC. The patient breathes at higher lung volumes to keep the airways open via increased radial traction. **2. Why Other Options are Incorrect:** * **Options A & C:** Residual Volume (RV) is **never reduced** in obstructive diseases like asthma or COPD; it is typically increased. A reduced RV is characteristic of restrictive lung diseases (e.g., pulmonary fibrosis). * **Options C & D:** FRC is **increased** in asthma due to hyperinflation. A reduced FRC occurs in conditions that cause lung collapse or stiffness (e.g., ARDS, obesity, or interstitial lung disease). **High-Yield Clinical Pearls for NEET-PG:** * **PFT Pattern:** Decreased FEV1, decreased FEV1/FVC ratio ( 12% and >200ml improvement in FEV1 after bronchodilator administration. * **Flow-Volume Loop:** Shows a characteristic **"scooped-out"** appearance during the expiratory phase. * **Status Asthmaticus:** A normal or rising PaCO2 in a severe attack is an ominous sign of impending respiratory failure (muscle fatigue).

Q: Which of the following is preferred for the diagnosis of obstructive airway disease?

Timed vital capacity. **Explanation:** The diagnosis of obstructive airway diseases (like Asthma and COPD) relies on assessing the **rate of airflow** rather than just the volume of air. **Why Timed Vital Capacity is correct:** Timed Vital Capacity, specifically **FEV1** (Forced Expiratory Volume in 1 second), measures the volume of air exhaled during the first second of a forced expiration. In obstructive diseases, the airway resistance is increased, leading to a prolonged expiratory phase and a significant reduction in FEV1. While the total Forced Vital Capacity (FVC) may remain normal or slightly decreased, the **FEV1/FVC ratio** (Tiffeneau Index) drops below 70%, making it the gold standard for identifying obstruction. **Why other options are incorrect:** * **Vital Capacity (VC):** This measures the maximum volume of air moved in or out. It is primarily reduced in **restrictive** lung diseases (like Pulmonary Fibrosis). In early obstruction, VC may be normal. * **Tidal Volume (TV):** This is the volume of air inspired or expired during normal quiet breathing (~500ml). It is non-specific and does not provide information about airway resistance or lung capacity. * **Blood Gas Analysis (ABG):** While useful for assessing the severity of an acute exacerbation (hypoxia/hypercapnia), it is not a diagnostic tool for the underlying airway disease itself. **High-Yield Clinical Pearls for NEET-PG:** * **Obstructive Pattern:** ↓FEV1, ↓FEV1/FVC ratio (<0.7), ↑Residual Volume (due to air trapping). * **Restrictive Pattern:** ↓FVC, **Normal or ↑FEV1/FVC ratio**, ↓Total Lung Capacity. * **MVV (Maximum Voluntary Ventilation):** Also significantly reduced in obstructive diseases but is more strenuous for the patient than FEV1.

Q: Which of the following is NOT true regarding restrictive lung disease?

FEV1% is decreased in interstitial lung disease.. **Explanation:** In **Restrictive Lung Diseases (RLD)**, the hallmark is a reduction in lung volumes due to either parenchymal stiffness (e.g., Interstitial Lung Disease) or extrapulmonary constraints (e.g., chest wall deformities, diaphragmatic paralysis). **Why Option D is the Correct Answer (The "False" Statement):** In RLD, both Forced Expiratory Volume in 1 second (FEV1) and Forced Vital Capacity (FVC) decrease. However, because the lung tissue is stiff (increased elastic recoil), the airways are pulled open wider (radial traction), allowing air to exit rapidly. Consequently, **FVC decreases more than FEV1**, leading to a **normal or increased FEV1/FVC ratio (FEV1%)**. A decreased FEV1% is characteristic of *obstructive* lung diseases like asthma or COPD. **Analysis of Other Options:** * **Option A (True):** In **extrapulmonary** restriction like diaphragmatic paralysis, the lungs cannot be fully emptied because the respiratory pump is weak, leading to an **increased Residual Volume (RV)**. * **Option B (True):** In **Interstitial Lung Disease (ILD)**, the alveolar-capillary membrane thickens (fibrosis), which increases the diffusion distance, thereby **decreasing the DLCO**. * **Option C (True):** In **intrapulmonary** restriction (ILD), the increased elastic recoil of the fibrotic lung parenchyma pulls the lungs inward, resulting in a **decreased RV** and Total Lung Capacity (TLC). **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard for Diagnosis:** A decrease in **Total Lung Capacity (TLC)** is the definitive marker for restriction. * **Flow-Volume Loop:** RLD shows a **"Witch’s Hat"** appearance (narrow, tall loop shifted to the right). * **DLCO Differentiation:** DLCO is **decreased** in intrinsic RLD (fibrosis) but typically **normal** in extrinsic RLD (obesity, kyphoscoliosis, neuromuscular weakness).

Q: What is the primary function of the carotid body?

To measure changes in PO2 in arterial blood. The **carotid bodies** are the primary peripheral chemoreceptors responsible for monitoring the chemical composition of arterial blood. ### **Why Option A is Correct** The carotid bodies are located at the bifurcation of the common carotid arteries. Their primary function is to detect a **decrease in the partial pressure of oxygen (PO2)** in arterial blood. When arterial PO2 drops below 60 mmHg, glomus cells (Type I cells) in the carotid body depolarize, sending signals via the **glossopharyngeal nerve (CN IX)** to the respiratory centers in the medulla to increase ventilation. While they also respond to increases in PCO2 and decreases in pH, their most critical and unique role is sensing **hypoxia**. ### **Why Other Options are Incorrect** * **Options B & D:** Chemoreceptors do not monitor venous blood. Venous blood parameters reflect tissue metabolism rather than the efficiency of gas exchange. Arterial blood provides the necessary information regarding how well the lungs are oxygenating the blood. * **Option C:** While carotid bodies are sensitive to arterial CO2, this is not their *primary* function. The **central chemoreceptors** in the medulla are the main sensors for arterial PCO2 (via changes in CSF pH) and are responsible for approximately 70-80% of the ventilatory response to CO2. ### **High-Yield Facts for NEET-PG** * **Blood Flow:** The carotid body has the **highest blood flow per unit weight** in the body (approx. 2000 mL/100g/min), allowing it to sense dissolved PO2 rather than oxygen content bound to hemoglobin. * **Anemia/CO Poisoning:** In these conditions, arterial PO2 is normal but oxygen content is low. Therefore, the **carotid bodies are NOT stimulated**, and ventilation does not increase. * **Innervation:** Carotid body → Hering’s nerve (branch of CN IX); Aortic body → Vagus nerve (CN X).

Q: Respiratory burst in neutrophils occurs due to which enzyme system?

NADPH oxidase. **Explanation:** **1. Why NADPH Oxidase is Correct:** Respiratory burst (or oxidative burst) is the rapid release of reactive oxygen species (ROS) from neutrophils and macrophages to destroy phagocytosed microbes. The key enzyme responsible for this process is **NADPH oxidase** (Nicotinamide adenine dinucleotide phosphate oxidase). * **Mechanism:** It transfers electrons from NADPH to molecular oxygen ($O_2$), converting it into the **Superoxide anion** ($O_2^-$). * **Reaction:** $NADPH + 2O_2 \xrightarrow{\text{NADPH Oxidase}} NADP^+ + H^+ + 2O_2^-$ * The superoxide is subsequently converted to hydrogen peroxide ($H_2O_2$) by superoxide dismutase, and finally into highly bactericidal hypochlorite ($HOCl$) by myeloperoxidase (MPO). **2. Why Other Options are Incorrect:** * **NADP oxidase:** This is a misnomer. The enzyme requires the reduced form (NADPH) as an electron donor, not the oxidized form (NADP). * **FADH2 oxidase / FAD:** While FAD is a cofactor in many redox reactions (like those in the Krebs cycle or Electron Transport Chain), it is not the primary enzyme system responsible for the phagocytic respiratory burst. **3. Clinical Pearls for NEET-PG:** * **Chronic Granulomatous Disease (CGD):** A high-yield clinical correlation. CGD is caused by a genetic **deficiency of NADPH oxidase**. Patients suffer from recurrent infections with catalase-positive organisms (e.g., *S. aureus*, *Aspergillus*) because they cannot produce their own $H_2O_2$. * **Nitroblue Tetrazolium (NBT) Test:** Used to diagnose CGD. In healthy neutrophils, NADPH oxidase reduces the yellow NBT dye to blue formazan. In CGD, the test remains negative (yellow). * **HMP Shunt:** This metabolic pathway is crucial for respiratory burst as it provides the necessary **NADPH** substrate.

Q: If the alveolar oxygenation is halved, what happens to the PACO2?

Halved in a few minutes. ### Explanation The relationship between alveolar ventilation and the partial pressure of arterial/alveolar carbon dioxide ($P_aCO_2$) is governed by the **Alveolar Ventilation Equation**: $$V_A \propto \frac{VCO_2}{P_A CO_2}$$ *(Where $V_A$ = Alveolar Ventilation and $VCO_2$ = Rate of $CO_2$ production)* **1. Why the Correct Answer is Right:** If alveolar ventilation is **doubled**, the removal of $CO_2$ from the lungs increases proportionally. Since $CO_2$ production ($VCO_2$) remains constant, the concentration of $CO_2$ in the alveoli (and subsequently the arterial blood) will be **halved**. However, this change is not instantaneous. It takes **a few minutes** for the body’s $CO_2$ stores (found in blood and tissues) to reach a new steady-state equilibrium after a change in ventilation. **2. Why the Incorrect Options are Wrong:** * **Options A & B (Doubled):** Doubling ventilation *decreases* $P_aCO_2$. $P_aCO_2$ would only double if ventilation were halved (hypoventilation). * **Option C (Halved instantly):** While the mathematical relationship is inverse, the physiological response is delayed. $CO_2$ must diffuse from the tissues and blood into the alveoli to be exhaled; therefore, the "washout" period prevents an instantaneous drop. **3. Clinical Pearls & High-Yield Facts:** * **Hyperventilation:** Defined as ventilation in excess of metabolic needs, leading to **hypocapnia** ($P_aCO_2 45$ mmHg) and respiratory acidosis. * **Dead Space:** Remember that $V_A = (\text{Tidal Volume} - \text{Dead Space}) \times \text{Respiratory Rate}$. Increasing tidal volume is more effective at lowering $P_aCO_2$ than increasing respiratory rate due to the constant nature of anatomical dead space.

Q: Adequate oxygen is delivered to the tissues in which type of hypoxia?

Histotoxic hypoxia. **Explanation:** The core concept in this question is the distinction between **oxygen delivery** ($DO_2$) and **oxygen utilization**. **Why Histotoxic Hypoxia is correct:** In histotoxic hypoxia (most commonly caused by **cyanide poisoning**), the partial pressure of oxygen in the blood ($PaO_2$), the hemoglobin concentration, and the cardiac output are all normal. Therefore, the **delivery of oxygen to the tissues is adequate**. The pathology lies at the cellular level: cyanide inhibits the **cytochrome oxidase enzyme** in the electron transport chain, preventing the mitochondria from utilizing the oxygen provided. Since oxygen is delivered but not consumed, the venous blood remains highly oxygenated, leading to a characteristic narrowing of the arterial-venous oxygen difference. **Why the other options are incorrect:** * **Hypoxic Hypoxia:** Characterized by low $PaO_2$ (e.g., high altitude, hypoventilation). Delivery is inadequate because the blood is not sufficiently loaded with oxygen in the lungs. * **Anemic Hypoxia:** Delivery is inadequate because the oxygen-carrying capacity of the blood is reduced due to low hemoglobin or carbon monoxide poisoning, despite normal $PaO_2$. * **Stagnant Hypoxia:** Delivery is inadequate because of reduced blood flow (low cardiac output or localized ischemia), even though the blood itself is well-oxygenated. **High-Yield NEET-PG Pearls:** * **Cyanosis** is absent in histotoxic hypoxia; the skin often appears **"cherry-red"** because venous blood remains saturated with oxyhemoglobin. * In histotoxic hypoxia, the **Arterial-Venous (A-V) oxygen difference** is significantly decreased (approaching zero). * **Specific Antidote for Cyanide:** Amyl nitrite/Sodium nitrite (creates methemoglobin to sequester cyanide) and Sodium thiosulfate. Hydroxocobalamin is the modern preferred agent.

Question 1

Which of the following statements is true regarding asthma?

Accepted Answer

Increased FRC and increased residual volume

Answer

Increased FRC and reduced residual volume

Answer

Reduced FRC and reduced residual volume

Answer

Reduced FRC and increased residual volume

Question 2

Which of the following is preferred for the diagnosis of obstructive airway disease?

Accepted Answer

Timed vital capacity

Answer

Vital capacity

Answer

Tidal volume

Answer

Blood gas analysis

Question 3

Which of the following is NOT true regarding restrictive lung disease?

Accepted Answer

FEV1% is decreased in interstitial lung disease.

Answer

Residual volume is increased in diaphragmatic paralysis.

Answer

Diffusion lung capacity for carbon monoxide is decreased in interstitial lung disease.

Answer

Residual volume is decreased in interstitial lung disease.

Question 4

What is the primary function of the carotid body?

Accepted Answer

To measure changes in PO2 in arterial blood

Answer

To measure PO2 in venous blood

Answer

To measure changes in CO2 in arterial blood

Answer

To measure changes in CO2 in venous blood

Question 5

A man connected to a body plethysmograph for estimation of FRC inspires against a closed glottis. Which of the following statements is true?

Accepted Answer

The pressure in the lungs decreases, but that in the box increases

Answer

The pressure in both the lungs and the box increases

Answer

The pressure in both the lungs and the box decreases

Answer

The pressure in the lungs increases, but that in the box decreases

Question 6

Respiratory burst in neutrophils occurs due to which enzyme system?

Accepted Answer

NADPH oxidase

Answer

NADP oxidase

Answer

FADH2 oxidase

Answer

FAD

Question 7

If the alveolar oxygenation is halved, what happens to the PACO2?

Accepted Answer

Halved in a few minutes

Answer

Doubled instantly

Answer

Doubled in a few minutes

Answer

Halved instantly

Question 8

Adequate oxygen is delivered to the tissues in which type of hypoxia?

Accepted Answer

Histotoxic hypoxia

Answer

Hypoxic hypoxia

Answer

Stagnant hypoxia

Answer

Anemic hypoxia

Question 9

A foreign body completely obstructing the right main bronchus causes what?

Accepted Answer

Decreased ventilation-perfusion ratio

Answer

Increased ventilation in the left lung

Answer

Perfusion to the right lung to double

Answer

Increased ventilation-perfusion ratio in the right lung

Question 10

Pulmonary micro-circulation differs from systemic circulation in having what characteristics?

Accepted Answer

Low resistance and low capillary pressure

Answer

Low resistance and high pulsatile flow

Answer

High resistance and low pulsatile flow

Answer

High resistance and high capillary pressure

Respiratory System — MCQs

Respiratory System — MCQs

On this page

Practice by Chapter

Want unlimited practice?