Respiratory System Practice Questions

Q: All of the following are risks seen in the administration of pure oxygen to hypoxic patients, except?

2,3-DPG toxicity. **Explanation:** The correct answer is **C. 2,3-DPG toxicity**. This is because 2,3-DPG (2,3-bisphosphoglycerate) is a metabolic byproduct of glycolysis in red blood cells that helps regulate hemoglobin's affinity for oxygen. It is not a substance that causes "toxicity" during oxygen therapy. In fact, chronic hypoxia typically *increases* 2,3-DPG levels to facilitate oxygen unloading to tissues. **Analysis of Options:** * **A. Apnea (Hypoxic Drive):** In patients with chronic hypercapnia (e.g., COPD), the central chemoreceptors become desensitized. Their primary stimulus for breathing becomes "hypoxic drive" via peripheral chemoreceptors. Administering pure oxygen removes this stimulus, potentially leading to respiratory depression or apnea. * **B. Pulmonary Edema:** High concentrations of oxygen (hyperoxia) lead to the formation of Reactive Oxygen Species (ROS) like superoxide radicals. These damage the alveolar-capillary membrane, leading to "Oxygen Toxicity" (Lorrain Smith effect), which manifests as pulmonary congestion and edema. * **D. Convulsions:** Exposure to high partial pressures of oxygen (hyperbaric oxygen) can affect the Central Nervous System (Paul Bert effect), leading to symptoms such as dizziness, muscle twitching, and generalized seizures (convulsions). **High-Yield Clinical Pearls for NEET-PG:** 1. **Absorption Atelectasis:** Pure oxygen can wash out nitrogen (which normally keeps alveoli splinted open), leading to alveolar collapse. 2. **Retinopathy of Prematurity (ROP):** In neonates, excessive oxygen therapy causes retinal vasoconstriction followed by abnormal vascular proliferation. 3. **Haldane Effect:** High $O_2$ promotes the displacement of $CO_2$ from hemoglobin, which can acutely worsen hypercapnia in certain patients.

Q: In the work of breathing, what percentage fraction does tissue resistance contribute?

7%. **Explanation:** The "Work of Breathing" (WOB) refers to the energy expended by the respiratory muscles to overcome the mechanical impedances of the respiratory system. This resistance is broadly divided into two categories: **Elastic Resistance** (65%) and **Non-elastic/Viscous Resistance** (35%). The **Non-elastic resistance** is further subdivided: 1. **Airway Resistance (80% of non-elastic):** Caused by friction between the air molecules and the walls of the tracheobronchial tree. 2. **Tissue Resistance (20% of non-elastic):** Also known as viscous resistance, this is caused by the friction between the lungs and the chest wall, and the sliding of the pleural surfaces. **Why 7% is correct:** Mathematically, tissue resistance accounts for approximately 20% of the non-elastic resistance. Since non-elastic resistance is 35% of the total work, the calculation is: **20% of 35% = 7%**. Therefore, tissue resistance contributes roughly 7% to the total work of breathing in a healthy individual. **Analysis of Incorrect Options:** * **B (14%):** This value is too high for tissue resistance in normal physiology; it may be seen in specific restrictive pathologies but is not the standard physiological value. * **C (28%):** This represents the majority of the non-elastic resistance (Airway Resistance), which is roughly 28% of the total work (80% of 35%). * **D (65%):** This represents the **Elastic Resistance** (Compliance work), which is the energy required to expand the elastic tissues of the lungs and chest wall. **High-Yield Facts for NEET-PG:** * **Most of the work of breathing** (65%) is spent overcoming elastic recoil. * **Airway resistance** is highest in the **medium-sized bronchi** (generations 2-5) and lowest in the terminal bronchioles due to the large total cross-sectional area. * In diseases like **Emphysema**, work increases due to loss of elastic recoil, while in **Asthma**, work increases due to high airway resistance.

Q: Pulmonary function abnormalities in interstitial lung diseases include all of the following except?

Reduced FEV1/FVC ratio. ### Explanation Interstitial Lung Diseases (ILD) are the prototype of **Restrictive Lung Diseases**. The core pathology involves inflammation and fibrosis of the alveolar walls, making the lungs "stiff" and less compliant. **1. Why "Reduced FEV1/FVC ratio" is the correct answer:** In restrictive diseases like ILD, both the Forced Expiratory Volume in 1 second (FEV1) and the Forced Vital Capacity (FVC) decrease proportionately because the lungs are small and stiff. Consequently, the **FEV1/FVC ratio remains normal or is often increased** (due to increased radial traction on the airways, which keeps them open during expiration). A *reduced* FEV1/FVC ratio (<0.7) is the hallmark of **Obstructive** lung diseases (e.g., Asthma, COPD). **2. Why the other options are incorrect:** * **Reduced Vital Capacity (VC) & Total Lung Capacity (TLC):** Because the lung parenchyma is fibrotic and non-compliant, the lungs cannot expand fully. This leads to a global reduction in all lung volumes and capacities (VC, TLC, FRC, and RV). * **Reduced Diffusion Capacity (DLCO):** The thickening of the alveolar-capillary membrane (interstitial fibrosis) increases the diffusion distance for gases, leading to a characteristic drop in DLCO. This is often the earliest functional abnormality in ILD. ### High-Yield Clinical Pearls for NEET-PG: * **Gold Standard Diagnosis:** HRCT (High-Resolution CT) showing "honeycombing" or "ground-glass opacities." * **Flow-Volume Loop:** In ILD, the loop is shifted to the right, appearing tall and narrow (witches' hat appearance). * **Compliance:** Static lung compliance is significantly **decreased** in ILD. * **Rule of Thumb:** * Obstructive = Ratio ↓ * Restrictive = Volumes ↓ (Ratio Normal/↑)

Q: Hyperventilation at high altitude is due to what physiological change?

Respiratory alkalosis. **Explanation:** At high altitudes, the barometric pressure decreases, leading to a fall in the partial pressure of inspired oxygen ($PiO_2$). This results in **arterial hypoxemia**. The peripheral chemoreceptors (primarily in the carotid bodies) sense this low $PaO_2$ and trigger the respiratory center to increase the rate and depth of breathing. **1. Why Respiratory Alkalosis is Correct:** The compensatory hyperventilation causes an excessive "washout" of Carbon Dioxide ($CO_2$). Since $CO_2$ is an acid, its depletion leads to a rise in blood pH (alkalosis). Therefore, the primary physiological state resulting from hyperventilation at high altitude is **Respiratory Alkalosis**. **2. Why the other options are incorrect:** * **B. Respiratory acidosis:** This occurs during hypoventilation (e.g., COPD or opioid overdose) where $CO_2$ is retained, not during hyperventilation. * **C. Hypercapnia:** This refers to high $PaCO_2$. Hyperventilation specifically causes *hypocapnia* (low $PaCO_2$). * **D. Decreased concentration of bicarbonate:** While bicarbonate levels do eventually decrease, this is a **delayed renal compensation** (taking 24–48 hours) to normalize the pH. It is a *consequence* of the alkalosis, not the immediate cause of hyperventilation itself. **High-Yield NEET-PG Pearls:** * **The "Hypoxic Drive":** Hyperventilation at altitude is driven by $PaO_2$ falling below **60 mmHg**. * **Oxygen-Dissociation Curve:** Respiratory alkalosis causes a **Left Shift** of the curve (increasing hemoglobin's affinity for $O_2$ in the lungs). * **Acetazolamide:** This drug is used for altitude sickness because it inhibits carbonic anhydrase, forcing bicarbonate excretion and creating a mild metabolic acidosis to counteract the respiratory alkalosis, thereby stimulating ventilation.

Q: What is the normal partial pressure of oxygen (PaO2) in a healthy adult?

80 mm Hg. **Explanation:** The partial pressure of arterial oxygen (**PaO2**) represents the amount of oxygen dissolved in the arterial blood. In a healthy adult breathing room air (21% O2) at sea level, the normal range is typically **80 to 100 mm Hg**. This value is determined by the alveolar oxygen tension (PAO2) and the efficiency of gas exchange across the alveolar-capillary membrane. **Why Option C is correct:** 80 mm Hg falls within the standard physiological range for a healthy adult. While the theoretical maximum at sea level is closer to 100 mm Hg, factors like the physiological shunt (bronchial and thebesian veins) slightly lower the arterial tension. **Analysis of Incorrect Options:** * **A (45 mm Hg):** This is the normal partial pressure of arterial **carbon dioxide (PaCO2)** or the partial pressure of oxygen in **mixed venous blood (PvO2)**. * **B (110 mm Hg):** This value is higher than what is achievable breathing room air at sea level. It would only be seen with supplemental oxygen therapy. * **D (60 mm Hg):** This is the threshold for **hypoxemia** and respiratory failure. At this point, the oxygen-hemoglobin dissociation curve enters its steep phase, leading to a rapid drop in SaO2. **High-Yield Clinical Pearls for NEET-PG:** * **Alveolar Gas Equation:** $PAO_2 = FiO_2(P_{atm} - P_{H2O}) - (PaCO_2 / R)$. * **A-a Gradient:** The difference between alveolar (A) and arterial (a) oxygen. Normal is **5–15 mm Hg**; an increase indicates intrinsic lung disease or a V/Q mismatch. * **Hypoxemia vs. Hypoxia:** Hypoxemia is low PaO2 in blood; Hypoxia is low oxygen delivery to tissues. * **P50 Value:** The PaO2 at which hemoglobin is 50% saturated is **26.7 mm Hg**.

Q: FEV1/FVC ratio is reduced in which of the following conditions?

Asthma. ### Explanation The **FEV1/FVC ratio** (Tiffeneau-Pinelli index) is the primary diagnostic tool used to differentiate between obstructive and restrictive lung diseases. **1. Why Asthma is Correct:** Asthma is an **obstructive lung disease**. In these conditions, airway resistance is increased (due to bronchospasm, inflammation, or mucus). While both FEV1 (Forced Expiratory Volume in 1 second) and FVC (Forced Vital Capacity) decrease, the **FEV1 decreases much more significantly** than the FVC because the obstruction limits the speed of air outflow. Consequently, the ratio (FEV1/FVC) falls below the normal limit (typically <0.7 or 70%). **2. Why Other Options are Incorrect:** * **Lung Fibrosis & Pleural Effusion:** These are **restrictive lung diseases** (intrinsic and extrinsic, respectively). In restriction, the lungs cannot expand fully, leading to a decrease in total lung volume. Both FEV1 and FVC decrease proportionately, or the FVC decreases more than the FEV1. Therefore, the FEV1/FVC ratio remains **normal or is even increased** (due to increased radial traction on airways in fibrosis). **3. High-Yield Clinical Pearls for NEET-PG:** * **Obstructive Pattern (↓ Ratio):** Asthma, COPD, Bronchiectasis, Cystic Fibrosis. * **Restrictive Pattern (Normal/↑ Ratio):** Interstitial Lung Disease (Fibrosis), Chest wall deformities (Kyphoscoliosis), Neuromuscular disorders (Polio, Myasthenia Gravis), and Pleural diseases. * **Flow-Volume Loops:** Look for a "scooped-out" appearance in obstructive disease and a "miniature/narrow" version of a normal loop in restrictive disease. * **Reversibility:** An increase in FEV1 of >12% and >200ml after bronchodilator inhalation suggests Asthma over COPD.

Question 1

All of the following are risks seen in the administration of pure oxygen to hypoxic patients, except?

Accepted Answer

2,3-DPG toxicity

Answer

Apnea occurs due to hypostimulation of peripheral receptors

Answer

Pulmonary edema

Answer

Convulsions

Question 2

What is true about ascent to high altitude?

Accepted Answer

Acetazolamide may be given prophylactically

Answer

Respiratory acidosis

Answer

Polycythemia due to dehydration

Answer

Acute mountain sickness starts to develop on the 7th day of ascent

Question 3

In the work of breathing, what percentage fraction does tissue resistance contribute?

Accepted Answer

7%

Answer

14%

Answer

28%

Answer

65%

Question 4

Pulmonary function abnormalities in interstitial lung diseases include all of the following except?

Accepted Answer

Reduced FEV1/FVC ratio

Answer

Reduced vital capacity

Answer

Reduced diffusion capacity

Answer

Reduced total lung capacity

Question 5

Hyperventilation at high altitude is due to what physiological change?

Accepted Answer

Respiratory alkalosis

Answer

Respiratory acidosis

Answer

Hypercapnia

Answer

Decreased concentration of bicarbonate

Question 6

All of the following pulmonary changes are seen in restrictive lung disease except:

Accepted Answer

VC

Answer

FEV1/FVC ratio

Answer

TLC

Answer

RV

Question 7

What is the normal partial pressure of oxygen (PaO2) in a healthy adult?

Accepted Answer

80 mm Hg

Answer

45 mm Hg

Answer

110 mm Hg

Answer

60 mm Hg

Question 8

FEV1/FVC ratio is reduced in which of the following conditions?

Accepted Answer

Asthma

Answer

Pleural effusion

Answer

Lung fibrosis

Answer

All of the above

Question 9

What is the sensitivity of chemoreceptors in COPD?

Accepted Answer

Increased to PCO2

Answer

Decreased to H+

Answer

Increased to H+

Answer

Increased to PO2

Question 10

Vital capacity is the sum of which of the following?

Accepted Answer

Inspiratory reserve volume, Tidal volume, and Expiratory reserve volume

Answer

Tidal volume, Inspiratory reserve volume, and Residual volume

Answer

Expiratory reserve volume, Inspiratory reserve volume, and Residual volume

Answer

Residual volume, Inspiratory volume, and Expiratory reserve volume

Respiratory System — MCQs

Respiratory System — MCQs

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