Free Respiratory Physiology MCQs with Answers

• A. 40 mm Hg
• B. 25 mm Hg
• C. 55 mm Hg
• D. 70 mm Hg

Explanation: Mixed venous blood has returned from the tissues after oxygen extraction, so its PO2 falls from the arterial value of about 95–100 mm Hg…

• A. Left
• B. Right
• C. Does not shift
• D. None of the above

Explanation: In the Haldane effect, oxygenation of haemoglobin in the lungs reduces its ability to carry CO2 and hydrogen ions, promoting CO2 release.

• A. Anemic
• B. Stagnant
• C. Hypoxic
• D. Histotoxic

Explanation: Hypoxic hypoxia is the commonest broad type and results from inadequate oxygenation of arterial blood, such as at high altitude or in lung…

• A. Stretching of airways
• B. Hypercapnia
• C. Acidosis
• D. Hypoxia

Explanation: Hypoxia, raised CO2 and acidosis stimulate ventilation through the respiratory control system.

• A. Anemia
• B. Pulmonary hypoventilation
• C. KCN poisoning
• D. CO poisoning

Explanation: Pulmonary hypoventilation reduces the amount of fresh air reaching alveoli, causing alveolar and arterial PO2 to fall while PCO2 rises.

• A. Fall in pH
• B. Rise in temperature
• C. HbF
• D. Increase of 2, 3 3 DPG

Explanation: A fall in pH, increased temperature and increased 2,3-DPG reduce haemoglobin’s oxygen affinity and shift the dissociation curve rightward.

• A. 2.5 lit/Min
• B. 4.0 lit /Min
• C. 9 Lit/Min
• D. 6.75 Lit/Min

Explanation: Alveolar ventilation equals (tidal volume − dead space) × respiratory rate. Thus, (600 − 150) × 15 = 6,750 ml/min, or 6.75 L/min.

• A. Increased by hyperventilation
• B. Decreased by hyperventilation
• C. Similar to venous O2 tension
• D. Not affected by respiratory depression

Explanation: Hyperventilation removes more CO₂ from the alveoli, and the alveolar gas equation therefore predicts a rise in alveolar PO₂.

• A. Pnemocyte I
• B. Pnemocyte II
• C. Goblet cells
• D. Pulmonary vessels

Explanation: Type II pneumocytes synthesize and release pulmonary surfactant, which lowers alveolar surface tension and helps prevent alveolar…

• A. Bronchial asthma
• B. Chronic bronchitis
• C. Scoliosis
• D. Acute bronchitis

Explanation: Scoliosis produces a restrictive ventilatory defect, reducing vital capacity while preserving the FEV₁/FVC percentage.

• A. Anemic Hypoxia
• B. Histotoxic Hypoxia
• C. Stagnant Hypoxia
• D. Hypoxic Hypoxia

Explanation: At high altitude, reduced atmospheric pressure lowers inspired and arterial PO₂, producing hypoxic or hypoxemic hypoxia.

• A. Expiratory reserve volume
• B. Functional residual capacity
• C. Residual volume
• D. Inspiratory reserve volume

Explanation: Functional residual capacity is the volume remaining in the lungs after a normal, quiet expiration.

• A. 125 ml
• B. 500 ml
• C. 1500 ml
• D. 2200 ml

Explanation: Normal adult tidal volume is approximately 500 ml during quiet breathing. It is the amount of air moved in or out with each normal breath.

• A. Carbon monoxide poisoning
• B. Increase in pH of blood
• C. Obstructive pulmonary disease
• D. Decrease in pH of blood

Explanation: Kussmaul breathing is a deep, laboured compensatory response to metabolic acidosis, in which reduced blood pH stimulates ventilation to…

• A. 2% - 3% of total energy spent
• B. 50% -75% of total energy spent
• C. 15% - 20% of total energy spent
• D. 25% - 50% of total energy spent

Explanation: Quiet breathing normally requires only about 2–3% of total body energy expenditure because lung and chest-wall resistance are low.

• A. -2
• B. -5
• C. 0
• D. -7

Explanation: At the start of inspiration, intrapleural pressure is subatmospheric, approximately −2 mmHg in commonly used clinical approximations, and…

• A. Increased pH of blood
• B. Increased oxygen concentration in blood
• C. Remains same
• D. Decreased pH of blood

Explanation: Hypercapnia means excess CO₂, which combines with water to form carbonic acid and increases hydrogen ions, thereby lowering blood pH.

• A. Oxygen dissociation curve shifts to left
• B. Hypoxic hypoxia
• C. Cyanosis
• D. Diffusion capacity of lungs decreases

Explanation: Carbon monoxide occupies haemoglobin binding sites and increases the oxygen affinity of the remaining sites, shifting the oxyhaemoglobin…

• A. Anion balance
• B. Sodium balance
• C. Potassium balance
• D. Ca+2 balance

Explanation: Through pulmonary conversion of angiotensin I to angiotensin II, the lungs influence aldosterone secretion and therefore sodium and water…

• A. Increased lung compliance
• B. Interpleural pressure becomes more negative
• C. The concentration of surfactant is reduced in alveoli
• D. Total chest wall diameter is increased

Explanation: In pneumothorax, pleural pressure approaches atmospheric pressure, so the lung recoils inward while the chest wall recoils outward…