Using the following data, calculate the physiological dead space, Tidal volume = 600 ml, Alveolar ventilation = 4.3 L/min, PaCO2 = 40 mmHg, PECO2 = 28 mmHg:

Correct Answer: C

Rationale: Physiological dead space (Vd) is 180 mL. Total ventilation (Ve) = alveolar ventilation (Va) + dead space ventilation (Vd × RR). Given Va = 4.3 L/min and tidal volume (Vt) = 600 mL, assume RR = 10 breaths/min (Ve = 6 L/min). Then, Ve = Va + Vd × RR → 6 = 4.3 + Vd × 10/1000 → Vd = (6 - 4.3) × 1000 / 10 = 170 mL. Bohr's method confirms: Vd/Vt = (PaCO2 - PECO2) / PaCO2 → Vd = 600 × (40 - 28) / 40 = 180 mL. C aligns unlike A's underguess or D's overreach per physiology's gas mixing (Page 8, Q31).

Correct Answer: D

Rationale: Physiological dead space isn't just alveolar dead space . It's anatomic (~150 mL) plus alveolar dead space (A, true). Lung disease (B) and high V/Q (C) increase it (e.g., embolism, Q34). D's equation misses anatomic part alveolar dead space varies (0 to >150 mL), while physiological sums both. Bohr's method (Q12) confirms. D's error unlike A's baseline misdefines total wasted ventilation, per physiology (Q3).

Correct Answer: A

Rationale: Cough suppressants aren't indicated in asthma. Resistance rises (B) via bronchoconstriction (Q8). FEV1/FVC falls (< 80%, C, true) in attacks (Q15). Bronchodilators (D) relieve spasms. Allergies trigger it. A's suppression cough clears mucus worsens obstruction, unlike B's mechanics or D's therapy, per asthma management (opposite Q13's bronchitis).

Correct Answer: D

Rationale: All (D) are true for rheumatoid lung disease. Rheumatoid arthritis (RA) raises idiopathic pulmonary fibrosis risk (A) interstitial inflammation scars lungs, a known extra-articular feature. Nodular lesions (B), akin to subcutaneous rheumatoid nodules, appear in lung parenchyma, histologically identical (necrobiotic centers). Progressive fibrosis in coal miners with RA and positive rheumatoid factor (C) Caplan's syndrome combines pneumoconiosis and RA's immune response. These manifestations, from fibrosis to nodules, reflect RA's systemic nature, complicating lung function (restrictive patterns), key in rheumatology-pulmonology overlap for diagnosis (e.g., HRCT) and management (e.g., immunosuppression).

Correct Answer: C

Rationale: Ventilation-perfusion (V/Q) inequality mismatched air and blood flow can cause both hypercapnia and hypocapnia (C). Low V/Q (e.g., pneumonia) traps COâ‚‚, raising PaCOâ‚‚ (hypercapnia). High V/Q (e.g., pulmonary embolism) over-ventilates, dropping COâ‚‚ (hypocapnia). Hypercapnia' (A) or hypocapnia' (B) alone ignores dual potential. Neither' (D) denies impact. V/Q mismatch, assessed via A-a gradient or scans, disrupts gas exchange, critical in diagnosing shunt or dead space, guiding oxygen or thrombolytic therapy in chest emergencies.