Following a stab wound in the chest wall, the lung will and the chest wall will?

Correct Answer: D

Rationale: A stab wound in the chest wall causing pneumothorax disrupts the negative intrapleural pressure (normally around -4 to -6 mmHg) that keeps the lungs expanded against the chest wall. When air enters the pleural space, this pressure equalizes with atmospheric pressure, eliminating the force holding the lung open. The lung, due to its elastic recoil, collapses inward toward the hilum, reducing its volume significantly. Conversely, the chest wall, with its outward elastic recoil, springs outward, expanding away from the lung. This results in the lung collapsing and the chest wall expanding, a classic feature of pneumothorax. The lung doesn't expand, as it loses the negative pressure tether, and the chest wall doesn't collapse, as its natural tendency is to spring outward when unrestrained. Other scenarios, like both expanding or fixing at FRC, don't reflect the mechanics of pleural pressure loss, making the collapse-expansion dynamic the expected outcome of such an injury.

Correct Answer: A

Rationale: Physiological dead space (VD) is the volume of ventilated air not participating in gas exchange, comprising anatomic dead space (conducting airways) and alveolar dead space (non-perfused alveoli). Pulmonary embolism (PE) blocks pulmonary arteries, reducing perfusion to ventilated alveoli, markedly increasing alveolar dead space and thus physiological VD (e.g., from 150 ml to 300+ ml), as large lung regions become wasted ventilation.' Atelectasis collapses alveoli, reducing ventilation and dead space, as unventilated areas don't contribute to VD. Pneumothorax collapses lung tissue, decreasing ventilated volume, not increasing dead space. Bronchoconstriction narrows airways, potentially reducing anatomic dead space slightly, and doesn't directly increase alveolar dead space unless severe hypoxia ensues. PE's perfusion defect creates the greatest VD rise, measurable via increased PaCO2-PECO2 difference, distinguishing it as the most impactful condition among these, reflecting a high V/Q mismatch.

Correct Answer: A

Rationale: Bronchial asthma involves reversible airway obstruction from inflammation, bronchoconstriction, and mucus. Airway resistance increases due to narrowed bronchi, reducing airflow. During an attack, FEV1/FVC drops below 80% (e.g., 50-60%) as FEV1 falls more than FVC, reflecting obstruction. Bronchodilators (e.g., albuterol) are standard treatment, relaxing smooth muscle to relieve constriction. Allergies (e.g., pollen) often trigger attacks, a common feature. However, cough suppressants aren't highly indicated asthma's productive cough clears mucus, and suppressing it worsens obstruction and infection risk. Therapy focuses on bronchodilation and inflammation control (e.g., corticosteroids), not cough suppression, which could exacerbate symptoms. This statement contradicts asthma management principles, making it the exception among true descriptions of the condition's pathophysiology and treatment.

Correct Answer: C

Rationale: Respiratory distress syndrome (RDS) in premature infants arises from immature lungs lacking sufficient surfactant, a phospholipid mixture from type II alveolar cells that reduces alveolar surface tension. Limited surfactant synthesis increases tension, causing alveolar collapse (atelectasis) and low lung compliance lungs become stiff, requiring higher pressures for ventilation, all true features. Positive pressure respirators are standard to maintain oxygenation and prevent collapse, also true. However, the statement about lung compliance being low is universally true in RDS, not the exception. A potential misinterpretation might expect a false statement like alveoli overexpand and burst,' but among these, all align with RDS pathophysiology. If NOT true' implies a trick, low compliance is still consistent, suggesting a contextual error yet, per options, none stand out as false. Assuming standard RDS traits, all are true, but compliance's consistency might confuse; still, it's not the exception intended, requiring re-evaluation of intent. Here, all fit RDS, making C a default choice if misworded.

Correct Answer: B

Rationale: Airway resistance follows Poiseuille's law (R ∝ 1/r^4), but total cross-sectional area governs overall resistance. The trachea, a single tube (~2 cm diameter), has ~3-4 cm² area. Bronchioles, numbering thousands, reach ~300 cm² collectively at terminal stages, yet pale beside alveoli. Alveoli (~300 million) total ~70-100 m² (~700,000-1,000,000 cm²) during inspiration, dwarfing other structures. This vast area slows airflow velocity, reducing resistance to negligible levels at the gas exchange site, where diffusion dominates. Resistance peaks in medium bronchi due to turbulent flow, not alveoli, despite their tiny individual size (~0.2 mm). Trachea and bronchioles handle bulk flow with higher resistance. Alveoli's massive area minimizes resistance, making them the correct choice, critical for efficient ventilation and distinguishing their role from conducting airways.