One of the following PFT values are consistent with both obstructive and restrictive lung diseases?

Correct Answer: D

Rationale: Pulmonary function tests (PFTs) differentiate lung diseases. Obstructive diseases (e.g., COPD) reduce airflow, decreasing FEV1 (<80% predicted) due to airway narrowing, with increased residual volume (RV) and total lung capacity (TLC) from air trapping. Restrictive diseases (e.g., fibrosis) limit expansion, also reducing FEV1 (<80% predicted) due to lower volumes, but RV and TLC decrease. Decreased FEV1 is common to both obstructive from airflow limitation, restrictive from reduced capacity making it consistent across types. Decreased RV fits restriction, not obstruction (increased RV). Normal or above TLC fits obstruction, not restriction (decreased TLC). Vascular resistance isn't a PFT metric; it rises in fibrosis, not decreases. Decreased FEV1's shared reduction reflects impaired exhalation, a unifying feature despite differing mechanisms, distinguishing it as the overlapping value.

Correct Answer: B

Rationale: Atmospheric air has ~21% oxygen (O2) and ~0.04% carbon dioxide (CO2), so O2's percentage vastly exceeds CO2's, reflecting their natural abundances. Solubility, per Henry's law, depends on the solubility coefficient: O2's is ~0.024 ml/mmHg/L blood, while CO2's is ~0.51 ml/mmHg/L over 20 times higher. Thus, O2 is less soluble than CO2, despite its higher atmospheric presence. In blood, O2 relies on hemoglobin (~98% bound, ~2% dissolved), while CO2 uses dissolved (~7%), bicarbonate (~70%), and hemoglobin (~23%) forms, leveraging its solubility. Option B (higher O2 percentage, lower O2 solubility) fits: 21% vs. 0.04%, and 0.024 vs. 0.51. This contrast drives distinct transport mechanisms O2's hemoglobin dependence vs. CO2's solubility advantage crucial for respiration and acid-base balance, making it the accurate physiological description.

Correct Answer: B

Rationale: Surfactant, from type II alveolar cells, reduces surface tension of alveolar fluid from water's high value (~72 dynes/cm) to ~5-10 dynes/cm, preventing collapse per Laplace's law (P = 2T/r). It doesn't increase pleural pressure, which stays negative (~-4 mmHg at rest) to keep lungs expanded surfactant acts intra-alveolarly. It doesn't lower alveolar pressure (atmospheric at rest, ~760 mmHg); that's muscle-driven. It eases inspiration by reducing tension, not hindering it, countering collapse and aiding neonates especially. Pneumothorax (not listed) involves pleural breach, unrelated to surfactant. Reducing surface tension is its core function, stabilizing alveoli and enhancing compliance, a vital adaptation for efficient breathing, making it the true statement amid pressure or effort misconceptions.

Correct Answer: A

Rationale: Work of breathing (WOB) is energy to overcome elastic (compliance) and resistive (airway) forces. Compliance (C = ΔV / ΔP) measures lung stretchability low C (stiff lungs) raises pressure needed, increasing WOB; thus, WOB is inversely related to compliance, true. During exercise, WOB rises with ventilation demand, not constant false. Airway resistance (R) directly increases WOB (e.g., asthma), contradicting not affected' false. In pulmonary fibrosis, low compliance elevates WOB, not reduces it false (emphysema might lower elastic work). The inverse compliance link (WOB = ∫P dV, P rises as C falls) is fundamental, reflecting effort to expand stiff lungs, making it the correct statement, critical for understanding respiratory workload in disease.

Correct Answer: D

Rationale: Inhalation sequence: (5) Diaphragm and intercostals contract, expanding the thorax. (1) Intrapleural pressure drops from -4 mmHg (756 mmHg) to -6 mmHg (754 mmHg), increasing transpulmonary pressure. (3) Lungs expand. (4) Intra-alveolar pressure falls to 759 mmHg (-1 mmHg) per Boyle's law, creating a gradient. (2) Air flows in. Order 5,1,3,4,2 reflects causality: muscle action lowers IPP, expands lungs, drops alveolar pressure, drives airflow. Others disrupt e.g., 5,2,3,4,1 puts flow before pressure; 1,3,4,5,2 starts without muscle action. This aligns with respiratory mechanics, ensuring logical progression for tidal breathing (~500 ml).