Match the following: 743. Anemia of infection, rheumatoid arthritis

Correct Answer: A

Rationale: Anemia of infection/rheumatoid arthritis chronic disease shows low plasma iron, low TIBC, high stores, low sideroblasts (A), from inflammation (e.g., IL-6) sequestering iron. Erythropoietin (B) fits renal. Normocytic (C) is pattern, not cause. Blood loss (D) is other anemias. Iron block is key, guiding nursing for inflammation control.

Correct Answer: C

Rationale: Asthma is an obstructive airway disease characterized by reversible bronchoconstriction, inflammation, and mucus production. During an asthmatic attack, narrowed airways increase resistance, particularly during expiration, when dynamic compression exacerbates airflow limitation, producing wheezing most prominent on expiration, not inspiration. The work of breathing increases significantly as patients struggle against this resistance and reduced airflow, requiring greater effort from respiratory muscles like the diaphragm and intercostals to maintain ventilation. Bronchodilators (e.g., albuterol) are the mainstay of treatment, relaxing bronchial smooth muscle to relieve constriction, so they are not contraindicated. Forced expiratory volume in 1 second (FEV1) decreases during an attack due to obstruction, not increases, as airflow is impeded. The increased work of breathing is a consistent expectation, reflecting the physiological burden of overcoming narrowed airways and trapped air, distinguishing it from the incorrect options that misalign with asthma's acute presentation.

Correct Answer: D

Rationale: Fick's law of diffusion states that the rate of gas diffusion across a membrane (e.g., alveolar-capillary) is proportional to the surface area (A), diffusion coefficient (D), and partial pressure gradient (ΔP), and inversely proportional to diffusion distance (d): Rate = (A × D × ΔP) / d. When comparing different gases (e.g., O2 vs. CO2), the diffusion coefficient (D) varies most significantly, as it depends on gas solubility and molecular weight (D ∝ solubility / √MW). CO2's solubility is ~20 times higher than O2's (0.51 vs. 0.024 ml/mmHg/L), though O2's molecular weight is slightly lower (32 vs. 44), making CO2 diffuse ~20 times faster despite similar gradients. Partial pressure gradient drives diffusion but is gas-specific and often comparable (e.g., O2: 100-40 mmHg, CO2: 46-40 mmHg). Temperature and distance affect all gases similarly in the lung. Thus, the diffusion coefficient has the most pronounced effect across different gases, explaining why CO2 equilibrates faster than O2 across the respiratory membrane.

Correct Answer: B

Rationale: Mixed expired PCO2 (PECO2) reflects CO2 in exhaled air, diluted by dead space ventilation. Given dead space (VD) is one-third of tidal volume (VT), VD/VT = 1/3. The Bohr equation relates physiological dead space to CO2: VD/VT = (PaCO2 - PECO2) / PaCO2, where PaCO2 (arterial PCO2) is 45 mmHg. Substituting: 1/3 = (45 - PECO2) / 45. Solving: 45 / 3 = 45 - PECO2, so 15 = 45 - PECO2, and PECO2 = 45 - 15 = 30 mmHg. This assumes physiological dead space equals anatomic here, as no alveolar dead space is specified. Intuitively, if one-third of each breath doesn't participate in gas exchange (PCO2 ~0 mmHg in inspired air), the expired CO2 is diluted from arterial levels (45 mmHg) to two-thirds strength (30 mmHg), matching the calculation. Options like 45 mmHg imply no dead space effect, while 20 mmHg overestimates dilution. Thus, 30 mmHg aligns with the given ratio and respiratory physiology principles.

Correct Answer: D

Rationale: Pulmonary fibrosis, a restrictive disease, stiffens lungs with interstitial scarring. The FEV1/FVC ratio is normal or high (≥80%) because both FEV1 and FVC decrease proportionally, unlike obstructive diseases. Increased pulmonary vascular resistance occurs as fibrosis compresses capillaries, raising resistance. Peak expiratory flow (PEF), when corrected for reduced lung volume, can remain normal or above, as airflow isn't obstructed, just limited by volume. However, residual volume (RV) decreases in pulmonary fibrosis (e.g., from 1.5 L to <1 L) due to stiff lungs limiting all volumes, contrasting with obstructive diseases (e.g., COPD) where RV increases from air trapping. Increased RV doesn't fit fibrosis's restrictive pattern, where reduced elasticity shrinks residual air, not expands it, making this the inconsistent value among the set, reflecting the disease's impact on lung mechanics.