Match the following: 745. Anemia of myxedema

Correct Answer: C

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: B

Rationale: Idiopathic pulmonary fibrosis (IPF) is a restrictive lung disease marked by progressive scarring of the lung interstitium, reducing lung elasticity and function. Total lung capacity (TLC) decreases in IPF because fibrotic tissue stiffens the lungs, limiting their expansion. Forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC) are both reduced, but the FEV1/FVC ratio remains normal or elevated, unlike in obstructive diseases. Arterial oxygen partial pressure (PaO2) drops due to impaired gas exchange across thickened alveolar walls, leading to hypoxemia. However, total pulmonary vascular resistance (PVR) increases in IPF as fibrosis compresses and obliterates pulmonary capillaries, narrowing the vascular bed and elevating resistance to blood flow. This increase can strain the right heart, potentially causing cor pulmonale. Among the options, only total pulmonary vascular resistance is expected to be higher than normal, aligning with IPF's impact on the pulmonary vasculature rather than lung volumes or oxygenation, which decline.

Correct Answer: D

Rationale: Inspiration occurs when air moves into the lungs due to a pressure gradient, as per Boyle's law: expanding the thoracic cavity decreases intrapulmonary pressure below atmospheric pressure (760 mmHg to ~758 mmHg), driving air inward. This gradient, the pressure difference between atmospheric and intrapulmonary pressure, is the primary force, created by diaphragm and intercostal muscle contraction. Atmospheric pressure alone isn't a force' but a reference; it's the difference that matters. Muscular spasm implies involuntary action, not the controlled contraction of respiration. Reduced surface tension, via surfactant, aids lung expansion but isn't the driving force it reduces resistance to expansion. Muscle relaxation occurs in expiration, not inspiration. The pressure difference is the fundamental mechanism, quantifiable (e.g., 1-2 mmHg drop suffices for tidal breathing), and directly ties muscle action to airflow, distinguishing it as the essential driver of ventilation.

Correct Answer: D

Rationale: Restrictive lung diseases (e.g., pulmonary fibrosis) stiffen lungs, reducing expansion and volumes like forced vital capacity (FVC), which drops below normal (e.g., from 4-5 L to 2-3 L) due to limited inspiratory capacity. Forced expiratory volume in 1 second (FEV1) also decreases proportionally (e.g., from 3-4 L to 1.5-2 L), as less air is available to exhale. However, the FEV1/FVC ratio remains normal or elevated (≥80%) because both values decline similarly, unlike obstructive diseases where FEV1 falls more, lowering the ratio (<70%). Ventilation/perfusion (V/Q) ratio may skew high in restrictive disease (e.g., fibrosis) due to reduced ventilation from stiff lungs, not normal matching. FEV1 and FVC individually are reduced, not normal. The FEV1/FVC ratio's preservation reflects the restrictive pattern impaired volume, not airflow obstruction making it the value least altered relative to healthy norms, a key diagnostic feature in spirometry.

Correct Answer: A

Rationale: Idiopathic pulmonary fibrosis (IPF) scars lung interstitium, reducing elasticity and volumes. Functional residual capacity (FRC), the resting volume (~2.5-3 L normally), decreases in IPF (e.g., to 2 L) as stiff lungs limit expansion, a hallmark of restrictive disease. Tidal volume (VT, ~500 ml) typically decreases, not increases, as breathing becomes shallow due to restricted capacity, often requiring faster rates to maintain ventilation. Pulmonary vascular resistance rises, not falls, as fibrosis compresses capillaries, increasing resistance and risking right heart strain. Total lung capacity (TLC, ~6 L) also drops (e.g., to 4 L), reflecting reduced maximum volume, not higher. Lower FRC aligns with IPF's mechanics stiff lungs reduce resting and total volumes, impair gas exchange, and elevate work of breathing, distinguishing it from options contradicting restrictive physiology.