A 60-year-old woman presents to the clinic with a 3-month history of shortness of breath that worsens on exertion. She also complains of chronic cough that has lasted for 10 years. Her symptoms are worsened even with light activities like climbing up a flight of stairs. She denies any weight loss, lightheadedness, or fever. Her medical history is significant for hypertension, for which she takes amlodipine daily. She has a 70-pack-year history of cigarette smoking and drinks 3–4 alcoholic beverages per week. Her blood pressure today is 128/84 mm Hg. A chest X-ray shows flattening of the diaphragm bilaterally. Physical examination is notable for coarse wheezing bilaterally. Which of the following is likely to be seen with pulmonary function testing?

Decreased FEV1: FVC and increased total lung capacity

Decreased FEV1: FVC and decreased total lung capacity

Normal FEV1: FVC and decreased total lung capacity

Increased FEV1: FVC and decreased total lung capacity

Increased FEV1: FVC and normal total lung capacity

Which of the following physiologic changes decreases pulmonary vascular resistance (PVR)?

Inhaling the entire vital capacity (VC)

Inhaling the inspiratory reserve volume (IRV)

Exhaling the entire vital capacity (VC)

Exhaling the expiratory reserve volume (ERV)

Breath holding maneuver at functional residual capacity (FRC)

A 62-year-old man presents to the emergency department for evaluation of a 2-year history of increasing shortness of breath. He also has an occasional nonproductive cough. The symptoms get worse with exertion. The medical history is significant for hypertension and he takes chlorthalidone. He is a smoker with a 40-pack-year smoking history. On physical examination, the patient is afebrile; the vital signs include: blood pressure 125/78 mm Hg, pulse 90/min, and respiratory rate 18/min. The body mass index (BMI) is 31 kg/m2. The oxygen saturation is 94% at rest on room air. A pulmonary examination reveals decreased breath sounds bilaterally, but is otherwise normal with no wheezes or crackles. The remainder of the examination is unremarkable. A chest radiograph shows hyperinflation of both lungs with mildly increased lung markings, but no focal findings. Based on this clinical presentation, which of the following is most likely?

FEV1/FVC of 80% with an FEV1 of 82%

In which of the following pathological states would the oxygen content of the trachea resemble the oxygen content in the affected alveoli?

Foreign body obstruction distal to the trachea

A 60-year-old man presents with breathlessness for the past 3 months. His symptoms have been getting progressively worse during this time. He denies any history of cough, fever, or chest pain. He works at a local shipyard and is responsible for installing the plumbing aboard the vessels. His past medical history is significant for hypertension for which he takes metoprolol every day. He denies smoking and any illicit drug use. His pulse is 74/min, respiratory rate is 14/min, blood pressure is 130/76 mm Hg, and temperature is 36.8°C (98.2°F). Physical examination is significant for fine bibasilar crackles at the end of inspiration without digital clubbing. Which of the following additional findings would most likely be present in this patient?

Decreased diffusing capacity of CO

Increased pulmonary capillary wedge pressure

Decreased pulmonary arterial pressure

A 55-year-old man with a 60 pack-year smoking history is referred by his primary care physician for a pulmonary function test (PFT). A previously obtained chest x-ray is shown below. Which of the following will most likely appear in his PFT report?

Residual volume increased, total lung capacity increased

Residual volume increased, total lung capacity decreased

Residual volume normal, total lung capacity decreased

Residual volume normal, total lung capacity normal

Residual volume decreased, total lung capacity increased

Altered compliance in disease states for USMLE Step 1: High-Yield Physiology Lessons

Pulmonary Compliance - The Stretch Factor

Pulmonary compliance is the lung's ability to stretch and expand. It's calculated as the change in volume per unit change in pressure: $C = \Delta V / \Delta P$.

↑ Increased Compliance (Floppy Lungs)
- Emphysema (COPD): Elastin fiber destruction leads to less recoil and higher compliance.
- Aging: Normal physiological changes reduce elastic recoil.
↓ Decreased Compliance (Stiff Lungs)
- Pulmonary Fibrosis: Scar tissue stiffens the lung parenchyma.
- Pneumonia/ARDS: Alveolar edema and inflammation reduce stretch.
- Pulmonary Edema: Fluid accumulation increases lung stiffness.

⭐ Saline vs. Air: A saline-filled lung is much more compliant than an air-filled lung because saline eliminates the air-water interface, thus abolishing surface tension, a major factor in resisting inflation.

Increased Compliance - Floppy Lungs

Pathophysiology: Lungs are abnormally easy to inflate but have lost elastic recoil, making expiration difficult. Think of a stretched-out rubber band.
Etiologies:
- Emphysema: Key cause; involves destruction of elastin fibers.
- Aging: Gradual, natural loss of elastic tissue.

Lung Compliance Changes in the P-V Loop

Pulmonary Function Tests (PFTs):
- Work of breathing is ↑ during active expiration.
- Shifts pressure-volume loop to the left.
- ↑ Total Lung Capacity (TLC)
- ↑ Functional Residual Capacity (FRC)
- ↑ Residual Volume (RV)

⭐ High-Yield: In emphysema, the loss of radial traction (from destroyed alveolar walls) on small airways leads to their collapse during expiration. This "expiratory airway collapse" is a major cause of air trapping and ↑RV.

Decreased Compliance - Stiff Lungs

Pathophysiology: Lungs are stiff and resist expansion, requiring ↑ work of breathing.
- A greater pressure change ($\\Delta$P) is needed for a given volume change ($\\Delta$V).
- Leads to a pattern of rapid, shallow breathing.
- The pressure-volume curve shifts to the right and flattens.
Etiologies:
- Parenchymal Disease:
  - Pulmonary Fibrosis: Idiopathic, asbestosis, silicosis (excess collagen).
  - ARDS: Non-cardiogenic pulmonary edema, inflammation, hyaline membranes.
  - Pulmonary Edema: Fluid in interstitium/alveoli.
- Extraparenchymal Restriction:
  - Chest Wall: Kyphoscoliosis, obesity.
  - Pleural: Large effusion, fibrosis.

Chest X-ray and CT of Idiopathic Pulmonary Fibrosis

⭐ In restrictive diseases, the FEV1/FVC ratio is characteristically normal or ↑ (often > 80%) because both FEV1 and FVC are proportionately reduced.

Compliance Curves - Visualizing Stiffness

Lung compliance curves: emphysema, normal, and fibrosis

The pressure-volume (P-V) loop's slope represents lung compliance: $C = \Delta V / \Delta P$.
↑ Compliance (Emphysema): Left-shifted curve. A small pressure change yields a large volume change. Lungs are "floppy."
↓ Compliance (Fibrosis, ARDS): Right-shifted curve. A large pressure change is needed for a small volume change. Lungs are "stiff."

⭐ A saline-filled lung is far more compliant than an air-filled one. This is because saline abolishes the air-water interface, eliminating the surface tension that accounts for ~2/3 of elastic recoil.

High-Yield Points - ⚡ Biggest Takeaways

Emphysema and aging lead to ↑ lung compliance due to loss of elastic fibers, resulting in a "floppy" lung and ↑ Functional Residual Capacity (FRC).

Pulmonary fibrosis, edema, and NRDS cause ↓ lung compliance, creating a "stiff" lung that is difficult to inflate, leading to ↓ FRC.

In Neonatal Respiratory Distress Syndrome (NRDS), low compliance is due to surfactant deficiency.

The pressure-volume loop shifts up and left for high compliance; it shifts down and right for low compliance.

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