Compliance & Disease Patterns
The PV loop in a patient with emphysema is shifted upward and to the left. What two mechanical properties explain this change?
↑ Compliance and ↓ Elastic recoil
Which loop shape change distinguishes an obstructive from restrictive pattern?
Obstructive = widened/hysteretic loop; Restrictive = narrow/shifted right
What does “work of breathing” represent in respiratory physiology?
The total energy required to overcome elastic and resistive forces to move air in and out of the lungs.
Which drug class can cause bronchoconstriction in asthmatics and should be avoided?
Nonselective NSAIDs
A patient with both emphysema and pulmonary fibrosis shows near-normal total compliance. Why?
High compliance of emphysema offsets low compliance of fibrosis
In idiopathic pulmonary fibrosis (IPF), why is compliance decreased and the work of breathing increased?
Fibrotic deposition thickens and stiffens alveolar walls, reducing distensibility and increasing elastic work needed for each breath.
What does widening of the PV loop at the same pressure indicate?
↑ Airway resistance (more pressure required for same volume)
Why is inspiratory pressure greater than expiratory pressure for the same volume in normal lungs?
Surfactant hysteresis and tissue viscoelasticity
Name one cytotoxic drug and one anti-TNF biologic that can cause drug-induced interstitial pneumonitis.
Bleomycin and Infliximab
What part of the medulla generates the basic inspiratory rhythm that can be overridden voluntarily by cortical input?
The dorsal respiratory group (DRG) in the medulla.
Compared with normal, which disease has a flatter inflation limb and why?
Pulmonary fibrosis → stiff lungs → ↓ compliance
What is the primary determinant of airway resistance in the lower respiratory tract?
Airway radius (to the fourth power) — resistance ∝ 1/r⁴ (Poiseuille’s law)
How does surfactant deficiency alter hysteresis?
Increases hysteresis → larger area (more work) due to ↑ surface tension
Montelukast blocks which specific receptor, and for what indication is it most effective?
CysLT₁ receptor → exercise- or aspirin-induced asthma
A patient with bilateral vagotomy develops deeper, slower breaths. What feedback mechanism was lost?
The Hering–Breuer inflation reflex — vagal stretch receptor feedback that normally limits inspiration to prevent overinflation.
Two patients have restrictive lung disease: one from pulmonary fibrosis, one from neuromuscular weakness. How does compliance differ between them?
Fibrosis → ↓ lung compliance (stiff tissue); neuromuscular weakness → normal lung compliance but ↓ total ventilation due to weak inspiratory effort.
During forced expiration, why can effort not further increase airflow in COPD?
Equal pressure point moves distally → airway compression (flow limitation)
Why do patients with COPD breathe slowly and deeply rather than rapidly and shallowly?
High airway resistance → increased resistive work; slower, deeper breaths reduce flow turbulence and resistive energy cost.
Why are ERA, PDE-5 inhibitors, and prostacyclin analogs ineffective or harmful in Group 2 PH?
They increase pulmonary venous return, worsening pulmonary edema in post-capillary PH.
Which cytokine is central to the fibrotic process in idiopathic pulmonary fibrosis, and what are two antifibrotic agents that target its downstream signaling?
Transforming growth factor-β (TGF-β); nintedanib (TK inhibitor) and pirfenidone (TGF-β modulator) slow disease progression.
In ARDS, the lower inflection point on the PV curve shifts right. What ventilator setting should be adjusted to prevent alveolar collapse below this point?
Increase PEEP to stay above the lower inflection pressure
In mechanical ventilation, what change in the loop distinguishes bronchospasm from decreased compliance?
Bronchospasm: loop widens (↑ resistance); ↓ compliance: slope flattens
Which reflex prevents aspiration by temporarily halting inspiration when the larynx is stimulated?
Laryngeal (protective) apnea reflex
A patient with IPF is prescribed pirfenidone. What is its mechanism and main benefit?
Inhibits TGF-β–driven fibroblast activation; slows progression of fibrosis and FVC decline.
Which ILD shows intraluminal fibroblast plugs (Masson bodies) without architectural distortion, and how does it respond to therapy?
Cryptogenic organizing pneumonia (COP); reversible with corticosteroids.