CPR APPLICATIONS FOUNDATION · CHAPTER 8 · NORMAL
Normal Foundations of the Pulmonary System
Organize the chapter before drilling into individual CPR concepts.
Supplemental foundation map: this page orients the detailed CPR Applications for Chapter 8. It is not part of the canonical CPR object inventory.
Move through Chapter 8
Normal Foundations · You are here
Abnormal Foundations
Treatment Foundations
8.1 · SOURCE CPR FOUNDATION
Concept
Pulmonary physiology is the foundation for gas exchange, respiratory mechanics, and acid-base control. Most Step 1 questions can be solved by identifying whether the primary problem is airflow limitation, restricted expansion, diffusion impairment, V/Q mismatch, shunt, dead space, or abnormal ventilatory drive. The disease name usually follows from the physiologic failure.
Pattern
Step 1 rarely rewards isolated fact recall in pulmonary physiology. It asks what happens to oxygenation, CO₂, A-a gradient, and work of breathing when a specific part of the system fails. Airway, alveolar, pleural, vascular, and control-center problems each produce predictable patterns.
Rule
- Start with what is failing: decide whether the problem is ventilation, perfusion, diffusion, mechanics, or ventilatory drive.
- Use the A–a gradient to localize hypoxemia: a gradient near the age- and oxygen-adjusted expected value supports hypoventilation or low inspired oxygen; an elevated gradient supports V/Q mismatch, diffusion limitation, or shunt.
- Use CO₂ to assess alveolar ventilation: CO₂ rises with hypoventilation and falls with hyperventilation.
Applications
- Asthma or COPD → obstructive airflow limitation
- Interstitial fibrosis → reduced compliance and lung volumes; ARDS → reduced compliance from diffuse alveolar injury
- Pulmonary embolism → dead space + V/Q mismatch
- Pneumonia → low V/Q or shunt-like physiology
- Tip: Identify ventilation, perfusion, or diffusion issue, then avoid answers that don’t match.
CPR APPLICATIONS · ACTIVE REASONING
Locate gas-exchange and ventilation failure
Choose a prediction before checking the mechanism. Expand the worked answers without scripts. No learner responses are stored or transmitted.
Reveal worked answer and transfer
Best answer: It is generally near the expected range for age and inspired oxygen. Isolated hypoventilation lowers alveolar and arterial oxygen together without usually widening the A–a gradient beyond its expected range.
Change one variable: How would pulmonary edema superimposed on hypoventilation change the expected A–a gradient?
Reveal worked answer and transfer
Best answer: Ventilation relative to perfusion (high V/Q, dead-space effect). Ventilated alveoli with little blood flow create high V/Q regions and wasted ventilation.
Change one variable: Why might other lung regions have lower V/Q as flow redistributes?
Reveal worked answer and transfer
Best answer: PaCO₂ is inversely related to effective alveolar ventilation. With steady CO₂ production, reduced alveolar ventilation increases arterial CO₂ tension.
Change one variable: If ventilation doubles and production remains constant, in a simplified steady state PaCO₂ tends toward half its prior value.
Change the mechanism
Compare the three scenarios without scripts
- Reduced alveolar ventilation: PaCO₂ rises and oxygen falls; the A–a gradient may remain near expected if gas exchange is otherwise intact.
- Impaired perfusion with maintained ventilation: Regional V/Q increases and wasted ventilation rises.
- Alveolar filling or shunt-like units: A–a gradient increases; oxygen response depends on shunt fraction and other mechanics.
Explain it back: Choose one decision, trace the causal mechanism, and identify the observation that would overturn your prediction.
These unscored exercises do not establish psychometric validation or patient-specific treatment recommendations.
How to use this foundation map
- Identify the organizing mechanism.
- Recognize the pattern.
- Restate the rule without looking.
- Test transfer with the applications and question practice.
Pair CPR with the 5P Approach™ when solving cases and questions.