Pulmonary Ventilation & Gas Exchange — INBDE Review
Lung volumes, mechanics of breathing, gas exchange physiology, the O₂–Hb curve, and obstructive vs restrictive PFT patterns. 11 board-style MCQs.
Concept summary & clinical relevance.
Quick-reference structure first, then nerve-by-nerve detail. Mnemonics in amber, clinical pearls in blue.
Pulmonary physiology questions on the INBDE focus on three things: lung volumes and what they measure, the obstructive-vs-restrictive PFT pattern, and the O₂–Hb dissociation curve (Bohr effect). Layered on top: clinical scenarios for asthma, COPD, fibrosis, and the hypoventilation/hyperventilation states you'll see in the dental chair.
| Measure | Definition | Notes |
|---|---|---|
| Tidal volume (TV) | Normal breath in/out | ~500 mL |
| Inspiratory reserve volume (IRV) | Extra inhaled after a normal breath | Measurable |
| Expiratory reserve volume (ERV) | Extra exhaled after a normal breath | Measurable |
| Residual volume (RV) | Air left after maximal exhalation | NOT measurable by spirometry |
| Vital capacity (VC) | TV + IRV + ERV | Maximum usable air |
| Total lung capacity (TLC) | VC + RV | All air the lungs can hold |
| FEV₁/FVC ratio | Forced expiratory volume in 1 sec ÷ forced vital capacity | Key obstructive vs restrictive marker |
| Pattern | Examples | FEV₁/FVC | TLC | RV |
|---|---|---|---|---|
| Obstructive | Asthma, COPD, emphysema | ↓ (< 70%) | Normal or ↑ | ↑ (air trapping) |
| Restrictive | Pulmonary fibrosis, sarcoidosis | Normal or ↑ | ↓ | Normal or ↓ |
| Shift | Meaning | Causes |
|---|---|---|
| Right shift | ↓ O₂ affinity → release O₂ to tissues | ↑ CO₂, ↑ H⁺ (acidosis), ↑ temperature, ↑ 2,3-BPG |
| Left shift | ↑ O₂ affinity → hold O₂ | ↓ CO₂, ↓ H⁺ (alkalosis), ↓ temperature, fetal Hb, carbon monoxide |
Mechanics of breathing
- Quiet inspiration: diaphragm contracts → thoracic volume increases → intrathoracic pressure drops → air flows in.
- Expiration at rest: passive — the elastic recoil of the lung tissue and chest wall returns volume to FRC.
- Forced expiration: active, using abdominal muscles and internal intercostals.
- Compliance = ΔV / ΔP; emphysema increases it, fibrosis decreases it.
Gas exchange & transport
- Diffusion across the alveolar-capillary membrane depends on surface area, barrier thickness, and partial pressure gradient.
- Oxygen is transported mostly bound to hemoglobin (~98%); a small fraction is dissolved in plasma.
- Carbon dioxide is transported mainly as bicarbonate (HCO₃⁻); some bound to hemoglobin and some dissolved.
- The S-shaped O₂–Hb curve: cooperative binding gives a steep middle and a flat plateau at high PO₂.
Pulmonary function patterns
- Obstructive (asthma, COPD, emphysema): airflow out is limited → ↓ FEV₁/FVC, ↑ RV from air trapping.
- Restrictive (fibrosis, sarcoidosis): lungs can't fully expand → ↓ TLC; FEV₁/FVC is preserved or even increased because both numerator and denominator fall together.
- Hypoventilation (e.g., opioid overdose): retains CO₂ → respiratory acidosis.
- Hyperventilation (anxiety): blows off CO₂ → respiratory alkalosis with tingling, lightheadedness, possible syncope.
11 board-style MCQs.
Active recall is the highest-yield study method for the INBDE. Pick an answer, check it, and read why every distractor is wrong — that's where the learning compounds.
The MCQs above are Core Recall — testing what you've memorized. The book adds a full Clinical Integration set: board-style patient scenarios where you apply this anatomy to real clinical reasoning. That's the section the INBDE actually weights heaviest.
- Question 1EasyWhich lung volume represents the air inhaled or exhaled in a normal breath?
- Question 2EasyWhich lung volume cannot be measured directly by spirometry?
- Question 3EasyWhich muscle is the primary driver of quiet inspiration?
- Question 4EasyExpiration at rest is primarily due to:
- Question 5ModerateWhich condition increases lung compliance?
- Question 6ModerateWhich condition decreases lung compliance?
- Question 7EasyThe main form of CO₂ transport in the blood is:
- Question 8EasyWhich factor causes a right shift of the O₂–hemoglobin dissociation curve?
- Question 9ModerateIn obstructive lung disease (e.g., asthma, COPD), which pulmonary function ratio decreases?
- Question 10ModerateIn restrictive lung disease (e.g., pulmonary fibrosis), the FEV₁/FVC ratio is typically:
- Question 11EasyHyperventilation in an anxious dental patient leads to:
900 INBDE-style MCQs with full explanations across 18 chapters — Core Recall plus board-style Clinical Integration scenarios — alongside Learning Summaries, Integration Bridges, and Review Boxes. Built by Dr. Isaac Sun for dental students who want to think like a clinician, not just memorize.
Founder, KYT Dental Services · Author, KYT INBDE series. These MCQs and Learning Summaries are part of a structural-thinking framework Dr. Sun uses with patients in the chair.