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.