Module Overview & Exam Review
Exam review target: use this page to tighten the numbers, patterns, safety rules, and interpretation steps that the fill-in guide highlighted. The fillable worksheet is under the Resources tab.
1. Spirometry Core
What Spirometry Measures
Spirometry measures air entering and leaving the lungs. It includes forced airflow and volume values during inspiration and expiration.
| Pattern | Memory aid | Main problem |
|---|
| Restriction | PAINT: pulmonary, alveolar, interstitial, neuromuscular, thoracic | Volume problem |
| Obstruction | CBABE: cystic fibrosis, bronchitis, asthma, bronchiectasis, emphysema | Flow problem |
Setup and Patient Data
Before testing, collect:
- Age
- Height, or arm span if the patient cannot stand
- Sex
- Race
- Smoking history
- Cough and sputum description
- Dyspnea pattern
- Occupational exposure history
Predicted values are based on race, age, sex, and height. Predicted percent values compare the patient's measured value against the predicted value.
ATS Maneuver Rules
| Item | High-yield value |
|---|
| Patient position for FVC maneuver | Seated |
| Minimum adult exhalation time | 6 seconds |
| Minimum child exhalation time | 3 seconds |
| Repeated efforts | 3 efforts meeting acceptability and reproducibility criteria |
| Start-of-test hesitation limit if FVC <2 L | 100 mL |
| Start-of-test hesitation limit if FVC >2 L | 5% |
Common unacceptable artifacts include poor initial blast, excessive extrapolated volume, cough in the first second, incomplete inhalation, variable effort, blocked mouthpiece, glottic closure, early termination/no plateau, extra breath, zero-flow error, and leak.
2. Spirometry Values
LLN and ULN
| Result | Meaning |
|---|
| >= LLN and <= ULN | Normal range |
| < LLN | Low |
| > ULN | High |
FVC
FVC is the volume expired as forcefully as possible after maximum inhalation.
| FVC percent predicted | Grade |
|---|
| >80% | Normal |
| 66-79% | Mild |
| 50-65% | Moderate |
| <50% | Severe |
Healthy patients have FVC = SVC. In obstruction, FVC may be less than SVC because of airway collapse and air trapping. In restriction, FVC is reduced because lung volume is reduced.
FEV1 and FEV1/FVC
FEV1 is the most commonly used timed interval and the best value to grade severity of airway obstruction.
| FEV1 percent predicted | Grade |
|---|
| >80% | Normal |
| 70-79% | Mild |
| 60-69% | Moderate |
| 50-59% | Moderately severe |
| 35-49% | Severe |
| <35% | Very severe |
| FEV1/FVC | Interpretation |
|---|
| >100% or >ULN | Restrictive disease pattern |
| About 70% | Normal adult |
| 65-70% | May be healthy in older patients |
| <70% | Obstructive disease pattern |
Flow Values
| Value | What it tells you |
|---|
| FEF25%-75% | Average flow during the middle half of the FVC maneuver; medium and small airways |
| PEFR | Maximum flow rate at the peak of the flow-volume loop; effort dependent |
3. Post-Bronchodilator Testing
Post-bronchodilator testing determines reversibility of airway obstruction, assesses need for additional medication, and can help diagnose asthma.
| Step | High-yield point |
|---|
| Medication | 4 puffs MDI per ATS source protocol |
| Wait time before post-spirometry | 15 minutes |
| Formula | (post - pre) / pre x 100 |
| Significant response | FEV1 or FVC increase >12% and 200 mL |
Failure to show a significant response does not completely exclude response. Patient fatigue in moderate to severe COPD and inadequate medication disposition can blunt results.
4. Lung Volumes
Lung volume studies measure FRC.
| Method | Core idea |
|---|
| Nitrogen washout | Patient breathes 100% O2 to wash N2 out of the lungs |
| Helium dilution | Patient rebreathes a known He concentration until stable |
| Body plethysmography / VTG / body box | Uses Boyle's law; quickest and most accurate for FRC |
Lung Volume Formulas
| Formula | Use |
|---|
| RV = FRC - ERV | Calculates residual volume |
| TLC = FRC + IC | Calculates total lung capacity |
| TLC = VC + RV | Another TLC calculation |
Restriction, Air Trapping, and Hyperinflation
| Pattern | Key finding |
|---|
| Restriction | TLC is decreased |
| Air trapping | FRC > ULN while TLC remains normal |
| Hyperinflation | FRC and TLC are both > ULN |
TLC Severity for Restriction
| TLC finding | Grade |
|---|
| TLC < LLN but >=70% predicted | Mild restriction |
| TLC <70% but >=60% predicted | Moderate restriction |
| TLC <59% predicted | Moderately severe restriction |
Nitrogen Washout
High-yield points:
- Uses 100% O2
- Can depress hypoxic drive in CO2 retainers
- Lasts up to 7 minutes or until exhaled N2 is <1%
Helium Dilution
High-yield points:
- Spirometer contains 10% He
- System needs a CO2 absorber, usually soda lime
- Oxygen is added to meet patient oxygen demand
Body Plethysmography
High-yield points:
- Based on Boyle's law
- Measures thoracic gas volume at end tidal expiration
- Patient pants against a closed shutter
- Panting frequency is 30-60 bpm
5. DLCO
DLCO measures gas exchange capacity of the lungs.
Preparation and Maneuver
| Step | High-yield value |
|---|
| Smoking | No smoking the day of test to reduce CO levels |
| Supplemental O2 | Off O2 for 10 minutes before testing |
| Maneuver | Exhale to RV, inhale quickly to TLC, hold 8-12 seconds |
| Wait between trials | At least 4 minutes |
| Minimum trials | 2 acceptable tests |
DLCO Severity
| DLCO finding | Grade |
|---|
| LLN-ULN | Normal |
| 60% to LLN | Mild |
| 40-60% | Moderate |
| <40% | Severe |
Decreased DLCO can occur with sarcoidosis, asbestosis, berylliosis, oxygen toxicity, pulmonary edema, emphysema, space-occupying lesions, lung resections, and V/Q mismatch.
6. Bronchoprovocation
Methacholine Challenge
Methacholine increases parasympathetic tone in bronchial smooth muscle and causes bronchoconstriction. It is used when the patient has asthma-like history or symptoms but PFTs or bronchodilator results are inconclusive.
| Item | High-yield point |
|---|
| Start requirement | Baseline FEV1 at least 60-70% predicted |
| Diluent response | Post-NaCl FEV1 drop >=10% from baseline is positive |
| Methacholine response | Sustained FEV1 drop of 20% is positive |
| Hazards | Dyspnea, cough, chest tightness, wheezing, headache |
| Safety | Physician should be immediately available |
Severe airflow obstruction with FEV1 <60% predicted is an absolute contraindication.
EIA/EIB Challenge
EIA/EIB testing is used for dyspnea on exertion with normal resting PFTs, uncertain methacholine results, known EIA/EIB therapy evaluation, or exercise limitation evaluation in asthmatic patients.
| Item | High-yield point |
|---|
| Avoid heavy exercise | At least 4 hours before test |
| Baseline FEV1 | At least 70% predicted |
| Target exercise | 80-90% predicted max HR for 6-8 minutes |
| First post-exercise spirometry | Within 1-2 minutes |
| Repeat spirometry | Every 5 minutes for 20-30 minutes |
| Positive test | Sustained FEV1 decrease of 10-15% |
7. CPX, CPEX, or CPET
Cardiopulmonary stress testing assesses ventilation, gas exchange, and cardiovascular function during exercise.
| Category | High-yield points |
|---|
| Contraindications | Limiting neurologic/neuromuscular disorders, limiting orthopedic disorders, PaO2 <40 mmHg on room air, PaCO2 >70 mmHg |
| Equipment | Treadmill or cycle ergometer, PFT machine, gas analyzers, 12-lead EKG, BP cuff, pulse oximeter, optional arterial line |
| Gas analyzers | Measure exhaled O2, CO2, and N2 |
| Prep | Comfortable clothing and tennis shoes, no smoking for 8 hours, no exercise the day of test |
Maximal study criteria include heart rate >85-90% predicted or SaO2 <80%. Once a single criterion is met, the test is graded as maximal effort.
8. Bronchoscopy
Bronchoscopy directly visualizes pathologic changes in the trachea and bronchi.
Therapeutic vs Diagnostic
| Type | Indications |
|---|
| Therapeutic | Removal of foreign bodies, aspiration/removal of thick secretions, localized medication administration, selective lavage such as BAL |
| Diagnostic | Suspicion of bronchogenic carcinoma, abnormal chest X-ray/mass, wheezing/cough/chest pain/dyspnea, positive sputum cytologic findings, hemoptysis |
Contraindications
| Relative | Absolute |
|---|
| Patient unable to cooperate | Absence of signed consent |
| Tracheal obstruction or uncontrolled asthma | Absence of experienced personnel |
| Cardiovascular instability | Lack of emergency equipment |
| Moderate to severe hypoxemia | Inability to adequately oxygenate |
Hazards and Route
| Item | High-yield point |
|---|
| Most fatal complications | Hemorrhage and pneumothorax |
| Other hazards | Hypoxemia, cardiac arrhythmia, bronchospasm/laryngospasm, topical anesthesia reaction |
| Most common route | Transnasal |
| Transoral route | Use a bite block |
9. Sleep Studies and PAP
Study Types
| Test | Purpose |
|---|
| PSG | Overnight definitive diagnosis of sleep apnea |
| Overnight pulse oximetry | Checks overnight oxygen saturation and CPAP/BiPAP effectiveness |
| HST | Home sleep test for obstructive sleep apnea |
| Actigraphy | Monitors rest/activity cycles by movement of a limb |
| MSLT | Diagnoses narcolepsy and idiopathic hypersomnia |
| MWT | Measures how alert a patient is during the day |
Sleep Apnea Patterns
| Pattern | Finding |
|---|
| Obstructive sleep apnea | Respiratory effort present but no airflow due to upper airway obstruction |
| Central sleep apnea | CNS fails to signal respiratory effort |
| Obstructive hypopnea | Effort detected with minimal airflow |
MSLT vs MWT
| Test | Structure | Stop point |
|---|
| MSLT | Five 15-minute naps separated by 2-hour breaks | Trial ends if the patient does not fall asleep in 20 minutes |
| MWT | Four sleep trials separated by 2-hour breaks | Trial ends if the patient does not fall asleep in 40 minutes |
AHI Ratings
| AHI | Rating |
|---|
| <5 | Normal |
| 5-15 | Mild sleep apnea |
| 15-30 | Moderate sleep apnea |
| >30 | Severe sleep apnea |
PAP
| Therapy | High-yield point |
|---|
| CPAP | First-line medical therapy for OSA |
| BiPAP | Separate pressures for inhalation and exhalation |
| Auto-CPAP | Adjusts based on snoring, hypopneas, and apneas |
Patient compliance and comfort are key for successful PAP treatment.