PULMONARY FUNCTION TESTS

Decision Algorithms — 6 Blocks × Cross-Paper Multiplier
SLOT: Investigation P(slot)=0.60 | Catalog: PI 2016, 2019 → 7yr gap = DUE | Pre-final LOADED | C(env)=1.30 biomass COPD
PI → PFTs standalone (10 marks) PIV → COPD/GOLD staging PIII → HP restrictive pattern PII/III → Asthma vs COPD
① DECISION TREE
② OBS vs REST
③ DLCO
④ FLOW-VOLUME
⑤ GOLD + BDR
⑥ CROSS-PAPER
The Gatekeeper Number: FEV1/FVC ratio is the FIRST thing you write. Everything branches from it. The examiner sees this and knows you understand PFTs.

STEP 1 — Perform Spirometry

Patient performs maximal forced expiration. Measure FEV1 (volume in 1st second) and FVC (total forced volume).

Normal FEV1 >80% predicted. Normal FVC >80% predicted.

STEP 2 — Calculate FEV1/FVC Ratio ▼ tap to branch

The gatekeeper. Normal ≥ 0.70 (or use Lower Limit of Normal in elderly).

FEV1/FVC < 0.70 → OBSTRUCTIVE

Airflow Limitation Confirmed — Grade Severity by FEV1

FEV1 % predicted determines severity: GOLD 1–4 staging. ▼ tap

GOLD 1: ≥80% — Mild

Often undiagnosed. Patient may have no symptoms or only exertional dyspnea.

GOLD 2: 50–79% — Moderate

Dyspnea on exertion. Most patients seek medical attention at this stage.

GOLD 3: 30–49% — Severe

Significant dyspnea. Exercise limitation. Exacerbations impact quality of life.

GOLD 4: <30% — Very Severe

Severe airflow limitation. Respiratory failure risk. Cor pulmonale. Consider transplant evaluation.

GOLD uses POST-BRONCHODILATOR FEV1. Must give salbutamol 400μg first, wait 15–20 min, then repeat. Pre-bronchodilator values are for initial screening only.

Next: Bronchodilator Reversibility Test ▼ tap

Salbutamol 400μg → repeat spirometry in 15–20 min. The asthma vs COPD separator.

SIGNIFICANT REVERSIBILITY

≥200 mL
AND ≥12%

Both criteria must be met. Favors Asthma or Asthma-COPD Overlap (ACO).

→

NO SIGNIFICANT REVERSIBILITY

Fixed

Obstruction is irreversible. Favors COPD. Proceed to GOLD staging.

Exam trap: Partial reversibility (some improvement but not meeting both criteria) = COPD with reversible component, or consider ACO. Asthma can also show incomplete reversibility during exacerbation. Context matters.

Then: DLCO — Distinguish Phenotype ▼ tap

Within obstruction, DLCO separates airway disease from parenchymal destruction.

Obstruction + Normal DLCO → Chronic Bronchitis / Asthma

Airways are narrowed but alveolar-capillary membrane is intact. Gas transfer is preserved.

Obstruction + Low DLCO → Emphysema

Alveolar walls destroyed → reduced surface area for gas exchange. The "pink puffer" phenotype.

FEV1/FVC ≥ 0.70 + FVC Reduced → SUSPECT RESTRICTIVE

Must Confirm with TLC ▼ tap

Spirometry alone CANNOT confirm restriction. You need Total Lung Capacity from body plethysmography or helium dilution.

The examiner's teaching point: A reduced FVC with normal ratio SUGGESTS restriction but could also be poor effort, obesity, or early disease. TLC < 80% predicted CONFIRMS restriction. Writing "spirometry confirms restrictive pattern" without mentioning TLC loses you a mark.

TLC Reduced → Confirmed Restrictive. Now: Where is the problem? ▼ tap

DLCO separates parenchymal (lung itself) from extrapulmonary (chest wall/neuromuscular).

Restriction + Low DLCO → Parenchymal Disease

ILD, IPF, Hypersensitivity Pneumonitis, Sarcoidosis, Asbestosis. Thickened/fibrotic interstitium impairs gas transfer.

This is the line you write for HP in PIII: "PFTs show restrictive pattern with reduced DLCO."

Restriction + Normal DLCO → Extrapulmonary Cause

Chest wall: Kyphoscoliosis, obesity, ankylosing spondylitis

Neuromuscular: Myasthenia gravis, GBS, diaphragm paralysis

Lung parenchyma is normal — it just can't expand. Gas transfer per unit volume is preserved.

BOTH FEV1/FVC ↓ AND TLC ↓ → MIXED PATTERN

Mixed Obstructive-Restrictive

Both airflow limitation AND reduced lung volumes. Seen in: combined COPD + obesity, COPD + ILD, sarcoidosis with airway involvement, CF.

Less commonly tested standalone. Know it exists for differential completeness.

FEV1/FVC ≥ 0.70 + FVC Normal → NORMAL SPIROMETRY

Normal Spirometry — But Symptoms Persist?

Consider: exercise-induced bronchospasm (methacholine challenge), small airway disease (FEF25-75, impulse oscillometry), DLCO for isolated gas transfer defect, vocal cord dysfunction.

ANSWER SKELETON — "Discuss Pulmonary Function Tests"

2 marks
Para 1 — Definition + Indications. Spirometry (FEV1, FVC, ratio), lung volumes (TLC, RV), DLCO, flow-volume loops. Indications: dyspnea evaluation, COPD diagnosis/staging, preoperative assessment, occupational lung disease, treatment monitoring, disability assessment.
3 marks
Para 2 — Spirometry: Obstructive vs Restrictive. FEV1/FVC ratio as gatekeeper (< 0.70 = obstructive). Table of parameter changes. TLC needed to confirm restriction. Mention mixed pattern.
2 marks
Para 3 — DLCO + Lung Volumes. What DLCO measures (gas transfer across alveolar-capillary membrane). Clinical interpretation: low = parenchymal, normal = extrapulmonary/airway. Lung volumes: TLC, RV, FRC by plethysmography.
2 marks
Para 4 — Clinical Applications. GOLD staging (post-BD FEV1). Bronchodilator reversibility (≥200mL AND ≥12% = asthma). Flow-volume loop patterns (scooped = obstructive, plateau = fixed upper airway).
1 mark
Para 5 — Modern tail. Biomass fuel COPD in India (non-smoking women, small airway phenotype). Indian reference equations vs NHANES. Impulse oscillometry for small airways. FEF25-75 limitations (high variability, not GOLD-recommended).
The Master Table: If you can reproduce this table from memory, you've nailed 3 marks of any PFT question. Practice drawing this grid.
Parameter Obstructive Restrictive Mixed
FEV1/FVC ↓↓ < 0.70 Normal or ↑ ↓
FEV1 ↓↓ ↓ ↓↓
FVC ↓ or Normal ↓↓ ↓↓
TLC ↑ (hyperinflation) ↓↓ ↓
RV ↑↑ (air trapping) ↓ Variable
RV/TLC ↑ Normal Variable
DLCO Normal (bronchitis) or ↓ (emphysema) ↓ (ILD) or Normal (chest wall) ↓
Flow-Volume Loop Scooped-out expiratory limb Narrow symmetrical (↓ volume axis) Combined features
OBSTRUCTIVE DISEASES (tap to expand)
OBSTRUCTIVE — PIV COPD/GOLD

COPD

Fixed airflow limitation. FEV1/FVC < 0.70 post-BD. GOLD 1–4.

PFT signature: ↓FEV1/FVC, ↑TLC, ↑RV (air trapping). Scooped flow-volume loop.
Emphysema subtype: ↓DLCO (destroyed alveoli).
Chronic bronchitis subtype: Normal DLCO (airways diseased, parenchyma intact).
Biomass COPD (Indian context): Non-smoking women, wood/cow dung fuel. More small airway disease, less emphysema. Same PFT pattern but younger onset, ↓DLCO less pronounced.
Key exam point: GOLD staging requires POST-bronchodilator FEV1.
OBSTRUCTIVE — PII/PIII

Asthma

Variable airflow limitation. REVERSIBLE obstruction.

PFT signature: ↓FEV1/FVC during exacerbation. May be NORMAL between attacks.
Key differentiator: Significant BDR (≥200mL AND ≥12%). DLCO is normal (parenchyma intact).
If spirometry normal: Methacholine/histamine challenge (provocation test). PC20 < 4mg/mL = positive = airway hyperresponsiveness.
Peak flow variability: >20% diurnal variation suggests asthma.
OBSTRUCTIVE

Bronchiectasis

Obstructive pattern. Often irreversible.

PFT signature: Obstructive pattern, usually NOT reversible. May progress to mixed pattern in advanced disease.
DLCO: Variable — may be normal or reduced depending on extent.
RESTRICTIVE DISEASES (tap to expand)
RESTRICTIVE — PIII HP

ILD / IPF / Hypersensitivity Pneumonitis

Parenchymal restriction. ↓TLC, ↓DLCO.

PFT signature: ↓TLC (confirmed restrictive), ↓DLCO (thickened/fibrotic interstitium), FEV1/FVC normal or ↑.
HP specific (Karnataka): Coir workers, rice paddy farmers, sugarcane workers — occupational exposure. Restrictive pattern + ↓DLCO + exposure history = diagnostic triad with HRCT.
IPF: Progressive ↓DLCO even before volume changes. DLCO is the most sensitive early marker.
The line for PIII answer: "PFTs reveal restrictive pattern with reduced DLCO, consistent with parenchymal disease."
RESTRICTIVE — EXTRAPULMONARY

Neuromuscular (MG, GBS, Diaphragm)

Restriction with NORMAL DLCO. Lungs are fine, muscles fail.

PFT signature: ↓TLC, ↓FVC, NORMAL DLCO. The parenchyma is healthy — the respiratory muscles can't generate enough force.
MG specific: FVC monitoring is CRITICAL for myasthenic crisis prediction. FVC < 20 mL/kg or negative inspiratory force (NIF) < -20 cmH₂O = intubation threshold.
GBS: Same monitoring. 20/30/40 rule — FVC <20, NIF <-30, MEP <40 = intubate.
Diaphragm paralysis: ≥25% drop in FVC from upright to supine = diagnostic.
RESTRICTIVE — EXTRAPULMONARY

Chest Wall (Kyphoscoliosis, Obesity)

Mechanical restriction. Normal DLCO.

PFT signature: ↓TLC, ↓FVC, NORMAL DLCO, ↓ERV (especially obesity).
Obesity: ERV (expiratory reserve volume) reduced disproportionately. FRC reduced. In severe obesity, FEV1/FVC may actually be slightly ↑ (because FVC drops more than FEV1).
Kyphoscoliosis: Restrictive physiology from chest wall deformity. Cobb angle >100° = severe restrictive disease.
RESTRICTIVE — PARENCHYMAL

Sarcoidosis

Can be restrictive, obstructive, or mixed depending on stage.

Early (Stage I-II): May be normal or mildly restrictive. ↓DLCO often the earliest abnormality.
Advanced (Stage III-IV): Restrictive pattern with ↓DLCO. Endobronchial involvement → obstructive component → mixed.
Unique: One of the few diseases where pattern can CHANGE over disease course.
What DLCO actually measures: Patient inhales a tiny known amount of carbon monoxide (CO) in a single breath, holds for 10 seconds, then exhales. The difference between inspired and expired CO = amount transferred across the alveolar-capillary membrane. This tests the integrity and surface area of the gas-exchange interface.
DLCO INTERPRETATION — The Clinical Decision Table
DLCO Mechanism Diseases Clinical Significance
↓↓ Severely Reduced Alveolar membrane destroyed / severely thickened Emphysema, IPF, HP, asbestosis Correlates with hypoxemia severity. Monitor for progression.
↓ Moderately Reduced ↓ capillary blood volume OR mild thickening Pulmonary HTN, anemia, early ILD, pulmonary embolism In anemia: correct DLCO for hemoglobin. Low Hb → falsely low DLCO.
Normal Membrane intact, adequate blood volume Asthma, chronic bronchitis, chest wall restriction, neuromuscular Airway/mechanical disease — not parenchymal.
↑ Elevated ↑ pulmonary capillary blood volume Alveolar hemorrhage (Goodpasture, Wegener), polycythemia, L→R shunt, exercise, supine position Alveolar hemorrhage: rising DLCO in context of hemoptysis = blood in alveoli absorbing CO.
The 2 DLCO traps examiners love:
1. Anemia falsely lowers DLCO — less hemoglobin in capillaries = less CO uptake. Always correct for Hb. A "low DLCO" in an anemic patient may be normal when corrected.
2. Alveolar hemorrhage RAISES DLCO — counterintuitive. Blood in alveolar space provides extra hemoglobin to bind CO. Rising DLCO + hemoptysis = think Goodpasture/vasculitis.
THE DLCO DECISION MATRIX — Combine with Spirometry
Spirometry Pattern DLCO → Diagnosis
Obstructive Normal Chronic bronchitis / Asthma — airways, not parenchyma
Obstructive ↓ Low Emphysema — alveolar destruction
Restrictive ↓ Low ILD / IPF / HP — parenchymal fibrosis
Restrictive Normal Chest wall / Neuromuscular — extrapulmonary cause
Normal spirometry ↓ Low Pulmonary vascular disease / Early ILD / Anemia
Normal spirometry ↑ High Alveolar hemorrhage / Polycythemia / L→R shunt
Pattern recognition: Flow-volume loops are shape-based diagnosis. The expiratory limb is above the x-axis, inspiratory below. Learn 5 shapes = 5 diagnoses.

NORMAL

Vol Flow
Normal: Sharp peak early in expiration (Peak Expiratory Flow), then smooth linear descent. Inspiratory limb is a smooth semicircle. Symmetric volume axis.

OBSTRUCTIVE (COPD/Asthma)

Scooped-out (concave) expiratory limb. The hallmark. Peak flow may be reduced, but the key is the concavity — air comes out fast initially then slows as airways collapse. More volume on right side (air trapping).

Mnemonic: "COPD scoops out the expiration."

RESTRICTIVE (ILD)

Normal shape but NARROWER on volume axis. The loop looks like a miniature version of normal. Flows may be preserved or slightly reduced but total volume is reduced. Shape is maintained because airways are normal — it's the lung volume that's small.

FIXED UPPER AIRWAY OBSTRUCTION

Both limbs flattened = plateau on BOTH expiration and inspiration. Flow is limited in both directions by a fixed obstruction.

Causes: Tracheal stenosis (post-intubation), goiter compressing trachea, tracheal tumor.
Key: Fixed = doesn't change with respiration phase. Both limbs equally affected.

VARIABLE EXTRATHORACIC

Flattened INSPIRATORY limb only. Expiration is normal.

Why: During inspiration, negative intrathoracic pressure pulls extrathoracic airway inward → obstruction worsens. During expiration, positive pressure splints it open → normal flow.
Causes: Vocal cord paralysis (bilateral), laryngeal tumor, post-tracheostomy tracheomalacia.

VARIABLE INTRATHORACIC

Flattened EXPIRATORY limb only. Inspiration is normal.

Why: During expiration, positive intrathoracic pressure compresses the intrathoracic airway → obstruction. During inspiration, negative pressure pulls it open → normal.
Causes: Tracheomalacia (intrathoracic portion), intrathoracic tracheal tumor, relapsing polychondritis.
The memory rule for variable obstruction:
"The problem limb matches where the obstruction is NOT."
• Extra-thoracic obstruction → Inspiratory flattening (negative pressure worsens it during inspiration)
• Intra-thoracic obstruction → Expiratory flattening (positive pressure worsens it during expiration)
Fixed obstruction → Both flattened (doesn't change with pressure phase)
This tab feeds PIV directly. COPD/GOLD was Sep25 PIV Q9 (TPP 1.20 for Feb26 PIV). Know GOLD staging cold — it's testable in PI as investigation AND in PIV as recent advances.
GOLD CLASSIFICATION — Click each stage
GOLD 1
≥80%
GOLD 1 — Mild
FEV1 ≥80% predicted (post-BD)
FEV1/FVC < 0.70

Often undiagnosed. Patient may be asymptomatic or have only mild chronic cough. The ratio is abnormal but absolute FEV1 is preserved.

Management: Short-acting bronchodilator PRN. Smoking cessation. Vaccination (influenza, pneumococcal).
GOLD 2
50–79%
GOLD 2 — Moderate
FEV1 50–79% predicted

Dyspnea on exertion. Most patients present at this stage. Exercise limitation begins.

Management: Long-acting bronchodilator (LABA or LAMA). Pulmonary rehabilitation. Add ICS if frequent exacerbations (≥2/year) + eosinophils ≥300.
GOLD 3
30–49%
GOLD 3 — Severe
FEV1 30–49% predicted

Significant dyspnea. Frequent exacerbations. Exercise severely limited. Reduced quality of life.

Management: LABA + LAMA. Consider triple therapy (LABA+LAMA+ICS) if exacerbation-prone. Pulmonary rehab. LTOT if PaO₂ ≤ 55 mmHg.
GOLD 4
<30%
GOLD 4 — Very Severe
FEV1 <30% predicted

Severe airflow limitation. Respiratory failure. Cor pulmonale. Quality of life severely impaired.

Management: Maximal inhaled therapy + LTOT + pulmonary rehab. Consider lung volume reduction surgery (LVRS) or lung transplant. Palliative care discussions.
Mild Moderate Severe Very Severe
GOLD 2023+ refinement (ABE assessment): Spirometry grades severity (GOLD 1–4). But TREATMENT is guided by symptoms (CAT score/mMRC) + exacerbation history → Groups A, B, E. Group E (≥2 exacerbations or ≥1 hospitalization) = escalate therapy regardless of FEV1.
BRONCHODILATOR REVERSIBILITY — The Protocol

STEP 1

Baseline spirometry
Record FEV1

→

STEP 2

Salbutamol 400μg
via MDI + spacer

→

STEP 3

Wait 15–20 min
Repeat spirometry

→

POSITIVE IF:

≥200 mL
AND ≥12%

Both criteria. Favors asthma.

INDIAN CONTEXT — Biomass COPD (Pattern 5 Upgrade)

Biomass Fuel COPD ≠ Smoking COPD

In India, 30-40% of COPD is from biomass fuel exposure (wood, cow dung, crop residue — indoor cooking). This predominantly affects non-smoking women in rural Karnataka and other states.

PFT differences: Same obstructive pattern (↓FEV1/FVC) but: more small airway involvement (↓FEF25-75), less emphysema (DLCO less reduced), younger age of onset. HRCT shows more air trapping, less emphysema.

Clinical significance: ICMR recognizes biomass COPD as distinct entity. Indian reference equations (not NHANES/Caucasian norms) should be used — Knudson/Crapo equations overestimate predicted values for Indian populations by 15-20%.

This paragraph in any PFT or COPD answer = 1 mark from Pattern 5 recovery. The setter is a Mangalore internist who sees biomass COPD in OPD.

The multiplier effect: PFT knowledge isn't a single-paper topic. It drops marks into 4 different answers across all papers. This tab maps exactly WHAT to write WHERE.
PI

Paper I — PFTs Standalone (10 marks)

Investigation slot. Full answer using the 5-paragraph skeleton.

Use the Decision Tree tab as your answer structure:
Para 1: Definition + Indications (2 marks)
Para 2: Spirometry — Obstructive vs Restrictive table (3 marks)
Para 3: DLCO + Lung volumes (2 marks)
Para 4: Clinical applications — GOLD, BDR, flow-volume loops (2 marks)
Para 5: Indian context — biomass COPD, Indian reference equations (1 mark)

Draw: The obstructive vs restrictive comparison table. If you add a small flow-volume loop sketch for obstructive (scooped) vs restrictive (narrow normal), you differentiate your answer.
PIV

Paper IV — COPD / GOLD Guidelines (TPP 1.20)

Sep25 PIV asked COPD. May repeat. PFT knowledge = the diagnostic backbone.

The PFT lines to insert in a COPD answer:
"COPD diagnosis requires spirometric confirmation: post-bronchodilator FEV1/FVC < 0.70 establishes airflow limitation. Severity is graded by GOLD classification (FEV1 ≥80% mild to <30% very severe). Bronchodilator reversibility testing separates COPD from asthma (significant if ≥200mL AND ≥12% improvement). DLCO distinguishes emphysema phenotype (reduced DLCO, alveolar destruction) from chronic bronchitis phenotype (normal DLCO, airway disease)."

Indian tail: "Biomass fuel COPD accounts for 30-40% of Indian COPD, predominantly affecting non-smoking women exposed to indoor cooking fuels. ICMR recognizes this as a distinct entity requiring Indian reference equations for spirometric interpretation."

Marks gained: ~2-3 marks from PFT content in a PIV COPD question.
PIII

Paper III — Hypersensitivity Pneumonitis (Pre-final loaded)

Sep25 PIII asked HP. Pre-final loaded. PFT = the investigation component.

The ONE LINE to write:
"Pulmonary function tests reveal a restrictive pattern (reduced TLC, preserved FEV1/FVC ratio) with reduced DLCO, consistent with parenchymal interstitial disease. In chronic HP, mixed obstructive-restrictive pattern may develop."

Karnataka context: "In coastal Karnataka, occupational exposure to coir dust, rice paddy, and sugarcane processing are recognized causes of HP. Detailed occupational history combined with PFT demonstrating restrictive physiology with reduced DLCO supports diagnosis alongside HRCT findings."

Marks gained: 1-2 marks from PFT line in HP answer.
PII

Paper II/III — Asthma vs COPD / Myasthenia Gravis

Background signal for differentiation questions.

Asthma vs COPD:
"Bronchodilator reversibility testing is the key spirometric differentiator. Significant reversibility (≥200mL AND ≥12% FEV1 improvement post-salbutamol) favors asthma. Fixed obstruction without significant reversibility favors COPD. Normal DLCO in asthma distinguishes from emphysema phenotype of COPD (reduced DLCO)."

Myasthenia Gravis (TPP 1.80 for PII/III):
"FVC monitoring is critical in myasthenic crisis assessment. FVC <20 mL/kg or NIF (negative inspiratory force) worse than -20 cmH₂O indicates impending respiratory failure requiring intubation. Restrictive pattern with preserved DLCO reflects neuromuscular weakness, not parenchymal disease."

Marks gained: 1 mark each from PFT content in asthma or MG answers.

RAPID-FIRE RECALL — Tap to reveal answers

1. FEV1/FVC < 0.70. What pattern? What's the next step?
Obstructive. Next: Bronchodilator reversibility test (salbutamol 400μg, repeat in 15-20 min). Then grade severity by post-BD FEV1 (GOLD 1-4).
2. Restrictive pattern on spirometry. Can you confirm restriction from spirometry alone?
NO. Spirometry can SUGGEST restriction (reduced FVC with normal ratio). Confirmation requires TLC measurement (body plethysmography or helium dilution). TLC < 80% predicted = confirmed restrictive.
3. Obstruction + Normal DLCO vs Obstruction + Low DLCO — what does each mean?
Normal DLCO = chronic bronchitis/asthma (airways diseased, parenchyma intact). Low DLCO = emphysema (alveolar membrane destroyed, reduced gas exchange surface area).
4. What are the two criteria for significant bronchodilator reversibility?
≥200 mL absolute increase in FEV1 AND ≥12% improvement from baseline. BOTH must be met. Favors asthma over COPD.
5. Flattened INSPIRATORY limb only on flow-volume loop. Where is the obstruction?
Variable EXTRATHORACIC obstruction (vocal cord paralysis, laryngeal tumor). During inspiration, negative pressure pulls extrathoracic airway inward → worsens obstruction. Expiration is normal because positive pressure splints it open.
6. DLCO is ELEVATED. What should you think?
Alveolar hemorrhage (Goodpasture, Wegener) — blood in alveoli provides extra Hb to bind CO. Also: polycythemia, L→R shunt. Rising DLCO + hemoptysis = alveolar hemorrhage until proven otherwise.
7. Biomass COPD differs from smoking COPD in India. How?
Biomass COPD: predominantly non-smoking women, indoor cooking with wood/cow dung. More small airway disease (↓FEF25-75), less emphysema (DLCO less reduced), younger onset. Same obstructive PFT pattern. ICMR recognizes as distinct entity. 30-40% of Indian COPD.
8. MG patient — what FVC threshold means intubate?
FVC < 20 mL/kg OR NIF worse than -20 cmH₂O. The 20/30/40 rule (GBS): FVC <20, NIF <-30, MEP <40 = intubate. Restrictive pattern with normal DLCO (neuromuscular, not parenchymal).

5 RETENTION ANCHORS — Close this page, recall these

1

FEV1/FVC < 0.70 = Obstructive. Reduced FVC + normal ratio + low TLC = Restrictive. The ratio is the gatekeeper. Write it first in any PFT answer. Spirometry alone cannot confirm restriction — need TLC.

2

DLCO separates WHERE the problem is. Obstruction + normal DLCO = airway (bronchitis/asthma). Obstruction + low DLCO = parenchyma (emphysema). Restriction + low DLCO = ILD. Restriction + normal DLCO = chest wall/neuromuscular.

3

BDR: ≥200mL AND ≥12%. Both criteria. Post-salbutamol 400μg, 15-20 min. Positive = asthma. Fixed = COPD. GOLD staging uses post-BD FEV1: ≥80 / 50-79 / 30-49 / <30.

4

Flow-volume loops: Scooped = obstructive. Narrow = restrictive. Flat top = fixed UAO. Flat bottom = extrathoracic. Flat top only = intrathoracic. "Problem limb matches where obstruction is NOT."

5

Indian context = marks. Biomass COPD (30-40% of Indian COPD, non-smoking women, wood/cow dung, small airway phenotype). Indian reference equations, not NHANES. ICMR recognizes. Write this in PI and PIV answers.