# Abnormal Pulmonary Function Patterns

> Obstructive vs restrictive PFT patterns in MBBS Physiology: FEV1/FVC cut-offs, GOLD grades, bronchodilator reversibility, flow-volume loops and DLCO.

- Canonical URL: https://prepelephant.com/topics/mbbs/physiology/pulmonary-function-abnormal-patterns
- Exam / course: MBBS · Subject: Physiology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Abnormal Pulmonary Function Patterns", PrepElephant, https://prepelephant.com/topics/mbbs/physiology/pulmonary-function-abnormal-patterns

## Direct answer

An obstructive pattern means FEV1 falls faster than FVC, driving the FEV1/FVC ratio below 0.70 with air trapping — residual volume rises and total lung capacity is normal or increased — as in asthma and COPD. A restrictive pattern drops FEV1 and FVC proportionately, leaving a normal or high ratio, with total lung capacity below 80 per cent of predicted in interstitial lung disease, kyphoscoliosis and neuromuscular weakness. Bronchodilator reversibility of at least 12 per cent and 200 mL in FEV1 separates asthma from largely irreversible COPD, whose GOLD severity runs on per cent-predicted FEV1. The flow-volume loop adds upper-airway lesions, and DLCO separates emphysema from asthma.

## What you must remember

- **Obstructive signature:** post-bronchodilator FEV1/FVC below 0.70; raised residual volume from air trapping; expiratory limb of the flow-volume loop scooped inward.
- **Restrictive signature:** TLC below 80 per cent predicted is the arbitrating number; the loop is small and tall; the ratio is normal or high because both volumes fall together.
- **Reversibility:** an FEV1 rise of 12 per cent and 200 mL or more after 200-400 micrograms of inhaled salbutamol supports asthma; a 20 per cent FEV1 fall after exercise or methacholine challenge (PC20 below 8 mg/mL) documents hyperreactivity.
- **GOLD grades of COPD by FEV1 per cent predicted:** 80 and above mild, 50-79 moderate, 30-49 severe, below 30 very severe — the ratio below 0.70 must be established first.
- **Flow-volume loop shapes:** fixed tracheal stenosis flattens both limbs; variable extrathoracic lesions (vocal cord palsy) flatten the inspiratory limb; variable intrathoracic lesions (tracheomalacia, tumour) flatten the expiratory limb.
- **DLCO:** low in emphysema, pulmonary embolism, anaemia and fibrosis; normal or high in asthma; high in alveolar haemorrhage and polycythaemia.
- **Peak-flow diaries:** diurnal variability above 20 per cent supports asthma; classically worst on returning to work in byssinosis, the cotton-dust asthma of Indian mills.

## Three reports, one algorithm

Work the first report the way the ward does. A 58-year-old smoker with FEV1 45 per cent predicted, FVC 82 per cent, ratio 0.48, residual volume 160 per cent predicted and DLCO 48 per cent has obstruction with air trapping plus a low DLCO — emphysema-predominant COPD, GOLD severe band — and absence of a bronchodilator response seals irreversibility. The second: a 34-year-old with dry cough and clubbing, FEV1 62 per cent, FVC 60 per cent, ratio 0.86 — proportionate loss, so order TLC; at 68 per cent predicted restriction is confirmed, and a low DLCO with reticulation on high-resolution CT points to interstitial lung disease. The third: stridor varying with neck position and a spirometric pattern that changes with posture — go straight to the loop, where flattening confined to inspiration declares a variable extrathoracic lesion; the loop, not the ratio, diagnoses airway lesions outside the lung.

The algorithm in one line: ratio first, absolute volumes second (residual volume for trapping, TLC for restriction), reversibility third, then DLCO and loop shape for character.

## How the exam frames it

Examiners trap candidates with a high FEV1/FVC and a low FEV1 in a restricted patient — many call it normal spirometry because the ratio looks healthy; the ratio is meaningless without volumes, and restriction is never diagnosed on spirometry alone. The second trap is quoting FEV1 per cent as severity before establishing the ratio below 0.70, which GOLD requires. Indian vivas then go physiological: why residual volume rises in obstruction (dynamic airway collapse traps air) and why the DLCO of asthma stays normal or high (larger pulmonary capillary blood volume). Naming the methacholine PC20 earns the extra mark; naming the Monday-morning chest tightness of byssinosis shows reading beyond handouts.

## Frequently asked questions

### What FEV1/FVC value defines airflow obstruction?

A post-bronchodilator ratio below 0.70 (70 per cent) defines persistent obstruction; severity is then graded by per cent-predicted FEV1, not by the ratio itself.

### What bronchodilator response supports a diagnosis of asthma?

A rise in FEV1 of at least 12 per cent and 200 mL within 15-20 minutes of an inhaled short-acting beta-2 agonist; absence at a single visit does not exclude asthma.

### Can restriction be diagnosed by spirometry alone?

No — a low FVC with a high ratio only suggests it; a TLC below 80 per cent predicted on body plethysmography or gas dilution confirms restriction.

### What does a flattened inspiratory limb of the flow-volume loop indicate?

Variable extrathoracic obstruction, classically bilateral vocal cord palsy; both limbs flatten together only in fixed central lesions such as tracheal stenosis.

### Why is DLCO normal in asthma but low in emphysema?

Asthma spares the alveolar-capillary membrane whereas emphysema destroys it; asthma may even raise DLCO through a greater pulmonary capillary blood volume.