SEPT 10 Built from the handwritten pages you uploaded on 10 September 2026.

Pulmonary function tests

Obstructive, restrictive and mixed patterns; GOLD staging; DLCO; and which volumes spirometry cannot measure.

The three patterns — the table to know cold

Parameter	Obstructive	Restrictive
FEV₁	↓↓	↓
FVC	Normal or mildly ↓	↓↓
FEV₁/FVC	↓ (<0.70) — the defining feature	Normal or ↑
TLC	↑	↓
RV	↑ (gas trapping)	↓
VC	Normal or ↓	↓
FEF 25–75%	↓ — small airways, the earliest change	Normal
DLCO	↓ in emphysema only	↓ in parenchymal disease

Why the ratio falls in obstruction

FEV₁ falls but FVC is relatively preserved, so the ratio drops.
In restriction both fall together, so the ratio is preserved or even rises.
FEV₁ is reduced in both — it is the RATIO that separates them, never FEV₁ alone.

Causes

Obstructive	Restrictive
COPD · Asthma · Bronchiectasis · Cystic fibrosis · Emphysema	Scoliosis · Obesity · Sarcoidosis · Interstitial lung disease · Ascites · Neuromuscular disease · Malignancy

Note that restrictive causes split into intrinsic (lung parenchyma — ILD, sarcoid) and extrinsic (chest wall, pleura, abdomen, neuromuscular). DLCO separates them: reduced in intrinsic disease, normal in extrinsic.

GOLD classification of COPD

Based on post-bronchodilator FEV₁. All stages require FEV₁/FVC < 0.70.

Stage	FEV₁ (% predicted)
I — Mild	≥ 80%
II — Moderate	50–80%
III — Severe	30–50%
IV — Very severe	< 30%, or < 50% with chronic respiratory failure

Clinically most often picked up in a smoker over 35 with cough, exertional breathlessness and sputum.

DLCO — transfer factor

Measures the functional integrity of the alveolar–capillary membrane, using carbon monoxide (diffusion limited, avidly bound by haemoglobin).
DLCO falls only when there is a genuine alveolar surface area or membrane defect — this is the key discriminator.
↓ DLCO: emphysema (lost surface area) · pulmonary fibrosis / ILD · pulmonary embolism · anaemia · pulmonary hypertension.
↑ DLCO: obesity · exercise · supine position · left-to-right shunt · pulmonary haemorrhage · polycythaemia · asthma.
Always correct for haemoglobin — anaemia falsely lowers it, polycythaemia falsely raises it.

What spirometry cannot measure

Any volume containing residual volume cannot be measured by spirometry — so RV, FRC and TLC are all off-limits.
Three methods measure FRC: nitrogen washout, body plethysmography, and helium dilution.
Plethysmography measures ALL gas in the thorax, including trapped gas and bullae. Helium dilution and nitrogen washout only measure gas in communicating airways — so they underestimate FRC in severe obstructive disease.

Predicting postoperative pulmonary complications

PEFR (peak expiratory flow rate) is the best single predictor — it reflects the ability to cough and clear secretions.
A PEFR of more than 200 L/min is the usual threshold for an effective cough.
Also relevant: maximum breathing capacity < 50% predicted and VO₂max < 10 ml/kg/min mark a high-risk patient.

Mechanism of hypoxaemia — a distinction worth holding

COPD: hypoxaemia is predominantly V/Q mismatch — so it responds well to supplemental oxygen.
Pneumonia, ARDS and atelectasis: hypoxaemia is predominantly shunt — so it responds poorly to increased FiO₂ and needs recruitment, PEEP or treatment of the underlying collapse.

Quick recall

FEV₁/FVC <0.70 obstruction

FEF 25–75 normal in restriction

TLC ↑ RV ↑ obstruction

DLCO needs an alveolar defect

PEFR >200 can cough

No RV on spirometry

Built from your spirometry and COPD pages.