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How to report lung function tests

Clinical pulmonary physiology

Lung function testing

• A brief history

• Why measure?

• What can you measure?

• Interpretation/ reporting

• Examples and case histories

• Exercise tests

• SCE questions

A brief history of spirometry

• 129-200 AD Galen got a boy to

blow into a bladder

• 1714 James Jurin measured tidal

volume and vital capacity

• 1840 John Hutchinson measured

vital capacity in 4000 people

• 1947 Robert Tiffineau described

FEV1 and FEV1/FVC ratio

• 1950s-1980s Modern clinical

respiratory physiology era

Respiratory physiology hall of fame

What are lung function tests for?

Diagnosis

Disease monitoring

Assessment for therapy

Therapeutic response

Assessment of disability/impairment

What is available?

CORE

• Airway function

– Spirometry

– Peak flow

– f/v loop

– Raw/SGaw

• Lung volumes

– He dilution

– Plethysmography

– Radiology

• Gas exchange

– TLCO/KCO

– ABGs

– SpO2

EXTENDED

• Respiratory muscle tests

– Pi&Pe Max

– Sniff

– Supine VC

• Bronchial challenge testing

• Sleep

– SpO2

– Polysomnography

• Exercise testing

– EIA

– Metabolic gas exchange

Interpretation of Lung function tests

OPINION

Physical descriptione.g. volumes

Airway functionFEV1 etc

Gas exchangeTLCO & ABGs

Reference values

Range

% predicted

Standardised residual (1.64 SD)

ATS/ERS algorithm for lung function diagnosis

ERS/ATS Interpretation strategies

Two tasks

1. “The classification of derived values with respect to a

reference population and assessment of the reliability of the

data”

(laboratory task)

2. “The integration of the obtained values into the diagnosis,

therapy and prognosis for an individual”

(physicians task)

ATS/ERS task force:standardisation of lung function testing No 1ERJ 2005: 26:153-161

The report structure

Technical

Simple pattern description

Relevant variations – Reference values

Explain anomalies– Poor effort– Best loop– Mouthpiece leaks– Coughing etc

Quality control– VCs equal– VA < TLC

Suggestions for further investigation

Clinician’s

Answer the question

Values in context

Confirm diagnosis

Suggest differential diagnosis

Further investigation

Advice on further management

Reference Equations

• Obtained from healthy subjects

• Gender, age and height

• Make your own

• Use reference equations for local population

• Use ECCS or ATS

• Ethnic correction

• GLI (Global, multi ethnic, all ages)

Lung function: categories of interpretation

Obstructive

– FEV1/VC

– Loop

– Raw

– TLC

– RV/TLC

– Gas trapping (TLC-VA)

Restrictive

– FEV1/VC

– TLC, RV

– TLCO (KCO)

Constrictive

– TLC (n RV)

– KCO

COPD, asthma, emphysema

“Big lungs”

ILD, sarcoid etc

“Small lungs”

Muscle weakness, obesity, scoliosis

“Squashed lungs”

Common requests

SOB ? Cause (COPD, ILD)

Is it asthma or COPD?

Upper airway obstruction?

Fit for surgery?

Disease progression?

Confirm diagnosis

What is the prognosis?

Is it asthma or COPD?

• Young patient• <20 pack year smoking history• Airway obstruction• PFTS may be normal!• Good bronchodilator response (normal or

600ml)

• May need to suggest – Explore the history further– Peak flow monitoring– PC20 etc– FeNO/ Sputum eosinophils

Is it upper airway obstruction?

Low FEV1/ FVC % ( not helpful )

Shape of spirogram (slow rise)

Appearance of flow volume loop

Airways resistance (Raw or SGaw)

Empey Index (FEV1 ml/PFR L/Min) >8

You can’t always tell!

Upper airway obstruction

Fit for surgery?Beware!

The anaesthetist knows best

Describe the situation

Point out the unusual (UAO etc)

Suggest how treatment can be improved

Some operations have less effect on lung function than others

– Eyes and prostate ok

– Abdominal and thoracic surgery worse

– Prediction pathways (SWT, V/Q etc)

Some surgery can improve lung function

– Decortication

– Bullectomy

– LVRS

– Transplantation

Prevalence of COPD is

overestimated > 50years

Bronchodilator response

• Various definitions

• 12% change in FEV1

• >200ml FEV

• >8% predicted FEV1

Miscellaneous reporting pitfalls

Look at the loop! (minor abnormalities,site & nature of AO)

Bronchodilator response in all? (not just FEV1)

What sort of TLC? BOX> He Dilution> VA

TLCO ( remember the haemoglobin etc)

Reference values (the normal abnormal)

Ethnic origin (10%)

Case 1

SOBE?

Case 1 Report

Context

Older lady, ex smoker, BMI 33

Airways

Unobstructed, restrictive pattern, lower range of normal.

Loop unhelpful

Lung Volumes

TLC 57% predicted, RV <50% predicted

Gas transfer

Low TLCO, relatively preserved KCO

Diagnosis and advice?

Case 1 Report

• Lung function test compatible with a severe restrictive

disorder. Low RV suggests intrinsic lung disease e.g IPF.

• Arterial blood gases would be helpful

• Suggest repeat PFTs after further investigation to monitor

progress or treatment response (VC 68%)

Case 2

Previous abnormal CXRProgress?

Case Report 2

Context

Age 33, BMI 23, Ex smoker, Previous lung function tests.

Airways

Previous tests shown mild airflow obstruction. Current test shows a restrictive pattern with recent fall in values. Still mild airflow obstruction on loop.

Lung Volumes

Sudden fall, TLC 60% predicted, RV <50% predicted

Gas transfer

Low TLCO, preserved KCO.

Diagnosis and advice?

Case Report 2

Previous PFTs show a mild mixed picture (AO + low RV)

No features of upper airway obstruction

Significant development of more severe restrictive pattern

Mixed picture compatible with ILD and smoking history or

sarcoidosis

Suggest repeat tests after treatment with corticosteroids

(two months)

Case 3

Progressive dyspnoea

Case Report 3

Context

Age 22 BMI 24, never smoked, lung function tests two years previously

Airways

Previous restrictive pattern worsened over time. FEV1 now 38% pred.

Lung Volumes

Low TLC (39%Pred), RV/TLC ratio 32%

Gas transfer

Low TLCO, High KCO.

Diagnosis and advice?

Case Report 3

• Severe restrictive pattern with progressive deterioration

• Preservation of RV/TLV ratio and KCO suggests external

restriction (constrictive pattern)

• Causes might include muscle weakness, scoliosis etc

• FEV1< 40% predicted indicates that ventilatory failure may

be imminent

• Suggest muscle studies, ABGs and sleep study as

appropriate

Why is the TLCO low?

Nocturnal hypoventilation

Case 4

Suitable for surgery?

Case Report 4

ContextAge 69, BMI 21, Previous lung function tests.

AirwaysSevere airflow obstruction, FEV1 23% predictedPressure dependent airway collapse on loopNo bronchodilator response performed

Lung VolumesGross hyperinflation on plethysmographyRV/TLC ratio 69%TLC-VA > 500ml (3L gas trapping)

Gas transferTLCO 25% predicted, low KCO, ABGs?

Diagnosis and advice?

Case Report 4

• Severe airflow obstruction with features of emphysema (loop and KCO)

• Gross hyperinflation and gas trapping

• Progressive deterioration

• Potentially suitable for LVRS (hyperinflation, FEV1, KCO>20% predicted)

• Other helpful investigations would include ABGs, SWT and imaging

Exercise is good for you

The uses of cardiopulmonary exercise testing (performance testing, diagnostic, laboratory and field)

• The differential diagnosis of breathlessness

• The objective assessment of impairment/disability

• Guide to prognosis

• The assessment of therapeutic intervention (drugs/rehab/LVRS)

• Preoperative assessment

• Training prescription

Spirometry and exercise performance

The context of exercise assessment in lung disease

Scientific exploration

Functional performance measures

Physical (domestic) activity

Methods Laboratory

(CPET)

Laboratory

(endurance)

ADL Questionnaires

Field testing (6MWD, ISWT,ESWT)

Physical activity monitors

Questionnaires (MRC, PFSS)

Methods of objective exercise testing in clinical

practice

Laboratory (Various platforms)

• Symptom-limited incremental test

• Constant workload (power) test

Field (walking)Tests

• Six minute walk

• Incremental shuttle walk test

• Endurance shuttle walk tests

Laboratory based exercise tests (CPET)

Gold standard

Precise physiological data

Expensive

Incremental exercise response in health

VO2

Time/workload

VO2maximal

“Metabolic threshold”

t

VE

HR/CO

VT

%VO2maxsustainable

CPET for diagnosis for diagnosis of unexplained

breathlessness

– Heart or lungs?

– Lack of fitness ?

– Dysfunctional breathing?

– Obesity?

– Normal but uncompetitive

Interpretation of the Symptom Limited Maximal

Incremental Exercise Test

• Has the subject made a good effort ?

• Have they achieved normal values ?

• Why did they stop ?

• How did they get there? (physiological response)

Has the subject made a good effort?

• Plateau of VO2 Max

• Patient exhaustion

• HR or VE close to predicted maximum

• Blood lactate > 4 mmol/L

• Respiratory Exchange Ratio >1.2

Reference values for exercise tests (VO2)

• E.g. Jones N.L. Am Rev Respir Dis 1985 131,700-8

• Age and Gender (ht and wt)

• Mostly USA

• Nearly all on cycle

• Small numbers (50)

• Mixed active and sedentary

See Cooper for combined equations

Why did they stop?

Identification of a ventilatory or cardiac limit to exercise

Ventilatory

• VE max > 80% VE max predicted (MVV)

• Ventilatory reserve (VE max pred- VE max) < 11 L/min

• VT > 50-70% of VC

• Breathing frequency > 50 min

• PaCO2 rise

Cardiovascular

• Chest pain

• High heart rate (220-age)

• Low Oxygen pulse

• Low AT

Interpretation

• Algorithmic (Wasserman)– Determined by VO2 peak and AT

– Can be computerised

• Analytical– Examination of data

– Pattern recognition

– Fixed point comparison (VO2 1.0 L/min, VE 30 L/min)

VO2 PEAK AT VD/VT SaO2 O2 pulse

VO2/HR

VE/VO2 HRR

Cardiac

Disease (may

be limited by

chest pain)

Low Low Normal Normal Low High Nil

Pulmonary

vascular

disease

Low Low High Low Low High Nil

Airway

Obstruction

Low High or

absent

High Normal Normal High High

Interstitial

Lung Disease

Low High or

absent

High Low Normal High

(High Bf

and low

VT)

High

Chest Wall

Restriction

Low High or

absent

Normal Normal/low Normal Normal

(High Bf

and low VT

High

Poor effort Low High or

Absent

Normal Normal (or

high)

Normal Normal High

Patterns of exercise abnormality

SCE Questions

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