PULMONARY FUNCTION TESTS – A REFRESHER

Khizer Hayat Khan

M Rahim Khan

York Teaching Hospital

INTRODUCTION

• Pulmonary function tests (PFTs) are non-invasive tests that show how well the lungs are working.

• The tests measure lung volume, capacity, rates of flow, and gas exchange

PURPOSE OF PFTs

• Diagnosis of symptomatic disease

• Screening of early asymptomatic disease

• Monitoring response to treatment

• Prognostication of known disease

TYPES OF PFTs

STANDARD PFTs

Spirometry

Lung volumes

Gas transfer

SPECIALIZED PFTs

Exercise oximetry

6 minute walk test

Peak flow

CATEGORIES OF LUNG DISEASES

• PFTs help classify disease in following categories:

• OBSTRUCITVE | This is when air has trouble flowing out of the lungs due to airway resistance. This causes a decreased flow of air

• RESTRICTIVE | This is when the lung tissue and/or chest muscles can’t expand enough

• PULMONARY VASCULAR DISEASES |

SPIROMETRY

VALIDITY OF PFTs

• Evaluate acceptability & reproducibility

• Acceptability• Good effort – a rapid increase in airflow at the start of exhalation

• Complete maneuver – at least 6s of exhalation ending up in plateau in flow

• Reproducibility• All 3 FEV1 within 200ml of each other

• All 3 FVC within 200ml of each other

LUNG VOLUMES

LUNG VOLUMES

VOLUME AGAINST TIME

FLOW VOLUME LOOP

SPIROMETRY PATTERNS

• Normal

• Obstructive

• Restrictive

• Mixed

• Fixed upper airway obstruction

• Variable intra thoracic upper airway obstruction

• Variable extra thoracic upper airway obstruction

OBSTRUCTIVE SPIROMETRY

• FEV1:FVC ratio <70%

• FEV1 falls disproportionately greater than FVC

• Conditions such as Asthma, COPD, Bronchiectasis and CF.

RESTRICTIVE SPIROMETRY

• FEV1:FVC ratio >80%

• Reduction of FEV1 and FVC

• Conditions such as ILD, pleural disease, NMD, Diaphragm dysfunction, kyphoscoliosis, obesity and pregnancy

MIXED OBSTRUCTIVE/RESTRICTIVE

• FEV1:FVC ratio<70%

• Reduction in FVC

FIXED UPPER AIRWAY OBSTRUCTION

• Flow volume loop: flattening in both inspiration and expiration

• Maximal flow rates limited

• Causes: tracheal/bronchial stenosis, goitre, upper airway tumours

VARIABLE EXTRA THORACIC OBSTRUCTION

• Acceleration of air into the lung reduces intraluminal pressures causing collapse at the site of extra thoracic obstruction.

• Flattened inspiratory flow curve

• Normal expiratory flow curve

• Causes: vocal cord paralysis, airway burns, glottic strictures

VARIABLE INTRATHORACIC OBSTRUCTION

• Decreased intrathoracic pressure splints open the airway lumen at the site of intrathoracic obstruction

• Normal inspiratory flow curve

• Flattened expiratory flow curve

• Causes: tracheomalacia, polychondritis, low tracheal/bronchial tumours.

DIFFUSION CAPACITY OF CO

• (DLCO) is also known as the transfer factor for carbon monoxide or TLCO

• It is a measure of the conductance of gas transfer from inspired gas to the red blood cells.

DLCO

Conditions and physiologic states that alter DLCO

INCREASED DLCO

• Exercise

• Asthma

• Polycythaemia

• Pulmonary haemorrhage

DECREASED DLCO

• Emphysema

• ILD

• Anaemia

Assess FEV1/FVC Assess FVCNormal/High

Assess FVCLow

Normal lung mechanics

Assess TLC

Assess DLC

Pulmonary vascular disease

Normal PFTs

Variety of explanations

Restriction

Assess DLCO

Probable ILDCWD/NMD/

Obesity

Assess TLC

ObstructionMixed

No

rmal/H

igh

Assess DLCO

EmphysemaChronic

Bronchitis/Asthma

PRACTICAL SCENARIOS

KEYPOINTS

Pattern recognition

The major limitation of PFTs is how they are interpreted

PFTs not standalone test

Requires organized approach

Identify and quantitate the abnormality

NORMAL

“Triangle over a semicircle”

FEV/FVC = 3.38/4.68 = 0.72 or 72%

FEV1 3.38

FVC 4.68

TLCO = KCO x VA

Don’t mix up TLC & TLCO!

TLC – Total Lung Capacity

TLCO – Transfer capacity of the Lung for Carbon monoOxide(may also be referred to as DLCO – Diffusion Capacity of the Lung for Carbon monOxide)

CASE 1

…53 year old gentleman with history

of asthma, complaining of dyspnea,

wheeze and cough. He had some relief

with inhaled therapy but remains

symptomatic. He is an ex-smoker of 22

pack year. I am concerned whether he

has developed COPD over the years

that he was smoking…

FEV1/FVC <70% OR <LLN?

GOLD - <70%ATS - <LLN

BRONCHODILATOR REVERSIBILITY

≥200ml & ≥12% 𝚫 in either FEV1 or FVC

𝚫 350ml𝚫 530ml

SEVERITY OF AIRFLOW OBSTRUCTION

Mild | FEV1 >=80%

Moderate | 80%< FEV1 >=50%

Severe | 50%< FEV1 >=30%

Very severe | FEV1 <30%

…..only if FEV1/FVC is obstructive

80-120% | Normal<80% | Restriction>120% | Hyperinflation

80-120% | Normal>120% | Air trapping

Airwary inflammation

Airway obstruction

Moderate severity

Positive bronchodilator response

Hyperinflation

Gas trapping

Slightly increased gas transfer

ASTHMA

CASE 2

…48 year old lady with COPD.

Current smoker of 30 cigarettes

a day. Remains short of breath

despite optimum treatment for

her COPD…

𝚫 0.05ml

𝚫 0.07ml

Severe airways obstruction

No reversibility

Hyperinflation

Gas trapping

Reduced transfer factor

EMPHYSEMA

CASE 3

...65 year old lady with

exertional shortness of breath

for 6 months. No other

respiratory symptoms. Hx of SLE

and recurrent UTIs. She is on

Prednisolone, Methotrexate and

Nitrofurantoin. She smoked 20

cigarettes a day for 31 years and

quit 18 years ago...

SEVERITY OF RESTRICTION

Restriction is graded by the decrement in FVC or TLC

% OF PREDICTED

Mild 80-65%

Moderate 65-50%

Severe <50%

RV

RV

TLC

FVC

FVC

Restriction - Pulmonary or Extrapulmonary?

• Extrapulmonary causes of restriction

• Large pleural effusion/pleural thickening

• Neuromuscular disease

• Chest wall deformity

• Obesity

Restrictive lung disease

Moderate severity

Reduced gas transfer

ILD

CASE 4

… 60 year old lady symptomatic

with progressive shortness of

breath on exertion for several

months. No other respiratory

symptoms of note. She never

smoked and has no past medical

history of note. Her only

medications is hormone

replacement therapy…

SPIROMETRY GAS TRANSFER DIAGNOSIS

Obstructive

Reduced Emphysema

Normal Chronic bronchitis

Normal / Increased Asthma

RestrictiveReduced Intrinsic lung disease

Normal Extrapulmonary restriction

Normal ReducedAnaemiaPulmonary vascular disease

Restrictive/Normal Increased Pulmonary haemorrhage

Normal spirometry

Normal lung volumes

Reduced gas transfer

Pulmonary vascular disease

CASE 5

... 25 year old gentleman with

mild asthma well controlled

with PRN Salbutamol. Has been

symptomatic with dyspnea and

wheeze for a year. 2 years ago

he was involved in a road

traffic accident and was

intubated and ventilated. He

had a tracheostomy that was

removed 2 months after his

discharge from the hospital...

Don’t just look at the numerical values

EMPEY’S INDEXFEV1 (ml) / PEF (L/min)>10 suggests upper airway obstructionThe higher the ratio, the greater the obstruction

REFERENCES / USEFUL RESOURCES

• ERS Handbook of Respiratory Medicine 2nd edition

• Oxford Handbook of Respiratory Medicine, 3rd edition

• www.depts.washington.edu/uwmedres/Library/eLearning/Pulmonary

• Interpretting PFTs, Clevelenad Journal of Medicine

• Ruppel’s Mannual Of Pulmonary Function Testing, 11th edition

• UpToDate.com – Interpretting pulmonary function testing