Interpreting PFT

7/29/2019 Interpreting PFT

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Objectives

Review basic pulmonary anatomy and physiology.

Understand the reasons pulmonary function tests (PFTs)are performed.

Understand the technique and basic interpretation ofspirometry.

Know the difference between obstructive and restrictivelung disease.

Know how PFTs are clinically applied.


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What do the lungs do? Primary function is gas exchange.

Let oxygen move in.

Let carbon dioxide move out.


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How do the lungs do this? First, air has to move to the region where gas exchange

occurs.

For this, you need a normal ribcage and respiratorymuscles that work properly (among other things).


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Conducting Airways Air travels through the

conducting airwayscomprised of thefollowing: nose,larynx,

trachea, lobar bronchi,segmental bronchi,subsegmental bronchi,small bronchi,

bronchioles, and terminalbronchioles.


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How do the lungs do this? (cont) Gas exchange takes place in the acinus.

This is defined as an anatomical unit of the lung made

of structures supplied by a terminal bronchiole.


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From NetterAtlas ofHumanAnatomy


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How does gas exchange occur? Numerous capillaries are wrapped around alveoli.

Gas diffuses across this alveolar-capillary barrier.

This barrier is as thin as 0.3 m in some places and hasa surface area of 2.8 square meters at birth increased toabout 75 square meters in adult male!


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Gas Exchange

From Netter

Atlas ofHumanAnatomy


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What exactly are PFTs? The term encompasses a wide variety of objective methods

to assess lung function.

Examples include: Spirometry

Blood gases

Exercise tests

Diffusion capacity

Bronchial challenge testing

Pulse oximetry


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Why PFTs? Help in diagnosis of diseases.

May help guide management of a disease process.

Can help monitor progression of disease andeffectiveness of treatment.


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Spirometry Spirometry is a medical test that measures the

volume of air an individual inhales or exhales as a

function of time.


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Lung Volumes and Capacities 4 volumes: inspiratory

reserve volume, tidalvolume, expiratory reservevolume, and residual

volume

4 capacites: vital capacity,inspiratory capacity,functional residual

capacity, and total lungcapacity


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Lung Volumes Tidal Volume (TV): volume ofair inhaled or exhaled with eachbreath during quiet breathing

Inspiratory Reserve Volume(IRV): maximum volume of air

inhaled from the end-inspiratorytidal position

Expiratory Reserve Volume(ERV): maximum volume of airthat can be exhaled from restingend-expiratory tidal position


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Lung Volumes Residual Volume (RV):

Volume of air remaining

in lungs after maximiumexhalation.


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Lung Capacities Total Lung Capacity (TLC): Sum

of all volume compartments orvolume of air in lungs aftermaximum inspiration

Vital Capacity (VC): TLC minus

RV or maximum volume of airexhaled from maximal inspiratorylevel

Inspiratory Capacity (IC): Sum ofIRV and TV or the maximum

volume of air that can be inhaledfrom the end-expiratory tidalposition


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Lung Capacities (cont.) Functional ResidualCapacity (FRC): Sum of RV and ERV or the

volume of air in the lungs atend-expiratory tidal position.


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What information does a spirometer

yield?A spirometer can be used to measure the

following:

FVC and its derivatives (such as FEV1, FEF 25-75%) Forced inspiratory vital capacity (FIVC)

Peak expiratory flow rate

Maximum voluntary ventilation (MVV)

IC, IRV, and ERV Pre and post bronchodilator studies


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Special Considerations in Pediatric

PatientsAbility to perform spirometry dependent on

developmental age of child.

Patients need a calm, relaxed environment and goodcoaching. Patience is the key.

Even with the best of environments and coaching, achild may not be able to perform spirometry.

Results are affected also by posture and neck position.


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Normal Flow-Volume Curve

and Spirogram


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Spirometry Interpretation: Normal values vary and depend on:

Height

Gender

Ethnic origin


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Acceptable and Unacceptable

Spirograms (from ATS)


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Measurements Obtained FEV1---the volume exhaled during the first second of the

FVC maneuver

FEF 25-75%---the mean expiratory flow during the middlehalf of the FVC maneuver; reflects flow through the small(


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Spirometry Interpretation: Obstructive

vs. Restrictive Defect Obstructive Disorders

Characterized by a limitationof expiratory airflow so thatairways cannot empty asrapidly compared to normal(such as through narrowedairways from bronchospasm,inflammation, etc.)

Examples:

Asthma Emphysema

Cystic Fibrosis

Restrictive Disorders Characterized by reduced

lung volumes/decreased lungcompliance

Examples:

Interstitial Fibrosis

Scoliosis

Obesity

Lung Resection Neuromuscular diseases

Cystic Fibrosis


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Normal vs. Obstructive vs. Restrictive


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Spirometry Interpretation: Obstructive

vs. Restrictive Defect Obstructive Disorders

FVC nl or

FEV1

FEF25-75%

FEV1/FVC

TLC nl or

Restrictive Disorders

FVC

FEV1

FEF 25-75% nl to

FEV1/FVC nl to

TLC


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Spirometry Interpretation: What do the

numbers mean? FVC

Interpretation of %predicted:

80-120% Normal 70-79% Mild reduction

50%-69% Moderatereduction

80% Normal 60%-79% Mild obstruction

50-59% Moderateobstruction


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Spirometry Interpretation: What do the

numbers mean? FEF 25-75%

Interpretation of %predicted:

>79% Normal

60-79% Mildobstruction

40-59% Moderateobstruction


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Maximal Inspiratory Flow Do FVC maneuver and then inhale as rapidly and as

much as able.

This makes an inspiratory curve.

The expiratory and inspiratory flow volume curves puttogether make a flow volume loop.


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Flow-Volume Loops


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How is a flow-volume loop helpful? Helpful in evaluation of air flow limitation on inspiration

and expiration

In addition to obstructive and restrictive patterns, flow-volume loops can provide information on upper airwayobstruction: Fixed obstruction: such as in tumor, tracheal stenosis

Variable extrathoracic obstruction: flattened inspiratory loop

such as in vocal cord dysfunction Variable intrathoracic obstruction: flattening of expiratory limb;

tracheomalacia


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Spirometry Pre and Post Bronchodilator

Obtained a minimum of 15 minutes after

administration of the bronchodilator. Calculate percent change (FEV1 most commonly

used---so % change FEV 1= [(FEV1 Post-FEV1Pre)/FEV1 Pre] X 100).

Reversibility is with 12% or greater change.


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THANK YOU

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Interpreting PFT