PFT Interpretation and Reference Values

transcript

PFT Interpretation and

Reference Values

September 21, 2018

Eric Wong

Objectives

• Understand the components of PFT

• Interpretation of PFT

• Clinical Patterns

• How to choose Reference Values

3 Components

• Spirometry

• Lung Volumes

• Diffusing Capacity

• Flow

• Capacity

• Gas Exchange

Distribution of TLC by

population:

PFT Interpretation

(Pellegrino et al., 2005)

Spirometry

FLOW-VOLUME LOOP

Volume

FRC RV

Tidal Breathing

Peak Flow

Volume

VOLUME-TIME CURVE

0 1 2 3 4 5

Forced Expired Flow

Definitions:

• PEF – Peak expiratory flow

• FVC – forced vital capacity

• FEV1 – Forced expiratory volume in 1 sec

• FEF25-75% - Mean forced expiratory flow between 25%

and 75% of FVC

• FEF75% - Forced expiratory flow at 75% FVC

Volume

THE FLOW-VOLUME LOOP IN PATIENTS

WITH SMALL AIRWAY OBSTRUCTION

Volume

WITH EMPHYSEMA & AIRWAY OBSTRUCTION

Volume

WITH A FIXED EXTRATHORACIC OBSTRUCTION

Volume

WITH A VARIABLE EXTRATHORACIC OBSTRUCTION

Floppy

Segment

Forced Inspiration = (-)Forced Expiration = (+)

Volume

AIRWAY REVERSIBILITY

Criteria for Reversibility:

> 12% and 200ml change in

FEV1 or FVC

Pre test Medication?

• If test is to determine reversibility – No short-acting beta agonist within

4hrs, no long-acting within 12hr prior

• If test is to determine whether patient’s lung function is improving w/

therapy, then patient can continue use of medication prior

LUNG VOLUMES

MEASURING LUNG VOLUMES

Gas dilution:

1. Nitrogen washout

2. Helium dilution

Body plethysmographyRV

Trapped AirVentilated Lung

Dilution methods measure only the ventilated lung

volume, but the Body box method measures all gas in

the lungs (trapped air + ventilated lung)

C1V1 = C2V2

THE LUNG VOLUME PATTERNS SEEN WITH

INCREASING AIRWAY OBSTRUCTION

Normal

Normal FRC

Normal RV

Zero Volume

Normal TLC

Slight

ModerateSevere

Very Severe

DIFFUSING CAPACITY

Carbon monoxide is used to measure diffusing capacity

because CO is usually not present in the blood and CO

is diffusion-limited.

DLCO =VCO.

PACO - PcCO

PcCO is usually 0, therefore: DLCO =

PcCOThe units are: ml/min VCO for

each mm Hg difference between

PACO and PcCO.

Diffusing capacity is dependent on:

DLCO ≈ (VA)(Pulmonary Cap Blood Volume)([Hb])

(Alveolar-capillary membrane thickness)([COHb])

DLCO/VA seems to be a way to eliminate the effects of VA but

this is not a perfect correction.

DLCO/VA overcorrects

when VA is low

EFFECTS OF LUNG VOLUME ON DLCO and DLCO/VA

0 25 50 75 100 125 1500

DLCO/V A

Alveolar Volume (% Predicted TLC)

PFT – Diffusion Capacity

• Pure airway disease – asthma, chronic

bronchitis – normal

• Restrictive Disease with normal lung

parenchyma and pulmonary vasculature

– Neuromuscular disease, obesity

– Low DLCO

– DLCO / VA – normal to high

PFT – Diffusion Capacity

• Low – DLCO

– Alveolar disease – emphysema, alveolitis, pulm edema

– Thickened Interstitium – Pulm fibrosis

– Pulmonary vascular disease – Pulm hypertension

– Anemia

– High carboxyhemoglobin – just after smoking, CO poisoning

– Low cardiac output – cardiogenic shock

PFT Interpretation

Spirometry

INTERPRETING PFTs

Is FVC normal?

Is there evidence for airway obstruction?

FEV1/VC < LLN

- more sensitive than FEV1/FVC to detect obstruction

- FVC more dependent on flow

- take largest of VC, FVC, Slow VC, Insp VC

Is there any change after bronchodilator?

FEV1 or FVC >12% and 200 ml

(Adapted from Pellegrino et al., 2005)

Spirometry

Global Strategy for Diagnosis, Management and Prevention of COPD

Classification of Severity of Airflow Limitation in COPD*

In patients with FEV1/FVC < 0.70:

GOLD 1: Mild FEV1 > 80% predicted

GOLD 2: Moderate 50% < FEV1 < 80% predicted

GOLD 3: Severe 30% < FEV1 < 50% predicted

GOLD 4: Very Severe FEV1 < 30% predicted

*Based on Post-Bronchodilator FEV1

For obstruction FEV1/VC previously determined to be

Classification of Severity

Lung Volumes

Is there evidence for a restrictive defect?

TLC < LLN

Are the lungs hyperinflated?

TLC > ULN

Is there a high RV or FRC?

RV or FRC > ULN

Is there evidence for air trapping?

RV / TLC > ULN

Diffusing Capacity

Are DLCO or DLCO / VA decreased?

Are DLCO or DLCO / VA increased?

Patterns

THE LUNG VOLUME PATTERNS SEEN WITH

INCREASING AIRWAY OBSTRUCTION

Normal

Normal FRC

Normal RV

Zero Volume

Normal TLC

Slight

ModerateSevere

Very Severe

LUNG VOLUME PATTERNS SEEN IN PATIENTS

WITH AIRWAY OBSTRUCTION

Degree of

Obstruction TLC VC FRC RV/TLC RV

N N N N N

Slight

Moderate

Severe

Very Severe

LUNG VOLUME PATTERNS SEEN IN PATIENTS

WITH RESTRICTIVE DISEASE

Causes of

Restriction TLC VC FRC RV/TLC RV

Obesity

Chest wall mechanics

Parenchyma

Pleural space disease

Weak chest muscles

N N N N

TYPICAL LUNG FUNCTION PATTERNS

AbnormalityFEV1

FVC VC TLC RV

TLC FRC DLCO

Asthma N N N

Emphysema N

Chronic Bronchitis N N

Chest wall or Obesity N N N N N N

Pulmonary Fibrosis N N N

Muscle Weakness N N N

PFT Interpretation

PFT Interpretation Algorithm

• Legend

– PV – pulmonary vascular

– CW – chest wall

– NM – neuromuscular

– ILD – interstitial lung diseases

– CB – chronic bronchitis

Reference Values

Ideal Reference Values

• Find healthy people and do PFT on

• Based on the results, develop equations

• Test equations on other normal and

patients with diseases

Realistic Approach

• Find reference set best fit to your

population

• Adopt their standard deviation if your

population has similar distribution

• Use one equation if possible to fit full

age range

Global Lung Function Initiative

• From European Respiratory Societ

• Clinical Research Group

• Submission of lung function results from

> 70 groups

• 2012 – Spirometry reference set

• 2017 – DLCO reference set

• ? – Lung Volumes reference set

Reference Sets

Canadian Thoracic Society

• Spirometry

– GLI

– NHANES

– Gutierrez / Peds

• Lung volumes & DLCO

– GLI

– Gutierrez / Peds

Summary

ATS approach to PFT interpretation

Poor quality test can lead to misdiagnosis

Reference Values – awaiting GLI

PFT Interpretation and Reference Values

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