PFT Interpretation and Reference Values
Transcript of PFT Interpretation and Reference Values
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
Flo
w
I
E
Volume
TLC
FRC RV
Tidal Breathing
Peak Flow
Time
Volume
VOLUME-TIME CURVE
RV
TLC
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
Flo
w
I
E
Volume
Flow
I
E
Volume
THE FLOW-VOLUME LOOP IN PATIENTS
WITH SMALL AIRWAY OBSTRUCTION
Pst
Palv
Palv
Pst
Flow
I
E
Volume
THE FLOW-VOLUME LOOP IN PATIENTS
WITH EMPHYSEMA & AIRWAY OBSTRUCTION
Pst
Palv
Palv
Pst
Flow
I
E
Volume
THE FLOW-VOLUME LOOP IN PATIENTS
WITH A FIXED EXTRATHORACIC OBSTRUCTION
Pst
Palv
Flow
I
E
Volume
THE FLOW-VOLUME LOOP IN PATIENTS
WITH A VARIABLE EXTRATHORACIC OBSTRUCTION
Floppy
Segment
Forced Inspiration = (-)Forced Expiration = (+)
P = 0
Pst
Palv
Flow
I
E
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
ERV
VT
IRV
FRC
VCIC
TLC
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
TLC
FRCRV
ERV
VC
Normal
Normal FRC
Normal RV
Zero Volume
Normal TLC
Slight
ModerateSevere
Very Severe
DIFFUSING CAPACITY
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 =
VCO.
PACO
VCO.
PACO
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
100
200
300
400
DLCO
DLCO/V A
Alveolar Volume (% Predicted TLC)
DLC
O (
% v
alu
e a
t n
orm
al
TL
C)
DLC
O/V
A(%
valu
e a
t n
orm
al
TL
C)
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
DLCO
PFT Interpretation
PFT Interpretation
(Pellegrino et al., 2005)
Spirometry
INTERPRETING PFTs
Is FVC normal?
>LLN
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
© 2015 Global Initiative for Chronic Obstructive Lung Disease
For obstruction FEV1/VC previously determined to be
<LLN
Classification of Severity
(Pellegrino et al., 2005)
Lung Volumes
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
Diffusing Capacity
Are DLCO or DLCO / VA decreased?
< LLN
Are DLCO or DLCO / VA increased?
> ULN
(Pellegrino et al., 2005)
Patterns
THE LUNG VOLUME PATTERNS SEEN WITH
INCREASING AIRWAY OBSTRUCTION
TLC
FRCRV
ERV
VC
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
N 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
N N
N N
N N
N
TYPICAL LUNG FUNCTION PATTERNS
AbnormalityFEV1
FVC VC TLC RV
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
(Pellegrino et al., 2005)
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
them
• 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
GLI
• 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