Pulmonary Function Testing (PFT)

what are the three indications for pulmonary function testing (PFT)

• to evaluate signs/symptoms (like hypoxemia or dyspnea)

• to assess progression of lung disease

• to monitor effectiveness of therapy

what are the three PFT options

• spirometry

• lung volumes

• diffusion capacity

_____________ can be performed in a clinic setting, but all other tests need to be performed in a pulmonary function laboratory

spirometry

what is a spirogram

is a graph that shows the volume of air a person breathes in and out over time

A

functional residual capacity

B

tidal volume (TV)

C

total lung capacity (TLC)

D

forced vital capacity (FVC)

E

residual volume (RV)

what is spirometry

can see lung function represented as volume vs time just during theforced exhalation from maximal inhalation from minimal exhalation

what is FEV₁

the volume of air that comes out in the first second

what is FRC

resting point at the end of a normal breath and represents the balance between the outward recoil of the chest wall and the inward recoil of the lung

what is FVC

the forced exhalation until the pt cannot blow out anymore air

what is RV

volume of air that is left in the chest after maximal exhalation

how to get TLC

add FCV and RV together

what is the normal range in spirometry

normal FEV₁/FVC >/= 0.7

describe a flow-volume loop

black dots demonstrate what we predict the loop to look like for the pt based on population norms

inhalation is at the bottom while exhalation is at the top

what are the two important things that can be pointed out on a flow-volume loop

• peak expiratory flow rate

• vital capacity

what is the peak expiratory flow rate on a flow-volume loop

the highest point on the expiratory curve — it's the maximum speed at which air is exhaled from the lungs after a full inhalation

what is vital capacity on a flow-volume loop

the volume of air exhaled form maximal inhalation to exhalation

any PFT value is abnormal if it is less than the (LLN) lower limit of normal (defined as the 5th percentile), corresponding to what Z-score

<-1.645

some PFT values can be abnormal if elevated (TLC, RV, DLCO) or greater than the (ULN) upper limit of normal (>95th percentile), corresponding to what Z-score

>1.645

what are the three main step sin approaching PFTs

1. check spirometry to evaluate for obstruction

2. check lung volumes to evaluate for restriction

3. check diffusing capacity

what is obstruction defined as

FEV₁/FVC < LLN

FEV₁/FVC Z-score < -1.645

pts w obstructive airflow will get less air out in the…

first one second (FEV₁) of exhalation

describe what a flow-volume loop looks like in a pt that has an obstruction

inspiratory limb looks normal

peak expiratory flow is lower (indicated lung funx is worse)

scooped out shape due to differential emptying of lung units

there is more rapid emptying of lung units w __________ (higher/lower) elastic recoil and __________ (faster/slower) emptying of more diseased lung units

higher; slower

what other clues, other than FEV₁/FVC, can give us clues of obstruction

if TLC>ULN or RV>ULN

TLC>ULN can signify

hyperinflation

RV>ULN can signify

air trapping

what is restriction defined by

TLC < LLN

TLC Z-score < -1.645

describe what a flow-volume loop look like in a pt w restriction

normal peak expiratory flow

no scooping out of the expiratory limb

dec in vital capacity

what are the two main causes of restriction

intrapulmonary and extrapulmonary

what is intrapulmonary restriction

diffuse parenchymal lung disease

what is extrapulmonary restriction

• chest wall diseases

• pleural diseases a

• abdominal distension

• neuromuscular weakness

what is hyperinflation of the lungs

when the lungs retain too much air, causing them to over-expand

what is air trapping

when air gets stuck in the lungs during exhalation due to narrowed or collapsed airways; is a big contributor to hyperinflation and makes it harder to fully breathe out

describe how a spirogram would look in a person w hyperinflation and air trapping

curve would shift right due to inc TLC

Inc RV

Scooped-out Expiratory Curve; expiratory limb of the flow-volume loop would show a concave or scooped shape, due to reduced airflow from obstructed airways

why does emphysema have a lot diffusion capacity

Emphysema has a low diffusion capacity (DLCO) because of destruction of the alveolar wall