Lung Function Tests
Normal and abnormal
Prof. J. Hanacek, MD, PhD
Introduction
Pulmonary function tests are valuable investigations in the
management of patients with suspected or previously
diagnosed respiratory disease. They aid diagnosis, help
monitor response to treatment and can guide decisions
regarding further treatment and intervention. The
interpretation of pulmonary functions tests requires
knowledge of respiratory physiology.
Normal or predicted ranges of values are obtained from
large population studies of healthy subjects. Values are
taken for people matched for age, height, sex and where
appropriate ethnicity.
PFTS should be performed three times to ensure that the
results are reproducible (less than 200ml variation) and
accurate.
Dynamic studies are performed first (spirometry, flow
volume curves, peak expiratory flow rates), followed by lung
volumes, bronchodilator testing and finally diffusion capacity.
Spirometry is the most frequently used measure of lung function and is a
measure of volume against time. It is a simple and quick procedure to
perform: patients are asked to take a maximal inspiration and then to
forcefully expel air for as long and as quickly as possible (a forced vital
capacity manoeuvre).
normal spirometry
obstructive lung disease restrictive lung disease
Parameters of spirographic curve
Common Terminology of Spirometry Tests Critical
in Diagnosing COPD
VC-Vital Capacity - The amount of air that can be forcibly exhaled
from your lung after a full inhalation.
FVC-Forced Vital Capacity - The amount of air which can be exhaled
from the lungs by maximal effort after taking the
deepest breath possible.
FEV1-Forced Expiratory Volume in One Second - The amount of air
which can be forcibly exhaled from the lungs in the
first second of a forced exhalation.
FEV1/FVC = FEV1-Percent (FEV1%) - The ratio of FEV1 to FVC and
tells the clinician what percentage of the total
amount of air is exhaled from the lungs during the
first second of forced exhalation.
PEFR- Peak Expiratory Flow Rate- Measures if treatment is
effective in improving airway diseases such as COPD.
FEF-Forced Expiratory Flow - A measure of how much air can be
exhaled from the lungs. It is an indicator of large airway
obstruction.
MVV-Maximal Voluntary Ventilation - A value determined by having
the patient inhale and exhale as rapidly and fully as
possible in 12 seconds. The results reflect the status of
the muscles used for breathing, how stiff the lungs are
and if there is any resistance in the airways when
breathing. This test tells surgeons how strong a patient's
lungs are prior to surgery. If patients demonstrate poor
performance on this test, it suggests to the doctor that
respiratory complications may occur after surgery.
Lung volume changes under physiological and pathological
conditions
GOLD Spirometric Criteria for COPD Severity
I. Mild COPD: FEV1/FVC < 0.7
FEV1 >/= 80% predicted
The patient is probably unaware that lung function is starting to decline
II. Moderate COPD: FEV1/FVC < 0.7
50% </= FEV1 < 80% predicted
Symptoms during this stage progress, with shortness of breath developing
upon exertion
III. Severe COPD: FEV1/FVC < 0.7
30% </= FEV1 < 50% predicted
Shortness of breath becomes worse at this stage and COPD exacerbations
are common
IV. Very Severe COPD: FEV1/FVC < 0.7
FEV1 < 30% predicted or FEV1< 50% predicted with
chronic respiratory failure
Quality of life at this stage is gravely impaired. COPD exacerbations
can be life threatening
Flow volume curves
are produced when a patient performs a maximal
inspiratory manoeuvre which is then followed by a maximal expiratory effort.
A graph is produced with a positive expiratory limb and a negative
inspiratory limb The maximal flow rate during expiration can also be
measured (peak expiratory flow rate PEFR). Furthermore the maximal flow
rates between 25%-75% of the vital capacity (FEF25-75%) can also be
measured and these provide important information regarding small airway
function.
Physiological
Obstructive
Restrictive