1 ‫محاضرة رقم‬
Spirometry
Definition:
Spirometry (meaning the measuring of breath) is the most common
pulmonary function tests, measuring lung function, specifically the
measurement of the amount (volume) and/or speed (flow) of air that can be
inhaled and exhaled. Spirometry is an important tool used for generating
pneumotachographs which are helpful in assessing conditions such as
asthma, pulmonary fibrosis, and chronic obstructive pulmonary disease
(COPD). The spirometry test is performed using a device called a
spirometer, which comes in several different varieties.
Types of spirometer
A. volume-displacement spirometers
Conventional spirometers provide a direct measure of respired volume
from the:
1. Displacement of a bell (water sealed)
2. Piston (rolling seal)
3. Bellows (wedge bellows)
Generally, volume spirometers are simple to use, accurate, reliable, and
easy to maintain and provide a clear and permanent record of the test. They
are, however, less portable than flow spirometers
B. flow-sensing spirometers
Flow spirometers generally utilize a sensor that measures flow as the
primary signal and calculate volumes by electronic (analog) or numerical
(digital) integration of the flow signal.
The most commonly use flow sensors detect and measure flow from the
pressure drop a cross a resistance (e.g. Fleisch-pneumotach), cooling of a
heated wire (Hot-wire anemometer), or by electronically counting the
rotation of a turbine blade (e.g. spirolab I, II, III).
They are usually portable and automatically calculate a large range
of ventilatory indices, assess the acceptability of each blow, store patient
results, calculate reference values for the patient being tested and provide a
print-out of the results including the spirogram and flow- volume loop.
Water seal spirometer.
Digital-anemometer spirometer.
Spirolab III spirometer.
Wedge bellow spirometer.
Spirometric indices
There are many indices, which are usually measured during spirometry but
the most commonly measured and used indices are:
1. Forced Vital Capacity (FVC)
Forced Vital Capacity is the volume of air that can forcibly be blown out
after full inspiration, measured in liters. Forced Vital Capacity is the most
basic maneuver in spirometry tests.
2. Forced Expiratory Volume in 1st second (FEV1)
Forced Expiratory Volume in 1st second is the volume of air that can
forcibly be blown out in the first second after full inspiration, measured in
liters. Average values for FEV1 in healthy people depend mainly on sex
and age, Values of between 80% and 120% of the average value are
considered normal. Predicted normal values for FEV1 depend on age, sex,
height, weight and ethnicity.
3. Forced Expiratory Volume in 1st second / Forced Vital Capacity
ratio (FEV1%)
Forced Expiratory Volume in 1st second ratio (FEV1%) is the ratio of FEV1
to FVC. In healthy adults this should be approximately 75–80%. In
obstructive diseases (asthma, COPD, chronic bronchitis, emphysema) FEV1
is diminished because of increased airway resistance to expiratory flow; the
FVC may be decreased as well, due to the premature closure of airway in
expiration, just not in the same proportion as FEV1 (for instance, both FEV1
and FVC are reduced, but the former is more affected because of the
increased airway resistance). This generates a reduced value (<80%, often
~45%). In restrictive diseases (such as pulmonary fibrosis) the FEV 1 and
FVC are both reduced proportionally and the value may be normal or even
increased as a result of decreased lung compliance.
Uses of spirometers
Spirometers are designed for use in all types of lung disease and it is a
reliable method of differentiating between obstructive airways disorders
(e.g. COPD, asthma) and restrictive diseases (where the size of the lungs is
reduced, e.g. fibrotic lung disease).
Clinical significance of spirometric indices:
Indices of obstructive disorder:
• FEV1 reduced (<80% predicted normal)
• FVC is usually reduced but to a lesser extent
than FEV1
• FEV1/FVC ratio reduced (<0.70)
Indices of restrictive disorder:
• FEV1 reduced (<80% predicted normal)
• FVC reduced (<80% predicted normal)
• FEV1/FVC ratio normal (> 0.70)
Limitation of the test:
The maneuver is highly dependent on patient cooperation and effort, and is
normally repeated at least three times to ensure reproducibility. Since
results are dependent on patient cooperation, FVC can only be
underestimated, never overestimated.
Peak expiratory flow rate
The peak expiratory flow (PEF), also called peak expiratory flow rate
(PEFR) is a person's maximum speed of expiration, as measured with a
peak flow meter, a small, hand-held device used to monitor a person's
ability to breathe out air. It measures the airflow through the bronchi and
thus the degree of obstruction in the airways.
Due to the wide range of normal values and high degree of variability, peak
flow is not the recommended test to identify airways obstruction. A small
proportion of people with asthma may benefit from regular peak flow
monitoring. When peak flow is being monitored regularly, the results may
be recorded on peak flow chart.
peak flow meter.