Spirometry principles - Grace

Spirometry
Antoni Torres MD
Grace Meeting
Stockholm 2007

• Asessment of vital capacity and airflow are
based on the forced expiratory volume
manever in wich the subject inhales
maximally to TLC, then exhales forcefully
and completely to RV

• To obtain a satisfactory spirogram, the
preceding inspiration must be maximal, and
the forced expiratory volume maneuver
must be continued to cessation of flow or,
when emptying is slowed, for at least 6 to
10 seconds

How to perform it?
FVC:
Minimum of 3 acceptable blows
A rapid start is essential: this is defined as a back-extrapolated
volume of 15 seconds; or stopped for
clinical reasons
Spirometer temperature between 17 and 40 degrees Celsius;
measure spirometer temperature to one degree Celsius
Use of nose clip is encouraged
Sitting or standing
Reproducibility: the highest and second highest FVC should agree
to within 0.2L
Largest VC or FVC is recorded

How to perform it?
• FEV1 :
• As for FVC
• Take largest FEV1 even if not from the same curve as the
best FVC
• "Zero time" determined by back-extrapolation -
extrapolated volume should be

Patient-Related Problems
The most common patient-related problems when
performing the FVC manoeuvre are:
Submaximal effort
Leaks between the lips and mouthpiece
Incomplete inspiration or expiration (prior to or during the
forced manoeuvre)
Hesitation at the start of the expiration
Cough (particularly within the first second of expiration)
Glottic closure
Obstruction of the mouthpiece by the tongue
Vocalisation during the forced manoeuvre
Poor posture.

Instrument-Related Problems
These depend largely on the type of spirometer being
used. On volume-displacement spirometers look for
leaks in the hose connections; on flow-sensing
spirometers look for rips and tears in the flowhead
connector tube; on electronic spirometers be particularly
careful about calibration, accuracy and linearity.
Standards recommend checking the calibration at least
daily and a simple self-test of the spirometer is an
additional, useful daily check that the instrument is
functioning correctly.

Resultant Information
• 1-The traditional spirogram plots volume versus
time, with the flow rate indicated by the steepness
of the plot
• 2-The flow-volume display, the flow rate is
measured and plotted on the vertical axis, with
volume in the horizontal axis. Time is not shown
on this plot but may be indicated by tick marcks

Basic Measurements
• Forced vital capacity (FVC)
• FEV1: The forced expiratory volume in one
second
• Ratio FEV1/FVC

Other measurements
• FEF 25-75: Is the averaged forced expiratory flow
rate between 25-75% of the exhaled volume
• FEV 0.5: Adds little diagnostic information
• Peak flow rate: cannot be easily calculated
• MVV: Maximal voluntary ventilation can be
measured on some office spirometers but this test
is primary a laboratory measurement

Prediction equations and limits of
normality
• Numerous prediction equations have been
derived from spirometric surveys of normal
populations (exclude all smokers and
cardiothoracic illness)
• Spirometric parameters can be predicted on
the basis of gender, age and heigth
• They use the lower limit of normal (LLN)

Different Patterns: obstructive
• FEV1/FVC ratio below the LLN
• Typically FVC is normal in the early course
of the disease but is reduced in more severe
disease
• When FEV1/FVC ratio is low, even
individuals with an FEV1 equal to 80% to
100% of the predicted values are considered
to have mild airflow obstruction

Different patterns: Restrictive
• Classically there is a reduction in TLC
(wich cannot be measured by spirometry)
• Is inferred from spirometry when a matched
decrement occurs in FEV1 and FVC so that
the FEV1/FVC ratio is normal or high

Different patterns: Mixed
• A reduced FVC together with a low FEV1/FVC%
ratio is a feature of a mixed ventilatory defect in
which a combination of both obstruction and
restriction appear to be present, or alternatively
may occur in airflow obstruction as a consequence
of airway closure resulting in gas trapping, rather
than as a result of small lungs. It is necessary to
measure the patient's total lung capacity to
distinguish between these two possibilities.

Bronchodilator response
• Spirometry is repeated after 15 min of the
administration of beta-agonist or 30 min after
ipratropium bromide
• An increase in 12-15% in the FEV1 represents a
significant response in an individual who has a
near normal spirometry
• With more severe obstructive disease the
magnitude of improvement should be at least 200
mL
• Because its large variability the improvement in
FEF 25-75 has to be of 30 to 40%.