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John Hutchinson, a surgeon by profession, invented
spirometer. He noted that air that can be exhaled from a fully
inflated lung is a powerful indicator of longevity. His basic
spirometer measured vital capacity or capacity to live. Much
later modern parameter like FEV1 (forced vital capacity in one
second) were invented. Spirometer measures airflow from fully
inflated lungs over time in liters. The two most important
measurements are Forced vital capacity (FVC) and FEV1. FVC is
maximum amount of air which can be forcefully exhaled from a
fully inflated lung.
Indications for spirometry:
Spirometer is an integral part of the evaluation, diagnosis
and management of patients with respiratory disorders. The main
indications are:
Evaluation a case with respiratory symptoms.
Assessment of severity of respiratory disorder.
Assessment of response to therapy.
Per-operative evaluation of respiratory system.
Detection of pulmonary functional abnormality in predisposed
individuals, e.g. occupational exposure, neuromuscular, chest
wall or upper airway disorders.
Spirometer are gold standard in the diagnosis and management
of asthma and
COPD.
Types of spirometer:
Spirometer is basically of two types:
Volume displacement spirometer, are the earlier versions.
Flow-sensing spirometer.All the latest spirometer are flow-sensing type. Flow-sensing
spirometer are either turbine based or pneumotach based.
Contraindications for spirometry:
Absolute contraindication for spirometry include recent
myocardial infarction ie less than one month old.
Relative contraindications to performing spirometry are:
Hemoptysis of unknown origin (forced expiratory maneuver may
aggravate the underlying condition).
Pneumothorax.
Unstable cardiovascular status (forced expiratory maneuver
may worsen angina or cause changes in blood pressure) or recent
myocardial infarction or pulmonary embolus.
Thoracic, abdominal, or cerebral aneurysms (danger of
rupture due to increased thoracic pressure).
Recent eye surgery (eg, cataract).
Presence of an acute disease process that might interfere
with test performance (eg, nausea, vomiting).
Recent surgery of thorax or abdomen.
Hazards and complications: Hazards of spirometry though rare include:
Pneumothorax.
Increased intracranial pressure.
Syncope, dizziness, light-headedness.
Chest pain.
Paroxysmal coughing.
Contraction of nosocomial infections.
Oxygen desaturation due to interruption of oxygen therapy.
Bronchospasm.
Recommended times for with holding commonly used
bronchodilators when bronchodilator response is to be assessed:
Drug withhold time varies according to the duration of action
of bronchodilator drugs. Bronchodilator response is necessary to
know the reversibility of obstructive disorder. This is
necessary to differentiate asthma from COPD, as both have
different treatment and outcome.
| Drug
|
Withholding Time (hours) |
| Salmeterol
|
12
|
| Ipratropium |
06
|
| Terbutaline
|
4-8
|
| Albuterol
|
4-6
|
| Metaproterenol
|
04
|
| Isoetharine
|
03
|
Activities that should be avoided prior to spirometry:
Smoking within one hour of testing.
Consuming alcohol within four hours of testing.
Performing vigorous exercise within 30 minutes of testing.
Wearing cloths that substantially restricts full chest and
abdominal expansion.
Eating a large meal within 2 hours of testing.
How to perform spirometry:
Following are the steps patient must perform to perform a
good spirometry test.
Patient must hold mouth piece between the lips to create a
good air tight seal.
Then breath in and out 2 or 3 times at normal pace.
Then patient must inhale as much air possible and expire as
fast and as hard as possible until no breath is left.
Inspire rapidly again to maximum capacity.
For seeing bronchodilator response spirometry should be
performed 15- 30 minutes after administering a short acting
beta-agonist like salbutamol or terbutaline.
The basic parameters used in spirometry are:
Vital Capacity (VC)
Is the change in volume of gas in the lungs from complete
inspiration to complete expiration.
Forced Vital Capacity (FVC)
The maximum volume of air in liters that can be forcibly and
rapidly exhaled following a maximum inspiration. FVC is the
basic maneuver in spirometry tests.
Forced Expiratory Volume in first second (FEV1)
Is the volume of air expelled in the first second of a forced
expiration starting from full inspiration.
FEV1%
This is the FEV1 expressed as a percentage of the total volume.
It is sometimes called the FEV1 Ratio or theFEV1/ VC% when it is
shown as a percentage of the VC volume, or the FEV1/FVC% when
shown as a percentage of the FVC. In normal lung function this
should generally be over 75%, ie. the subject should get at
least three quarters of their total air out in the first second.
Peak Expiratory Flow Rate (PEFR)
Is the greatest flow that can be sustained for 10 milliseconds
on forced expiration starting from full inflation of the lungs.
It is measured in Liters per minute with a spirometer or a peak
flow meter.
Forced Expiratory Flow Rate (FEFR 25% - 75%)
This is the average forced expiratory flow rate at the middle
part of the FVC maneuver. Expressed in Liters per second it
gives an indication of what is happening in the lower airways.
It is a more sensitive parameter and not as reproducible as the
others. It is a useful serial measurement because it will be
affected before FEV, so can act as an early warning sign of
disease.
Interpretation of spirometry test:
Obstructive Ventilatory Defect:
An obstructive disorder refers to any disease that affects the
lumen of the airways. This could be due to excessive mucus
production, inflammation or bronchoconstriction. Asthma and
Chronic Bronchitis are examples of obstructive disorders. In
general terms the obstructive pattern presents itself as reduced
flow rates and normal lung volumes (but with a reduced FEV1) on
the FVC maneuver.
Restrictive Ventilatory Defect:
A restrictive disorder is one that may affect the lung tissue
itself or the capacity of the lungs to expand and hold predicted
volumes of air. This could be due to fibrosis and scarring, or a
physical deformity that is restricting expansion. Someone who
has had part of their lung removed would show a restrictive
pattern and another example of a restrictive disease is
pneumoconiosis. The restrictive pattern usually presents itself
as reduced volumes and normal flow rates on the FVC maneuver.
Combined Ventilatory Defect:
A combined disorder is ventilatory disorder exhibiting the
features of both an obstructive and restrictive deficit.
Examples of this pattern include Cystic Fibrosis, which causes
excess mucus production and damage to the lung tissue. Severe
asthma may also show
Click to visit spirometer photo gallery. Modified on
03-12-2008 |
