What is a spirometer  







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 of spirometry:

    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.


      Withholding Time (hours)













    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.


    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

  • combined ventilatory disorder.

    Click to visit spirometer photo gallery.

    Modified on 23-8-2010

    Asthma FAQs

    Is my asthma under control