Introduction to Spirometers & Lung Diseases

Author: Scott A. Sheffield MS

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Pulmonary Diseases:

Normal ventilation of the lungs is affected by many types of obstructive and restrictive pulmonary diseases:

1. Obstructive Diseases (obstructions of the trachea, bronchi, and bronchioles). Common causes:

a. Asthma – smooth muscle contractions and/or inflammation that causes the respiratory tubes to narrow. Asthma is often triggered by allergens, infections, exercise, cold air, and irritants.

b. Bronchitis – inflammation of the respiratory tubes due to infections or airborne irritants (cigarets smoke).

c. Bronchiectasis – widening of the respiratory tubes and an inability to clear secreted mucus. The condition is frequently caused by infections (severe pneumonia) and inherited dysfunctions (cystic fibrosis).

d. Chronic obstructive pulmonary disease (COPD) – chronic inflammation of the respiratory tubes and/or lung tissues most often caused by chronic bronchitis or emphysema.

2. Restrictive Diseases (inability to expand the lungs).

  • Intrinsic Causes:

a. Destruction of the lung tissues (parenchyma) – due to infections (tuberculosis), autoimmune disorders (sarcoidosis), drugs, asbestos, radiation, and cancers.

  • Extrinsic Causes:

a. Problems with the tissue layers lining the lungs (pleurae) – due to inflammation (pleurisy) or damage.

b. Extrapulmonary problems – due to neurological disorders (spinal cord injury), neuromuscular disorders that affect the breathing muscles (ALS, myasthenia graves) and chest wall deformities (scoliosis, kyphosis).


  • Spirometry is one of the primary Pulmonary Function Tests (PFT) used to check the health of the image descriptionlungs and respiratory passageways. When a spirometry test is performed, the subject breathes through a mechanical or electronic airflow sensor called a spirometer.


Anterior view of the lungs
Lungs with labels: Larynx, trachea, bronchiole, bronchus, left lung and right lung
  • The simplest image descriptionmechanical spirometers are hand-held devices that contain a set of blades arranged like a windmill. The blades rotate during exhalation, which causes a volume indicator to move or digital display to change values.
Mechanical spirometer
Mechanical spirometer exhalation
The blades rotate during exhalation which causes the volume indicator to change values.
  • image descriptionElectronic spirometers have no moving parts and act as transducers. They digitally convert airflow rates and volumes into electronic signals, which can be digitally analyzed and displayed.

How’s your respiratory system anatomy knowledge? Find out here.

Electronic spirometer image with labels: Digital display and electronic spirometer
Electronic spirometer digitally convert airflow rate and volumes into electronic signals.
  • A recording of a subject’s airflow is referred to as a spirogram. The vertical axis of a spirogram indicates airflow volume (in liters) and the horizontal axis indicates time (in seconds). Inhalation causes an upward deflection of a scan line and exhalation causes a downward deflection. Airflow rate is determined by combining the information recorded on the vertical and horizontal axes (volume per second).

Recording airflow in a spirogram

  • The results of the spirogram are compared with normal values for an individual’s height, weight, sex, and age.
  • A reduced rate of airflow indicates a blockage in one or more of the airways (an obstructive disorder), and a reduced volume indicates an inability to fully expand the lungs (a restrictive disorder).

An Overview of the Spirometry:

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