- Spirometer Definition: A spirometer is defined as a biomedical device that measures lung capacity and lung volume.
- Working Principle of Water Seal Spirometer: The water seal spirometer uses a water-filled cylinder and a bell jar to measure changes in air volume during breathing.
- Breathing Pipe Mechanism: Breathing into the spirometer moves the bell jar up and down, changing the weight’s position.
- Kymograph Production: A pen attached to the weight records breathing patterns as a graph called a Kymograph.
- Electrical Signal Conversion: The vertical movement of the weight can be converted to an electrical signal for display using a linear potentiometer.
A spirometer is defined as a biomedical device that measures lung capacity and volume. Its construction is simple, consisting mainly of a gas-collecting container. To understand the spirometer’s working principle, let’s look at its basic construction. The water-sealed model is a popular type. We’ll discuss its construction and working for clarity.
Water Seal Spirometer
It consists of an upright, water-filled cylinder of capacity 6 to 8 liters. Inside the cylinder, an inverted weighted bell jar is attached. The breathing piping arrangement from the bottom of the water-filled container is projected above the water level inside the bell jar as shown below.
When a person breathes into the bell jar through the pipe, the air volume changes. This change moves the bell jar vertically, altering the weight’s position via pulleys. The patient breathes through a mouthpiece, causing the jar to move up and down with each breath cycle, depending on the air volume inhaled or exhaled.
The weight moves up and down with the bell jar. A pen attached to the weight draws a graph on paper on a rotating drum. This graph is called a Kymograph.
The vertical movement of the weight can be converted into an electrical signal for display on an instrument screen. A linear potentiometer attached to the weight creates the signal. The resulting graph is a Kymograph. A spirometer acts as a mechanical integrator, with airflow as input and volume displacement as output.
Other types of spirometers include the Wedge Spirometer and Ultrasonic Spirometer.
