Spirometry is a common test that measures how much air you can inhale and exhale, and how quickly. The wet spirometer is a foundational instrument for this purpose, providing insights into lung capacity and airflow. This device has a long history in pulmonary medicine.
What is a Wet Spirometer?
A wet spirometer measures lung volumes by collecting exhaled air over water. Its core components include an inverted bell or cylinder suspended in a tank of water, creating a sealed chamber. A mouthpiece connects to this chamber via tubing, allowing a person to breathe directly into the system. The “wet” designation comes from the water seal, which prevents air from escaping and ensures accurate measurement of the displaced volume.
This instrument represents an early development in respiratory physiology, tracing back to the mid-19th century. Early models used a counterweight system and a pen to record tracings on a rotating drum. Despite technological advancements, the fundamental principle of air displacement in water remains consistent.
How a Wet Spirometer Measures Lung Function
When a person exhales forcefully into the mouthpiece, the expelled air enters the inverted bell, causing it to rise out of the water. The volume of air exhaled directly corresponds to the bell’s upward displacement. As the bell moves, a connected mechanism, often a pen on a kymograph, creates a graphic representation of airflow and volume over time. Modern wet spirometers use digital sensors to record this displacement, converting it into electronic data.
The measurement process begins with the individual taking the deepest breath possible, then exhaling as forcefully and completely as they can into the mouthpiece. This forced exhalation is sustained until no more air can be expelled. The resulting tracing or digital readout provides data points like the total volume of air exhaled and its expulsion speed.
Common Uses of Wet Spirometers
Wet spirometers are used in medical and research settings to evaluate respiratory health. They help diagnose chronic conditions like asthma and chronic obstructive pulmonary disease (COPD). By measuring lung volumes and airflow rates, healthcare professionals identify patterns indicative of airway obstruction or restrictive lung diseases. A reduced ability to quickly exhale air might suggest an obstructive condition.
The device also monitors the progression of known lung diseases over time, allowing clinicians to assess treatment effectiveness. Before certain surgical procedures, especially those involving the chest or abdomen, spirometry may be performed to gauge a patient’s lung reserve and predict potential post-operative complications. In occupational health, it can screen individuals exposed to respiratory hazards, detecting early changes in lung function.
Understanding Your Spirometry Results
Key measurements are derived from a spirometry test. The Forced Vital Capacity (FVC) represents the total volume of air a person can forcefully exhale after taking the deepest breath possible. A lower than expected FVC can indicate a restrictive lung condition, where the lungs cannot fully expand.
The Forced Expiratory Volume in 1 second (FEV1) measures the volume of air exhaled during the first second of a forced exhalation. This value reflects how quickly air can be expelled from the lungs. A diminished FEV1 often points to an obstructive lung disease, where airflow is hindered.
The FEV1/FVC ratio, calculated by dividing FEV1 by FVC, is an informative metric. A low ratio suggests airway obstruction, while a preserved ratio with reduced FVC may indicate a restrictive pattern. These numerical results are compared to predicted normal values based on age, sex, height, and ethnicity, and a healthcare professional interprets them within the context of an individual’s overall health.