Spirometry vs Pulmonary Function Test: Difference and Comparison

Key Takeaways

1. Spirometry is a type of pulmonary function test that measures lung volumes and airflow limitations by having the individual breathe into a spirometer.
2. Pulmonary function tests (PFTs) encompass a broader range of tests used to assess lung function, including spirometry and measurements of lung volumes, diffusing capacity, and airway resistance.
3. While spirometry focuses on specific parameters like forced vital capacity (FVC) and forced expiratory volume in one second (FEV1), PFTs provide a more comprehensive evaluation of lung function, diagnose respiratory conditions, monitor treatment effectiveness, and assess overall lung health.

What is Spirometry?

 Spirometry is a simple test to measure how much air is breathed in and inhaled in a set amount of time. It is one type of pulmonary function test that measures the inflow and outflow of air during breathing.

The Tiffeneau- Pinelli index is calculated in this test and compared to the reference values.  Any fluctuation in this average index indicates that a person suffers from respiratory or lung problems.

Spirometry involves using a device where a patient needs to keep a spirometer of the device in the mouth, and a soft clip is placed on his nose to stop air from escaping from it. A person is asked to take a deep breath and blow into a small spirometer tube. Inhaling and exhaling are done forcefully to ensure the person’s lungs are empty.

The test is repeated three times to ensure reliable results. The test can indicate whether there is any obstructive Airways disease or restrictive lung disease to a person performing the test. The test can also indicate asthma, chronic obstructive pulmonary disease, cystic fibrosis, pulmonary Fibrosis, etc. In some cases, spirometry is also used to test rheumatoid arthritis.

What is a Pulmonary Function Test?

There are two types of pulmonary function tests: spirometry and body plethysmography. Lung volumes such as tidal volume, inspiratory reserve volume, and expiratory reserve volume can be measured using spirometry. Other lung functions, including reserve volume, forceful respiration capacity, peak expiratory flow rate, and total lung capacity, are measured using body plethysmography.

The pulmonary function test gas diffusion study also measures how much oxygen and other gasses transfer from the lungs into the blood. A cardiopulmonary exercise test is also performed in some instances in the pulmonary function test, which measures how well the heart and lung muscles work when you exercise.

Average values of Pulmonary function tests vary from person to person. A person’s test result is compared to the average values of the PFT test of a person with the same age, height, sex, race, etc. Doctors also compare the previous PFT test results of the person before getting to any conclusion.

Difference Between Spirometry and Pulmonary Function Tests

1. Spirometry cannot fully diagnose asthma, whereas pulmonary function tests can fully diagnose asthma and other respiratory disorders.
2. Spirometry tests can only tell about a few lung disorders. At the same time, PFT can give the entire profile of the lung, which gives ideas about many chronic lung-related disorders.
3. Complete lung function cannot be understated in the case of spirometry; however, pulmonary function tests give a complete idea of the functioning of the lungs.
4. Spirometry can be performed on anyone. However, children find the procedures of pulmonary function tests difficult.
5. Spirometry does not involve any risks. However, Pulmonary function tests may cause dizziness, breathlessness, and asthma attacks.

Comparison Between Spirometry and Pulmonary Function Test

Parameter of comparison	Spirometry	Pulmonary Function Test
Definition	Spirometry is a technique that measures the inflow and outflow of air.	It is the test of the lung function
Number of tests	One	Two
What does it measure	Forced inspiration and expiration volume are measured.	Residual lung volume, lung capacity, forced inspiration volume, and expiration volume.
Pros	It is quick to test in case of drug effect.	More than one test is done. Thus, many parameters can be measured.
Cons	It doesn’t measure all the lung parameters.	It can be difficult for children.

References

1. https://www.frontiersin.org/articles/10.3389/fped.2019.00054/full
2. https://www.sciencedirect.com/science/article/pii/S0012369216348140