Interpreting Pulmonary Diagnostics: Normal vs. Abnormal Results

Instructor: Dan Washmuth

Dan has taught college Nutrition, Anatomy, Physiology, and Sports Nutrition courses and has a master's degree in Dietetics & Nutrition.

There are many different tests that can be performed to see how well the lungs are working. Learn how to analyze and interpret the results of some specific pulmonary function tests.

Difficulty Breathing

Pretend you are a nurse working in a hospital when a patient having severe difficulty breathing is admitted. A doctor orders for this patient to undergo several pulmonary function tests. Once the results of these tests come back, a doctor hands them to you and asks for your thoughts.

Would you know how to interpret results from these pulmonary function tests? This lesson will provide information so you will be able to do just that!

Pulmonary Function Tests

Pulmonary function tests (PFTs) are tests that are used to help determine how well a person's lungs are working, and the main method to perform a PFT is spirometry. Spirometry involves a person breathing in and out of a mouthpiece that is hooked up to a machine that measures various areas of lung function. These areas of lung function include:

  • Forced Vital Capacity (FVC): The total amount of air a person can forcefully exhale after taking the deepest breath that they can.
  • Forced Expiratory Volume-One Second (FEV1): The total amount of air that a person can exhale during the first second of a very forceful exhale.
  • FEV1/FVC ratio: This ratio measures the amount of FVC that a person can exhale during the first second.

There are two main types of lung disorders or diseases that PFTs are used to diagnose: restrictive and obstructive lung diseases. Restrictive lung diseases are conditions that prevent the lungs from expanding properly, such as pulmonary fibrosis or acute respiratory distress syndrome (ARDS). Obstructive lung diseases are conditions that block air from flowing in and out of the lungs, such as chronic obstructive pulmonary disease (COPD) or asthma.

Spirometry is the main method to perform a pulmonary function test.
spirometry

Interpreting PFT Results

FVC is dependent on both body size and age. For example, a person who is 6 feet tall will have much larger lungs than a person who is under 5 feet tall. Therefore, they will also have a larger FVC. A normal FVC is considered to be greater than or equal to 80% of the national average FVC based on body size and age. A normal FEV1 for adults is 80% or more. A healthy FEV1/FVC for adults is considered to be greater than or equal to 70%. This means that a healthy adult's lungs should be able to blow out about 70% of their maximum exhale during the first second.

If FVC is lower than what is to be expected for a person's body size and age (less than 80% of the average), but their FEV1/FVC is in the normal range (greater than or equal to 70%), this person is likely to have a restrictive lung disease.

If the FVC or FEV1, and FEV1/FVC are low, a person is likely to have a chronic obstructive pulmonary disease.

If FVC or FEV1, and FEV1/FVC are both lower than normal, a person is likely to have an obstructive pulmonary disease such as COPD.
copd

Arterial Blood Gas Test

Another test that can be used to examine lung function is an arterial blood gas (ABG) test, which involves taking a blood sample from a patient and measuring the amount of oxygen and carbon dioxide (CO2) in the sample. One of the main functions of the lungs is to provide the blood with oxygen so it can deliver this oxygen to all the cells of the body. The lungs also play an important role in getting rid of CO2 from the blood (when we exhale, we are exhaling CO2).

The normal amount of oxygen in the blood is 75-100 mm Hg, and the normal amount of CO2 in the blood is 38-42 mm Hg. Less than normal levels of oxygen and higher than normal levels of CO2 can indicate lung problems, such as COPD and asthma.

Lesson Summary

Pulmonary function tests (PFTs) are tests that are used to help determine how well a person's lungs are working. The main method to perform a PFT is by using spirometry, which involves a person breathing in and out of a mouthpiece that measures various areas of lung function, such as:

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