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This is the first in a series of articles we intend to write about spirometry and why it is important to those who want to keep their lungs healthy. Our plan is to speak directly to people who want to use a home spirometry device to measure their lung health. To do this, we may have to use occasional medical jargon, but we hope to explain any terms and concepts to make them more understandable. Many of you, after all, are comfortable with measuring your own blood pressure or body temperature at home, and that required you to learn a few new things. So think of these articles as a short course in how to measure, understand, and improve your own respiratory health.
Spirometry is a common medical procedure used to test and monitor lung function. It works by measuring how much air you can inhale into your lungs and then breathe out in one breath, as quickly and forcefully as you can. The test is performed using a machine called a spirometer, which consists of a mouthpiece and sensing device attached either to a specialized computer in a hospital or doctor's office, or more recently, to a smartphone in portable versions. The latter will be the focus of most subsequent articles in this series, as we explain to you how a spirometer connected to a smartphone can be used in a home setting.
Wherever the test is performed, spirometry works by measuring the amount or volume of air you inhaled and the speed at which you are able to exhale it. The results are then used to calculate the current state of your pulmonary health and present it in the form of numerical parameters and graphs.
When might spirometry be recommended by your doctor?
- To diagnose lung problems if you have a persistent cough or shortness of breath.
- To diagnose or manage asthma, a long-term condition in which your airways become swollen and narrowed.
- To detect and monitor chronic obstructive pulmonary disease (COPD), a group of lung conditions often associated with smoking.
- To detect cystic fibrosis, a genetic disorder that clogs the lungs with mucus.
- To diagnose pulmonary fibrosis (scarring of the lungs).
These medical conditions reduce the amount of air you can breathe in a specific time frame. If you have them, spirometry helps your doctor diagnose the severity of the condition and choose the most effective treatment. Spirometry can also be used to measure the effectiveness of any treatments for these conditions, to determine whether they should be continued, changed, or discontinued. In some cases, spirometry can be useful even if you do not have any specific conditions. For example, portable spirometers are often used by athletes to measure their lung capacity and improve their performance.
What is a spirometry test like? What do I need to know?
The test is very quick, and takes only a few seconds. You might want to set aside a few minutes, however, because you may need to repeat the test several times to ensure a reliable result. The test is considered extremely safe, but you may feel dizzy afterwards. If you have angina, high blood pressure, or recent heart disease, you should inform your doctor before performing the test.
You can perform a spirometry test either sitting or standing, whichever is more comfortable for you. The most important consideration is that your chest is upright and unrestricted, and that you are as relaxed as possible. After breathing normally for a few seconds, seal your lips around the mouthpiece so that no air can escape, and breathe in as deeply as you can. Then blow out into the mouthpiece, as quickly and as forcefully as you can. Blow as fast as you can, until no more air comes out.
In terms of "preparing for the test," if it is being performed in a hospital or in a doctor's office, you should follow your doctors' specific advice. In general, however, you should wear loose, comfortable clothing that doesn't restrict your breathing. If you smoke, you should try to avoid it for 24 hours before the test. Also, you should refrain from eating a large meal, drinking alcohol, or exercising heavily for several hours before the test. If you use bronchodialator medications, you should not use them before the test.
What do the results of the test mean?
The results of your spirometry test can be analyzed in two different ways. First, your results will be compared to the predicted results of patients of the same age, gender, body type, and ethnicity as you. Results that are less than 80% of the predicted values are considered abnormal and may be an indication of a respiratory disease or condition that requires treatment. Second, your most recent results can also be compared to previous tests to determine whether your condition is improving or getting worse.
Many different measurements may appear in your results. Some of the most common are PIC (peak inspiratory flow), FVC (forced vital capacity), FEV1 (forced expiratory volume in one second), FEV1/ FVC ratio and PEF (peak expiratory flow). Most spirometers also produce a series of graphs such as a volume-time curve or a flow-volume loop that help to visualize the results. In future articles we will explain more about how to ensure the best possible results from your spirometer, and how to interpret the results yourself.