A spirometer is a device that can measure the amount of air you can exhale and how fast you can exhale it. There are numerous ways to measure the flow and volume of exhaled air but almost all spirometers that are intended for personal use are electronic turbines. The major advantage a spirometer has over a peak flow meter is that a spirometer can measure both the speed and volume of your exhaled air throughout your entire exhalation and this means it can be used to monitor both the condition of your airways and the capacity of your lungs.
Why would you perform your own spirometry?
Spirometry is usually performed only in a doctor’s office or hospital lab. Some lung conditions need frequent and relatively comprehensive monitoring however, and the ability to do this at home can decrease the need to travel. In addition, more frequent testing can sometimes provide a physician with insights into lung conditions that can’t be provided with intermittent office visits.
Some personal spirometers are able to electronically transmit their results to a clinic or doctor’s office. When combined with other information such as blood pressure, temperature and pulse oximetry this is known as Telemedicine and it allows physicians and nurses to monitor and treat a variety of complex medical conditions while the patient remains at home.
What does a spirometer measure?
The most common measurements that are made by a spirometer are:
- FVC – the maximum amount of air you could exhale
- FEV1 – the amount of air you exhaled after 1 second
- FEV1/FVC ratio – the ratio between the FEV1 and FVC
- Peak Flow – the maximum speed of your exhaled air
Towards the end of everybody’s exhalation, the speed the air decreases a lot and due to technical limitations some of the less expensive spirometers have difficulty measuring these low flow rates. Some personal spirometers therefore substitute FEV6 (the amount of air exhaled after 6 seconds) and the FEV1/FEV6 ratio for the FVC and the FEV1/FVC ratio.
There are a large number of other measurements that can be made during a spirometry maneuver but for most purposes these are far less important than the FVC, FEV1 and FEV1/FVC ratio.
How would you measure your spirometry?
To do this you would:
- put the spirometer mouthpiece in your mouth
- seal your lips around the mouthpiece
- take as deep a breath as you possible can
- blow out as fast and as hard as you can for as long as you can
- inhale completely and come off the mouthpiece
What are normal values?
You should perform the spirometry maneuver at least three times. The effort that has the highest combined FVC and FEV1 is usually selected as the best maneuver. All electronic spirometers include at least one set of normal values and your results are usually compared as a percent of what would be predicted for somebody your age, height, gender and race or ethnicity.
A personal spirometer is more useful for monitoring than it is for diagnosing problems however, so it is the changes in FVC and FEV1 over time that are far more important than whether or not they are normal. This also means that the ability to remember and then compare your test results over time (trending) is an important software feature for a personal spirometer.
Should you have your own spirometer?
If you have undergone a lung transplant you have a high level of risk for complications. Regular spirometry testing has been shown to accurately and consistently provide an early warning of infection and tissue rejection.
For conditions such as Asthma, Emphysema, Chronic Bronchitis and Cystic Fibrosis FEV1 can often be a more accurate way to monitor the condition of your airways than can peak flow.
Sarcoidosis can have both an airway component and a lung capacity component, and many individuals with this lung disorder also have Asthma. Depending on the mix of these components regular FEV1 and FVC measurements may be useful.
FVC or FEV6 can be useful for monitoring the progression of neuromuscular disorders like Amyotrophic Lateral Sclerosis (ALS) and restrictive disorders like Pulmonary Fibrosis (IPF).
How do you get a spirometer?
At this time, medical insurance will only pay for a spirometer following a lung transplant. For all other conditions a spirometer is considered an experimental and/or investigational device and you will most likely have to pay for it yourself.
Personal spirometers usually cost between $200 and $1500, and are available from a number of different internet sources. In general, there is a relationship between a personal spirometer’s cost and:
- the number of measurements it can make
- software features such as memory, normal values and reporting
Because a spirometer is relatively expensive and its operation requires a relatively high level of expertise and knowledge, a spirometer should only be considered if it has a clear benefit to your health and wellbeing. There are no clear guidelines for this but the points to be considered should include:
Does a spirometer make a measurement (such as FEV1) that monitors your condition better than any other possible measurement?
Does your lung condition really require frequent testing? Many lung disorders are chronic and although there are changes over time there is usually little need to perform spirometry more often than a couple times a year.
Do you know what you’re going to do with the spirometry results? If it’s part of a treatment plan do you know when you should raise or lower medications and when you should call your physician?
Other things to consider:
Expect that it will take some practice to learn the proper way to perform a spirometry maneuver. You will need to blow your air out in a forceful huff and to blow it out completely. A spirometry maneuver is not a single, short blast; it is not a cough; it is not a sigh; and it’s not like blowing out candles.
Almost all personal spirometers use a turbine to measure expiratory flow and volume. Although all manufacturers claim that these devices do not need to be calibrated and at least one scientific study has verified that this is true for one specific brand of turbine spirometers, this does not mean that this fact has been verified for all turbine spirometers. In addition, turbines can become damaged if they are dropped and because they are essentially mechanical devices over time they are subject to wear and tear. The humidity in exhaled air can also condense onto the turbine’s vanes and this will affect their inertia and possibly the amount of friction. When turbine spirometers are used in a hospital lab they undergo daily calibration and testing to ensure their accuracy but the precision 3-liter syringe pump used for this purpose can be more expensive than a personal spirometer. Moreover, the least expensive personal spirometers have no provision for calibration. For all these reasons, it should be accepted that a personal spirometer will probably not be as accurate as the spirometers used in a hospital lab and that their performance and accuracy may well decrease over time.
Telemedicine has been around in one form or another for at least 30 years. At first glance telemedicine would seem to hold a great deal of promise for improving patient care at home, and reducing doctor’s office visits and trips to the emergency room. There have been dozens of studies of telemedicine, including a number for patients with COPD, asthma and Cystic Fibrosis but the results have been equivocal, with some studies showing significant improvements, some showing minimal improvements and some showing no improvements at all. This lack of clear improvement in patient care is the reason that telemedicine has not become more commonplace and that medical insurance usually will not pay for it. A number of companies sell spirometers that are part of a telemedicine system but since each of these systems are proprietary, in order for them to be of any benefit to you this requires the cooperation of your physician, clinic or hospital. Conversely, if your physician, clinic or hospital has a telemedicine program you will likely be limited to a single company’s spirometer.
PFT Patient by Richard Johnston is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.