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How is asthma diagnosed? What is a spirometer? What is a peak flow meter? How is asthma diagnosed? Asthma is diagnosed based on a physical examination, personal history, and lung function tests. The physical examination looks for typical asthma symptoms such as wheezing or coughing, and the personal history provides additional clues such as allergies or a familial tendency towards asthma. Although lung function tests have not always been used for diagnosis in the past, the NHLBI Guidelines for the Diagnosis and Management of Asthma state that "Pulmonary function studies are essential for diagnosing asthma and for assessing the severity of asthma in order to make appropriate therapeutic recommendations. The use of objective measures of lung function is particularly important because subjective measures, such as patient symptom reports and physicians' physical examination findings, often do not correlate with the variability and severity of airflow obstruction." Lung function tests may be as simple as measuring peak flow with a peak flow meter, or using a simple spirometer, or may involve a battery of spirometry tests in a pulmonary function lab. What is a spirometer? A spirometer is a machine for testing lung function that you breathe in and out of through a hose attached to a mouthpiece. You are usually given nose clips so that all the air you breathe goes through the machine. One I've been tested on had a little expanding tank surrounded by water into which the air goes, and I could see the top rising and falling as I breathed out and in. It can measure a fair number of characteristics of your lungs, including FVC, FEV1, and PEPR. FVC, or forced vital capacity, is the amount of air that you can exhale forcefully after taking a deep breath. FEV1, or forced expiratory volume in one second, is the amount of air that you can be exhale in one second. Peak flow, or PEPR, is described in section 1.2.2. The sophisticated spirometers I've seen have a PC attached, and have neat little curves generated with each breath, which apparently have characteristic shapes for different respiratory diseases. There is a slightly less sophisticated machine that I've blown into, and I'm not sure if this is also classed as a spirometer or not, but you take a deep breath and blow into it, much like a peak flow meter, except that it draws a little graph of how much volume you've blown out, and I'd imagine that you can get the FVC and FEV1 off this graph. What is a peak flow meter? A peak flow meter is a little plastic device which you blow hard into, after having taken a deep breath. It records the rate at which you've blown into it in litres exhaled per minute (L/min) -- this is called the peak expiratory flow rate (PEF or PEFR). The meter is essentially a cylinder with a mouthpiece at one end, a place for the air to escape at the other end, and a calibrated meter along the side. When you blow into it, a marker is pushed along the scale and comes to rest at a point which indicates your PEF. Since you want to measure your maximum peak flow, it is important to take a deep breath and blow as hard and as fast as you can. Many asthmatics find that their maximum peak flow provides a good objective measure of how their asthma is doing, so peak flow meters now are used extensively for self-monitoring of asthma, and also for monitoring the effectiveness of asthma medications. |