What Do Spirometry Results Tell Us?
Spirometry results are displayed on a spirograph. An example of this is in the picture below. In addition to the graphical representation of the results, a table listing different numerical values or calculations is included. They are:
Force vital capacity (FVC): a measure of how much air the patient can exhale with force immediately following a deep breath in.
Forced expiratory volume (FEV): the measure of the amount of air that can be exhaled forcefully in one breath. FEV is measured at 1 (FEV1) second, 2 (FEV2) seconds, or 3 (FEV3) seconds. In the case of CF, FEV1 is most commonly used to diagnose the progression of the disease.
Forced expiratory flow (FEF)25% to 75%: these values give a measure of the amount of flow halfway through the exhaled breath.
Peak expiratory flow (PEF): In the past, pediatricians only used peak flow (determined by a simple hand held device called a peak-flow meter) to gauge breathlessness. Although this measurement gives a good indication of how quickly a patient can exhale, it is not very useful in determining whether the small airways or the larger airways are constricted.
Measures of capacity and volume are expressed as liters (L). All measurements of flow are expressed as liters per minute (L/min).
What Does the Doctor Do With the Results?
Everyone will experience a loss of lung function over time. People with CF lose it at a much quicker rate than their healthy peers. By keeping track of spirometry results, the respiratory therapist and CF specialist can determine the rate of progression of lung disease. By identifying problems early, severe damage can possibly be averted.
For example, if a patient who typically has an FEV1 of 2.7 Liters suddenly drops to 2.1Liters, this may indicate the presence of infection. Based on that assumption, the doctor may immediately prescribe anti-inflammatory medication, request a sputum sample to look for infection, or order a chest x-ray to get a better look at what's going on in the patient's lungs.
Some doctors are very proactive about preventive antibiotics. As such, patients who exhibit a dramatic decrease in FEV1 in a short period of time may find themselves hospitalized immediately. When a patient's baseline pulmonary status decreases by 10%, the patient is said to be experiencing an exacerbation requiring treatment.
