Lung function test (aka pulmonary function test, PFT's) measures how well the lungs work. It can be used to Dx asthma, COPD, and the extent of damage caused by pulmonary fibrosis and sarcoidosis.

Tests include:

• Spirometry, which tets how much air you can breathe in and out, and how fast you can blow air out. Parameters include:
  • FVC (Forced vital capacity), is the volume of air that can forcibly be blown out after fulll inspiration, measured in liters
  • FEV1 (Forced expiratory volume in 1 second), is the volume of air that can be forcibly be blown out in 1 second, after full inspiration. Values between 80-120% of the average value are considered normal, depending mainly on gender and age, but also height, mass, and ethnicity. Can be calculated here: http://dynamicmt.com/dataform3.html
  • FEV1/FVC ratio (FEV1%), is the ratio of FEV1 to FVC. It should between 70-85%, declining with age. In OBSTRUCTIVE diseases (e.g. asthma, COPD, chronic bronchitis, emphysema), FEV1 is decreased because of increased airway resistance to expiratory flow. The FVC may be decreased too, due to premature closure of the airway in expiration, but not in the same proportion as FEV1. This combination creates a reduced FEV1/FVC ratio. In contrast, in RESTRICTIVE disease (e.g. pulmonary fibrosis), the FEV1 and FVC are both reduced proportionately, or even increased, due ot decreased lung compliance. FEV1% predicted is where this is divided by the average FEV1% in patients of similar age, gender, and body composition
  • FEF (Forced expiratory flow), is the flow/speed of air coming out of the lung during the middle portion of a forced expiration. It is given at discrete times, defined by what fraction remains of the FVC (forced vital capacity). The intervals usually used are 25% (FEF25), 50% (FEF50), and 75% (FEF75). It can also be given as the average flow during an interval, deliinated by when specific fractions remain of FVC, usually 25-75% (FEF25-75%). Values ranging from 55% to 130% of the average are considered normal, depending on age, gender, height, mas, and ethnicity. Research suggests that FEF may be more sensitive than FEV1 to detect obstructive small airway disease
  • PEF (Peak expiratory flow), is the maximal flow/speed achieved during the maximally forced expiration initiated at full inspiration, measured in L/min, or L/sec
  • TV (Tidal volume), is the amount of air inhaled and exhaled normally at rest
  • TLC (Total lung capacity), is the maximum volume of air present in the lungs
  • DLCO (Diffusing capacity), is the carbon monoxide uptake from a single inspiration in a standard time, usually 10 seconds. Since air consists of only a trace of CO, 10 seconds is considered the standard time for inhalation, then rapidly blown out. The exhaled gas is tested to determine how much of the tracer gas was absorbed during the breath. It can help detect diffusion impairments, e.g. in pulmonary fibrosis. However, it has to be corrected for hemoglobin levels (as in anemia, or pulmonary ehmorrhage), and altitude/pressure
  • MVV (Maximum voluntary ventilation), is a measure of the maximum amount of air that can be inhaled and exhaled in 1 minute. For the comfort of the patient, it is done over 15 seconds, and extrapolated to a value for 1 minute, and expressed as L/min. Average values are 140-180L/min in males, and 80-120L/min in females
  • Cst (Static lung compliance), is where volume measurements are taken by the spirometry, in conjunction with pressure transducers, to simultaneously measure the transpulmonary pressure. Cst is the slope of the curve, of,the relations between changes in volume, vs changes in transpulmonary pressure, ΔV/ΔP. It is the most sensitive parameter for detecting abnormal pulmonary mechanics. It is considered normal if it is 60-140% of the average, in populations of similar age, gender, and body composition
• Lung diffusion capacity, which measures how well oxygen passes from the lungs to the bloodstream

• Asthma
• COPD