Pulmonary function testing in the evaluation of patients with allergic and immunologic disorders.

The Pulmonary Function Laboratory plays an important role in the evaluation of patients with respiratory diseases, including those that have diseases that occur on an allergic or immunologic basis. The American Thoracic Society (ATS) and European Respiratory Society (ERS) created a task force to standardize lung function testing and published a series of position papers that serve as the most current resource available on this subject [1–5]. Physicians performing pulmonary function studies should refer to these guidelines and use them as the standard methodology so as to be consistent with all laboratories in North America and Europe. This issue will cover the performance of spirometry, lung volume measurements, the determination of the diffusing capacity that is also called transfer factor or carbon monoxide uptake, bronchoprovocation challenge, and a provocative discussion of the problems in the interpretation of the results of the studies. Spirometry is a dynamic test that is best for measuring flow rates. The FEV1 is a volume that is exhaled in 1 s and thus is a flow rate. The FVC is a volume and not a flow rate and is dependent on the total expiratory time, especially in patients with airway obstruction. Spirometry is an effortdependent study, and it is necessary to have the patient blow out as hard and as fast as possible to get optimum results. Thus, the technician performing the test must be well trained. There are two types of spirometers. Volume displacement spirometers are those where air is expelled into the device and this moves a bellows or piston. This motion is measured and provides the values used in patient evaluation. Volume displacement spirometers have the advantage of maintaining their calibration from day to day and week to week, although they do need to be regularly calibrated and checked for air leaks. The disadvantages of volume displacement spirometers are that they tend to be bulky and have moving parts that can be damaged. Thus, they are difficult to use in field studies. The other type of spirometer is an electronic device that measures airflow using a pneumotachygraph and then electronically converting the result into the various measurements used. They have the advantage of being small, lightweight, and have no moving parts. Their disadvantage is that electronic drift can occur and any material collecting on the screen in the pneumotachygraph will alter the values. They require more frequent calibration checks. The newer models have been devised to minimize these problems. Electronic spirometers are well suited for field studies. It is important that a calibrating syringe be available to check the calibration of all spirometers. These are usually 3-l syringes. Lung volume measurements are essentially static procedures and are best for determining volumes. The two general methods employed are 1) gas dilution using an inert gas that does not cross the alveolar barrier such as helium or neon and, in the past, by nitrogen washout with collection of the expired gases and 2) thoracic gas volume that is determined by plethysmography or radiographic techniques. The gas dilution and nitrogen washout techniques are less accurate when there is poor distribution of the gas throughout the lung, as is seen in patients with chronic obstructive pulmonary disease and asthma. This is because the percentage of the inhaled marker gas varies from area to area in the lung and the sampled expired specimen is apt to underestimate the total lung capacity due to the overall uneven distribution of the tracer gas throughout the lung. Clinic Rev Allerg Immunol (2009) 37:135–136 DOI 10.1007/s12016-009-8124-3