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SPIROMETRY:The term spirometry is defined as the use of a spirometer to obtain measurements of breathing capacity, however the term is used more generically to mean Lung or Pulmonary Function Testing (PFT) to acquire information about the lung volumes, flow rates and the physiological function. The reason for assessing someone's Pulmonary Function will determine exactly what sort of PFT will be required. Sometimes just the most basic test, a Peak Flow, will suffice and provide enough information of a patient's condition for the clinician. Mostly a whole bselection of investigations will be required to provide more information to enable an accurate diagnosis or prognosis. Questionnaires can also provide useful information by asking about any symptoms, frequency of episodes and if or when Bronchodilators were last used (The use of Bronchodilators, such as Salbutamol, can often affect PFT results). When performing spirometry the clinician must try and ensure that maximal effort is obtained at each attempt as sub-par effort will limit the clinical value of the tests. Whatever procedures are indicated they are always compared to a set of Normal Values. These values take into consideration common factors such as gender, age, height and race, on occasion other parameters are used such as Body Surface Area (BSA). There are three main sets of Normal Values: 1. European Respiratory Society (ERS) 1993 regression values, are recommended by American Thoracic Society/European Respiratory Society (ATS/ERS) Task Force as the 'Standardisation of Lung Function testing for Europeans'. These tables are the most widely used in Europe and elsewhere and were published in 1993. 2. National Health and Nutrition Examination Survey (NHANES) in it's current form of NHANES III, is recommended for ethnically appropriate individuals by ATS/ERS and is used in the Americas and elsewhere. These tables were published in 1999. 3. Global Lungs Quanjer (GLI-2012) regressions are based on the NHANES III but use an added method (Lambda-mu-sigma (LMS)) to process thenormal values. These values were published in 2008, accepted by ERS in 2010 but are not widely used. Peak FlowThe most commonest PFT testing that can be done is the Peak Flow. A Peak Flow Meter is a small, portable handheld device that is quite inexpensive. It's purpose is to record a person's Peak Expiratory Flow Rate (PEF or PEFR) or the fastest that a person can breathe out. This measurement is recorded in litres per minute. Procedure: The person is instructed to inhale fully, place the tube in the mouth and exhale as hard as they can, so 'take a deep breath and blow out as hard as you can' should elicit maximum results. This procedure can repeated a number of times (best of three) until a consistent result is obtained. Many repeated attempts must be avoided due to fatigue with a resultant drop in the score. This item is an ideal way to monitor some respiratory disorders quickly and easily in a doctors Practice or even at home, over a period of time keeping a log of the results to see if any trend is apparent, such as low scores at dawn/dusk possibly relating to pollen counts. SpirometrySpirometry is probably the most commonest clinical form of PFT. The type of machine varies and can be either a 'Bellows' type or a Strain gauge variant, although they look different they perform the same test. Spirometry records expelled volume over time and from this certain measurements may be taken. Procedure: The person is instructed to take a deep breath and then to blow out as hard as they can and to continue to empty their lungs until told to stop (usually 6 seconds). In some cases a longer period is required for subjects to empty their lungs completely and care must be taken when this is required, especially the elderly and children. A slight amendment to the procedure is required if the Vital Capacity is to be recorded as apposed to the Forced Vital Capacity, in this case the subject is instructed to take a deep breath and then in their own time, without forcing the air, the empty their lungs completely and then stop. With this technique people can usually empty their lungs for up to 12 seconds. Peak Expiratory Flow (PEF) can be recorded as the calculated fastest velocity of exhaled breath. Forced Expiratory Volume in 1 second (FEV1) is calculated as the volume that was expired at 1 second once breathing out was commenced. Further FEV measurements can be recorded but these are not done routinely such as FEV0.5, FEV3 and FEV6 (½, 3 and 6 seconds respectively). Forced Vital Capacity (FVC) and Vital Capacity (VC), this records total volume of air expelled with slightly different techniques. If there is a difference between VC and FVC it usually indicates a collapse of the small airways. FEV1/FVC Ratio (Tiffenau-Pinelli Index) is a calculation comparing the FEV1 to the FVC and expressed as a percentage. Forced Expiratory Flow at 25%-75% (FEF25-75) also called the Maximum Mid-Expiratory Flow calculates the ratio of expired flow between 25% volume and 75% volume. This measurement was used to aid detection of obstruction in the small airways but has since been shown to correlate with the conventional measurements of FEV1, FVC, PEF and Tiffenau-Pinelli Index (http://dx.doi.org/10.1183/09031936.00128113) The results of this should be able to differentiate between normal, obstructive or restrictive spirometry.
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© 2016 by Lee Boswell
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