Pulmonary function testing


Pulmonary function testing PFT is a complete evaluation of the respiratory system including patient history, physical examinations, chest x-ray examinations, arterial blood gas analysis, and tests of pulmonary function The primary purpose of pulmonary function testing is to identify the severity of pulmonary impairment1 Pulmonary function testing has diagnostic and therapeutic roles and helps clinicians answer some general questions about patients with lung disease PFTs are normally performed by a respiratory therapist

Contents

  • 1 Indications
    • 11 Pediatric neuromuscular disorders
  • 2 Measurements
    • 21 Spirometry
      • 211 Complications of spirometry
    • 22 Lung volumes
    • 23 Maximal respiratory pressures
    • 24 Diffusing capacity
    • 25 Oxygen desaturation during exercise
    • 26 Arterial blood gases
  • 3 Techniques
    • 31 Helium Dilution
    • 32 Nitrogen Washout
    • 33 Plethysmography
  • 4 Interpretation of tests
  • 5 Significance
  • 6 References

Indicationsedit

Pulmonary function testing is a diagnostic and management tool used for a variety of reasons, such as:

  • Chronic shortness of breath
  • Asthma
  • Chronic obstructive pulmonary disease
  • Restrictive lung disease
  • Preoperative testing
  • Impairment or disability

Pediatric neuromuscular disordersedit

Neuromuscular disorders such as Duchenne muscular dystrophy are associated with gradual loss of muscle function over time Involvement of respiratory muscles results in poor ability to cough and decreased ability to breathe well and leads to collapse of part or all of the lung leading to impaired gas exchange and an overall insufficiency in lung strength2 Pulmonary function testing in patients with neuromuscular disorders helps to evaluate the respiratory status of patients at the time of diagnosis, monitor their progress and course, evaluate them for possible surgery, and gives an overall idea of the prognosis3

Measurementsedit

Spirometryedit

Main article: Spirometry

Spirometry includes tests of pulmonary mechanics – measurements of FVC, FEV1, FEF values, forced inspiratory flow rates FIFs, and MVV Measuring pulmonary mechanics assesses the ability of the lungs to move large volumes of air quickly through the airways to identify airway obstruction

The measurements taken by the spirometry device are used to generate a pneumotachograph that can help to assess lung conditions such as: asthma, pulmonary fibrosis, cystic fibrosis, and chronic obstructive pulmonary disease Physicians may also use the test results to diagnose bronchial hyperresponsiveness to exercise, cold air, or pharmaceutical agents4

Complications of spirometryedit

Spirometry is a safe procedure; however, there is cause for concern regarding untoward reactions The value of the test data should be weighed against potential hazards Some complications have been reported, including pneumothorax, increased intracranial pressure, fainting, chest pain, paroxysmal coughing, nosocomial infections, oxygen desaturation, and bronchospasm

Lung volumesedit

Main article: Lung volumes

There are four lung volumes and four lung capacities A lung capacity consists of two or more lung volumes The lung volumes are tidal volume VT, inspiratory reserve volume IRV, expiratory reserve volume ERV, and residual volume RV The four lung capacities are total lung capacity TLC, inspiratory capacity IC, functional residual capacity FRC and vital capacity VC

Maximal respiratory pressuresedit

Measurement of maximal inspiratory and expiratory pressures is indicated whenever there is an unexplained decrease in vital capacity or respiratory muscle weakness is suspected clinically Maximal inspiratory pressure MIP is the maximal pressure that can be produced by the patient trying to inhale through a blocked mouthpiece Maximal expiratory pressure MEP is the maximal pressure measured during forced expiration with cheeks bulging through a blocked mouthpiece after a full inhalation Repeated measurements of MIP and MEP are useful in following the course of patients with neuromuscular disorders

Diffusing capacityedit

Main article: Diffusing capacity

Measurement of the single-breath diffusing capacity for carbon monoxide DLCO is a fast and safe tool in the evaluation of both restrictive and obstructive lung disease

Oxygen desaturation during exerciseedit

The six-minute walk test is a good index of physical function and therapeutic response in patients with chronic lung disease, such as COPD or idiopathic pulmonary fibrosis567

Arterial blood gasesedit

Arterial blood gases ABGs are a helpful measurement in pulmonary function testing in selected patients The primary role of measuring ABGs in individuals that are healthy and stable is to confirm hypoventilation when it is suspected on the basis of medical history, such as respiratory muscle weakness or advanced COPD

ABGs also provide a more detailed assessment of the severity of hypoxemia in patients who have low normal oxyhemoglobin saturation

Techniquesedit

Helium Dilutionedit

Main article: Helium dilution technique

The helium dilution technique for measuring lung volumes uses a closed, rebreathing circuit8 This technique is based on the assumptions that a known volume and concentration of helium in air begin in the closed spirometer, that the patient has no helium in their lungs, and that an equilibration of helium can occur between the spirometer and the lungs

Nitrogen Washoutedit

Main article: Nitrogen washout

The nitrogen washout technique uses a non-rebreathing open circuit The technique is based on the assumptions that the nitrogen concentration in the lungs is 78% and in equilibrium with the atmosphere, that the patient inhales 100% oxygen and that the oxygen replaces all of the nitrogen in the lungs9

Plethysmographyedit

Main article: Plethysmograph

The plethysmography technique applies Boyle's law and uses measurements of volume and pressure changes to determine lung volume, assuming temperature is constant10

Interpretation of testsedit

See also: Spirometer § History - Interpreting Spirometry

Professional societies such as the American Thoracic Society/ European Respiratory Society have published guidelines regarding conduct and interpretation of pulmonary function testing to ensure standardization and uniformity in performance of tests The interpretation of tests depends on comparing the patients values to published normals from previous studies Deviation from guidelines can result in false-positive or false negative test results Mohanka MR et al recently demonstrated that only a small minority of pulmonary function laboratories followed published guidelines for spirometry, lung volumes and diffusing capacity in 201211

Significanceedit

Changes in lung volumes and capacities are generally consistent with the pattern of impairment TLC, FRC, and RV increase with obstructive lung diseases and decrease with restrictive impairment

Referencesedit

  1. ^ Pulmonary terms and symbols: a report of the ACCP-ATS Joint Committee on Pulmonary Nomenclature, Chest 67:583, 1975
  2. ^ Finder JD, Birnkrant D, Carl J, et al Respiratory care of the patients with Duchenne muscular dystrophy: ATS consensus statement Am J Respir Crit Care Med2004;170 4:456– 465
  3. ^ Sharma GD 2009 "Pulmonary function testing in neuromuscular disorders" Pediatrics 123 Suppl 4: S219–21 PMID 19420147 doi:101542/peds2008-2952D 
  4. ^ Pulmonary Function Test in New York, Article June 2010 Dr Marina Gafanovich, MD - 1550 York Ave, New York NY 10028 - 212 249-6218 NYC Pulmonary Function Test
  5. ^ Enright PL 2003 "The six-minute walk test" Respir Care 48 8: 783–5 PMID 12890299 
  6. ^ Swigris JJ, Wamboldt FS, Behr J, du Bois RM, King TE, Raghu G, et al 2010 "The 6 minute walk in idiopathic pulmonary fibrosis: longitudinal changes and minimum important difference" Thorax 65 2: 173–7 PMC 3144486  PMID 19996335 doi:101136/thx2009113498 
  7. ^ ATS Committee on Proficiency Standards for Clinical Pulmonary Function Laboratories 2002 "ATS statement: guidelines for the six-minute walk test" Am J Respir Crit Care Med 166 1: 111–7 PMID 12091180 doi:101164/ajrccm1661at1102 
  8. ^ Hathirat S, Renzetti AD, Mitchell M: Measurement of the total lung capacity by helium dilution in a constant volume system, Am Rev Respir Dis 102:760, 1970
  9. ^ Boren HG, Kory RC, Snyder JC: The veterans Administration-Army cooperative study of pulmonary function, II: the lung volume and its subdivisions in normal men, Am J Med 41:96, 1966
  10. ^ Dubois AB, et al: A rapid plethysmographic method for measuring thoracic gas volume: a comparison with a nitrogen washout method for measure FRC in normal patients, J Clin Invest 35:322, 1956
  11. ^ Mohanka, Manish R; McCarthy, Kevin; Xu, Meng; Stoller, James K April 2012 "A Survey of Practices of Pulmonary Function Interpretation in Laboratories in Northeast Ohio" Chest 141 4: 1040–1046 doi:101378/chest11-1141  |access-date= requires |url= help


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