Pulmonary function testing

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Lungvolumes Updated.png
TLC

Total lung capacity: the volume in the lungs at maximal

inflation, the sum of VC and RV.
TV

Tidal volume: that volume of air moved into or out of the lungs during quiet breathing (VT indicates a subdivision of the lung; when tidal volume is precisely measured, as in gas exchange calculation,

the symbol VT or VT is used.)
RV

Residual volume: the volume of air remaining in the lungs

after a maximal exhalation
ERV

Expiratory reserve volume: the maximal volume of air that can

be exhaled from the end-expiratory position
IRV

Inspiratory reserve volume: the maximal volume that can be

inhaled from the end-inspiratory level
IC Inspiratory capacity: the sum of IRV and TV
IVC

Inspiratory vital capacity: the maximum volume of air inhaled

from the point of maximum expiration
VC

Vital capacity: the volume of air breathed out after the

deepest inhalation.
VT

Tidal volume: that volume of air moved into or out of the lungs during quiet breathing (VT indicates a subdivision of the lung; when tidal volume is precisely measured, as in gas exchange calculation,

the symbol VT or VT is used.)
FRC

Functional residual capacity: the volume in the lungs at the

end-expiratory position
RV/TLC% Residual volume expressed as percent of TLC
VA Alveolar gas volume
VL

Actual volume of the lung including the volume of the

conducting airway.
FVC

Forced vital capacity: the determination of the vital

capacity from a maximally forced expiratory effort
FEVt

Forced expiratory volume (time): a generic term indicating the volume of air exhaled under forced conditions in the first t

seconds
FEV1

Volume that has been exhaled at the end of the first second

of forced expiration
FEFx

Forced expiratory flow related to some portion of the FVC

curve; modifiers refer to amount of FVC already exhaled
FEFmax

The maximum instantaneous flow achieved during a FVC

maneuver
FIF

Forced inspiratory flow: (Specific measurement of the forced inspiratory curve is denoted by nomenclature analogous to that for the forced expiratory curve. For example, maximum inspiratory flow is denoted FIFmax. Unless otherwise specified, volume qualifiers

indicate the volume inspired from RV at the point of measurement.)
PEF

Peak expiratory flow: The highest forced expiratory flow

measured with a peak flow meter
MVV

Maximal voluntary ventilation: volume of air expired in a

specified period during repetitive maximal effort
Pulmonary function testing
Diagnostics
MeSH D012129
OPS-301 code 1-71
MedlinePlus 003853

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 impairment.[1] Pulmonary function testing has diagnostic and therapeutic roles and helps clinicians answer some general questions about patients with lung disease. PFT's are normally performed by a specialist technician.

Indications[edit]

Pulmonary function testing is a diagnostic and management tool used for a variety of reasons.

Pediatric neuromuscular disorders[edit]

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 atelectasis (the inability of the lungs to gain oxygen) and an overall insufficiency in lung strength.[2] A combination of reduced lung compliance caused by generalized and widespread microatelectasis and chest wall deformity caused by increased chest wall compliance results in increased work of breathing and chronic respiratory insufficiency.[3] Musculoskeletal deformities such as kyphoscoliosis contribute to restrictive lung disease.

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 prognosis.[4]

Other indications[edit]

Measurements[edit]

Spirometry[edit]

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 agents.[5]

Complications of spirometry[edit]

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, syncope, chest pain, paroxysmal coughing, nosocomial infections, oxygen desaturation, and bronchospasm. '

Lung volumes[edit]

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 pressures[edit]

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 capacity[edit]

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 exercise[edit]

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 fibrosis[6][7][8]

Arterial blood gases[edit]

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.

An elevated serum hydrogencarbonate level, or chronic hypoxemia. ABGs also provide a more detailed assessment of the severity of hypoxemia in patients who have low normal oxyhemoglobin saturation.

Techniques[edit]

Helium Dilution[edit]

The helium dilution technique for measuring lung volumes uses a closed, rebreathing circuit.[9] 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 Washout[edit]

Main article: Nitrogen washout

The nitrogen washout technique "also called the brian 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 lungs.[10]

Plethysmography[edit]

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 constant.[11]

Interpretation of tests[edit]

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 2012. Ref. A survey of practices of pulmonary function interpretation in laboratories in Northeast Ohio Mohanka MR, et al. Chest. 2012;141(4):1040-1046

Significance[edit]

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.

References[edit]

  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 Med.2004;170 (4):456– 465
  3. ^ Wang CH, Finkel RS, Bertini ES, et al. Consensus statement for standard of care in spinal muscular atrophy. J Child Neurol.2007;22 (8):1027–1049
  4. ^ Sharma GD (2009). "Pulmonary function testing in neuromuscular disorders.". Pediatrics. 123 Suppl 4: S219–21. doi:10.1542/peds.2008-2952D. PMID 19420147. 
  5. ^ 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.
  6. ^ Enright PL (2003). "The six-minute walk test.". Respir Care 48 (8): 783–5. PMID 12890299. 
  7. ^ 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. doi:10.1136/thx.2009.113498. PMC 3144486. PMID 19996335. 
  8. ^ 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. doi:10.1164/ajrccm.166.1.at1102. PMID 12091180. 
  9. ^ 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.
  10. ^ 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.
  11. ^ 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.