Spirometry

FOR PATIENTS

NLHEP has as its theme: “Test Your Lungs – Know Your Numbers“. Spirometry measures air flow out of your lungs (FEV₁) along with lung volume (FVC).  These are the numbers you need to know.  These noninvasive tests can be done in the physician’s office with a spirometer, a device used to measure lung health.

Here is a patient performing a spirometry test. Blowing forcefully into the tube provides a quick, easy measure of both FEV₁ and FVC.

FEV₁    The amount of air you blast out in the first second

FVC    The total amount of air you blast out in 6 seconds or longer

To measure your FEV₁ and FVC, you will be asked to hold the tube of a spirometer in your mouth, inhale as much air as possible, then exhale forcefully into the spirometer for six seconds or more.

You will be asked to repeat the test several times so that your maximum values for FEV₁ and FVC can be recorded. Your measured values are then compared to the predicted values from healthy subjects to determine if you have airway obstruction, and if so, how severe the obstruction may be.  You may also be asked to inhale a bronchodilator and repeat the spirometry measurements to assess whether your airway obstruction is reversible.

FOR HEALTH CARE PROFESSIONALS

Spirometry is the accepted standard for assessing whether airway obstruction is present, as well as for gauging its severity[1].  Spirometric measurements that are required include the FEV₁, FVC and the ratio of these two values, the FEV₁/FVC.  Some spirometers provide measurement of the FEV₆ as a surrogate for the FVC, in which case the FEV₁/FEV₆ ratio is reported.   Most spirometers can report additional variables such as PEF (peak expiratory flow) and FEF25-75% but these are not required to make the diagnosis of airway obstruction.   In order to distinguish whether air flow obstruction is reversible, spirometry must be performed before and after inhalation of a bronchodilator.

SPIROMETER STANDARDS

All spirometers should meet or exceed the minimum requirements published by the American Thoracic Society and European Respiratory Society (ATS/ERS)[2].  In addition to meeting the accuracy and precision guidelines of the ATS/ERS, spirometers should be easily configurable by the user to provide reports that include the patient’s FEV₁, FVC and FEV₁/FVC ratio, before and after bronchodilator.  In addition to the patient’s measured values, each spirometer should provide functionality to display the predicted value or predicted range to assist in identifying abnormal lung function, particularly airway obstruction.  The ATS/ERS guidelines recommend using the lower limit of normal (LLN based on the 95th percentile for healthy never-smokers) to establish a diagnosis of obstruction, so spirometers should provide these values as well[3].  Spirometers for use in the U.S. should utilize the NHANES III reference equations which include predicted and LLN values for the parameters noted above [3].  Additional reference equations for subjects 3-95 years of age of various ethnicities are available from the Global Lungs Initiative (GLI)[4].  Spirometers should be able to record pre- and post-bronchodilator spirometry, and display the % change after bronchodilator as part of the report.  Most spirometers require calibration for each day they are used; a 3 liter syringe is the standard device for calibration recommended by the ATS/ERS guidelines.  Some portable spirometers use disposable flow sensors which are calibrated at the time of manufacture.  A method of checking the accuracy of these types of spirometers is recommended by NLHEP.

PERFORMANCE OF SPIROMETRY

Although spirometry is a relatively simple test to perform, it is largely dependent on patient effort.  Acceptability and repeatability criteria have been published by the ATS/ERS2:

• • The patient must inhale maximally to total lung capacity, then blast the air out
  • There should be no cough or hesitation during the first second of the maximal exhalation
  • The patient must continue to exhale forcefully for at least 6 seconds and until a plateau is reached (3 seconds for children under age 10)
  • A minimum of three acceptable maneuvers is required
  • The largest and second largest FVC and FEV₁ values should be repeatable within 150 ml (100 ml if the FVC is less than 1.00 L)
  • The largest FVC and FEV₁ from acceptable efforts are reported; the FEV₁/FVC is calculated from these values

Subjects who exhibit airway obstruction on spirometry, should have the measurements repeated following inhalation of a beta-adrenergic bronchodilator.  Post-bronchodilator spirometry which returns to within normal limits suggests that the patient has reversible airway obstruction.  If the FEV₁ or FVC improves by at least 12% and 200 ml following inhaled bronchodilator, there is some element of reversible airway obstruction.

 

INTERPRETATION OF SPIROMETRY

 

NLHEP recommends the following guidelines for interpreting spirometry [5]:

1. Check the acceptability and repeatability to see if ATS/ERS criteria have been met.
   – pay special attention to the EOT; was a plateau reached before 6 seconds?
2. Use NHANES III or GLI reference values to calculate predicteds and LLNs for FEV1, FVC and FEV1/FVC; FEV6 may be substituted for FVC if NHANES III is used.
3. If the FEV1/FVC (FEV1/FEV6) ratio and FEV1 are both below the LLN in a test with good quality, airway obstruction is present. Use of the 0.70 fixed ratio is NOT recommended.
4. Grade the severity of obstruction using the FEV1 LLN and %predicted:
   LLN > FEV1 ≥ 60% = mild obstruction
   60% > FEV1 ≥ 40% = moderate obstruction
   FEV1 < 40% = severe obstruction
5. If the FEV1/FVC (FEV1/FEV6) ratio is > LLN but the FVC (FEV6) is below the LLN, the patient may have a restrictive disease; consider lung volumes.
6. If the patient has airway obstruction, post-bronchodilator testing should be performed.
   If the FEV1/FVC (FEV1/FEV6) ratio and FEV1 both improve above their respective LLNs, a significant asthmatic component is likely present.
   If the FEV1 increases by 12% or more, but the FEV1/FVC (FEV1/FEV6) ratio remains below the LLN, the patient may have combined COPD and asthma.

SCREENING SPIROMETRY

Screening to “rule out” significant airway obstruction can be done using a simple questionnaire along with measurement of either FEV₁ or PEF (peak expiratory flow)[6],[7].  Subjects with significant risk factors (smoking history, cough, dyspnea, etc.) may perform a series of maximal expiratory efforts to measure FEV₁ or PEF using a small portable device.  If the measured FEV₁ or PEF is within normal limits for the subject’s age, gender, height and ethnicity, airway obstruction is unlikely.  If the measured variables are NOT within normal limits or the subject is unable to perform the maneuvers acceptably, he/she should be referred for formal spirometry with pre- and post-bronchodilator measurements.

REFERENCES

[1] https://goldcopd.org/wp-content/uploads/2017/11/GOLD-2018-v6.0-FINAL-revised-20-Nov_WMS.pdf   Accessed July 13, 2018.

[2] Miller MR, Hankinson J, Brusasco V, Burgos F, et al: Standardisation of spirometry. Eur Respir J 2005; 26: 319–338.

[3] Pellegrino R, Viegi G, Brusasco V, Crapo RO, et al: Interpretative strategies for lung function tests. Eur Respir J 2005; 26: 948–968.

[4] Quanjer PH, Stanojevic S, Cole T, Baur X, et al, on behalf of the ERS Global Lung Function Initiative. Multi-ethnic reference values for spirometry for the 3-95 year age range: the global lung function 2012 equations.  Eur Respir J. 2012 Dec;40(6):1324-43.

[5] Ruppel GL, Carlin BW, Hart M, Doherty DE: Office spirometry in primary care for the diagnosis and management of copd: National Lung Health Education Program update.  RespirCare 2018;63(2):242–252.

[6] Nelson SB, LaVange LM, Nie Y, Walsh JW, et al: Questionnaires and pocket spirometers provide an alternative approach for COPD screening in the general population. Chest. 2012 Aug;142(2):358-66.

[7] Jithoo A, Enright PL, Burney P, Buist AS, et al: Case-finding options for COPD: Results from the BOLD Study.  Eur Respir J. 2012 Jun 27. [Epub ahead of print]