PEF values (picture 1) depend on the size of the airways, the strength of the expiratory muscles and the compliance of lung tissue. PEF measurement can be used to assess ventilatory capacity. However, PEF values are not significantly affected by the obstruction of medium-sized or small airways, which is common in mild asthma and incipient chronic obstructive pulmonary disease (COPD).
In smokers, a lowered PEF may suggest COPD.
PEF is reduced in asthma when the large bronchi are contracted.
PEF may become reduced also in restrictive pulmonary diseases.
PEF recording is easy to perform in a doctor's office.
Indications
Assessment of ventilatory capacity
Diagnosis of asthma
Monitoring of diurnal variation in airway obstruction and response to bronchodilators at home and at the workplace
Performance of a screening-type bronchodilator test in the doctor's office (preferably with a FEV1 meter)
Follow-up of asthma therapy
Suspicion of COPD
Recording PEF
A PEF meter with a nonlinear scale conforming to the EU standard should be used.
The test is performed with the patient standing or sitting.
A maximal short expiration is performed after maximal inspiration.
The lips are closed tightly around the mouthpiece to prevent flow of air from the corners of the mouth when exhaling.
The test is repeated three times, or more if the difference between the best two readings exceeds 20 l/min.
The best reading is recorded.
The results are compared to age-, sex- and height-adjusted reference values (picture 1).
PEF monitoring in the diagnosis of asthma
Recording PEF
PEF is recorded for two weeks in the morning and in the evening before the inhalation of a bronchodilator (usually a betasympathomimetic) and 15 minutes thereafter.
If symptoms occur, additional PEF recordings should be made under other conditions (exposure, exercise, etc).
Interpretation
A PEF variation of at least 20% (and exceeding 60 l/min) within 24 hours (difference between the highest and lowest PEF values divided by their mean) should be interpreted as abnormal. Computer software is available for calculating the PEF variation percentage Pef Calculator.
If PEF values improve by 15% or more and by at least 60 l/min from the baseline value, the response to bronchodilator is exceptionally high.
The change is diagnostic for asthma if an exceptionally large diurnal variation and/or exceptionally high response to bronchodilator is observed at least 3 times during a follow-up of 2 weeks.
Low PEF values without diurnal variation may suggest COPD, but the finding is not specific.
Follow-up recordings should always be made at the same time in the morning and in the evening. The greatest difference in the diurnal variation is often shown between tests performed early in the morning and late in the evening.
PEF monitoring at the workplace
Recording PEF
PEF recording is performed when first waking up in the morning, about every 2 hours during the day, in the evening before going to bed, and as needed whenever symptoms occur.
Monitoring should be continued for at least 4 weeks on both working days and days off; there should be an equal number of each included.
Spirometry
Essentials
Spirometry is the most significant lung function test.
Spirometry is used to record ventilatory capacity and lung volumes.
Indications
Assessment of pulmonary function (pocket-size spirometer)
Clarification of respiratory symptoms (dyspnoea, cough, wheezing)
Diagnosis and follow-up of obstructive lung diseases (asthma, COPD)
Diagnosis and follow-up of restrictive lung diseases (e.g. lung tissue diseases, neuromuscular diseases)
Assessment of working capacity and degree of disability in patients with lung disease
Assessment of surgical and interventional reserves
Monitoring of the effects of radiotherapy, surgical and pharmacotherapy
Preparation for the examination
Before the examination
No smoking for 2 hours
No coffee, tea, cola or other stimulating drinks for 4 hours
No heavy meals for 4 hours
Heavy physical exercise and inhaling cold air should be avoided for 2 hours.
Alcoholic beverages should be avoided for 24 hours.
Medication before spirometry
If the examination is to be diagnostic, medication affecting the bronchi should be interrupted according to the following guidelines:
short-acting betasympathomimetics and anticholinergics, as well as leukotriene receptor antagonists: 12 h - 3 days
theophyllines, antitussives: 3 days
long-acting betasympathomimetics and anticholinergics: 2-12 days
combination preparations (glucocorticoid plus formoterol or salmeterol):
48 h to eliminate the sympathomimetic effect only
4 weeks to eliminate the effect of the glucocorticoid as well
Antihistamines need not be discontinued before diagnostic spirometry.
If spirometry is performed to assess the efficacy of pulmonary medication, working capacity or surgical risks, medication should not be interrupted before the test.
Contraindications
Acute respiratory infection within the preceding 2 weeks
Severe coronary artery disease
Severe arrhythmias (which can be provoked by the bronchodilator test)
Pocket-size spirometers for office use (only for FEV1 and FVC measurements)
Flow-volume spirometers for laboratory use (ATS/ERS quality criteria)
The calibration of flow-volume spirometers must be checked by a calibration pump every day they are used.
Personnel must be trained in correct use of spirometers.
Methods and parameters
Measure the patient's height and weight.
Record any pulmonary medication taken (when was the last dose taken).
Ask the patient to sit up straight. Place the nose clip.
Ask the patient to close his/her lips tightly around the mouthpiece.
Ask the patient to inhale fully and then exhale as quickly and fully as possible.
The aim is to obtain 3 uniform flow-volume curves or, with a pocket-size spirometer, the most similar possible 3 FEV1 values (see reproducibility criteria).
Criteria for approval of a single curve
Continuous curve
No coughing during expiration
Sufficiently rapid onset of expiration to rapidly achieve the peak flow rate
Sufficiently long expiration ("all out")
Criteria for reproducibility of the test
FEV1: the difference between the two highest values must not exceed 150 ml
FVC: the difference between the two highest values must not exceed 150 ml
Forced vital capacity (FVC; the highest value of any approved curve)
Forced expiration in one second (FEV1; the highest value of any approved curve)
FEV1/FVC (ratio of the highest values)
Peak expiratory flow (PEF) and flow in the middle and at the end of expiration (MEF50 and MMEF) are printed out from the curve with the highest sum of FEV1 + FVC.
Evaluation of the spirometry finding
Spirometry results are evaluated by comparing the measured values to reference values and examining curve profiles (picture 3).
The new multi-ethnic reference values GLI 2012 are recommended 2. A number of countries (e.g. Finland) have their own population-specific reference values. Find out about local policy on reference values.
When using the new reference values, the lower limits of normal FEV1 and FVC variation are defined by the z-score (same as standard deviation SD). The lower limit of normal for all parameters is z-score -1.65, which means that 95% of healthy persons will have values higher than this.
For FEV1, z-score -1.65 equals to about 80% of the reference value in 40-year-old persons, but in 70-year-olds to about 70% of the reference value, which is due to the wider dispersion of the measurement results in older age groups.
Criterion for airway obstruction: z-score for FEV1/FVC below -1.65
Findings suggesting obstruction: PEF, MEF50 or MMEF value decreased (z-score below -1.65), when FVC is normal (in which case the curve has a concave form).
Criteria for reduced lung volume, i.e. restriction
Vital capacity (either FVC and slow vital capacity [SVC]) is reduced (z-score below -1.65).
In patients with bronchial obstruction, FVC is often decreased due to entrapment of air in the small airways (dynamic restriction).
Inspiratory spirometry
Inspiratory spirometry complements the regular spirometry in obstruction of central airways or when such a condition is suspected. Especially inspiratory flow is restricted by laryngeal stenosis, vocal cord paralysis and functional vocal cord dysfunction (VCD).
In healthy persons, peak inspiratory flow (PIF) is about 70% of the expiratory PEF.
Find out about locally used reference values. Population-specific reference values are used in some countries.
The bronchodilator test
Indications
Detection of reversible obstruction (asthma? COPD?)
Assessment of the adequacy of drug therapy for asthma: the patient should use his/her normal medication as instructed (ascertain the use of the drug and record the timing of the administration in the report.)
Performing the test
Spirometry is recorded before the inhalation of a sympathomimetic (0.4 mg salbutamol) and 10-15 minutes thereafter.
Interpretation
Changes diagnostic for asthma:
FEV1 and/or FVC improved by no less than 12% and 0.20 l
Changes suggesting asthma:
MMEF improved by no less than 33% and 0.4 l
MEF50 improved by no less than 36% and 0.5 l/s
PEF improved by no less than 23% and 1.0 l/s
Changes in flow rates can involve sources of error that require special competence to detect.
Typical result profiles
Flow-volume curves in various types of pulmonary changes are presented in picture 3.
Asthma
FEV1, FEV1/FVC, PEF, MEF50 and MMEF are decreased (obstruction), or temporarily normal in mild or well-controlled asthma.
FVC may also be decreased (dynamic restriction) but VC is often higher than FVC.
FVC may be decreased (dynamic restriction) in severe asthma, and in such cases VC may be clearly higher than FVC.
Significant improvement is seen in the bronchodilator test (see above).
Chronic obstructive pulmonary disease (COPD)
FEV1 and FEV1/FVC are decreased. In incipient disease, only MMEF or MEF50 may be decreased (small airway obstruction).
Particularly in emphysema, MMEF and MEF50 may be very low (collapse-type finding).
FVC is often decreased (dynamic restriction).
No significant response is observed in the bronchodilator test.
Restrictive pulmonary disease
FEV1, FVC and VC are decreased but FEV1/FVC is normal.
Causes may include pulmonary parenchymal processes (alveolitis, fibrosis), fibrous deposits on the pleura, pleural effusion, chest or thoracic spine deformities, obesity, chronic cardiac insufficiency and sequelae of coronary bypass surgery.
No significant response is observed in the bronchodilator test.
Other lung function tests
Other common lung function tests include
measurement of lung diffusion capacity that can be used to examine the dysfunction of lung tissue (e.g. in pulmonary fibrosis and emphysema) in more detail
measurement of bronchial contractility (exposure to histamine or methacholine), which is important in the diagnosis of asthma
measurement of nitric oxide in exhaled air, showing any eosinophilic inflammation in the airways that is most commonly associated with asthma
measurement of lung volumes by He-spirometry or body plethysmography (total capacity and residual air).
References
Quanjer PH, Stanojevic S, Cole TJ et al. Multi-ethnic reference values for spirometry for the 3-95-yr age range: the global lung function 2012 equations. Eur Respir J 2012;40(6):1324-43. [PubMed]
Kainu A, Timonen KL, Toikka J et al. Reference values of spirometry for Finnish adults. Clin Physiol Funct Imaging 2016;36(5):346-58. [PubMed]
Kainu A, Timonen KL, Vanninen E, Sovijärvi AR. Reference values of inspiratory spirometry for Finnish adults. Scand J Clin Lab Invest 2018;78(4):245-252. [PubMed]