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So far, the common ECCS practice has been to consider a lung function value as pathological if it is less than 80 % of the predicted value. However, this seems to be reasonable only for patients up to the age of 40. The lower limit deciding on the assessment "normal" or "pathological" (also called Lower Limit of Normal (LLN)) is for example below 70 % of the old predicted value for 80- year-old people, so this was wrongly considered as pathological in the past. According to these data, the limit between "normal" and "pathological", expressed in percentages of the predicted value, depends on age. This is why a parameter was searched which describes this limit independently of age. This is the so-called "z-score" indicating how far the measured value deviates from the average value and the lower limit of normal (LLN), independent of age and gender.
Table 1: Differences between GLI and ECCS predicted values (acc. to: Criée et al., 2015)
Comparison criterion | ECCS | GLI |
|---|---|---|
FVC and FEV1 in middle to higher age | Up to 10% lower than GLI | Up to 10 % higher than ECSC |
Ethnicity | Is not considered | Is considered |
Dispersion of measured values | Is not considered | Varies according to age:
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Limit values | Static, as a rule 80% below predicted value is considered pathological | Dynamic, due to separate calculation of normal value and lower limit of normal (LLN) |
Reference equations | "easier" | "more complex" (see also www.lungfunction.org) |
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If the scatter range of normal values is to be considered, percentiles will be found which establish a relationship between the examination result and its statistic normal distribution in percentage steps. LLN and percentiles can be correlated, so the 5% percentile has been stipulated as the pathological limit of LLN (corresponding to a z-score of -1.645). In the guideline for spirometry (Criée et al, 2015) the severity classification is not recommended in percent of predicted value anymore as it used to be, but a classification according to the z-score. As a criterion for decision in serial examinations GLI recommends GLI the 2.5{^}th^ th percentile as LLN. As a criterion for clinical assessment of ill persons the 5{^}th^ th percentile is considered acceptable as LLN. The use of LLN as criterion for decision differs from the so-far common practice where e. g. an obstructive ventilation disorder was detected when the FEV1/FVC ratio was inferior to 0.7. A fix limit of 0.7 does not take into account the considerable physiological dependence of the FEV1/FVC ratio on the age of the examined person. Significant differences in the clinical assessment are to be expected particularly in young and old persons (see also Fig. 1).
*Age \[years\]**Potentially over-diagnosed**Potentially under-diagnosed* !worddav5254ee43caf3dd1406afeeb83ee2a96a.png|height=360,width=634!
*Figure 1:* *Comparison between diagnosing obstruction by using a fix FEV1/FVC ratio (blue line) and the use of an age-adjusted lower limit* *of normal (LLN, red line).* _Source: Mannino et al. 2007_
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Figure 1:
Comparison between diagnosing obstruction by using a fix FEV1/FVC ratio (blue line) and the use of an age-adjusted lower limit of normal (LLN, red line). Source: Mannino et al. 2007
Performance Performance of a spirometry and important measures
The current guideline for spirometry (Crieé et al., 2015) describes in detail how spirometry is to be performed in practice. The creation of a meaningful flow-volume curve by the spirometer requires well-trained personnel as well as motivated cooperation of the examined person. Certain quality criteria have to be taken into account as well. Usually, at least three successive measurements are carried out which comply with the quality criteria of the American Thoracic Society (Miller et al. 2005). The best trial will be evaluated. The most important measures of spirometry are listed in table 2.
Table 2: Important measures of spirometry
Measure | Abbr. | Explanation |
|---|---|---|
Vital capacity | VC | The maximum lung volume that can be exhaled after maximum inspiration (3.3 to 4.9 liters of air). |
Inspiratory Vital Capacity | IVC | The lung volume which can be inspired at once after maximum expiration (approx. 3.5 liters of air). |
Forced expiratory Vital Capacity | FVC | The lung volume that can be forcibly exhaled in one breath after maximum inspiration. |
One-second capacity (Forced Expiratory Volume) | FEV1 | The volume of air that can be maximally exhaled in one second after maximum inspiration (at least 70 percent of Vital Capacity). |
Maximum respiratory flow rate (Peak Expiratory Flow) | PEF | Describes the strongest airflow exhaled from the lungs at the beginning of strong expiration (max. 600 l/min) |
Mean respiratory flow rate (75%, 50%, 25%) (Maximal Expiratory Flow) | MEF | Expiratory flow at 25/50/75 % of FVC. It is the maximum expiratory flow rate at 25/50/75% of vital capacity in the thorax, which means when 75/50/25 % of vital capacity have already been exhaled. |
Tidal volume | TV | Corresponds to the volume of air inhaled or exhaled. With normal breathing and under resting conditions this is approximately 0.5 liters of air. |
Inspiratory Reserve Volume | IRV | This is the volume that can be additionally inhaled after normal inspiration (approximately 3 liters of air). |
Expiratory Reserve Volume | ERV | This is the volume that can be additionally exhaled after normal expiration (approximately 1.7 liters of air). |
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It happens again and again that in pulmonary function measurements the patients start the forced expiration with delay. This is why the zero point on the time axis has to be adapted accordingly in order not to falsify the calculation of FEV1. This adaptation is made by means of a back calculation in which a new zero point is determined. The relevant criteria for a new calculation of the zero point on the time axis are: Expiratory volume <5% or already expired volume in the first second below 150ml. delay during exspiration
Figure 2:
Normal measurement (blue line) and measurement with clearly recognizable delay (red line)
Notice in case of shallow tidal breathing
*Please inhale and exhale more deeply!*Prior to performing a breathing maneuver, the user can set how many tidal breaths the test person has to do before the breathing maneuver. The system gives a hint if tidal breathing is insufficient and asks the patient to inhale and exhale more deeply.
Figure 3: Notice when tidal breathing is insufficientinsufficien
Notice in case of three reproducible measurements (5% rule)
As soon as the patient has performed three reproducible measurements, a notice appears that the series of measurements can be terminated. The German Airway League and the ATS recommend performing at least 3 comparable measurements in order to be able to make a statement as to quality and cooperation of the patient. After each measurement, first a check is made whether there are already 3 measurements. If this is the case, the relation of the values FVC, FEV1 and PEF to each other will be verified, whether they are within the set limits. The limits for FVC and FEV1 are at a value of 5%. If the ratios of the 3 best measurements are within the defined limits, the progress monitoring display will appear indicating that the series of measurements can be terminated now. These 3 best measurements can be printed both for the reference measurements and for the spasmolysis measurements.
There are 3 reproducible measurements now. The series of measurements can be terminated.
Figure 4: Notice when there are three reproducible measurements
Hints as to the settings for this function can be found in chapter 7.5 (a: Reproducibility).
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If the patient's age is included in the formula for calculating FEV1, the lung age can be determined by comparing predicted values. The FEV1 decreases with growing age. For example, the FEV1 of a 75-year-old is only about 70% of the FEV1 of a 25-year-old. It is important to consider that the lung age cannot be determined for each predicted author - when the formula for FEV1 does not depend on age. 
Lung age in relation to best measurement for
Reference 36 years
Spasmolysis 31 years
Figure 5: Calculation of the spirometric lung age
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Miller's Prediction Quadrant
The Miller's Prediction Quadrant is a simple prognostic tool indicating the probability for the existence of an abnormality and its severity. The diagram is subdivided in four quadrants: obstructive disease, restrictive diseases, obstructive / restrictive disease or normal. The measurement results are shown in each quadrant, according to the prediction.
Figure 6: View of measurement results in the Miller's prediction quadrant
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Implementation of ATS specifications (American Thoracic Society)
Wiki Markup 
Figure 7: Flow-volume chart according to ATS (2:1 view)
A further specification according to ATS is that the expiratory volume-time diagram is displayed over a period of 6 seconds (see Fig. 8). This specification is also implemented in custo diagnostic.
Figure 8: Volume-time diagram only expiratory
For quality management, ATS requests that the date, the calibration result and the person having performed the calibration are protocolled each time a spirometer (Miller et al., 2005) is calibrated. This information is recorded and saved in custo diagnostic, together with the volume of the calibration pump, and can be called up and printed under the option "Calibrations" at any time.
Novelties in spirometry from custo diagnostic version 4.5.1 or higher
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When carrying out an examination, ECSC provides a predicted value curve that helps to detect if a patient is within or outside the standard range. This predicted value curve is constructed on the basis of PEF and MEF75, 50, 25. These values are not relevant in GLI, however, in other software there is sometimes an envelope curve based on PEF. This is due to the aspect "orientation" but is, as this envelope curve is based on another predicted author, misleading and the guideline authors even recommend not using this procedure because the combination of two predicted authors in one examination results in a validity that is limited, difficult to interpret and doubtful. Figure 9: Predicted curve drawn from FVC and FEF25-75 with LLN bars
However,
However, it is allowed to create an orientation guide out of the course of an imaginary line resulting from FVC and the limit of FEF25-75. Measurements whose line charts are above or within the corridor of LLN bars can be considered as acceptable (see Fig. 9). As soon as at least 2 repro ducible measurements have been achieved, the corresponding hint will appear and the examination can be terminated.
Figure 9: Predicted curve drawn from FVC and FEF25-75 with LLN bars
Display measurement result
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The measurement results are displayed in various manners, dependent on the phase of examination. In the reference measurement, the bars below the flow-volume curve show the results for FEV1, FVC and FEV1/FVC. The blue arrows mark the results of the reference measurement. Beside the predicted values and the achieved measured values and their percentage deviations, the results for the z-score are indicated in the measured value table.
If the z-score is in the predicted range, each result will be marked with a green square. If it is below the LLN (which means below -1.645) this will be highlighted with an orange square. The presentation of the results of spasmolysis measurement is comparable to the reference measurement, it just uses other colors (red) (see Fig. 10).
Fig. 10: Representation of results of reference and spasmolysis measurement with GLI
Automatic report
It is a new feature of custo diagnostic that the software provides the physician with a comprehensive overview of measurement results of the spirometric examination and that the criteria of evaluation are explained. The user can select four different options for creating a report (see Fig.11):
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For each selected option the patient-specific results are calculated and displayed.
Fig. 11: Options for creating reports
(1) Proposal as before, with 70% rule for FEV1/FVC and 80% rule for IVC and FVC
The clinical assessment of a spirometry is based on the patient-specific predicted values and/or on their deviation from them. If for example the measurement result for FEV1 (FVC) is between 40% and 60% of the predicted value, there is suspicion of a moderately severe obstruction (restriction).
When assessing according to occupational medical aspects, the limits are moved further towards the top and there is a moderately severe obstruction (or restriction) if FEV1 (and/or FVC) is between 55% and 85% of the predicted value. These report explanations support the physician in evaluating a patient according to the guidelines. They can be called up for the report (predicted author: GLI) under "Options" >> "Explanations" and also provide hints for COPD limit values according to GOLD (see Fig.12), in addition to the clinical and occupational-medical evaluation.
Fig. 12: Report explanation according to guideline of predicted author GLI
Extension of printing options
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The menu item "Settings" has been extended by some functions. Under "Menu/Functions" the criteria for reproducibility of a measurement can be viewed and be easily adapted if necessary. The following illustration shows which parameters are relevant here (see Fig.13).
Fig. 13: Setting options for the criteria of reproducibility
- View of measured values and determination of the best measurement
In the menu item "Diagnostics" >> "Parameter", the user can select the parameters to be displayed on the screen. It is possible to select a maximum of 7 parameters and the selection can be made separately for each predicted author.
In addition, it is possible to set according to which parameter the "best measurement" is determined. The parameters IVC, FVC, FEV1 as well as the sum of FEV1 and FVC can be selected. The last one has proved to be particularly significant (see also Fig. 14).
Fig. 14: Options for view of measured values and for determination of best value
- Flow-volume curve
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="cd770712-246b-4735-920f-03474a3c10c5"><ac:plain-text-body><![CDATA[ | Volume FVC [L] | Scaling x axis [L] | ]]></ac:plain-text-body></ac:structured-macro> |
< 3 | 0-4 | ||
3-5 | 0-6 | ||
> 5 | 0-8 | ||
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Fig. 14: Options for view of measured values and for determination of best value
- Flow-volume curve
In the menu item "Diagnostics" >> "Parameter", the view of the flow-volume curve can be set. It is possible to select the view according to ATS (2:1 view) or with automatic scaling. If automatic scaling is selected, the scaling of x axis will be adapted according to FVC (see also table opposite and Fig.15).
Volume FVC [L] | Scaling x axis [L] |
< 3 | 0-4 |
3-5 | 0-6 |
> 5 | 0-8 |
Fig. 15: Setting options for the flow-volume curve
Practical suggestions for interpreting spirometry
Among the methods for pulmonary function testing, spirometry has an outstanding position because it is easy to conduct and because ventilation disorders can be well excluded. Of course, the lack of evidence for a ventilation disorder must not result in a general exclusion of a lung function disorder. Furthermore, spirometry only provides a snap-shot of a fluctuating ventilation function which is partly due to a disease.
The international task force of ATS/ERS has published a simplified flow for implementing a pulmonary function test for clinical practice. VC, FEV1, FEV1/VC and TLC are the relevant parameters here. A normal relative one second capacity (FEV1/VC) excludes a ventilation disorder when otherwise normal vital capacity (VC) is given (Bösch & Crie, 2013).
In order to further exclude a pulmonary vascular disorder, diffusion testing is required which also helps differentiate a restriction and can indicate the existence of emphysema or bronchial asthma if there is an obstruction. 
Figure 16: Simplified lung function algorithm for clinical practice (according to Criée et al. 2015)
Conclusion
At the end of the year 2012, the common taskforce of the European Respiratory Society (ERS)/ "Global Lung Initiative" published new reference value recommendations for spirometry which came into being after 5 years of work on the basis of evaluations of comprehensible study material. More than 97,000 spirometry measurements of healthy non-smokers (55.3% women) were evaluated, the examination including more than 57,000 Caucasians (incl. Europeans).
It was a major finding that the most important spirometric parameters such as forced vital capacity (VC) and one second capacity (FEV1) were approx. 10% higher in the middle to late stage of life than according to the previous reference value recommendations. This means that the frequently used practice to consider a lung function test as pathological if it is less than 80% of the predicted value (e. g. ECCS), is only justifiable for patients up to the age of 40. The lower limit deciding on the assessment "normal" or "pathological" (also called Lower Limit of Normal LLN), is for example inferior to 70 % of the previous predicted value in 80-year-old patients. This used to be wrongly considered as pathological. As the limit between "normal" and "pathological" according to these data, expressed in percentages of the predicted value, depends on age, a parameter has been searched which indicates this limit independently of age. This is the so-called "z-score" indicating how far the measured value is situated from the average value and from the lower normal limit (also called Lower Limit of Normal – LLN), independent of age and gender.
A side effect of the reference values according to GLI is the confirmation by older normal values that the definition of COPD according to GOLD guidelines is wrong from a pathophysiological point of view because the dependence on age has not been taken into account. This results in overestimation of COPD diagnoses in the older population (Airway League, 2015).
The software "Spirometry" as part of custo diagnostic implements the specifications according to GLI and ATS in compliance with the guidelines.
"Finally, it is important to mention that the validity of the individual examinations depends to a high degree on the performance and/or the cooperation of the patients and can be increased by good information flow regarding the clinical conditions, anamnesis and further cardiopulmonary examination results" (Bösch & Criée, 2013, S.164).
Yours sincerely, custo med team
Important notice:
The contents made available here have been generated to the best of our knowledge and belief. We do not assume any responsibility for damages resulting from the use of the information contained herein. All liability claims are invalid. The readers are advised to check the accuracy of all product-related information.
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Literature
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Bösch, D. & Criée, C.-P. (2013): Lungenfunktionsprüfung. Durchführung – Interpretation – Befundung. 3. vollständig überarbeitete und erweiterte Auflage. Springer Verlag. 196 S.
Criée, C.-P., X. Baur, D. Berdel, D. Bösch, M. Gappa, P. Haidl, K. Husemann, R.A. Jörres, H.-J. Kabitz, P. Kardos, D. Köhler, H. Magnussen, R. Merget, H, Mitfessel, D. Nowak, U. Ochmann, W. Schürmann, H.-J. Smith, S. Sorichter, T. Voshaar, H. Wort. (2015): Leitlinie zur Spirometrie. Leitlinie der Deutschen Atemwegsliga, der Deutschen Gesellschaft für Pneumologie und Beatmungsmedizin und der Deutschen Gesellschaft für Arbeitsmedizin und Umweltmedizin zur Spirometrie. Pneumologie 2015; 69: 147-164
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Mannino, D.M. Buist, A.S. & W.D. Vollmer (2007): Chronic obstructive pulmonary disease in the older adult: what defines abnormal lung function? Thorax 62(3): 237-41.
Marek W, Marek E, Mückenhoff K, Smith HJ, Kotschy-Lang N, Kohlhäufl M. (2009): Lungenfunktion im Alter - Brauchen wir neue Referenzwerte? Pneumologie 2009, 63: 235–243.
Miller, M.R., R. Crapo, J. Hankinson, V. Brusasco, F. Burgos, R. Casaburi, A. Coates, P. Enright, C.P.M. van der Grinten, P. Gustafsson, R. Jensen, D.C. Johnson, N. MacIntyre, R. McKay, D. Navajas, O.F. Pedersen, R. Pellegrino, G. Viegi und J. Wanger (2005): General considerations for lung function testing. SERIES "ATS/ERS TASK FORCE: STANDARDISATION OF LUNG FUNCTION TESTING". Edited by V. Brusasco, R. Crapo and G. Viegi.Number 1 in this Series. Eur. Respir. J. 26: 153–161.
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