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• How to interpret spirometry data in 2023? The new criteria to retain the diagnosis of ventilatory impairments
  Helmi BEN SAAD
  Published on: 31 July 2023

• Published on: 31 July 2023

  How to interpret spirometry data in 2023? The new criteria to retain the diagnosis of ventilatory impairments

  • Helmi BEN SAAD, Professor of physiology and functional exploration. University of Sousse, Farhat HACHED Hospital, Heart Failure (LR12SP09) Research Laboratory, Sousse, Tunisia

  I read with interest the Saavedra et al.’s study1 aiming to evaluate the associations of cardiorespiratory fitness and body-mass-index with incident restrictive-ventilatory-impairment (RVI). The study’ rational is interesting since the RVI is frequent (eg; prevalence: 3 to 50%).2 One strong point of the aforementioned study1 was the use of the 2012 global-lung-function-initiative (GLI) task force of multi-ethnic norms for spirometry (GLI-2012).3 Saavedra et al.1 retained the diagnosis of a RVI in front of the combination of a low forced-vital-capacity (FVC) (ie; FVC < lower-limit-of-normal (LLN)) and a normal ratio between forced-expiratory-volume-in-one-second (FEV1) and FVC (ie; FEV1/FVC ≥ LLN). Saavedra et al.1 followed some “old” approaches. In 2022, the European-respiratory-society and the American-thoracic-society (ERS/ATS) published a “new” technical standard on interpretive strategies for lung function tests.4 This guidelines should be considered by researchers in the field of sports medicine.4 The definition applied by Saavedra et al.1 to retain the diagnosis of a RVI is questionable, and the following two points need to be clarified: i) what is a low spirometric data?, ii) what is a RVI?
  What is a low spirometric data?
  Interpretation of spirometric data necessitates 2 steps: i) comparison of the spirometric data with these of reference.4 5 , and ii) comparison of the data’ value with the distinctive thresholds of the main ventilatory-impairment not...

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  I read with interest the Saavedra et al.’s study1 aiming to evaluate the associations of cardiorespiratory fitness and body-mass-index with incident restrictive-ventilatory-impairment (RVI). The study’ rational is interesting since the RVI is frequent (eg; prevalence: 3 to 50%).2 One strong point of the aforementioned study1 was the use of the 2012 global-lung-function-initiative (GLI) task force of multi-ethnic norms for spirometry (GLI-2012).3 Saavedra et al.1 retained the diagnosis of a RVI in front of the combination of a low forced-vital-capacity (FVC) (ie; FVC < lower-limit-of-normal (LLN)) and a normal ratio between forced-expiratory-volume-in-one-second (FEV1) and FVC (ie; FEV1/FVC ≥ LLN). Saavedra et al.1 followed some “old” approaches. In 2022, the European-respiratory-society and the American-thoracic-society (ERS/ATS) published a “new” technical standard on interpretive strategies for lung function tests.4 This guidelines should be considered by researchers in the field of sports medicine.4 The definition applied by Saavedra et al.1 to retain the diagnosis of a RVI is questionable, and the following two points need to be clarified: i) what is a low spirometric data?, ii) what is a RVI?
  What is a low spirometric data?
  Interpretation of spirometric data necessitates 2 steps: i) comparison of the spirometric data with these of reference.4 5 , and ii) comparison of the data’ value with the distinctive thresholds of the main ventilatory-impairment noted during chronic diseases [eg; obstructive-ventilatory-impairment (OVI), RVI, mixed-ventilatory-impairment (MVI)].4 5 In this context, norms are useful for classifying a spirometric data as decreased, normal, or increased based on the 95% confidence interval (eg; LLN and upper-limit-of-normal).4 5 After the development of the GLI-2012 spirometric norms,3 the application of a more suitable and new statistical techniques for determining the LLN is commended.3 6 The LMS [lambda, mu, sigma] technique was used.3 6 Based on the LMS method, a further approach based on the determined data’ z-scores, was suggested to interpret spirometric data.3 6 The z-score specifies by how many standard-deviations a subject’ spirometric data is deviated from its predicted normal value, with merely 5% of healthy subjects having a z-score ≤ -1.645.3 6 Disparate percentage predicted, z-score is free from bias due to sex, age, height, and ethnicity, and is consequently principally convenient in defining the LLN.3 6 Z-score simplifies uniform analysis of spirometric results.3 6 In brief, a lung function data value is considered low when its z-score is < -1.645, and normal when its z-score is ≥ -1.645.4 7 In Saavedra et al’s study.1, it is unclear if the authors have applied the z-score approach.
  What is a RVI?
  A reduction in lung volumes defines a RVI, which is classically characterized by a low total-lung-capacity (TLC).4 The presence of a RVI may be suspected (but not confirmed) from spirometry alone when FVC is low, FEV1/FVC is normal, and the flow-volume curve displays a convex pattern (ie; revealing a high elastic recoil).4 Nevertheless, a low FVC by itself does not confirm a RVI.2 4 Certainly, a low FVC is connected with a low TLC less than half the time.8 Contrariwise, normal “FVC and FEV1/FVC” are greatly trustworthy at ruling out a RVI as measured by low TLC.8 Finally, a MVI (ie, presence of both OVI and RVI) is retained in front of the association of “low TLC and low FEV1/FVC ratio”.4
  To conclude, in practice, two distinct, yet complementary aspects of spirometry interpretation, should be considered.4 First, cataloging the observed values as within/outside the normal range with respect to the GLI-2012 norms (eg, z-score < 1.645 or ≥ 1.645). Second, incorporating information of physiologic factors of test results into a functional classification of the recognized impairments (eg, OVI, RVI, MVI).

  REFERENCES
  1. Saavedra JM, Brellenthin AG, Song BK, et al. Associations of cardiorespiratory fitness and body mass index with incident restrictive spirometry pattern. Br J Sports Med 2023 doi: 10.1136/bjsports-2022-106136 [published Online First: 20230106]
  2. Backman H, Eriksson B, Hedman L, et al. Restrictive spirometric pattern in the general adult population: Methods of defining the condition and consequences on prevalence. Respir Med 2016;120:116-23. doi: 10.1016/j.rmed.2016.10.005 [published Online First: 20161012]
  3. 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. doi: 10.1183/09031936.00080312 [published Online First: 20120627]
  4. Stanojevic S, Kaminsky DA, Miller MR, et al. ERS/ATS technical standard on interpretive strategies for routine lung function tests. Eur Respir J 2022;60(1) doi: 10.1183/13993003.01499-2021 [published Online First: 20220713]
  5. Ben Saad H. Interpretation of respiratory functional explorations of deficiency and incapacity in adult. Tunis Med 2020;98(11):797-815. [published Online First: 2021/01/23]
  6. Hall GL, Filipow N, Ruppel G, et al. Official ERS technical standard: Global Lung Function Initiative reference values for static lung volumes in individuals of European ancestry. Eur Respir J 2021;57(3) doi: 10.1183/13993003.00289-2020 [published Online First: 20210311]
  7. Ben Saad H. Review of the current use of global lung function initiative norms for spirometry (GLI-2012) and static lung volumes (GLI-2021) in Great Arab Maghreb (GAM) countries and steps required to improve their utilization. Libyan J Med 2022;17(1):2031596. doi: 10.1080/19932820.2022.2031596
  8. Aaron SD, Dales RE, Cardinal P. How accurate is spirometry at predicting restrictive pulmonary impairment? Chest 1999;115(3):869-73. doi: 10.1378/chest.115.3.869.

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  Conflict of Interest:
  None declared.

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