Clinical Spirometry Testing and Walk Tests
Pulmonary function tests (PFTs) are crucial tools in the field of respiratory medicine, allowing us to assess lung function and helping to diagnose a wide range of respiratory disorders. Like the majority of physiological parameters, respiratory measures adhere to a normal Gaussian distribution. Consequently, determining whether a specific parameter falls within the realm of normalcy or deviates into pathology can be a nuanced challenge. We provide the latest ATS / ERS standards.
Trying to catch your breath should not always be hard
1.
Decreased Respiratory Capacity
Across the adult life span, there are reductions in physioogical capacity, including ventilatory control, respiratory muscle strength, respiratory mechanics, and gas exchange. These age-related changes have two important implications. First, from a clinical perspective, the age-related decline in physiological reserve may increase the vulnerability of developing a respiratory impairment, particularly in response to tobacco smoke or a respiratory infection [1]. Second, from a diagnostic perspective, the age-related decline in physiological capacity must be considered before attributing a reduction in pulmonary function to a pathological process. Lower limits of normal (LLN)s do not necessarily indicate a pathophysiological abnormality, nor do they serve as a clinically meaningful threshold for diagnosing diseases. Instead, they offer insight into whether the observed result aligns with what can be expected in otherwise healthy individuals of similar age, sex, and height [2].
The ERS and ATS recently revised their interpretive strategies for routine pulmonary function test (PFT)s [2], alongside their established spirometry standardisation [5].
Vaz Fragoso CA, Gill TM. Defining chronic obstructive pulmonary disease in an aging population. [Editorial]. J Am Geriatr Soc. 2010;58:2224–2226.
Stanojevic, S.; Kaminsky, D.A.; Miller, M.R.; Thompson, B.; Aliverti, A.; Barjaktarevic, I.; Cooper, B.G.; Culver, B.; Derom, E.; Hall, G.L.; et al. ERS/ATS technical standard on interpretive strategies for routine lung function tests. Eur. Respir. J. 2022, 60, 2101499.
2.
Accurate PFT Interpretation
We note that spirometry results should not be viewed as a standalone clinical diagnosis but must be interpreted in conjunction with other preclinical tests and clinical symptoms [3]. Additionally, it is important to note that normal spirometric results do not necessarily indicate the absence of underlying lung issues. Other tests, such as the forced oscillometry technique (FOT) and cardiopulmonary exercise test (CPET) may be needed to detect potential problems for example [4].
However the cornerstone of accurate PFT interpretation lies in the acceptability and reproducibility of these manoeuvres. To ensure high-quality reproducibility, at least three acceptable manoeuvres are required. We consider it crucial to account for safety—ensuring there are no contraindications to performing the test which encompasses acceptability and reproducibility of PFT manoeuvres [5].
3. Calle Rubio, M.; Rodríguez Hermosa, J.L.; Miravitlles, M.; López-Campos, J.L. Determinants in the Underdiagnosis of COPD in Spain-CONOCEPOC Study. J. Clin. Med. 2022, 11, 2670.
4. Veneroni, C.; Valach, C.; Wouters, E.F.M.; Gobbi, A.; Dellacà, R.L.; Breyer, M.-K.; Hartl, S.; Sunanta, O.; Irvin, C.G.; Schiffers, C.; et al. Diagnostic Potential of Oscillometry: A Population-based Approach. Am. J. Respir. Crit. Care Med. 2024, 209, 444–453.
5. Graham, B.L.; Steenbruggen, I.; Miller, M.R.; Barjaktarevic, I.Z.; Cooper, B.G.; Hall, G.L.; Hallstrand, T.S.; Kaminsky, D.A.; McCarthy, K.; McCormack, M.C.; et al. Standardization of Spirometry 2019 Update. An Official American Thoracic Society and European Respiratory Society Technical Statement. Am. J. Respir. Crit. Care Med. 2019, 200, e70–e88.
3.
FEV1/FVC and FEV1/VCmax
We use both forced expiratory volume in one second / forced vital capacity or FEV1/FVC ratio and forced expiratory volume in one second / maximum vital capacity or FEV1/VCmax to help diagnose obstruction, restriction or both given a restrictive pattern is defined based on total lung capacity rather than FVC alone, (a normal FVC does not preclude a decreased total lung capacity).
Historically the true Pinelli-Tiffeneau index is defined as the FEV1/VC ratio [6]. This metric is favoured due to its superior assessment of static lung volumes through a quasi-static manoeuvre, such as the slow vital capacity (SVC), in contrast to forced manoeuvres that may exacerbate alveolar collapse [7, resulting in lower measurements. For these reasons, SVC should be preferred. Alternatively, integrating the differences, the maximum vital capacity (VC max) could be a valid option.
Solution
The unified flow chart, shown in part above, incorporates FEV1/VCmax to enhance the sensitivity of detecting obstructive patterns. It strongly recommends reporting if the FEV1/FVC is below 0.7, allowing for the possibility of identifying a normal spirometric pattern in the elderly with a reduced ratio. This approach alleviates potential issues regardless of whether only the forced maneuver or both slow and forced maneuvers are performed, using VCmax. Additionally, if the FEV1/FVC ratio is below 0.7 this also provides a clearer pathway to diagnosing COPD, assuming other conditions are met.
6. Yernault, J. The birth and development of the forced expiratory manoeuvre: A tribute to Robert Tiffeneau (1910–1961). Eur. Respir. J. 1997, 10, 2704–2710.
7. Fernandez, J.J.; Castellano, M.V.C.d.O.; Vianna, F.d.A.F.; Nacif, S.R.; Rodrigues Junior, R.; Rodrigues, S.C.S. Clinical and functional correlations of the difference between slow vital capacity and FVC. J. Bras. Pneumol. 2020, 46, e20180328.
New PFT Assessment Standards
The American Thoracic Society (ATS) has recommended a major change in the reporting format of pulmonary function tests (PFTs) with the inclusion of terms, lower limit of normal (LLN) to define abnormality, and z-scores, to define deviation from predicted values [1]. This was endorsed in the recent statement of the ATS and European Respiratory Society (ERS) on the interpretation of PFTs. The latter further recommended that the severity of impairment should be categorised in terms of Z scores.
The predicted values, LLN, and z scores are calculated using the equations from the Global Lung Function Initiative GLI [2]. The guidelines for interpreting bronchodilation results have recently changed according to spirometric guidelines, now evaluating a positive response if the FEV1 or FVC increases by more than 10% of the predicted value. Conversely, the interpretation of DLco remains unchanged, with only the severity now being assessed using z-score criteria [1].
LLN = Predicted value – (1.645 × SEE)
Thus, only 5% of the normal population will have values less than the LLN and will be wrongly labeled as abnormal (i.e., false positives). This is considered an acceptable rate of error in statistics. Similarly, the 95% percentile (+1.64 SEE) represents the ULN or the upper limit of normal. For spirometry parameters, there is no upper limit of normal (ULN) while lung volume and diffusion capacity parameters have both LLN and ULN. In essence The LLN defines the lower end of the normal range, and the z-score quantifies the deviation or difference from the predicted value [3].
A z-score of −1 means that the measured value is one SEE unit less than the predicted value.
z-score = (Predicted – Measured value)/SEE
FEV1 is considered a valuable indicator for classifying the severity of respiratory disorders [67,68]. In terms of quantifying this severity, the FEV1 is interpreted as
follows: a pattern is considered;
‘mild’ if FEV1 is between−1.645 and−2.5 standard deviations from the norm,
‘severe’ if between−2.5 and−4,
and ‘very severe’ if below−4 standard deviations.‘very severe’ if below−4 standard deviations.
References
Stanojevic, S.; Kaminsky, D.A.; Miller, M.R.; Thompson, B.; Aliverti, A.; Barjaktarevic, I.; Cooper, B.G.; Culver, B.; Derom, E.; Hall, G.L.; et al. ERS/ATS technical standard on interpretive strategies for routine lung function tests. Eur. Respir. J. 2022, 60, 2101499.
Cooper, B. G., Stocks, J., Hall, G. L., Culver, B., Steenbruggen, I., Carter, K. W., Thompson, B. R., Graham, B. L., Miller, M. R., Ruppel, G., Henderson, J., Vaz Fragoso, C. A., & Stanojevic, S. (2017). The Global Lung Function Initiative (GLI) Network: bringing the world's respiratory reference values together. Breathe (Sheff), 13(3), e56-e64.
Chhabra, S. K. (2025). Understanding the use of z-scores and LLN in pulmonary function test reports. Lung India, 42(1), 1-3.
* SEE = Standard Error of Estimate