Reference Equations for Spirometry in the Canadian Population

Effectiveness of Aspirin on Major COPD Outcomes: A Prevalent New-User Design Observational Study

Observational studies that have reported an association between aspirin use in chronic obstructive pulmonary disease (COPD) with reductions in mortality and COPD exacerbations were shown to be affected by time-related biases. We assessed this association using a prevalent new-user study design that avoids these biases. We used the United Kingdom's Clinical Practice Research Datalink (CPRD) to form a cohort of patients with COPD. Aspirin initiators were matched on time and propensity score with nonusers during 2002-2018. The outcomes were all-cause mortality and COPD exacerbation within a one-year follow-up. Hazard ratios (HR) and 95% confidence interval (CI) of each outcome associated with aspirin use compared to nonuse were estimated using an as-treated approach. The study cohort included 10,287 initiators of aspirin and 10,287 matched nonusers. The cumulative incidence of all-cause mortality at one year was 11.5% for aspirin users and 9.2% for nonusers. The HR of all-cause mortality associated with aspirin initiation was 1.22 (95% CI: 1.08-1.37), while for severe exacerbation it was 1.21 (95% CI 1.08-1.37), compared with nonuse. The HR of a first moderate or severe exacerbation with aspirin use was 0.90 (95% CI 0.85-0.95). These estimates did not vary by platelet count. This large population-based study, designed to emulate a trial, found aspirin use in patients with COPD associated with a higher risk of all-cause mortality and severe exacerbation, but a lower risk of moderate or severe exacerbation. Further research is warranted to assess this reduction in moderate or severe exacerbations, particularly in patients with cardiovascular risk factors.

Reference Values for Spirometry in Moroccan Adults

INTRODUCTION

This novel study aimed to establish spirometric reference values and prediction equations based on a sample of the adult Moroccan population, an endeavor that has not been attempted previously.

METHODS

In this cross-sectional study involving healthy Moroccan adults, data was collected through a mobile spirometry setup.

RESULTS

Our sample comprised 841 healthy adults (384 men and 457 women) aged 18-86 years who underwent spirometry. For both sexes, the Global Lung Function Initiative 2012 equations for Caucasians corresponded the best to the studied sample but were not perfectly compatible.

CONCLUSION

The spirometric prediction equations established in this study for Moroccan adults aged 18-86 years best represent the Moroccan population. More extensive future studies are needed to enrich the database of reference values and prediction equations derived from our research.

Virtual pulmonary rehabilitation approaches in patients with post COVID syndrome: a pilot study

BACKGROUND

The characteristics of optimal virtual pulmonary rehabilitation (PR) for individuals with post-COVID syndrome (PCS) have not been identified. This study aimed to assess the feasibility, safety, and satisfaction associated with a virtual PR program with the exercise component delivered through group or self-directed sessions.

METHODS

Adults with PCS-respiratory symptoms were randomly assigned to the video conference (PRVC) or self-directed (PRSD) group and completed an exercise program (aerobic, strengthening, and breathing exercises) three times/week for eight weeks. PRVC sessions were led by a physiotherapist via Zoom, whereas the PRSD group exercised individually following a pre-recorded video. Both groups received personalized exercise recommendations, education related to the condition, and a weekly follow up call. Satisfaction was assessed through a patient survey. Lung function, dyspnea, fatigue, sit-to-stand capacity, health-related quality of life, and participation were assessed pre- and post-PR.

RESULTS

Fourteen PCS individuals (49 ± 9 years, 86% females) completed 83% of the sessions. All participants were satisfied with information provided by the therapist and frequency of data submission, whereas most were satisfied with the frequency and duration of exercise sessions (88% in PRVC and 83% in PRSD). A higher proportion of participants in the PRVC (88%) were satisfied with the level of difficulty of exercises compared with the PRSD (67%), and 84% of the sample reported a positive impact of the program on their health. No adverse events were reported. Significant changes in sit-to-stand capacity (p = 0.012, Cohen's r = 0.67) and questions related to fatigue (p = 0.027, Cohen's r = 0.58), neurocognitive (p = 0.045, Cohen's r = 0.53), and autonomic (p = 0.024, Cohen's r = 0.60) domains of the DePaul Symptom Questionnaire short-form were also found between groups.

CONCLUSION

Virtual PR with exercises delivered via video conference or pre-recorded video were feasible, safe, and well-received by individuals with PCS.

TRIAL REGISTRATION

NCT05003271 (first posted: 12/08/2021).

Using Remote Technology to Engage Patients with Interstitial Lung Diseases in a Home Exercise Program: A Pilot Study

INTRODUCTION

The access and compliance of patients with interstitial lung diseases (ILDs) to exercise programs (EPs) remain challenges.

OBJECTIVES

We assessed the dropout rate, intervention completion, compliance with data acquisition and submission, safety, and satisfaction of a home EP delivered via video conference (EPVC group) or self-directed (EPSD group) to patients with ILD. Pre- and post-intervention changes in patient outcomes (dyspnea, fatigue, exercise capacity, lung function, and quality of life) were secondarily explored.

MATERIAL AND METHODS

Groups performed an eight-week virtual EP three times/week. Video conferences were led by a registered respiratory therapist, whereas self-directed exercises were completed following a pre-recorded video. Participants submitted spirometry, heart rate, and SpO2 results weekly to the research team.

RESULTS

Fourteen patients with ILD were equally assigned to the EPVC and EPSD groups, but three from the EPSD group dropped out after the initial assessment (dropout rate of 42.8% in the EPSD group). Eleven patients (mean age of 67 ± 12 years) completed 96.5% of sessions. Compliance with data acquisition and submission was optimal (≥97.6% in both groups), and no adverse events were reported. Changes in overall fatigue severity were significantly different between groups (p = 0.014, Cohen's r = 0.64).

CONCLUSIONS

The results suggest that a structured virtual EP delivered via video conference or pre-recorded video can be feasible, safe, and acceptable for patients with ILD.

Development and validation of predictive equations for spirometry in Portuguese children

Background

There are no data on lung function reference values for Portuguese children, and the contribution from the Portuguese data set in the Global Lung Function Initiative (GLI) is scant.

Objectives

We aimed to estimate new up-to-date reference values for Portuguese children by fitting a multivariable regression model to a general population sample. Further, we intended to assess the external validity of the obtained reference values and to compare them to the GLI reference values.

Methods

A random sample of 858 children from 20 primary schools were screened by health questionnaire, physical examination, and spirometry. Spirometric parameters recorded were FVC, FEV1, and FEF25-75. Multiple regression models were used to derive reference equations.

Results

Overall, 481 children, aged between 7 and 12 years, 267 boys (55.5%), were included. Boys had higher values for FVC and FEV1 than girls (P < .05). The strongest correlation was found for FVC with height (r = 0.71 for boys and 0.70 for girls), while the lowest correlation was observed in both sexes for FEF25-75 with age (r = 0.23). Height was the most significant predictor of FVC, FEV1, and FEF25-75 in our models. Weight and body mass index were not significant predictors for boys but had a significant effect on girls' equations for all spirometry parameters. Compared to obtained reference equations with GLI, they performed better for FVC in boys, FEV1 in girls, and FEF25-75 in both boys and girls.

Conclusion

We offer up-to-date reference values of spirometry for Portuguese children that can be used in clinical practice and research.

Sex-specific characteristics for the coexistence of asthma and COPD in the Canadian population: a cross-sectional analysis of CLSA data

Objective: The coexistence of asthma and COPD (asthma + COPD) is a condition found among patients who present with clinical features of both asthma and COPD. Epidemiological evidence points to an increasingly disproportionate burden of asthma + COPD and COPD in females. The objective of this cross-sectional study is to identify female and male-specific epidemiological and clinical characteristics associated with asthma + COPD.Methods: Baseline data from the comprehensive cohort of Canadian Longitudinal Study on Aging (CLSA) were used in this cross-sectional study which included 30,097 subjects between the ages of 45- and 85-years Participants were categorized into four mutually exclusive groups: asthma + COPD, COPD-only, asthma-only and neither asthma nor COPD.Results: The prevalence was significantly greater in females than males for asthma + COPD (2.71% vs. 1.41%; p < 0.001), COPD-only (3.22% vs. 2.87%; p < 0.001) and asthma-only (13.31% vs. 10.11%; p < 0.001). The association between smoking and asthma + COPD was modified by age in females. Osteoporosis and underactive thyroid disease were significantly more prevalent in females than in males in asthma + COPD, COPD-only and asthma-only groups. In asthma + COPD group, a greater proportion of respiratory symptoms associated with asthma was observed in females whereas a greater proportion of respiratory symptoms associated with COPD was observed in males. Severity of airway obstruction determined by spirometry measurements was greater in males than females.Conclusions: In the Canadian adult population, several epidemiological and clinical characteristics in asthma + COPD varied between females and males. The findings in this study will help healthcare professional in the recognition and management of coexisting asthma and COPD in females and males.

Exploring the 175-year history of spirometry and the vital lessons it can teach us today

175 years have elapsed since John Hutchinson introduced the world to his version of an apparatus that had been in development for nearly two centuries, the spirometer. Though he was not the first to build a device that sought to measure breathing and quantify the impact of disease and occupation on lung function, Hutchison coined the terms spirometer and vital capacity that are still in use today, securing his place in medical history. As Hutchinson envisioned, spirometry would become crucial to our growing knowledge of respiratory pathophysiology, from Tiffeneau and Pinelli's work on forced expiratory volumes, to Fry and Hyatt's description of the flow-volume curve. In the 20th century, standardization of spirometry further broadened its reach and prognostic potential. Today, spirometry is recognized as essential to respiratory disease diagnosis, management and research. However, controversy exists in some of its applications, uptake in primary care remains sub-optimal and there are concerns related to the way in which race is factored into interpretation. Moving forward, these failings must be addressed, and innovations like Internet-enabled portable spirometers may present novel opportunities. We must also consider the physiologic and practical limitations inherent to spirometry and further investigate complementary technologies such as respiratory oscillometry and other emerging technologies that assess lung function. Through an exploration of the storied history of spirometry, we can better contextualize its current landscape and appreciate the trends that have repeatedly arisen over time. This may help to improve our current use of spirometry and may allow us to anticipate the obstacles confronting emerging pulmonary function technologies.

A simplified strategy for donor-recipient size-matching in lung transplant for interstitial lung disease

BACKGROUND

Donor-recipient size-matching has been repeatedly reported to improve outcomes following lung transplantation (LTx). However, there is significant variability in practice and the optimal strategy for size-matching is yet to be defined. For recipients with ILD, size-matching decisions are complicated by concerns regarding the potential impact of pre-LTx pulmonary restriction. We evaluate whether a specific donor-to-recipient size-matching strategy, based on predicted total lung capacity, benefits this patient group.

METHODS

This retrospective, single-centre, cohort study describes the post-LTx outcomes of adults who underwent LTx for ILD between 1983 and 2020. Only patients with restrictive physiology, based on pre-LTx pulmonary function testing were included. Post-LTx outcomes were compared based on donor-recipient predicted TLC (D-R pTLC) ratio. A D-R pTLC ratio of ≥0.8 or <1.2 for DLTx, and a D-R pTLC ratio of ≥0.8 or <1.0 for SLTx were classified as 'size-matched'.

RESULTS

Five-hundred and fifty LTx recipients met inclusion criteria. Of these, 404 underwent DLTx and 146 underwent SLTx. Size-matching was achieved in 78% of DLTx and 47% of SLTx. Overall survival (p = 0.007) and CLAD-free survival (p < 0.001) was significantly improved following a size-matched DLTx, compared to those with D-R pTLC ratios <0.8 or ≥1.2. Size-matching based on a D-R pTLC ratio 0.8≥ <1.0 for SLTX did not significantly improve survival.

CONCLUSIONS

D-R pTLC size-matching, based on a ratio of 0.8≥ <1.2 improved post-DLTx outcomes for patients with restrictive lung disease. This is simple to do, and if applied clinically, could improve overall outcomes in lung transplantation.

Respiratory health, occupation and the healthy worker effect

BACKGROUND

Workers are exposed to physical, chemical and other hazards in the workplace, which may impact their respiratory health.

AIMS

To examine the healthy worker effect in the Canadian working population and to identify the association between occupation and respiratory health.

METHODS

Data from four cycles of the Canadian Health Measures Survey were utilized. The current occupation of employed participants was classified into 10 broad categories based on National Occupation Category 2011 codes. Data relating to 15 400 subjects were analysed.

RESULTS

A significantly lower proportion of those in current employment than those not in current employment reported respiratory symptoms or diseases or had airway obstruction. Similarly, those currently employed reported better general health and had greater mean values for percent-predicted forced vital capacity (FVC), forced expiratory volume in one second (FEV1), forced expiratory flow between 25% and 75% of FVC (FEF25-75%) and FEV1/FVC ratio. Among males, females and older age groups, significant differences were observed for almost all the respiratory outcomes for those in current employment. Those in 'Occupations unique to primary industry' had a significantly greater likelihood of regular cough with sputum and ever asthma and had lower mean values of percent-predicted FEV1/FVC and FEF25-75% than those in 'Management occupations'. Those in 'Health occupations' had the highest proportion of current asthma.

CONCLUSIONS

Participants in current employment were healthier than those not in current employment providing further support for the healthy worker effect. Those in 'Occupations unique to primary industry' had an increased risk of adverse respiratory outcomes and reducing workplace exposures in these occupations has the potential to improve their respiratory health.

Comparison of five major airflow limitation criteria to identify high-risk individuals with COPD: a contemporary population-based cohort

Background

Different airflow limitation criteria are often used to diagnose COPD. We investigated head-to-head whether Global Initiative for Chronic Obstructive Lung Disease (GOLD) (FEV1/FVC <0.70) and four lower limit of normal (LLN) (FEV1/FVC <LLN) criteria to diagnose airflow limitation differ in identifying individuals at risk of COPD exacerbations and mortality.

Methods

108 246 individuals aged 20–100 years randomly selected from the general population were followed from 2003 through 2018 to determine risk of COPD exacerbations, respiratory mortality and all-cause mortality. LLN criteria used equations from Global Lung Initiative (GLI), National Health and Nutrition Examination Survey (NHANES), European Community for Steel and Coal (ECSC) and Copenhagen City Heart Study (CCHS)/Copenhagen General Population Study (CGPS).

Results

Prevalence of airflow limitation was 17% for GOLD, 8.6% for GLI, 10% for NHANES, 8.2% for ECSC and 14% for CCHS/CGPS. During 14.4 years follow-up, we observed 2745 COPD exacerbations, 762 respiratory deaths and 10 338 all-cause deaths. Comparing individuals with versus without airflow limitation, HRs for COPD exacerbations were 17 (95% CI 14 to 20) for GOLD, 21 (18 to 24) for GLI, 20 (17 to 23) for NHANES, 21 (18 to 24) for ECSC and 18 (16 to 21) for CCHS/CGPS. Corresponding HRs for respiratory mortality were 3.7 (3.1 to 4.3), 6.4 (5.6 to 7.5), 5.7 (4.9 to 6.6), 6.2 (5.3 to 7.2) and 4.5 (3.9 to 5.2), and for all-cause mortality 1.5 (1.4 to 1.5), 1.9 (1.8 to 2.0), 1.8 (1.7 to 1.9), 1.9 (1.8 to 2.0) and 1.7 (1.6 to 1.7), respectively. Differences in Harrell’s C were minute for these outcomes; nonetheless, Harrell’s C was slightly higher for LLN criteria compared with GOLD for mortality outcomes.

Conclusions

The prevalence of airflow limitation ranged from 8% to 17% using GOLD and four different LLN criteria; however, identified individuals with the five different criteria had similar risk of COPD exacerbations and mortality.

Reduced forced vital capacity is independently associated with ethnicity, metabolic factors and respiratory symptoms in a Caribbean population: a cross-sectional study

Background

Relationships between low forced vital capacity (FVC), and morbidity have previously been studied but there are no data available for the Caribbean population. This study assessed the association of low FVC with risk factors, health variables and socioeconomic status in a community-based study of the Trinidad and Tobago population.

Methods

A cross-sectional survey was conducted using the Burden of Obstructive Lung Disease (BOLD) study protocol. Participants aged 40 years and above were selected using a two-stage stratified cluster sampling. Generalized linear models were used to examine associations between FVC and risk factors.

Results

Among the 1104 participants studied a lower post-bronchodilator FVC was independently associated with a large waist circumference (− 172 ml; 95% CI, − 66 to − 278), Indo-Caribbean ethnicity (− 180 ml; 95% CI, − 90 to − 269) and being underweight (− 185 ml; 95% CI, − 40 to − 330). A higher FVC was associated with smoking cannabis (+ 155 ml; 95% CI, + 27 to + 282). Separate analyses to examine associations with health variables indicated that participants with diabetes (p = 0∙041), history of breathlessness (p = 0∙007), and wheeze in the past 12 months (p = 0∙040) also exhibited lower post-bronchodilator FVC.

Conclusion

These findings suggest that low FVC in this Caribbean population is associated with ethnicity, low body mass index (BMI), large waist circumference, chronic respiratory symptoms, and diabetes.

Electronic supplementary material

The online version of this article (10.1186/s12890-019-0823-9) contains supplementary material, which is available to authorized users.

Daily Objective Physical Activity and Sedentary Time in Adults with COPD Using Spirometry Data from Canadian Measures Health Survey

Chronic obstructive pulmonary disease (COPD) is expected to be the third leading cause of premature death and disability in Canada and around the world by the year 2020. The study aims to compare objective physical activity (PA) and sedentary time in a population-based sample of adults with chronic obstructive pulmonary disease (COPD) and compare a group, and to investigate whether these behaviors differ according to COPD severity. From the 2007–2013 Canadian Health Measures Survey dataset, accelerometer and prebronchodilator spirometry data were available for 6441 participants, aged 35 to 79. Two weighted analyses of covariance were performed with adjustments for age, sex, body mass index, accelerometer wearing time, season, work, smoking (cotinine), education level, and income. A set of sensitivity analyses were carried out to examine the possible effect of COPD and type of control group. A cross-sectional weighted analysis indicated that 14.6% of study participants had a measured airflow obstruction consistent with COPD. Time in PA (moderate-vigorous and light PA), number of steps, and sedentary duration were not significantly different in participants with COPD, taken together, compared to controls. However, moderate to severe COPD participants (stages ≥2) had a significantly lower daily time spent in PA of moderate and vigorous intensity level compared to controls. Canadian adults with COPD with all disease severity levels combined did not show lower daily duration of light, moderate, and vigorous PA, and number of steps and higher daily sedentary time than those without airflow obstruction. Both groups are extremely sedentary and have low PA duration. Thus, “move more and sit less” public health strategy could equally target adults with or without COPD.

Characteristics of asthma and COPD overlap syndrome (ACOS) in the Canadian population

Objective: Asthma is a chronic disease affecting both children and adults, whereas chronic obstructive pulmonary disease (COPD) is a respiratory disease most commonly related to smoking and is usually seen in adults. When the airway disease shares features of both asthma and COPD, the phenotype is referred to as asthma and COPD overlap syndrome (ACOS). The objective of this cross-sectional study is to characterize ACOS in the Canadian population. Methods: Data from the first three cycles of the Canadian Health Measures Survey (CHMS) were used in this study. The study included 9059 subjects aged 30 years and above. The CHMS included a detailed interviewer-administered questionnaire and spirometry measurements. Based on the self-report, subjects were categorized into control, ACOS, COPD only and asthma only groups. Results: The prevalence of ACOS, COPD and asthma groups was 1.59%, 2.21% and 6.65%, respectively. The proportion of females was significantly greater than males in the ACOS group. The proportion of wheeze was highest in the ACOS group (64.93%) whereas the prevalence of shortness of breath was the highest in the COPD group (46.25%). Heart disease, cancer, arthritis and liver disease were more prevalent in the ACOS group than in COPD, asthma and control groups. Severity of airway obstruction was the highest in the ACOS group and was followed by COPD, asthma and control groups, respectively. Conclusions: Characteristics of ACOS in the Canadian population were similar to those observed in the developed countries and longitudinal studies are required to determine the incidence and risk factors of ACOS.

Does Size Matter When Calculating the "Correct" Tidal Volume for Pediatric Mechanical Ventilation?: A Hypothesis Based on FVC

BACKGROUND

Tidal volumes standardized to predicted body weight are recommended for adult mechanical ventilation, but children are frequently ventilated by using measured body weight. The goal of this study was to examine the difference in FVC (in milliliters per kilogram [mL/kg]) by using measured body weight compared with predicted body weight in children.

METHODS

This retrospective analysis included outpatient pulmonary function tests (PFTs) from two datasets. Dataset one included 6- to 19-year-old patients undergoing PFTs from the nationally representative Canadian Health Measures Survey. Dataset two included 6- to 20-year-old patients undergoing PFTs at a freestanding children's hospital. FVC mL/kg values were analyzed against BMI z scores to show changes in FVC vs BMI between measured and predicted weight.

RESULTS

Dataset one included 5,394 PFTs from the Canadian survey. FVC from measured weight decreased as the BMI z score group increased. The median FVC from measured weight was 81.4 mL/kg in the lowest BMI z score group and 51.7 mL/kg in the highest BMI z score group. FVC from predicted weight increased slightly with increasing BMI z score group. Dataset two included 8,472 patient PFTs from clinical measurement. A decline in median FVC from measured weight (from 69.4 to 37.6 mL/kg) as BMI z score group increased was also seen.

CONCLUSIONS

FVC differs significantly when standardizing to measured weight vs predicted weight. Obese children have lung volumes reflecting their predicted body weight from height. Children with low or normal BMI have lung volumes reflecting measured body weight. These findings suggest that targeting tidal volume by using the lower of measured and predicted body weights would be the most lung-protective strategy.

Review of biomarkers to assess the effects of switching from cigarettes to modified risk tobacco products

Context: One approach to reducing the harm caused by cigarette smoking, at both individual and population level, is to develop, assess and commercialize modified risk alternatives that adult smokers can switch to. Studies to demonstrate the exposure and risk reduction potential of such products generally involve the measuring of biomarkers, of both exposure and effect, sampled in various biological matrices.Objective: In this review, we detail the pros and cons for using several biomarkers as indicators of effects of changing from conventional cigarettes to modified risk products.Materials and methods: English language publications between 2008 and 2017 were retrieved from PubMed using the same search criteria for each of the 25 assessed biomarkers. Nine exclusion criteria were applied to exclude non-relevant publications.Results: A total of 8876 articles were retrieved (of which 7476 were excluded according to the exclusion criteria). The literature indicates that not all assessed biomarkers return to baseline levels following smoking cessation during the study periods but that nine had potential for use in medium to long-term studies.Discussion and conclusion: In clinical studies, it is important to choose biomarkers that show the biological effect of cessation within the duration of the study.

Recommendations for a Standardized Pulmonary Function Report. An Official American Thoracic Society Technical Statement

BACKGROUND

The American Thoracic Society committee on Proficiency Standards for Pulmonary Function Laboratories has recognized the need for a standardized reporting format for pulmonary function tests. Although prior documents have offered guidance on the reporting of test data, there is considerable variability in how these results are presented to end users, leading to potential confusion and miscommunication.

METHODS

A project task force, consisting of the committee as a whole, was approved to develop a new Technical Standard on reporting pulmonary function test results. Three working groups addressed the presentation format, the reference data supporting interpretation of results, and a system for grading quality of test efforts. Each group reviewed relevant literature and wrote drafts that were merged into the final document.

RESULTS

This document presents a reporting format in test-specific units for spirometry, lung volumes, and diffusing capacity that can be assembled into a report appropriate for a laboratory's practice. Recommended reference sources are updated with data for spirometry and diffusing capacity published since prior documents. A grading system is presented to encourage uniformity in the important function of test quality assessment.

CONCLUSIONS

The committee believes that wide adoption of these formats and their underlying principles by equipment manufacturers and pulmonary function laboratories can improve the interpretation, communication, and understanding of test results.

The Global Lung Function Initiative (GLI) Network: bringing the world's respiratory reference values together

The Global Lung Function Initiative (GLI) Network has become the largest resource for reference values for routine lung function testing ever assembled. This article addresses how the GLI Network came about, why it is important, and its current challenges and future directions. It is an extension of an article published in Breathe in 2013 [1], and summarises recent developments and the future of the GLI Network.

Learn about the GLI Network, the largest resource reference for routine lung function testinghttp://ow.ly/ZZor30epWgi

Global Lung Function Initiative 2012 reference values for spirometry in South Italian children

RATIONALE

Despite the widespread use of the Global Lung Function Initiative (GLI) 2012 reference values, there is still the need of testing their applicability in local areas.

OBJECTIVES

The aims of this study are to evaluate applicability of GLI reference equations in a large population-based sample of normal schoolchildren from Sicily, and to compare GLI and previous prediction equations in terms of spirometry test interpretation.

METHODS

GLI equations were evaluated in 1243 normal schoolchildren, 49% males, aged 7-16 years, height 116-187 cm. Normality assumptions for the GLI z-scores (FEV₁, FVC, FEV₁/FVC) were tested, and bootstrap confidence intervals for the mean (0 expected) and the variance (1 expected) were derived. GLI and other reference equations were compared in terms of probabilities to fall below the lower limit of normal (LLN).

RESULTS

The GLI z-score normality assumption held for males but not for females (p < 0.001). According to the mean z-score, predicted values were: slightly underestimated for FEV₁ (0.15 in males, 0.07 in females); overestimated for FVC (-0.27 in males, -0.32 in females); highly underestimated for FEV₁/FVC (0.75 in males, 0.81 in females). Variability was correctly estimated. The probability of FEV₁<LLN correctly approached 0.05 when using GLI, Hankinson and Quanjer equations. Wang equations yielded correct probabilities of abnormal FVC; Pistelli equations yielded correct probabilities of abnormal FEV₁/FVC for females.

CONCLUSIONS

GLI 2012 references underestimate FEV₁/FVC predicted values in a sample of normal South Italian children. Physicians interpreting spirometry should be aware to test reference values prior to their use in a local area.