Maximal Expiratory Flow-volume Research Articles

The Concavity of the Maximal Expiratory Flow\u2013Volume Curve Reflects the Extent of Emphysema in Obstructive Lung Diseases

A concave-shaped maximal expiratory flow-volume (MEFV) curve is a spirometric feature in chronic obstructive pulmonary disease (COPD). The MEFV curve is characterized by an increase in the Obstructive Index, which is defined as a ratio of forced vital capacity to the volume-difference between two points of half of the peak expiratory flow on the MEFV curve. We hypothesized that the Obstructive Index would reflect the severity of emphysema in patients with COPD and asthma-COPD overlap (ACO). Thus, the aim of this retrospective study was to evaluate whether the Obstructive Index on spirometry is associated with the extent of emphysema on computed tomography (CT) in patients with COPD, ACO, and asthma (N = 65, 15, and 53, respectively). The percentage of low-attenuation volume (LAV%) and wall area (WA%) were measured on CT. The Obstructive Index was higher in patients with COPD and ACO than in those with asthma. Spearman correlation showed that a greater Obstructive Index was associated with a higher LAV%, but not WA%. Multivariate analysis showed that Obstructive Index was associated with LAV% (standardized β = 0.43, P < 0.0001) independent of other spirometric indices. The Obstructive Index is a useful spirometric index that reflects the extent of emphysema.

Analysis of maximal expiratory flow-volume curves in adult survivors of preterm birth.

Adult survivors of very preterm (≤32 wk gestational age) birth without (PRE) and with bronchopulmonary dysplasia (BPD) have variable degrees of airflow obstruction at rest. Assessment of the shape of the maximal expiratory flow-volume (MEFV) curve in PRE and BPD may provide information concerning their unique pattern of airflow obstruction. The purposes of the present study were to 1) quantitatively assess the shape of the MEFV curve in PRE, BPD, and healthy adults born at full-term (CON), 2) identify where along the MEFV curve differences in shape existed between groups, and 3) determine the association between an index of MEFV curve shape and characteristics of preterm birth (i.e., gestational age, mass at birth, duration of oxygen therapy) in PRE and BPD. To do so, we calculated the average slope ratio (SR) throughout the effort-independent portion of the MEFV curve and at increments of 5% of forced vital capacity (FVC) between 20 and 80% of FVC in PRE (n = 19), BPD (n = 25), and CON (n = 20). We found that average SR was significantly higher in PRE (1.34 ± 0.35) and BPD (1.33 ± 0.45) compared with CON (1.03 ± 0.22; both P < 0.05) but similar between PRE and BPD (P = 0.99). Differences in SR between groups occurred early in expiration (i.e., 20-30% of FVC). There was no association between SR and characteristics of preterm birth in PRE and BPD groups (all P > 0.05). The mechanism(s) of increased SR during early expiration in PRE/BPD relative to CON is unknown but may be due to differences in the structural and mechanical properties of the airways.

Area under the forced expiratory flow-volume loop in spirometry indicates severe hyperinflation in COPD patients.

BackgroundSevere hyperinflation causes detrimental effects such as dyspnea and reduced exercise capacity and is an independent predictor of mortality in COPD patients. Static lung volumes are required to diagnose severe hyperinflation, which are not always accessible in primary care. Several studies have shown that the area under the forced expiratory flow-volume loop (AreaFE) is highly sensitive to bronchodilator response and is correlated with residual volume/total lung capacity (RV/TLC), a common index of air trapping. In this study, we investigate the role of AreaFE% (AreaFE expressed as a percentage of reference value) and conventional spirometry parameters in indicating severe hyperinflation.Materials and methodsWe used a cohort of 215 individuals with COPD. The presence of severe hyperinflation was defined as elevated air trapping (RV/TLC >60%) or reduced inspiratory fraction (inspiratory capacity [IC]/TLC <25%) measured using body plethysmography. AreaFE% was calculated by integrating the maximal expiratory flow-volume loop with the trapezoidal rule and expressing it as a percentage of the reference value estimated using predicted values of FVC, peak expiratory flow and forced expiratory flow at 25%, 50% and 75% of FVC. Receiver operating characteristics (ROC) curve analysis was used to identify cut-offs that were used to indicate severe hyperinflation, which were then validated in a separate group of 104 COPD subjects.ResultsROC analysis identified cut-offs of 15% and 20% for AreaFE% in indicating RV/TLC >60% and IC/TLC <25%, respectively (N=215). On validation (N=104), these cut-offs consistently registered the highest accuracy (80% each), sensitivity (68% and 75%) and specificity (83% and 80%) among conventional parameters in both criteria of severe hyperinflation.ConclusionAreaFE% consistently provides a superior estimation of severe hyperinflation using different indices, and may provide a convenient way to refer COPD patients for body plethysmography to address static lung volumes.

The link between chronic obstructive pulmonary disease phenotypes and histological subtypes of lung cancer: a case-control study.

BackgroundCOPD is considered an independent risk factor for lung cancer. COPD and lung cancer are both very heterogeneous diseases, and the study herein investigates the link between COPD phenotypes and specific histological subtypes of lung cancer.MethodsThis case–control study comprised 2,283 patients with newly diagnosed pathological lung cancer and 2,323 non-lung cancer controls. All participants underwent pulmonary function tests. The diagnosis of COPD was based on Global Initiative for Chronic Obstructive Lung Disease criteria. Subtypes of the two diseases were categorized according to 2015 World Health Organization classification of lung cancer and computer quantification of airway collapse on maximum expiratory flow volume. ORs were estimated using logistic regression analysis.ResultsThe prevalence of COPD was higher (32.8%) in lung cancer patients compared to controls (16.0%). After adjustment for age, sex, body-mass index, and smoking status, the presence of COPD significantly increased the risk of lung cancer (OR 2.88, 95% CI 2.48–3.34) and all common histological subtypes (ORs 2.04–5.26). Both emphysema-predominant and non-emphysema-predominant phenotypes of COPD significantly increased the risk of lung cancer (OR 4.43, 95% CI 2.85–6.88; OR 2.82, 95% CI 2.40–3.31). Higher risk of squamous-cell carcinoma and small-cell lung cancer was observed in patients with the emphysema-predominant than the non-emphysema-predominant phenotype (OR 1.73, 95% CI 1.03–2.89; OR 3.74, 95% CI 1.64–8.53).ConclusionCOPD was an independent risk factor for lung cancer and all common histological subtypes. Both emphysema-predominant and non-emphysema-predominant phenotypes of COPD significantly increased the risk of lung cancer. Relative to non-emphysema-predominant phenotype of COPD, emphysema-predominant phenotype had a higher risk of squamous-cell carcinoma and small-cell lung cancer.

The influence of thoracic gas compression and airflow density dependence on the assessment of pulmonary function at high altitude.

The purpose of this report was to illustrate how thoracic gas compression (TGC) artifact, and differences in air density, may together conflate the interpretation of changes in the forced expiratory flows (FEFs) at high altitude (>2400 m). Twenty‐four adults (10 women; 44 ± 15 year) with normal baseline pulmonary function (>90% predicted) completed a 12‐day sojourn at Mt. Kilimanjaro. Participants were assessed at Moshi (Day 0, 853 m) and at Barafu Camp (Day 9, 4837 m). Typical maximal expiratory flow‐volume (MEFV) curves were obtained in accordance with ATS/ERS guidelines, and were either: (1) left unadjusted; (2) adjusted for TGC by constructing a “maximal perimeter” MEFV curve; or (3) adjusted for both TGC and differences in air density between altitudes. Forced vital capacity (FVC) was lower at Barafu compared with Moshi camp (5.19 ± 1.29 L vs. 5.40 ± 1.45 L, P < 0.05). Unadjusted data indicated no difference in the mid‐expiratory flows (FEF 25–75%) between altitudes (∆ + 0.03 ± 0.53 L sec−1; ∆ + 1.2 ± 11.9%). Conversely, TGC‐adjusted data revealed that FEF 25–75% was significantly improved by sojourning at high altitude (∆ + 0.58 ± 0.78 L sec−1; ∆ + 12.9 ± 16.5%, P < 0.05). Finally, when data were adjusted for TGC and air density, FEFs were “less than expected” due to the lower air density at Barafu compared with Moshi camp (∆–0.54 ± 0.68 L sec−1; ∆–10.9 ± 13.0%, P < 0.05), indicating a mild obstructive defect had developed on ascent to high altitude. These findings clearly demonstrate the influence that TGC artifact, and differences in air density, bear on flow‐volume data; consequently, it is imperative that future investigators adjust for, or at least acknowledge, these confounding factors when comparing FEFs between altitudes.

Pulmonary Function Testing

Intelligent management of pulmonary disease requires a fundamental understanding of the complex interrelationships between multiple elements that interact to maintain homeostasis in the respiratory system. This chapter discusses the physiologic basis for pulmonary function testing and the use of these tests to diagnose disease, quantitate functional impairments, and follow the effects of treatment. Figures illustrate the relationships between lung volume, airway conductance, and airway resistance; the relationship between forced expiratory volume and time (spirogram); the relationship between spirometry and maximum expiratory flow volume; dynamic airway compression; patterns of abnormalities seen on flow-volume curves; lung volumes and capacities; pressure-volume relationships in health and disease; and the clinical assessment of lung function. Tables list the capacities and volumes of gas contained in the lungs during various breathing maneuvers, conditions associated with alterations in diffusing capacity, and recommendations for tests for various clinical scenarios. This review contains 7 highly rendered figures, 3 tables, and 86 references.

Pulmonary Function Testing

Intelligent management of pulmonary disease requires a fundamental understanding of the complex interrelationships between multiple elements that interact to maintain homeostasis in the respiratory system. This chapter discusses the physiologic basis for pulmonary function testing and the use of these tests to diagnose disease, quantitate functional impairments, and follow the effects of treatment. Figures illustrate the relationships between lung volume, airway conductance, and airway resistance; the relationship between forced expiratory volume and time (spirogram); the relationship between spirometry and maximum expiratory flow volume; dynamic airway compression; patterns of abnormalities seen on flow-volume curves; lung volumes and capacities; pressure-volume relationships in health and disease; and the clinical assessment of lung function. Tables list the capacities and volumes of gas contained in the lungs during various breathing maneuvers, conditions associated with alterations in diffusing capacity, and recommendations for tests for various clinical scenarios. This review contains 7 highly rendered figures, 3 tables, and 86 references.

The relationship between volumetric capnography and the severity of chronic obstructive pulmonary disease

Objective To explore the correlation between volumetric capnography(VCap)and traditional pulmonary function in chronic obstructive pulmonary disease(COPD), so as to assess whether VCap can be used as alternative indicators for the evaluation of COPD severity when some of the elderly COPD patients do not accomplish the traditional pulmonary function tests. Methods 960 patients admitted to Fujian Geriatric Hospital from June 2008 to June 2015 and undergoing pulmonary function tests were included in the study.They were divided into 2 groups of the COPD group(640 cases)and the control group(320 cases). The pulmonary function of COPD group was divided into 4 subgroups(Ⅰ~Ⅳ). All persons received tests of traditional pulmonary function and VCap.The correlations between VCap and traditional pulmonary function indexes and between VCap and COPD severity were observed. Results The differences in Vm25-50/VT, Vm50-75/VT, dC/dV3, SR23 of VCap between the 4 subgroups(COPDⅠ~COPDⅣ)and control group were statistically significant(all P 0.05). The difference in CO2 max between the COPD Ⅲ group(severe or more severe group)and control group was statistically significant(t=6.91 and 4.65, all P 0.555, P<0.05). The specificity of Vm25-50/VT of VCap for the diagnosis of COPD was best, but its sensitivity was poor than other indexes of VCap.The indexes with both high sensitivity and high specificity were Vm50-75/VT and dC/dV3. Conclusions When the patients with COPD manifest the mild airflow limited, Vm25-50/VT, Vm50-75/VT, dC/dV3 and SR23 of VCap are gradually increased with abnormal VCap figures when the illness progressed.The CO2max of VCap might be one of the indexes for assessing the severity of severe or more severe COPD. Key words: Pulmonary disease, chronic obstructive; Respiratory function tests; Maximal expiratory flow-volume curves

Accuracy of maximal expiratory flow-volume curve curvilinearity and fractional exhaled nitric oxide for detection of children with atopic asthma.

PurposeAirway pathology in children with atopic asthma can be reflected by the concave shape of the maximal expiratory flow-volume (MEFV) curve and high fractional exhaled nitric oxide (FeNO) values. We evaluated the capacity of the curvilinearity of the MEFV curve, FeNO, and their combination to distinguish subjects with atopic asthma from healthy individuals.MethodsFeNO and angle β, which characterizes the general configuration of the MEFV curve, were determined in 119 steroid-naïve individuals with atopic asthma aged 8 to 16 years, and in 92 age-matched healthy controls. Receiver operating characteristic (ROC) curve analyses were performed to determine the cutoff points of FeNO and angle β that provided the best combination of sensitivity and specificity for asthma detection.ResultsAsthmatic patients had a significantly smaller angle β and higher FeNO compared with healthy controls (both, P<0.001). For asthma detection, the best cutoff values of angle β and FeNO were observed at 189.3° and 22 parts per billion, respectively. The area under the ROC curve for the combination of angle β and FeNO improved to 0.91 (95% confidence interval [CI], 0.87–0.95) from 0.80 (95% CI, 0.75–0.86; P<0.001) for angle β alone and 0.86 (95% CI, 0.82–0.91; P=0.002) for FeNO alone. In addition, the combination enhanced sensitivity with no significant decrease in specificity.ConclusionThese data suggest that the combined use of the curvilinearity of the MEFV curve and FeNO is a useful tool to differentiate between children with and without atopic asthma.

Computer quantification of "angle of collapse" on maximum expiratory flow volume curve for diagnosing asthma-COPD overlap syndrome.

BackgroundIn a previous study, we demonstrated that asthma patients with signs of emphysema on quantitative computed tomography (CT) fulfill the diagnosis of asthma-COPD overlap syndrome (ACOS). However, quantitative CT measurements of emphysema are not routinely available for patients with chronic airway disease, which limits their application. Spirometry was a widely used examination tool in clinical settings and shows emphysema as a sharp angle in the maximum expiratory flow volume (MEFV) curve, called the “angle of collapse (AC)”. The aim of this study was to investigate the value of the AC in the diagnosis of emphysema and ACOS.MethodsThis study included 716 participants: 151 asthma patients, 173 COPD patients, and 392 normal control subjects. All the participants underwent pulmonary function tests. COPD and asthma patients also underwent quantitative CT measurements of emphysema. The AC was measured using computer models based on Matlab software. The value of the AC in the diagnosis of emphysema and ACOS was evaluated using receiver-operating characteristic (ROC) curve analysis.ResultsThe AC of COPD patients was significantly lower than that of asthma patients and control subjects. The AC was significantly negatively correlated with emphysema index (EI; r=−0.666, P<0.001), and patients with high EI had a lower AC than those with low EI. The ROC curve analysis showed that the AC had higher diagnostic efficiency for high EI (area under the curve =0.876) than did other spirometry parameters. In asthma patients, using the AC ≤137° as a surrogate criterion for the diagnosis of ACOS, the sensitivity and specificity were 62.5% and 89.1%, respectively.ConclusionThe AC on the MEFV curve quantified by computer models correlates with the extent of emphysema. The AC may become a surrogate marker for the diagnosis of emphysema and help to diagnose ACOS.

Angle β of greater than 80° at the start of spirometry may identify high-quality flow volume curves.

The American Thoracic Society (ATS) and European Respiratory Society (ERS) emphasize a satisfactory start in maximal expiratory flow-volume (MEFV) curves and highlight subjective parameters: performance without hesitation and expiration with maximum force. We described a new parameter, angle β for characterization of the start to the MEFV curve. Subjects completed the MEFV curve at least three times and at least two curves met ATS/ERS quality. Subjects were divided into normal, restrictive and obstructive groups according to pulmonary function test results. The tangent line was drawn at the start of the MEFV curve's ascending limb to the x-axis and the angle β between the tangent line and x-axis was obtained. The relationships between tangent of β, pulmonary function parameters (PFPs) and anthropometric data were assessed. The MEFV curves with insufficient explosion at the start were considered as poor-quality MEFV curves. In 998 subjects with high-quality spirometry, although PFP varied in relation to the three aspects: the angle β and its tangent were similar (P > 0.05), the tangent of β did not correlate with PFP or anthropometric measurements (P > 0.05) and the lower limit of normal (LLN) of the angle β was 80° in the group with high-quality spirometry (P < 0.05). Angle β derived from poor-quality MEFV curves was smaller than that from good quality one (P < 0.05). Angle β may function as a parameter to assess the expiratory efforts, which can be used to assess the quality of the MEFV curve start.

Evaluation of Pulmonary Function in Car Spray Paint Sprayers

Evaluation of Pulmonary Function in Car Spray Paint Sprayers

Subjective and Objective Assessments of Flow-Volume Curve Configuration in Children and Young Adults.

Analysis of maximal expiratory flow-volume curves (MEFVCs) allows for determination of airway obstruction, but quantitative methods to describe these curves are not commonly used. We sought to determine the variability in MEFVC concavity assessment by pulmonary physicians, whether objective indices of concavity can be substituted for subjective expert impression, and whether MEFVC concavity correlates with clinical outcomes. A survey of 37 MEFVCs (plus 3 duplicates) was sent to pulmonologists for quantitative assessment of MEFVC concavity. Objective indices (β-angle, ratio forced expiratory flow at 50% of total lung volume to peak expiratory flow rate [FEF50/PEFR], ratio of maximum mid-expiratory flow to FVC [MMEF/FVC], kmax, and averaged flow-volume second derivatives) were calculated for each MEFVC and were correlated with the mean expert score. Both the mean expert scores and the best-performing index were then correlated with hospitalizations. Ninety-two respondents provided usable data. There was substantial variability in concavity scores between subjects, but strong intrasubject reliability. Mean expert score did not differ by physician years of experience. Several indices (β-angle, FEF50/PEFR, FEV1/FVC, MMEF/FVC, FEF50, and forced expiratory flow between 25 and 75% of total lung volume) correlated strongly with mean expert scores. A new variable (β-MMEF) was constructed using coefficients from stepwise linear regression and accurately predicted the mean expert score (R(2) = 0.96). Mean expert score and β-MMEF showed similar odds ratios for hospitalization (2.13 and 2.32, respectively) with identical positive (∼71%) and negative (87%) predictive values. The β-MMEF was also associated with hospitalizations in two independent cohorts of children with asthma and cystic fibrosis. The β-MMEF is an objective measure of maximal expiratory flow-volume curve concavity and highly correlates with expert impression. Both the mean expert score for expiratory curve concavity and the β-MMEF were associated with increased risk of subsequent hospitalization. The β-MMEF may be a useful biomarker for disease severity in asthma and cystic fibrosis.

Quantifying the shape of maximal expiratory flow-volume curves in healthy humans and asthmatic patients

Differences in the absolute flow and volume of maximal expiratory flow-volume (MEFV) curves have been studied extensively in health and disease. However, the shapes of MEFV curves have received less attention. We questioned if the MEFV curve shape was associated with (i) expiratory flow limitation (EFL) in health and (ii) changes in bronchial caliber in asthmatics. Using the slope-ratio (SR) index, we quantified MEFV curve shape in 84 healthy subjects and 8 matched asthmatics. Healthy subjects performed a maximal exercise test to assess EFL. Those with EFL during had a greater SR (1.15±0.20 vs. 0.85±0.20, p<0.05) yet, there was no association between maximal oxygen consumption and SR (r=0.14, p>0.05). Asthmatics average SR was greater than the healthy subjects (1.35±0.03 vs. 0.90±0.11, p<0.05), but there were no differences when bronchial caliber was manipulated. In conclusion, a greater SR is related to EFL and this metric could aid in discriminating between groups known to differ in the absolute size of MEFV curves.

Quantifying the shape of the maximal expiratory flow–volume curve in mild COPD

Maximal expiratory flow–volume (MEFV) curve evaluation using absolute and percent predicted values of flow and volume are used to diagnose respiratory disease, but the shape of the curve is rarely used. Three mathematical methods were used to quantify shape of MEFV curves in subjects with mild COPD (n=19) and matched healthy controls (n=15). Those with mild COPD had a significantly greater slope-ratio (SR) (1.90±0.24 vs. 1.28±0.32) and Beta-angle (160±6.7 vs. 186±15.0) compared to healthy individuals (p<0.05). The flow-ratio method showed no difference between groups. A significant positive SR-volume relationship during expiration was observed in a greater number of mild COPD subjects (94%) compared to controls (20%) (p<0.001). With its increased spatial resolution and the potential to discern etiology behind specific curvature, we suggest using the SR method when available. The change in SR throughout expiration could help identify those who fall within the lower limit of normal lung function and those who may have pathological obstruction.

Closing volume and flow volume abnormalities in alpha(1)-antitrypsin phenotype groups in a community population.

Alpha1-antitrypsin phenotype groups, found in a community population studied in Tucson, were compared by using the maximum expiratory flow volume curve and the single-breath nitrogen test, alone and in combination. Subjects 25 to 54 years of age were used for the comparison, among whom there were 728 Pi M, 29 Pi MZ, and 62 Pi MS phenotypes. None of the flow volume parameters or closing volume parameters was able to differentiate among the phenotype groups; subjects in groups heterozygous for alpha1-antitrypsin did not differ from individuals homozygous for Pi M with regard to any or all flow volume or closing volume parameters.

Elite Swimmers Have Larger Lung Volumes But More Severe Bronchial Hyperresponsiveness Than Elite Cross Country Skiers

A few previous reports have shown that lung volumes, diffusion capacity as well as bronchial hyperresponsiveness (BHR) are increased in well trained swimmers as compared to other athletes and controls. It is unknown if this can be applied to elite athletes and if this is due to genetic or environmental factors such as the specificity of the swim training and the exposure to chlorine derivatives in the swimming pools. PURPOSE: To compare lung function, BHR and respiratory symptoms in elite swimmers and cross country skiers. METHODS: In a cross sectional study, 29 elite swimmers (17♂/12♀) aged 16–28 years and 30 elite cross-country skiers (20♂/10♀) aged 20–37 years, all competing at high international level, measured lung function by maximal expiratory flow volume loops, forced expiratory flow the first second (FEV1), forced vital capacity (FVC), forced expiratory flow at 50 % of FVC (FEF50) and bronchial hyperresponsiveness was measured by methacholine provocation test, provocation dose at 20 % reduction in FEV1 (PD20meth). Training time per week, symptoms and use of antiasthmatic medication were recorded with the AQUA-questionnaire and by a clinical examination. Antiasthmatic medication was withheld according to ERS guidelines. RESULTS: The elite swimmers had a significant higher FEV1, as compared to the cross country skiers, 4.73L (4.39, 5.07) mean (95 % confidence interval) vs 4.31L (4.06, 4.57) (p=0.05) respectively, FEV1 (% predicted), 114.7 % (110.2, 119.2) vs 103.0 % (99.2, 106.7) (p<0.001) respectively and FVC (% predicted), 122.4 % (116.9, 127.8) vs112.2 % (108.4, 115.9) (p=0.002) respectively. Twenty-three swimmers had a PD20meth ≤ 4 umol as compared to six cross country skiers. Mean training time per week was significant higher in swimmers, 23.8 hours (23.1, 24.4) vs 17.1 hours (16.6, 17.6) (p< 0.001). 27.6 % of the swimmers and 70 % of the skiers had an asthma diagnosis and 37.9 % of the swimmers and 83.3 % of the skiers used daily antiasthmatic medication. No differences were found in the other lung function variables or in self-reported symptoms. CONCLUSION: Elite swimmers have larger lung volumes and FEV1 than elite cross country skiers, but it seems that swimmers are more likely to develop severe BHR due to exposure to chlorine derivatives during their prolonged daily training sessions.

Reference ranges for shape indices of the flow-volume loop of healthy children.

The concavity of the descending limb of the maximum expiratory flow-volume loop (MEFVL) is the earliest change associated with airflow obstruction in small airways (ATS/ERS Task Force). The shape of the MEFVL changes with age but there are no reference values for shape indices for preschool and school children. To define pediatric reference values for spirometric data and 3 shape indices of MEFVL: 2 geometric indices: the β angle i.e., the angle between the first ½ part and the 2nd part of the MEFVL and the forced expiratory flow after 50% of the forced vital capacity (FVC) has been exhaled/peak expiratory flow (FEF50 /PEF) ratio; and a ratio that describes relative growth between airway and lung parenchyma, the forced expiratory flow between 25 and 75% of FVC/FVC ratio (FEF25-75 /FVC ratio). Data were obtained from 446 Caucasian children (2.5 to 15-year-old). The lambda, mu, sigma method was applied. References for spirometric parameters and 3 shape indices. The geometric indices decreased with age from 3 years of age (mean β angle was 215° and FEF50 /PEF ratio was 0.82) until 8 years of age (mean β angle was 191° and FEF50 /PEF ratio was 0.60) and then remained constant. The FEF25-75 /FVC ratio also decreased with age. Sex was a significant determinant for FEF25-75 /FVC ratio predicted values. This study provides standard reference equations for indices of mid-expiratory flows in children and we suggest using the FEF50 /PEF index.

Prevalence and correlates of a 'knee' pattern on the maximal expiratory flow-volume loop in young adults.

Visual inspection of the maximal flow-volume curve is an important step in interpreting spirometry. Many young people have a convex inflection or 'knee' on the expiratory part of the loop. This is thought to be a normal variant, but this view is based on theoretical grounds, and the epidemiology of the knee pattern has never been reported. Flow-volume loops from an unselected birth cohort of 1037 individuals at ages 18, 26, 32 and 38 years were visually inspected for a knee pattern. Associations with asthma diagnoses, smoking history, body mass index (BMI) and spirometry were assessed. The knee pattern was found in approximately two thirds of men and women at age 18. The prevalence decreased with age, but it was more likely to persist in women. The knee was more common after bronchodilator and was associated with higher forced expiratory volume in 1 s/forced vital capacity ratios and mid-expiratory flow rates. There was no association with smoking, except for an inverse correlation in men at age 18. No association was found with BMI. Women with asthma were less likely to have a knee at both ages 18 and 38, whereas men with asthma showed an inverse association at age 18. A knee is a very common pattern on flow-volume loop in young adults. In accordance with theoretical predictions, the prevalence of the knee declines with age, but it is more likely to persist in women. It is associated with less airflow obstruction and is less common in people with asthma.

Factors associated with aerobic fitness in adolescents with asthma

In adolescents with asthma, information on factors associated with cardiorespiratory fitness levels is limited. The present study aimed to determine if objectively measured physical activity as well as potential relevant factors such as lung function, asthma exacerbations, use of inhaled corticosteroids or skin fold thickness are associated with direct measurements of peak oxygen uptake (V˙O2peak) in adolescents with asthma. From a nested case-control study at 13-years in the Environment and Childhood Asthma birth cohort study in Oslo, Norway, 86 13-years old adolescents with and 76 without asthma performed maximal running on a treadmill with V˙O2peak measured. The sum of four skin fold thicknesses was recorded, followed by wearing an activity monitor for four consecutive days. Lung function was measured by maximum forced expiratory flow-volume curves and body plethysmography. Asthma exacerbations and use of medication were registered by parental structured interview. Data were analysed using multiple regression analysis. Vigorous physical activity (coefficients with 95% confidence intervals; 1.73 (0.32, 3.14)) and skin fold thickness -0.35 (-0.41, -0.28)) were significantly associated with V˙O2peak in adolescents with asthma. Neither use of inhaled corticosteroids, lung function nor number of asthma exacerbations was associated with V˙O2peak when taking physical activity and skin fold thickness into account. In the adolescents without asthma only skin fold thicknesses was negatively associated with V˙O2peak -3.5 (-4.1, -2.8). V˙O2peak appears to be determined by vigorous physical activity level in Norwegian adolescents with asthma and not by asthma-related factors such as use of inhaled corticosteroids, lung function nor number of asthma exacerbations.