Progressive Flow-to-Volume Dysanapsis in Cystic Fibrosis

Predicting disease progression in cystic fibrosis

INTRODUCTION

Progressive lung disease is the major cause of morbidity and mortality in patients with cystic fibrosis (CF). Methods of correctly predicting the future progression of lung disease in patients with CF are essential for directing aggressive treatment to prevent loss of lung function and end stage respiratory failure. Areas covered: This review addresses predictors of respiratory disease progression in patients with CF. We searched Web of Science and Medline, with no restriction on publication date, with the search terms 'cystic fibrosis' and 'disease progression', 'lung function decline', 'prognosis', 'prediction/predictive', 'prediction/prognostic scores', 'risk factors', 'outcome measures/endpoints/disease surrogate', 'longitudinal/long term', 'statistical model', and 'survival'. Expert commentary: Forced expiratory volume in 1 sec (FEV₁) and rate of FEV₁ decline, remain the most significant predictors of mortality in patients with CF while CT scores and airway secretion biomarkers are the main predictors of early CF lung disease. Comprehensive scores incorporating clinical, lung function, imaging and laboratory data will become essential in the future for predicting disease progression and for use in clinical trials. Early interventions may delay the progression of structural lung disease.

Obesity and Airway Dysanapsis in Children with and without Asthma

RATIONALE

For unclear reasons, obese children with asthma have higher morbidity and reduced response to inhaled corticosteroids.

OBJECTIVES

To assess whether childhood obesity is associated with airway dysanapsis (an incongruence between the growth of the lungs and the airways) and whether dysanapsis is associated with asthma morbidity.

METHODS

We examined the relationship between obesity and dysanapsis in six cohorts of children with and without asthma, as well as the relationship between dysanapsis and clinical outcomes in children with asthma. Adjusted odds ratios (ORs) were calculated for each cohort and in a combined analysis of all cohorts; longitudinal analyses were also performed for cohorts with available data. Hazard ratios (HRs) for clinical outcomes were calculated for children with asthma in the Childhood Asthma Management Program.

MEASUREMENTS AND MAIN RESULTS

Being overweight or obese was associated with dysanapsis in both the cross-sectional (OR, 1.95; 95% confidence interval [CI], 1.62-2.35 [for overweight/obese compared with normal weight children]) and the longitudinal (OR, 4.31; 95% CI, 2.99-6.22 [for children who were overweight/obese at all visits compared with normal weight children]) analyses. Dysanapsis was associated with greater lung volumes (FVC, vital capacity, and total lung capacity) and lesser flows (FEV1 and forced expiratory flow, midexpiratory phase), and with indicators of ventilation inhomogeneity and anisotropic lung and airway growth. Among overweight/obese children with asthma, dysanapsis was associated with severe disease exacerbations (HR, 1.95; 95% CI, 1.38-2.75) and use of systemic steroids (HR, 3.22; 95% CI, 2.02-5.14).

CONCLUSIONS

Obesity is associated with airway dysanapsis in children. Dysanapsis is associated with increased morbidity among obese children with asthma and may partly explain their reduced response to inhaled corticosteroids.

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

BACKGROUND

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.

OBJECTIVES

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).

METHODS

Data were obtained from 446 Caucasian children (2.5 to 15-year-old). The lambda, mu, sigma method was applied.

RESULTS

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.

CONCLUSIONS

This study provides standard reference equations for indices of mid-expiratory flows in children and we suggest using the FEF50 /PEF index.

Mortality Risk and Pulmonary Function in Adults With Cystic Fibrosis at Time of Wait Listing for Lung Transplantation

BACKGROUND

Lung transplantation (LTx) benefit for survival in cystic fibrosis (CF) patients placed on the wait list is not well studied.

METHODS

To predict the relationship between initial forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC) and the hazard ratio (HR) associated with LTx in CF patients, the United Network for Organ Sharing database was queried from 2005 to 2006 for adult patients with CF. Survival was assessed from wait list entry time until death on wait list, death after LTx, or censoring. Multivariate Cox proportional hazards models were used to assess the effect of LTx. The first model estimated the HR of LTx with adjustment for FEV1 or FVC and other covariates, and the second model estimated the HR of LTx conditional on FEV1 or FVC at listing.

RESULTS

Two hundred seventy-eight patients with CF were included in the cohort, and 277 were used for survival analysis. Lung transplantation reduced the risk for death controlling for FEV1 (HR, 0.601; 95% confidence interval, 0.375 to 0.964; p = 0.035) or controlling for FVC (HR, 0.547; 95% confidence interval, 0.336 to 0.889; p = 0.015). Interaction models found that the HR of LTx varied significantly across initial FEV1 and FVC, with the predicted LTx HR and 95% confidence interval being protective (HR < 1) at FEV1 of 25% or less and FVC of 40% or less, respectively.

CONCLUSIONS

The benefit of LTx in adults with CF was significant at a lower baseline FEV1 than expected. A threshold for baseline FVC was established below which LTx was protective.

FVC deterioration, airway obstruction determination, and life span in Ataxia telangiectasia

RATIONALE

Forced vital capacity (FVC) values decrease with progress of the disease in Ataxia telangiectasia (AT).

OBJECTIVE

To study the effect of this process on airway obstruction determination and life span in AT.

METHODS

Clinical data and yearly best spirometry maneuvers were collected retrospectively from 37 AT patients (196 spirometry tests) during 5.4 ± 1.8yrs (initial age 4-21 y). Twelve patients were walking (7 of them had recurrent respiratory system infections); 25 subjects were confined to wheelchair, of them 8 patients were towards end-stage lung disease. Spirometry indices included Forced Vital Capacity (FVC), mid-expiratory-flow (FEF25-75), and tidal volume (VT). We calculated FEF25-75/FVC and VT/FVC ratios.

RESULTS

FVC declined from 67 ± 8 while walking to 19 ± 6 %predicted values. FEF25-75 values that were elevated (116 ± 23 %predicted) while walking, decreased to 69 ± 27 %predicted at end-stage where 7 patients responded to bronchodilators. VT/FVC ratio was 0.25 ± 0.06 while walking, increased to 0.35 once on wheelchairs, and further increased to 0.57 ± 0.19 at end-stage disease. FEF25-75/FVC ratio was 2.54 ± 0.70 above normal (∼1.0) increasing to 4.16 ± 0.75 at end stage. A sharp elevation was seen in FEF25-75/FVC ratio when FEV1 was still ∼45 %predicted and 2-years prior to death.

CONCLUSIONS

Having a low baseline-FVC (60% predicted) artificially raises FEF25-75 values, so FEF25-75 of "mild obstruction" values may indicate severe airway obstruction in AT subjects. VT/FVC and FEF25-75/FVC ratios may therefore assist in revealing higher than normal breathing effort. The results further suggest adding VT/FVC and FEF25-75/FVC ratios to pulmonary function assessments in patients with AT.

Association of pulmonary function with adiposity and metabolic abnormalities in urban minority adolescents

RATIONALE

Childhood obesity is a known risk factor for pulmonary diseases, likely due to obesity-mediated alteration of pulmonary function. Inflammation and mechanical fat load are two proposed causative mechanisms for altered pulmonary function among obese children; however, the association of metabolic abnormalities with pulmonary function among children is poorly understood.

OBJECTIVES

We investigated the independent association of truncal and general adiposity and metabolic abnormalities with pulmonary function in a sample of urban minority adolescents.

METHODS

Spirometry and lung volume indices were compared between adolescents with general (body mass index [BMI] > 95th percentile) or truncal adiposity (waist circumference > 90th percentile) and normal-weight (BMI < 85th percentile or waist circumference ≤ 90th percentile) and between those with metabolic abnormalities (homeostatic model assessment of insulin resistance [HOMA-IR] in the top quartile or high-density lipoprotein [HDL] < 40 mg/dl) and those with a normal metabolic profile.

MEASUREMENTS AND MAIN RESULTS

Obese adolescents had lower lung volumes, including residual volume (RV), RV/TLC ratio, expiratory reserve volume (ERV), and FRC, and higher inspiratory capacity (IC) than normal-weight adolescents, but did not differ in measures of lower airway obstruction, FEV1/FVC ratio, and mid-expiratory flow rate. Adolescents with high HOMA-IR had lower FEV1/FVC ratio, RV, RV/TLC ratio, ERV, and FRC and higher IC, whereas those with low HDL had lower FEV1/FVC and RV/TLC ratios. After adjusting for adiposity, HOMA-IR remained a predictor of ERV (β = -1.4; P = 0.02) and FEV1/FVC ratio (β = -0.5; P = 0.03), and HDL remained a predictor of FEV1/FVC ratio (β = 0.1; P = 0.01). General adiposity was a predictor of FRC (β = -0.5; P < 0.001), IC (β = 0.3; P < 0.001), RV (β = -0.8; P < 0.0001), and RV/TLC ratio (β = -0.2; P < 0.0001), and truncal adiposity was a predictor of RV (β = -20.3; P = 0.03) and FRC (β = -13.8; P = 0.004). Thus, adiposity and metabolic abnormalities were independent predictors of ERV, but only metabolic abnormalities independently predicted FEV1/FVC ratio. Although general adiposity predicted RV and RV/TLC ratio, truncal adiposity was predictive of RV and FRC, conferring additional risk above general adiposity.

CONCLUSIONS

These results suggest that metabolic abnormalities and adiposity are independently associated with pulmonary function deficits among urban adolescents. Metabolic assessment of obese adolescents may identify those at risk of developing obesity-associated pulmonary morbidity.

Multi-modality monitoring of cystic fibrosis lung disease: the role of chest computed tomography

Cystic fibrosis [CF] lung disease is characterized by progressive bronchiectasis and small airways disease. To monitor CF lung disease traditionally spirometry has been the most important modality. In addition to spirometry chest radiography was used to monitor progression of structural lung abnormalities. However, the importance of chest radiography in disease management has been limited due to its poor sensitivity and specificity to detect disease progression. Over the last decade chest CT has become the gold standard for monitoring the severity and progression of bronchiectasis. Small airways disease can be monitored using spirometry, multiple breath washout techniques, and chest CT. In modern CF-care a multi-modality approach is needed to monitor CF lung disease and to personalize treatment for the needs of the patient. When state-of-the-art low dose bi-annual chest CT protocols are used radiation risk is considered to be low. In between chest CT imaging, physiologic measures are important to obtain for monitoring. Stratification of monitoring protocols based on the risk profile of the patient can help us in the future to better care for people with CF.

Small airway involvement in cystic fibrosis lung disease: routine spirometry as an early and sensitive marker

BACKGROUND

In young children with cystic fibrosis (CF) the forced expiratory volume in 1 second (FEV1 ) is often normal and a more sensitive measure to detect early obstructive lung disease is needed.

AIM

To evaluate the progression of selected spirometry parameters with age in a cohort of CF patients and healthy children aged 6 to 20 years.

METHODS

Retrospective comparison of longitudinal spirometry data from CF patients with data from two cohort studies in healthy subjects. Quantile regression was used to calculate the longitudinal 10th percentile (P10 ), 50th percentile (P50 ), and 90th percentile (P90 ) of forced vital capacity (FVC), FEV1 , and the forced expiratory flow at 75% of FVC (FEF75 ). Sample size estimates were calculated using these three parameters as clinical trial endpoints.

RESULTS

FVC, FEV1 , and FEF75 were all significantly lower in CF patients than healthy children. Abnormalities in FEF75 occurred at younger ages and remained substantially larger than abnormalities in FEV1 or FVC throughout childhood. Therefore, fewer patients would be required to detect a similar treatment effect if FEF75 is used as a primary endpoint compared with FEV1 or FVC.

CONCLUSIONS

Our data support the use of FEF75 as a more sensitive marker of early CF lung disease than FEV1 and FVC, because abnormalities in FEF75 occur at younger age and FEF75 is diminished more than other parameters.

Forced expiratory decay in asthmatic preschool children--is it adult type?

BACKGROUND

The forced expiratory decay in healthy preschool children portrays a convex shape that differs from the linear decay in the older healthy population. The "adult-type" expiratory decay during airway obstruction is concave. The study objective was to determine if the expiratory decay in young asthmatic children is "adult-type".

METHODS

Among 245 children (age 3-7 yrs), 178 had asthma (asthmatics) and 67 were non-asthmatic (controls). The expiratory flow decay was inspected by FEF25-75/FVC ratio (=1.0 when linear). Values were compared to those of our formerly studied (n = 108) healthy children. A meaningful obstruction in FEF25-75/FVC ratio was defined as 2-zScores from healthy. A meaningful response to bronchodilators was related to non-asthmatics.

RESULTS

In healthy subjects FEF25-75/FVC ratio declined with age from 1.73 ± 0.17 to 1.28 ± 0.11. Non-asthmatics portrayed ratio values similar to those of healthy subjects. In asthmatics, 118/178 displayed a convex to linear expiratory decay (FEF25-75/FVC = 1.33 ± 0.22). Sixty/178 asthmatics portrayed concavity (FEF25-75/FVC-0.79 ± 0.16) that appeared when FEF50 was 43.4 ± 12%healthy. Concavity appearance was also age-dependent (30.4% of 3-4 y old and 59.1% of 6-7 y). Vital-Capacity decreased in either decays, forming a visually petit curve. Most asthmatic children respond to bronchodilators by a meaningful elevation in FEF25-75/FVC values and by a visual change in the shape of the curve. Other common spirometry indices also increased meaningfully.

CONCLUSION

Most asthmatic preschool children portray convex to linear expiratory decay with diminished vital-capacity, resulting in a visually smaller than healthy curve, with seemingly normal expiratory decay. These curves may be misinterpreted as "normal" or as "no-cooperation" and may lead to misinterpretation. In response to bronchodilators, FEF25-75/FVC value increases in asthmatics and the curve changes from concave to linear or from linear to convex contour.