When classified by baseline spirometry pattern (Table 1), the most common abnormal pattern was low FVC, a finding similar to that previously published.8,15,19,24 Distributions of race/ethnicity, body mass index, and tobacco differed among spirometry patterns. WTC dust cloud exposure was not associated with baseline spirometry pattern, whereas the distribution of WTC exposure categories differed among spirometry patterns (P = 0.014) with the Low FVC/Obstructed group having the highest proportion of local workers.
The average number of repeated observations was 3 (range, 2 to 10). The average duration of follow-up was 2.43 years (SD = 1.37 years) and the longest was 5.94 years. Initial analyses, based on crude estimates of individual annual change (Appendix Table 1, http://links.lww.com/JOM/A109), indicated that smoking status, spirometry pattern and WTC-related exposure category might be associated with the temporal change of FVC,% FVC, FEV1, and% FEV1, but not WTC dust cloud exposure or the presence of respiratory symptoms. Therefore, we conducted longitudinal analyses in the population as whole and then stratified by smoking status, spirometry pattern and WTC-related exposure category.
Annual change of FVC, %FVC, FEV1, and % FEV1 estimated via linear mixed-effects models adjusted for appropriate variables, as shown in Table 2, revealed significant improvement in spirometry parameters in the overall sample: with a 54.4 mL/yr improvement in FVC (95% confidence interval [CI], 45 to 63.8) and a 36.8 mL/yr in FEV1 (95% CI, 29.3 to 44.3). These changes translated into a 1.37%/yr (95% CI, 1.11 to 1.64) improvement in % FVC and a 1.12%/yr (95% CI, 0.85 to 1.38) improvement in % FEV1. Temporal trends in lung function differed between heavy smokers and non- or light smokers (Table 2), with the non- or light-smoker group showing significant (P < 0.0001) improvement in all spirometry parameters, whereas no improvement was observed among heavy smokers.
Longitudinal Analysis and Spirometry Pattern
Changes in longitudinal spirometry differed between each spirometry pattern group (Table 2). The Normal group demonstrated improvement in both FVC and FEV1: FVC (47.3; 95% CI, 36.5 to 58.2), %FVC (1.16; 95% CI, 0.85 to 1.47), FEV1 (29.2; 95% CI, 20.7 to 37.7), and %FEV1 (0.82; 95% CI, 0.5 to 1.14). In the groups with abnormal spirometry, the Low FVC group and the Low FVC/Obstructed group demonstrated significant increases in all spirometry parameters. In contrast, the Obstructed group only showed a significant increase in FEV1 (50.2; 95% CI, 14.2 to 84.2). The Low FVC/Obstructed group had the greatest improvement for both FVC and FEV1.
We further examined spirometry measurements as predicted values at the participants' last visit to the WTCEHC stratified by initial spirometry patterns (Fig. 2). At their last visit, the Low FVC group and the Low FVC/Obstructed group continued to have abnormal spirometry with median values of %FVC and % FEV1 less than 80%. The Obstructed group had lower FEV1 measurements compared with the Normal group at the last visit.
Longitudinal Spirometry and WTC Exposure Category
When stratified by WTC-related exposure category (Table 2), longitudinal analysis indicated statistically significant improvement in all lung function parameters among local worker, resident, rescue/recovery, and clean-up workers, with the exception of %FEV1 among the clean-up group (P ≥ 0.01). The rescue/recovery group demonstrated the greatest annual improvement in all lung function parameters, whereas the local worker group showed the least improvement.
We report longitudinal assessment of spirometry parameters in a group of community members with potential for WTC dust exposures. Our analyses of a group of patients with heterogeneous exposures to environmental contaminants related to the September 11 disaster showed statistically significant temporal improvements in lung function in the group as a whole, with the degree of improvement varying by the pattern of spirometry at enrollment, the category of WTC-related exposure, and smoking status.
We demonstrated overall improvement in spirometry parameters during an average 2.4-year follow-up period in this community cohort enrolled in a treatment program about 4 years after the WTC disaster on September 11, 2001. These data are in contrast with longitudinal analyses of lung function in those involved in rescue and recovery.14,15 Among firefighters, an initial loss of lung function was detected within the first year after exposure with subsequent decline in lung function approximating the expected age-related change.14 Analysis of an additional rescue and recovery population also demonstrated a reduction of lung function over time, although analysis was limited by lack of antecedent data.15 Our baseline observational period started 4 years after the event, and unlike data in firefighters, we did not have lung function data before or within the years immediately after exposure. The increase in spirometry measurements is also in contrast with the anticipated loss of 31 mL/yr in FEV1 that has been reported in longitudinal studies of nonsmokers with asthma and the loss in lung function in patients with chronic obstructive pulmonary disease.25–27 The improvement in lung function in the WTCEHC population suggests the presence of a reversible component of lung injury in the population despite the delayed time of entry into the treatment program.
We demonstrated heterogeneity in response over time among the spirometry patterns. The distribution of the four spirometry patterns in our population was consistent with other populations19 and with the spectrum of diseases that have been described for WTC-exposed individuals, which include reactive airways dysfunction, irritant-induced asthma, sarcoidosis, and other interstitial lung diseases.4,6,12,28,29 The variability in improvement among the four spirometry patterns suggests different mechanisms for the development of each pattern. A normal spirometry pattern can be seen in patients without any underlying lung disease but is also consistent with asthma or airway hyperresponsiveness. Alternatively, exposed patients with the normal pattern may have distal airway disease that is not reflected by spirometry.30,31 Indeed, the improvement in FVC in this population, and the absence of decline in FEV1, suggested the presence of reversible airway closure even in this group with a normal spirometry pattern. Although most patients with WTC exposures and lower respiratory symptoms have been suggested to have asthma, an obstructed pattern is uncommon in this and other reported WTC-exposed cohorts.19 The Obstructed group improved both FVC and FEV1 parameters, consistent with airway disease. The low FVC pattern has been described as the predominant spirometry abnormality in WTC-exposed populations.19 A reduced FVC can be consistent with submaximal effort, parenchymal disease, obesity, or alternatively can be associated with patchy peripheral air trapping.20 Patients with the low FVC pattern predominantly improved FVC over time, consistent with a component of reversible airflow obstruction. Patients with the combined low FVC/obstructed pattern had the most abnormal lung function at baseline and yet the greatest improvement in spirometry. Nevertheless, lung function in this group, and in the Low FVC group failed to return to the normal range. These findings suggest that all groups had some potential for reversibility of injury; however, the components that improved differed, reinforcing differences in type or location of injury or response to treatment.
The WTCEHC includes individuals with a variety of potential exposures to the WTC dust and fumes and we grouped patients according to their potential for exposure. Longitudinal changes in lung function differed in these WTC exposure categories, with the local workers demonstrating the least improvement. The local worker category included people who worked either within the WTC towers or worked in surrounding buildings, many of whom evacuated on September 11, 2001, and returned to work in the surrounding buildings 1 week later. This category also had the highest likelihood of dust cloud exposure. We did not see a relationship with dust cloud exposure and temporal longitudinal changes in lung function in the cohort as a whole; however, the possibility remains that this intense exposure combined with subsequent exposures influenced disease pattern and longitudinal change in a specific category. Further detailed characterization of the specific exposure within each of these categories is warranted to improve our understanding of a dose–response relationship. Moreover, the data suggest that close observation of the local worker group is warranted.
The use of tobacco had an important influence in our findings. In contrast with the group as a whole, we did not detect temporal improvement in lung function among heavy smokers. The finding of a lack of improvement among heavy smokers may be particularly important as the information can be used in counseling WTC-affected patients regarding the importance of smoking cessation.
The longitudinal analyses were modeled with a linear time trend for changes in spirometry over time and showed improvement in lung function over the observation period. Nevertheless, it would be unreasonable to expect that this improvement would be sustained over prolonged periods of time and we expect the positive changes to be counterbalanced by normal age-related decline in spirometry measurements. Our current data were too sparse at the longer time points for a definitive long-term analysis of this issue. Exploratory analysis using an alternate model with quadratic time trend (data not shown) suggested an initial improvement in lung function followed by a subsequent decline. Future studies with a longer follow-up period will fully characterize the long-term changes in lung function in this population.
There are several potential limitations to this study. Although patients were treated in a standardized manner and were provided medications free of charge, we did not have data to assess medication adherence and thus could not directly attribute changes in lung function to treatment. Nevertheless, the improvements in FVC and FEV1 suggest the potential for reversibility of airway injury. The possibility exists that the initial spirometry measurements were suboptimal and improved over time with patient experience. Nevertheless, we used stringent criteria for inclusion of spirometry values making this explanation unlikely. Previous investigators have demonstrated that the reduced FVC pattern is associated with weight gain15; however, our patients with a reduced FVC improved despite the absence of significant changes in weight over time (data not shown). Our data are collected in the practical setting of a treatment program with patient's follow-up visits being clinically indicated or after a routine monitoring visit, and only 39% of symptomatic patients with valid baseline spirometry measurement had follow-up visits raising the possibility of bias in our results. We acknowledge that the findings might differ for a general population but these findings seem to have important implications for WTC treatment programs.
We have observed an improvement in lung function among community members of the WTCEHC during their initial years of enrollment. The improvement in lung function suggests reversible injury amenable to treatment. The different initial lung function patterns and their varied responses over time reinforce the heterogeneity of potential lung injury. The effect of tobacco use on lung function reinforces that WTCEHC patients should be urged to avoid other potential sources of lung injury and in particular to stop all exposures to tobacco. Although subjects with abnormal lung function improved, predicted spirometry measurements did not return to normal values and differences were noted between exposure categories. The residual abnormalities reinforce the need for treatment and continued monitoring for populations affected by this environmental disaster and suggest the importance of clinical interventions for other environmental disasters.
The authors thank Terry Miles for his continued support and advice; Ruchel Ramos and Edith Davis for their help in administering the program; and the members of the WTC Community Advisory Committee for their invaluable advice and efforts on behalf of the program.
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