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An Investigation of Inhaled Ozone Dose and the Magnitude of Airway Inflammation in Healthy Adults

Lung Biology, School of Health & Life Sciences, King's College London, University of London, United Kingdom

Correspondence and requests for reprints should be addressed to Frank J. Kelly, Ph.D., School of Health & Life Sciences, Franklin-Wilkins Building, 150 Stamford Street, Kings College London, London SE1 9NN, UK. E-mail: frank.kelly{at}kcl.ac.uk

Exposure to ozone has been associated in epidemiologic and field studies with a range of health outcomes: increased daily mortality (1); impaired lung function (2–4); and inflammation and epithelial injury in recreational runners (5) and cyclists (6), as well as increased hospital admissions for preexisting respiratory disease (7, 8). A biological basis for these responses has been provided by findings from animal (9) and human laboratory-based studies (10), where transient decrements in lung function, increased hyperreactivity, and airway inflammation have all been demonstrated after exposure to environmentally relevant concentrations of ozone (11, 12). Although the database for ozone-induced health effects is considerable, a number of issues remain unresolved. The relationship between inhaled ozone dose and the magnitude of the resultant pulmonary response has been limited to a consideration of transient lung function decrements (12–14), as these measurements are noninvasive and easy to perform. Similar analyses addressing the relationship between ozone dose and acute pulmonary inflammation and tissue injury have not been performed. Here, the available database is more limited, and issues related to variation in study design, airway sampling, and the endpoints studied have made a similar approach more problematic. Establishing these relationships is vital in determining threshold doses of ozone below which adverse responses are negligible in the healthy population. As the magnitude of lung function decrements is not simplistically related to epithelial injury or inflammation (15), one cannot rely on estimates derived from these modeling studies to determine threshold values for these other biologically important endpoints.

Here, we describe the first attempt to model the ozone dose–inflammatory response based on a metaanalysis of data from published human chamber studies, where airway responses were assessed using bronchoscopy-based lavage. Analyses of inflammatory responses were based on the percentage of neutrophils recovered by bronchoscopy-based lavage in response to a set ozone dose, expressed as a function of concentration (mg/m³), E (L/minute/m² body surface area), and exposure time (minutes) – CVT (mg/m² body surface area). Analysis of altered permeability responses was more complex and relied on the fold increase in lavage total protein between the ozone and air exposures. This metaanalysis included data from 21 publications containing 23 exposures, with responses stratified into those measured early (0–6 hours) or late (18–24 hours) postexposure.

We observed evidence of a relatively simple linear relationship between ozone dose (CVT) and neutrophilia in bronchoalveolar lavage fluid samples (r² = 0.44, p < 0.01 at 0–6 hours, and r² = 0.51, p < 0.01 at 18–24 hours), with the regressions cutting the upper 95% confidence interval of the control neutrophil level (postair) at CVT values of 645 (408–883) mg/m², intercept with 95% confidence intervals at 0 to 6 hours, and 810 (491–1,130) mg/m² at 18 to 24 hours. Simple linear relationships were also observed between ozone dose and protein leak into the airways over the early- and late-acute response time points. Together, these data highlight an underlying association between ozone dose and airway responses and indicate that an appropriately designed large-scale exposure study could investigate the question of an ozone threshold level for such endpoints. Some of the results of these studies have been reported previously in the form of an abstract (16).

METHODS

Study Selection Criteria
Only randomized air-controlled studies were considered for inclusion. Double-blinded studies were preferred, but single-blinded and open studies were also reviewed for inclusion.

Study Populations
All subjects included in this metaanalysis were healthy nonsmokers (18–40 years, predominately male). Where subjects were exposed on two separate occasions (control air and ozone), intervals of 2 to 6 weeks were used to limit carry over effects. One of the selected studies addressed inflammatory responses in healthy subjects classified as responders or nonresponders on the basis of the magnitude of their FEV₁ decrement after ozone (17, 18). On the basis of their preselection, they are treated as two separate groups in this metaanalysis. Smokers (19), subjects with asthma (17, 20, 21), and subjects taking antioxidant supplements (22) were excluded from these analyses, but data from healthy control subjects from these studies were included where paired ozone- and air-exposure data were available. In the case of the study described in Samet and colleagues (22), the control group had received a placebo compound for a 14-day period after a period of dietary restriction. However, as neither intervention had a significant impact on the outcome, these data were included.

Exposure Conditions
Ozone concentrations ranged from 0.08 to 0.6 ppm, with exposure durations of 60 to 396 minutes. The majority of exposures were conducted in whole-body chambers ( 20–25°C) supplied with humidified air, though mouthpieces (23, 24) and head domes (25) were also used. With the exception of these studies and those where subjects wore nose clips during exposures (26–28), subjects were allowed to follow their normal breathing pattern. The work rate ventilatory response ranged from 14.8 to 35 L/minute/m² body surface area. In all studies, with the exception of studies by Schelegle and colleagues (24) and Hazbun and colleagues (28), subjects alternated between exercise and rest, with the duration of exercise varying between 48.2 and 100% of the exposure period (Table 1) .

Bronchoscopy Procedure
Generally, the studies can be classified into those in which a large volume of saline is instilled into defined lung segments as multiple aliquots and then pooled to obtain a representative distal lung sample (23, 26, 27, 32, 33) or into those in which a small, variable volume of the first instillation is retained separately from the remaining aspirates (17, 19, 21, 34, 35) to reflect the bronchial airways. Balmes and colleagues also performed peripheral airway lavage using a modified balloon catheter to isolate specific airway segments (17, 36).

Assessment of Airway Neutrophilia
Total and differential cell counts were performed in all studies using standard methods, usually based on counts of not less than 300 cells per slide. To avoid complications with variable dilution, we elected to use the percentage of lavage fluid neutrophils as our response endpoint.

Assessment of Altered Epithelial Permeability
Total protein and albumin were determined using a range of standard methodologies.

Data Abstraction
For studies where the original data (or a useful summary) were not presented, where possible, they were extracted from manuscript illustrations using image capture and scaling software. Where data were only alluded to in text, the study authors were contacted to obtain data. All data were expressed as mean and SE. As described previously, where data were summarized using nonparametric expressions, raw data were obtained and reanalyzed.

Data Analysis
Data were classified as early or late responses, as well as with respect to whether the lavages were of the bronchial or alveolar regions of the lung. Least-squares regressions were performed on plots of the mean neutrophil count after ozone at a given CVT value, weighted for the SE on these values. In all cases, the data met the requirements for equal variance and normality (see online supplement for further details). To obtain estimates of threshold ozone doses, the intercept point between this regression line and the upper 95% confidence interval of the overall postair percentage of polymorphonuclear leukocytes was calculated. This control value was based, in the majority of studies, on a parallel lavage after a control filtered-air exposure with exercise. It was assumed that although significant increases in neutrophils may have occurred in individual studies at CVT doses below this point, they were unlikely to be biologically significant. To ascertain whether high neutrophil background numbers postair were biasing interactions, regression analyses were also performed using the absolute change in polymorphonuclear leukocytes (ozone–air) versus dose. All statistical analyses were performed using SPSS for Windows, version 11.5 (SPSS Inc., Chicago, IL), MicrocalOrigin, version 5 (Microcal Software Inc., Northampton, MA), or the Unistat Excel plug-in, version 4.53 (Unistat Ltd., London, UK).

RESULTS

Temporal Profile of Ozone-induced Neutrophilia
As airway inflammation is progressive, it was necessary to understand the response profile before performing any dose–response analysis. This issue has been investigated in five studies (19, 24, 27, 37, 38), each considering only a limited number of time points. Using the data set assembled for this metaanalysis, we examined the temporal neutrophil response by dividing the studies into high (> 1,000) and low (< 1,000) CVT dose exposures. Data were segregated as it was thought that response induction might occur more rapidly in the high-dose studies. The alveolar lavage neutrophil data set, including information from all 23 studies cited in Table 1, indicated a rapid induction of neutrophilia in the high-dose studies, peaking at 3 hours (26). A similar pattern was observed in the low ozone dose studies, with the peak response also at 3 hours, again based on a single observation (27). The response profile in the bronchial airways was less clear. At low ozone doses, the neutrophil peak occurred 6 hours postexposure, with a slow resolution phase. In contrast, the induction of the neutrophil response under high-dose exposures was very rapid, persisting until 18 to 20 hours postexposure. At 24 hours, the neutrophilic response appeared to attenuate, although this was based on data from a single study (35). On the basis of these results, we decided to examine the ozone dose–neutrophil response over two defined periods: early, between 0 and 6 hours, and late, 18 to 24 hours postexposure. These data are illustrated in Figure E1 in the online supplement.

Ozone-induced Neutrophilia in the Alveolar Lavages
The range of neutrophil responses occurring 0 to 6 hours postozone in the alveolar lavage samples is illustrated in Figure 1 , on the basis of results from 13 peer reviewed studies. We observed significant associations between ozone-induced neutrophilia and the CVT dose expression (r² = 0.44, p < 0.01). As the majority of these studies examined airway responses at 1 to 2 hours postexposure, we repeated these analyses excluding data from those studies with lavage performed between 3 and 6 hours (21, 23, 25, 31, 32). This did not significantly affect the strength of the underlying CVT response relationship (r² = 0.48). The threshold response value was calculated as 645 (408–883) mg/m² from the intercept between the linear regression through neutrophil data after ozone and the upper 95% confidence interval of the mean proportion of neutrophils observed postair (1.5 [0.9–2.1]% based on data from all 13 studies).

View larger version (26K): [in this window] [in a new window]   Figure 1. Relationship between ozone-induced neutrophilia in the distal airways during the early-acute response and inhaled dose defined using the CVT expression. Data are illustrated in the main figures (left) as the mean (SEM) % neutrophils after ozone (inverted triangles) or air (circles). Numbers above these data refer to the reference from which the data were drawn. The mean proportion of neutrophils seen after the controlled air exposures for each study is illustrated as a dotted line. The shading bordering this mean value represents the 95% confidence interval (CI). The solid line represents the linear regression line passed through the % neutrophils after ozone. The 95% CIs for this regression are illustrated. The data points enclosed with solid borders indicate that more than one time point was considered (1 and 6 hours in Reference 24 and 0, 2, and 4 hours in Reference 27). The results of the regression analysis illustrated in italics are based only on the data with lavage performed before the 3-hour postexposure time point. The regression results given in bold text refer to the whole data set. The figure inset on the right shows the overall neutrophil response corrected for the air controls (percent polymorphonuclear leukocytes [%PMNs] postozone – air) versus CVT with regression lines and results inset.

View larger version (23K): [in this window] [in a new window]   Figure 2. Relationship between ozone-induced neutrophilia in the distal airways during the late-acute response and CVT. Data are illustrated as outlined in the legend to Figure 1. Data from Reference 34 were omitted from the regression analysis as the reported response deviated markedly from the overall trend line. The smaller figure offset to the right shows the overall neutrophil response corrected for the air controls (percent polymorphonuclear leukocytes [%PMNs] postozone – air) versus CVT with regression lines and results inset.

Seven studies consisting of nine exposures were available to examine late (18–24 hours) neutrophil responses in the bronchial airways after ozone. Data obtained using peripheral airway lavage were omitted from these analyses due to their high postair-exposure neutrophil levels (17, 36). Using these data, we observed no evidence of a simple relationship between ozone dose and neutrophilia (r² = 0.02, p = 0.69, n = 9). Omitting the studies by Stenfors and colleagues (39), on the basis of an abnormally high bronchial wash neutrophil number postair challenge, as well as that by Christian and colleagues (34), for the reasons outlined earlier, did not reveal a clearer relationship between dose and induced neutrophilia (r² = 0.24, p = 0.27, n = 7). Notably, and similar to the situation at 0 to 6 hours, when the overall response was examined in the restricted data set (n = 7), some evidence of an underlying association did emerge (r² = 0.65, p < 0.05). These data are illustrated in Figures E2 and E3 in the online supplement.

Altered Permeability in Alveolar Lavage
This analysis was limited by the lack of comparative data between studies, with albumin concentrations determined in only 9 of the 21 cited studies (Table 1). Consequently, only bronchoalveolar lavage fluid total protein concentrations were considered, with responses expressed as fold changes over the early and late postexposure period. Over the early postexposure period, no significant relationship between CVT and the total protein response was observed (r² = 0.07, p = 0.45). However, the data from the study performed by Hazbun and colleagues (28) clearly distorted any underlying association, and removal of this data revealed a linear relationship (r² = 0.51, p < 0.05, n = 9), which was further strengthened by excluding those studies with bronchoscopy performed between 3 and 6 hours postexposure (r² = 0.74, p < 0.05, n = 6). These data are illustrated in Figure E4 in the online supplement. A similar relationship was observed over the late postexposure period (see Figure E4 in the online supplement) CVT (r² = 0.41, p < 0.05, n = 10).

DISCUSSION

Studies investigating the relationship between ozone dose and transient lung function decrements have revealed both the existence of a relatively simple sigmoidal relationship and emphasized the importance of ventilation rate on the magnitude of the decrements observed (12–14). In this study, we investigated whether a similar simple relationship existed between ozone dose, defined using the CVT convention (29) and the magnitude of ozone-induced neutrophilia observed in healthy subjects after controlled exposures. This preliminary study was based on a metaanalysis of the preexisting human-exposure literature, using the percentage of neutrophils recovered by lavage after ozone as well as the fold increase in lavage total protein as markers of inflammation and disruption of the airway epithelium, respectively. Although these markers of transient airway responses cannot be simplistically associated with the reported health effects of ozone (increased cardiopulmonary mortality, asthma exacerbations, increased rates of airway infection, abnormal lung growth during childhood), they are probably contributory factors in the development of these chronic/acute responses.

Using this approach, we demonstrated a linear exposure–response relationship between neutrophilia in alveolar lavage samples and ozone dose. Although the regressions through the data sets left a considerable proportion of the variance unexplained, the fact that any association could be identified in light of the variations in airway sampling protocols and the known individual variations in sensitivity to ozone (14, 17, 19, 21) is important. As the metaanalysis produced a good estimate of the basal airway neutrophilia, we examined at what point the regression through the ozone-response data would cut the upper 95% interval of the basal airway neutrophil data. We tentatively interpreted this as representing a threshold dose for the induction of airway neutrophilia, obtaining values of 645 (408–883) mg/m² for the early and 810 (490–1,130) mg/m² for the late ozone-induced neutrophil response. Clearly, these data refer to the majority of healthy subjects, as certain individuals will elicit responses below this dose (21, 23, 46). To place these estimates into context, at the current 1-hour National Ambient Air Quality ozone standard (0.12 ppm, 235 µg/m³) ventilation rates greater than 45 L/minute/m² would be required to exceed the early-acute response threshold (645.1 mg/m²). In contrast, at the 8-hour standard (0.08 ppm, 157 µg/m³), exceedences of this early-acute threshold would occur at moderate E values greater than 10 L/minute/m² or for the persistent response at greater than 11 L/minute/m². These relationships are illustrated in Figure E5 in the online supplement. It was not possible to demonstrate such a simple relationship in bronchial airway lavages probably due to the greater heterogeneity in lavage techniques used to assess responses in this compartment.

Thus, on the basis of this preliminary analysis, individuals performing even relatively mild exercise for prolonged periods during ozone episodes appear likely to develop acute airway inflammation. Given the difficulty in reducing further ambient ozone concentrations and in light of the fact that exceedences of CVT thresholds are driven by exposure duration and ventilation rate, we suggest that further emphasis should be placed on limiting physical activity during pollution episodes. The detrimental effect of exercise in polluted environments has recently been demonstrated in an epidemiologic study addressing the induction of childhood asthma (40), and indeed, the current advice already emphasizes reducing outdoor activity during ozone episodes and limiting physical activity to the early morning and late afternoon when ambient ozone levels are reduced.

A number of important caveats must be made regarding the findings of this study and the limitations of the data treatment. It is clear from the regressions that much of the variance in the data is not explained by the least-squares regression. This is hardly surprising given the nature of the metaanalysis as none of the studies was specifically designed to test exposure–response relationship or to make estimates for response thresholds. The fact that a linear association exists was therefore all the more significant, and other fitting procedures, polynomial and sigmoidal, did not improve the observed association. It is also important to emphasize that we only addressed acute responses in this study and did not consider multiple exposures. Thus, we do not exclude the possibility that cumulative exposures below the cited threshold values might have chronic impacts on other health indices (41, 42). We elected to rely solely on bronchoscopy-based human studies in this metaanalysis and did not include data obtained using less-invasive techniques: induced sputum (43), exhaled nitric oxide (44), or breath condensate (44). We believe that bronchoscopy-based lavage remains the gold standard for assessing distal and proximal airway inflammation. Although some studies have attempted to validate indirect methods against bronchoscopy-based techniques (45), these are, in our opinion, rather preliminary and underpowered. Although less invasive methods would permit, once validated, detailed dose–inflammatory response relationships to be drawn, to date, they have been used only in high-dose studies where bronchoscopy-based data are already available.

It was notable that the dose threshold for the early inflammatory response was lower (645 [408–883] mg/m²) than that for the late response (810 [491–1,130] mg/m²). This suggests that responses to low-dose challenges are very transient, whereas persistent effects are more characteristic of high-dose challenges. This is an important point, as one of the initial problems identified in performing this type of analysis was how to control for response progression. In many of the studies cited, especially those examining early airway effects postchallenge, and in which neutrophilia was not observed, significant increases in proinflammatory mediators (23) or vascular endothelium adhesion molecules (46) were seen. Of interest in these low-dose studies is whether these early responses would manifest themselves at a later time point as an established neutrophilia. These data, suggesting a lower threshold for early versus late postexposure responses, would tend to argue against this, but the scarcity of low-dose ozone studies addressing early and late responses limits resolution of this issue.

We also made an attempt to examine the exposure–response relationship between ozone dose and altered airway permeability using bronchoalveolar lavage fluid total protein as an injury marker. Insufficient data were available to use albumin for this purpose, and it should be noted that more sensitive markers might display a clearer relationship (6). Despite this limitation, we observed surprising strong associations between total protein responses and ozone dose (CVT) for both early and late postexposure periods. Due to the necessity to express the data as fold increases to control for variable lavage dilution, it was not possible to estimate a threshold value. However, it was notable that there was little evidence of a significant increase in lavage fluid total protein or albumin below a CVT of 800 mg/m² (Table 1).

This preliminary analysis therefore suggests that there is a relatively simple relationship between ozone-induced airway responses and ozone. Identification of such a relationship by metaanalysis suggests that this approach could provide a definitive threshold value in a specifically designed large-scale exposure study.

FOOTNOTES

Supported by the UK Department of Health.

The views expressed in this publication are those of the authors and not necessarily those of the Department of Health (UK).

This article has an online supplement, which is accessible from this issue's table of contents online at www.atsjournals.org

Conflict of Interest Statement: I.S.M. has no declared conflict of interest; F.J.K. has no declared conflict of interest.

Received in original form September 25, 2003; accepted in final form January 26, 2004

REFERENCES

1. Thurston GD, Ito K. Epidemiological studies of acute ozone exposures and mortality. J Expo Anal Environ Epidemiol 2001;11:286–294.[CrossRef][Medline]
2. Kinney PL, Thurston GD, Raizenne M. The effects of ambient ozone on lung function in children: a reanalysis of six summer camp studies. Environ Health Perspect 1996;104:170–174.[Medline]
3. Romieu I, Meneses F, Ramirez M, Ruiz S, Perez Padilla R, Sienra JJ, Gerber M, Grievink L, Dekker R, Walda I, et al. Antioxidant supplementation and respiratory functions among workers exposed to high levels of ozone. Am J Respir Crit Care Med 1998;158:226–232.
4. Peters JM, Avol E, Gauderman WJ, Linn WS, Navidi W, London SJ, Margolis H, Rappaport E, Vora H, Gong H Jr, et al. A study of twelve Southern California communities with differing levels and types of air pollution. II: effects on pulmonary function. Am J Respir Crit Care Med 1999;159:768–775.[Abstract/Free Full Text]
5. Kinney PL, Nilsen DM, Lippmann M, Brescia M, Gordon T, McGovern T, El-Fawal H, Devlin RB, Rom WN. Biomarkers of lung inflammation in recreational joggers exposed to ozone. Am J Respir Crit Care Med 1996;154:1430–1435.[Abstract]
6. Broeckaert F, Arsalane K, Hermans C, Bergamaschi E, Brustolin A, Mutti A, Bernard A. Lung epithelial damage at low concentrations of ambient ozone. Lancet 1999;353:900–901.[Medline]
7. Thurston GD, Ito K, Kinney PL, Lippmann M. A multi-year study of air pollution and respiratory hospital admissions in three New York State metropolitan areas: results for 1988 and 1989 summers. J Expo Anal Environ Epidemiol 1992;2:429–450.[Medline]
8. Thurston GD, Ito K, Hayes CG, Bates DV, Lippmann M. Respiratory hospital admissions and summertime haze air pollution in Toronto, Ontario: consideration of the role of acid aerosols. Environ Res 1994;65:271–290.[Medline]
9. Mustafa MG. Biochemical basis of ozone toxicity. Free Radic Biol Med 1990;9:245–265.[CrossRef][Medline]
10. Committee of the Environmental and Occupational Health Assembly of the American Thoracic Society. Health effects of outdoor air pollution. Am J Respir Crit Care Med 1996;153:3–50.[Abstract]
11. Devlin RB, McDonnell WF, Mann R, Becker S, House DE, Schreinemachers D, Koren HS. Exposure of humans to ambient levels of ozone for 6.6 hours causes cellular and biochemical changes in the lung. Am J Respir Cell Mol Biol 1991;4:72–81.
12. McDonnell WF, Horstman DH, Hazucha MJ, Seal E Jr, Haak ED, Salaam SA, House DE. Pulmonary effects of ozone exposure during exercise: dose–response characteristics. J Appl Physiol 1983;54:1345–1352.[Abstract/Free Full Text]
13. McDonnell WF, Stewart PW, Andreoni S, Seal E Jr, Kehrl HR, Horstman DH, Folinsbee LJ, Smith MV. Prediction of ozone-induced FEV1 changes: effects of concentration, duration, and ventilation. Am J Respir Crit Care Med 1997;156:715–722.[Abstract/Free Full Text]
14. McDonnell WF, Stewart PW, Smith MV, Pan WK, Pan J. Ozone-induced respiratory symptoms: exposure-response models and association with lung function. Eur Respir J 1999;14:845–853.[Abstract/Free Full Text]
15. Blomberg A, Mudway IS, Nordenhall C, Hedenstrom H, Kelly FJ, Frew AJ, Holgate ST, Sandstrom T. Ozone-induced lung function decrements do not correlate with early airway inflammatory or antioxidant responses. Eur Respir J 1999;13:1418–1428.[Abstract]
16. Mudway IS, Kelly FJ. Identification of the inflammatory threshold of ozone (O3) in healthy adults . Exp Lung Res 2003;29:425–427.
17. Balmes JR, Aris RM, Chen LL, Scannell C, Tager IB, Finkbeiner W, Christian D, Kelly T, Hearne PQ, Ferrando R, et al. Effects of ozone on normal and potentially sensitive human subjects. Part I: airway inflammation and responsiveness to ozone in normal and asthmatic subjects. Res Rep Health Eff Inst 1997;78:1–37.
18. Balmes JR, Chen LL, Scannell C, Tager I, Christian D, Hearne PQ, Kelly T, Aris RM. Ozone-induced decrements in FEV1 and FVC do not correlate with measures of inflammation. Am J Respir Crit Care Med 1996;153:904–909.[Abstract]
19. Torres A, Utell MJ, Morow PE, Voter KZ, Whitin JC, Cox C, Looney RJ, Speers DM, Tsai Y, Frampton MW. Airway inflammation in smokers and nonsmokers with varying responsiveness to ozone. Am J Respir Crit Care Med 1997;156:728–736.[Abstract/Free Full Text]
20. Basha MA, Gross KB, Gwizdala CJ, Haidar AH, Popovich J Jr. Bronchoalveolar lavage neutrophilia in asthmatic and healthy volunteers after controlled exposure to ozone and filtered purified air. Chest 1994;106:1757–1765.[Abstract/Free Full Text]
21. Mudway IS, Stenfors N, Blomberg A, Helleday R, Dunster C, Marklund SL, Frew AJ, Sandstrom T, Kelly FJ. Differences in basal airway antioxidant concentrations are not predictive of individual responsiveness to ozone: a comparison of healthy and mild asthmatic subjects. Free Radic Biol Med 2001;31:962–974.[CrossRef][Medline]
22. Samet JM, Hatch GE, Horstman D, Steck-Scott S, Arab L, Bromberg PA, Levine M, McDonnell WF, Devlin RB. Effect of antioxidant supplementation on ozone-induced lung injury in human subjects. Am J Respir Crit Care Med 2001;164:819–825.[Abstract/Free Full Text]
23. Krishna MT, Madden J, Teran LM, Biscione GL, Lau LC, Withers NJ, Sandstrom T, Mudway I, Kelly FJ, Walls A, et al. Effects of 0.2 ppm ozone on biomarkers of inflammation in bronchoalveolar lavage fluid and bronchial mucosa of healthy subjects. Eur Respir J 1998;11:1294–1300.[Abstract]
24. Schelegle ES, Siefkin AD, McDonald RJ. Time course of ozone-induced neutrophilia in normal humans. Am Rev Respir Dis 1991;143:1353–1358.[Medline]
25. Jorres RA, Holz O, Zachgo W, Timm P, Koschyk S, Muller B, Grimminger F, Seeger W, Kelly FJ, Dunster C, et al. The effect of repeated ozone exposures on inflammatory markers in bronchoalveolar lavage fluid and mucosal biopsies. Am J Respir Crit Care Med 2000;161:1855–1861.[Abstract/Free Full Text]
26. Seltzer J, Bigby BG, Stulbarg M, Holtzman MJ, Nadel JA, Ueki IF, Leikauf GD, Goetzl EJ, Boushey HA. O3-induced change in bronchial reactivity to methacholine and airway inflammation in humans. J Appl Physiol 1986;60:1321–1326.[Abstract/Free Full Text]
27. Coffey MJ, Wheeler CS, Gross KB, Eschenbacher WL, Sporn PH, Peters-Golden M. Increased 5-lipoxygenase metabolism in the lungs of human subjects exposed to ozone. Toxicology 1996;114:187–197.[Medline]
28. Hazbun ME, Hamilton R, Holian A, Eschenbacher WL. Ozone-induced increases in substance P and 8-epi-prostaglandin F2 alpha in the airways of human subjects. Am J Respir Cell Mol Biol 1993;9:568–572.
29. Silverman F, Folinsbee LJ, Barnard J, Shephard RJ. Pulmonary function changes in ozone-interaction of concentration and ventilation. J Appl Physiol 1976;41:859–864.[Abstract/Free Full Text]
30. Hazucha MJ. Relationship between ozone exposure and pulmonary function changes. J Appl Physiol 1987;62:1671–1680.[Abstract/Free Full Text]
31. Hazucha MJ, Folinsbee LJ, Seal E. Effects of steady-state and variable ozone concentration profiles on pulmonary function. Am Rev Respir Dis 1992;146:1487–1493.[Medline]
32. Koren HS, Devlin RB, Graham DE, Mann R, McGee MP, Horstman DH, Kozumbo WJ, Becker S, House DE, McDonnell WF, et al. Ozone-induced inflammation in the lower airways of human subjects. Am Rev Respir Dis 1989;139:407–415.[Medline]
33. Hatch GE, Slade R, Harris LP, McDonnell WF, Devlin RB, Koren HS, Costa DL, McKee J. Ozone dose and effect in humans and rats: a comparison using oxygen-18 labeling and bronchoalveolar lavage. Am J Respir Crit Care Med 1994;150:676–683.[Abstract]
34. Christian DL, Chen LL, Scannell CH, Ferrando RE, Welch BS, Balmes JR. Ozone-induced inflammation is attenuated with multiday exposure. Am J Respir Crit Care Med 1998;158:532–537.[Abstract/Free Full Text]
35. Weinmann GG, Liu MC, Proud D, Weidenbach-Gerbase M, Hubbard W, Frank R. Ozone exposure in humans: inflammatory, small and peripheral airway responses. Am J Respir Crit Care Med 1995;152:1175–1182.[Abstract]
36. Aris RM, Christian D, Hearne PQ, Kerr K, Finkbeiner WE, Balmes JR. Ozone-induced airway inflammation in human subjects as determined by airway lavage and biopsy. Am Rev Respir Dis 1993;148:1363–1372.[Medline]
37. Devlin RB, McDonnell WF, Becker S, Madden MC, McGee MP, Perez R, Hatch G, House DE, Koren HS. Time-dependent changes of inflammatory mediators in the lungs of humans exposed to 0.4 ppm ozone for 2 hr: a comparison of mediators found in bronchoalveolar lavage fluid 1 and 18 hr after exposure. Toxicol Appl Pharmacol 1996;138:176–185.[CrossRef][Medline]
38. Koren HS, Devlin RB, Becker S, Perez R, McDonnell WF. Time-dependent changes of markers associated with inflammation in the lungs of humans exposed to ambient levels of ozone. Toxicol Pathol 1991;19:406–411.[Medline]
39. Stenfors N, Pourazar J, Blomberg A, Krishna MT, Mudway I, Helleday R, Kelly FJ, Frew AJ, Sandstrom T. Effect of ozone on bronchial mucosal inflammation in asthmatic and healthy subjects. Respir Med 2002;96:352–358.[CrossRef][Medline]
40. McConnell R, Berhane K, Gilliland F, London SJ, Islam T, Gauderman WJ, Avol E, Margolis HG, Peters JM. Asthma in exercising children exposed to ozone: a cohort study. Lancet 2002;359:386–391.[CrossRef][Medline]
41. Schwartz J. Lung function and chronic exposure to air pollution: a cross-sectional analysis of NHANES II. Environ Res 1989;50:309–321.[Medline]
42. Schelegle ES, Miller LA, Gershwin LJ, Fanucchi MV, Van Winkle LS, Gerriets JE, Walby WF, Mitchell V, Tarkington BK, Wong VJ, et al. Repeated episodes of ozone inhalation amplifies the effects of allergen sensitization and inhalation on airway immune and structural development in Rhesus monkeys. Toxicol Appl Pharmacol 2003;191:74–85.[CrossRef][Medline]
43. Holz O, Jorres RA, Timm P, Mucke M, Richter K, Koschyk S, Magnussen H. Ozone-induced airway inflammatory changes differ between individuals and are reproducible. Am J Respir Crit Care Med 1999;159:776–784.[Abstract/Free Full Text]
44. Nightingale JA, Rogers DF, Barnes PJ. Effect of inhaled ozone on exhaled nitric oxide, pulmonary function, and induced sputum in normal and asthmatic subjects. Thorax 1999;54:1061–1069.[Abstract/Free Full Text]
45. Hiltermann JT, Lapperre TS, van Bree L, Steerenberg PA, Brahim JJ, Sont JK, Sterk PJ, Hiemstra PS, Stolk J. Ozone-induced inflammation assessed in sputum and bronchial lavage fluid from asthmatics: a new noninvasive tool in epidemiologic studies on air pollution and asthma. Free Radic Biol Med 1999;27:1448–1454.[CrossRef][Medline]
46. Krishna MT, Blomberg A, Biscione GL, Kelly F, Sandstrom T, Frew A, Holgate S. Short-term ozone exposure upregulates P-selectin in normal human airways. Am J Respir Crit Care Med 1997;155:1798–1803.[Abstract]

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