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Biomedical subjects

E L Avol

Publications and source records attributed to E L Avol.

At least 19 recordsLinked to original sources
PubMed2001

Respiratory effects of relocating to areas of differing air pollution levels.

We studied 110 children (59 boys and 51 girls, who were 10 yr of age at enrollment and 15 yr of age at follow-up) who had moved from communities participating in a 10-yr prospective study of respiratory health (The Children's Health Study [CHS]) to determine whether changes in air quality caused by relocation were associated with changes in annual lung function growth rates. The subjects were given health questionnaires and underwent spirometry in their homes across six western states, according to a protocol identical to evaluations performed annually on the CHS cohort in school. Changes in annual average exposure to particulate matter with a mean diameter of 10 microm (PM(10)) were associated with differences in annual lung function growth rates for FEV(1), maximal midexpiratory flow, and peak expiratory flow rate. As a group, subjects who had moved to areas of lower PM(10) showed increased growth in lung function and subjects who moved to communities with a higher PM(10) showed decreased growth in lung function. A stronger trend was found for subjects who had migrated at least 3 yr before the follow-up visit than for those who had moved in the previous 1 to 2 yr. We conclude that changes in air pollution exposure during adolescent growth years have a measurable and potentially important effect on lung function growth and performance.

Adolescent↗
PubMed2000

Quality of spirometry test performance in children and adolescents : experience in a large field study.

STUDY OBJECTIVE: To determine the ability of children and adolescents to meet the American Thoracic Society (ATS) goals for spirometry quality that were based on results from adults. DESIGN: Observational. PARTICIPANTS: More than 4,000 public school students, ages 9 to 18 years. MEASUREMENTS: Spirometry was performed annually for 3 years, with the recording of maneuver quality measures of forced expiratory time, end-of-test volume, back-extrapolated volume, and time to peak expiratory flow (PEFT), and the recording of differences between best and second-best FVC, FEV(1), and peak expiratory flow (PEF) values. RESULTS: Regression analyses showed significant influences of participant age, gender, ethnicity, size, clinical status, and previous testing experience, as well as differences among individual test technicians. In general, these influences were small and explained little of the variance in performance. On average, children with a history of asthma or wheeze performed better quality spirometry than did others. Only PEFT improved significantly from year to year. Overall, only 15% of girls' tests and 32% of boys' tests met the PEFT criterion derived from adults in the Lung Health Study. CONCLUSION: Most of the children met adult-based ATS goals for spirometry test performance. Age group-specific criteria are needed to ensure adequately fast PEFT and reproducible PEF values.

Adolescent↗
PubMed1998

Temperature standardization of multiple spirometers.

In respiratory health surveys involving multiple spirometers, spirometer differences may introduce important biases. We investigated temperature measurement variability as a cause of spirometer differences. Digital thermometers recorded internal (cylinder) and external (outer casing) temperatures of six similar rolling-seal spirometers during field use and in laboratory tests at controlled room temperatures. Internal and external thermometers substantially agreed in recording spirometer temperature changes, which lagged room temperature changes. Offsets of individual thermometers from overall mean readings were roughly the same in field testing of 3908 students in > 60 schools over 5 months and in subsequent laboratory tests. Thermometers differed by as much as 1.3 degrees C, causing differences as large as 0.8% in vital capacity measurements. We conclude that (1) interior and exterior temperatures of typical rolling-seal spirometers do not differ greatly, although both may differ from surrounding air temperature; and (2) variations between individual digital thermometers may be large enough to bias spirometric data appreciably in large-scale surveys. Variations should be controlled by selection of similar-reading thermometers and/or correction to a uniform standard.

Analysis of Variance↗
PubMed1998

Acute effects of ambient ozone on asthmatic, wheezy, and healthy children.

Southern California children (10 to 12 years old) participated in a two-season study to assess the potential acute respiratory effects of ambient ozone (O3). Asthmatic (n = 49), wheezy (n = 53), and healthy (n = 93) children completed a four-day (Friday through Monday) study protocol, once in spring and again in summer, that included the use of daily activity and symptom diaries, heart rate recording devices, personal O3 samplers, and maximal effort spirometry several times per day. Data from regional monitoring stations were used to establish ambient hourly O3 concentrations. Analyses revealed that the children spent more time outdoors and were more physically active in the spring. Girls spent less time outdoors and were less physically active than boys. Personal O3 samplers correlated poorly with, and generally gave lower readings than, outdoor ambient monitors. Higher personal O3 exposures were associated generally with increased inhaler use, more outdoor time, and more physical activity. Children with asthma spent more time outdoors and were more active in the spring on high-O3 days (measured by personal sampler), and had the most trouble breathing, the most wheezing, and the most inhaler use on these days. Activity pattern data suggested that children with asthma protected themselves by being less physically active outdoors during the summer on high-O3 days. Wheezy children had the most trouble breathing during the summer on low-O3 days (measured by personal sampler). Observed relationships between O3 and pulmonary function were erratic and difficult to reconcile with existing knowledge about the acute respiratory effects of air pollution. We conclude that although asthmatic and wheezy children behave differently from their healthy peers with regard to symptoms and patterns of activity when challenged by ambient ozone, the nature of these changes remains inconsistent and ill-defined.

Acute Disease↗
PubMed1996

Standardization of multiple spirometers at widely separated times and places.

We designed a system for a multiyear longitudinal study of lung function in 12 widely separated communities, intending to minimize variation in instrument-related data. We used multiple rolling-seal spirometer/personal computer systems. Calibrations were checked before, during, and after each day's field testing, using multiple calibration syringes with electronic readouts. The syringes were rotated to obtain data for each syringe-spirometer combination. Before and after each annual field testing season, a laboratory reference spirometer system was calibrated against a water-displacement device and an electronic frequency counter, and then compared against each field spirometer and syringe. Field equipment consistently met American Thoracic Society (ATS) specifications. Variance among spirometers exceeded variance among syringes. A spirometer occasionally changed its volume readout by approximately 1 to 2 %. More rarely, a syringe changed its delivered volume by approximately 1%. Syringes' electronic readouts tracked changes in delivered volume. Syringe readouts were the most stable component of the system, and were more reproducible than the laboratory water-displacement calibration. We conclude that variation in spirometers may limit the reliability of epidemiologic findings, even when these spirometers meet ATS specifications. Frequent calibration checks traceable to an independent standard, and adjustment of individual test results, can reduce measurement error.

Calibration↗
PubMed1994

Effects of prolonged, repeated exposure to ozone, sulfuric acid, and their combination in healthy and asthmatic volunteers.

To evaluate effects of "acid summer haze" on individuals who exercise extensively outdoors, we exposed 45 adult volunteers (15 normal or atopic, 30 asthmatic) in a chamber to a mixture of 0.12 ppm ozone (O3) and approximately 100 micrograms/m3 of respirable sulfuric acid aerosol (H2SO4). On separate occasions we exposed the same subjects to O3 alone, to H2SO4 alone, and to clean air. In exposures involving H2SO4, excess acid was generated to consume ammonia released by the subjects, and the aerosol therefore contained ammonium salts in addition to H2SO4. Subjects were exposed to each atmosphere on two successive days, for 6.5 h/d, with six 50-min exercise periods at ventilation rates averaging 29 L/min. Exposures were conducted during four successive weeks, in random order. Lung function and symptoms were measured before exposure and hourly during exposure. Bronchial reactivity to inhaled methacholine was measured just after the end of each exposure. Exposure to H2SO4 alone caused no significant changes in lung function, symptoms, or bronchial reactivity relative to clean air. Exposure to O3 alone or O3 + H2SO4 caused a progressive, statistically significant (p < 0.05) decline in forced expiratory function, smaller on the second day than the first, as previously found by others for O3 exposure. Bronchial reactivity increased significantly after exposure to O3 with or without H2SO4. Changes in mean lung function and bronchial reactivity with O3 + H2SO4 exposure were modestly larger than changes with O3 exposure, but the differences were nonsignificant or marginally significant. A minority of individual asthmatic and nonasthmatic subjects showed substantially greater declines in function with exposure to O3 + H2SO4 relative to O3 alone. Repeat exposure studies of these subjects again showed an excess response to O3 + H2SO4 on the average, but there was no significant correlation between the excess responses of individual subjects in the original and repeat studies. We conclude that for typical healthy or asthmatic adults heavily exposed to acid summer haze, O3 is more important than H2SO4 as a cause of short-term respiratory irritant effects.

Adolescent↗
PubMed1994

Active and passive ozone samplers based on a reaction with a binary reagent.

Ozone is one of the most toxic common air pollutants (judging from short-term animal and human exposure studies at realistic concentrations) and one of the most difficult and expensive pollutants to control. Because of ozone's high chemical reactivity, its concentrations may vary greatly over short distances, and fixed-site air quality monitors may not accurately estimate exposures of human populations. Epidemiologic research on ozone's long-term health effects has been inconclusive, partly because of the lack of reliable personal exposure information. The objective of this project was to develop a practical personal ozone exposure monitoring technique, and to document its precision and accuracy in actual use by representatives of freely ranging, ozone-exposed populations. The project site, Los Angeles, is the nation's metropolitan area with the highest level of ozone pollution and, thus, probably the most important locale for personal exposure assessment. Our overall strategy was (1) to select the most promising laboratory technique for ozone detection from published literature and private communications; (2) to design and test personal monitors using this technique; and (3) when feasible, to evaluate concurrently alternative methodologies developed by others. As indicated below, parts 1 and 2 of our strategy yielded a limited success with respect to short-term active sampling, i.e., measuring personal ozone exposure levels during one to two hours with a monitor incorporating a battery-powered air pump of the type used in industrial hygiene investigations. The same approach was not successful in passive sampling, i.e., measuring exposure levels during multihour or multiday periods with a light-weight, diffusion-controlled "badge" sampler having no moving parts. Passive badge samplers could be calibrated reasonably well in laboratory exposures to ozone in otherwise pure air, but they greatly overestimated ozone levels in outdoor ambient air. Part 3 of our strategy yielded more promising information on an alternative passive badge design. After testing and rejecting two other possibilities, we chose a binary organic reagents, 3-methyl-2-benzothiazolinone acetone azine with 2-phenylphenol, as the most promising chemical detector of ozone. Filter papers impregnated with the binary reagent develop a characteristic intense pink color when exposed to ozone. The inventors, J.E. Lambert and associates of Kansas State University, had intended only to develop a rough qualitative ozone monitor (Lambert et al. 1989). However, our initial laboratory testing (in exposure chambers containing ozone in otherwise very clean air, away from humans), revealed fairly accurate quantitative response.(ABSTRACT TRUNCATED AT 400 WORDS)

Benzothiazoles↗
PubMed1992

Controlled exposures of volunteers to respirable carbon and sulfuric acid aerosols.

Respirable carbon or fly ash particles are suspected to increase the respiratory toxicity of coexisting acidic air pollutants, by concentrating acid on their surfaces and so delivering it efficiently to the lower respiratory tract. To investigate this issue, we exposed 15 healthy and 15 asthmatic volunteers in a controlled-environment chamber (21 degrees C, 50 percent relative humidity) to four test atmospheres: (i) clean air; (ii) 0.5-microns H2SO4 aerosol at approximately 100 micrograms/m3, generated from water solution; (iii) 0.5-microns carbon aerosol at approximately 250 micrograms/m3, generated from highly pure carbon black with specific surface area comparable to ambient pollution particles; and (iv) carbon as in (iii) plus approximately 100 micrograms/m3 of ultrafine H2SO4 aerosol generated from fuming sulfuric acid. Electron microscopy showed that nearly all acid in (iv) became attached to carbon particle surfaces, and that most particles remained in the sub-micron size range. Exposures were performed double-blind, 1 week apart. They lasted 1 hr each, with alternate 10-min periods of heavy exercise (ventilation approximately 50 L/min) and rest. Subjects gargled citrus juice before exposure to suppress airway ammonia. Lung function and symptoms were measured pre-exposure, after initial exercise, and at end-exposure. Bronchial reactivity to methacholine was measured after exposure. Statistical analyses tested for effects of H2SO4 or carbon, separate or interactive, on health measures. Group data showed no more than small equivocal effects of any exposure on any health measure.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Exposures of older adults with chronic respiratory illness to nitrogen dioxide. A combined laboratory and field study.

We combined field and laboratory experimentation to evaluate the effects of nitrogen dioxide in a panel of Los Angeles area residents with chronic respiratory illness, 15 men and 11 women aged 47 to 69. All had heavy smoking history, chronic symptoms, and low FEV1; some also had low FVC. During the fall-winter high-NO2 season, they monitored themselves for 2-wk periods using spirometers in the home, passive NO2 sampling badges, and diaries to record time and activity patterns and clinical status. In the middle of each self-monitoring week they were exposed in a chamber, once to clean air and once to 0.3 ppm NO2. Chamber exposures were double blind, lasted 4 h, and included four 7-min exercise sessions with average ventilation rates near 25 L/min. Symptom reports and hourly forced expiratory function tests showed no statistically significant differences between clean air and NO2 chamber exposures, although peak flow showed a approximately 3% loss with NO2 relative to clean air during the first 2 h of exposure only (p = 0.056). No significant overall differences were found between field self-measurements and measurements of lung function in the chamber or between field measurements in clean air and NO2 exposure weeks. Field data showed that group average lung function and symptom levels were worse in the morning than later in the day (p < 0.005) but otherwise were stable over 2 wk. Even though most subjects smoked and stayed indoors 80 to 90% of the time, personal NO2 exposures correlated significantly with outdoor NO2 concentrations as reported by local monitoring stations.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1990

Effect of exposures to ambient ozone on ventilatory lung function in children.

This study was undertaken to determine if the ventilatory capacity of children is affected by hourly concentrations of ozone inhaled during their daily activity. Over a 3-wk period (June-July 1987) children who were attending a summer camp in the San Bernardino mountains of California performed spirometry up to three times per day during their stay at the camp. A total of 43 children were tested a total of 461 times. Ozone, oxides of nitrogen, sulfur dioxide, temperature, and relative humidity were measured continuously. Daily average measurements of total suspended particulate and the PM10 particulate fraction (less than or equal to 10 microns) were also made. Hourly ozone concentrations at the time of testing varied between 20 and 245 ppb. Regressions of each individual's FEV1 and FVC supported the view that high ozone levels reduced these lung function parameters. The average regression coefficient for FEV1 on ozone was -0.39 ml/ppb (SEM = 0.12) and for FVC -0.44 ml/ppb (SEM = 0.15), both of which were significantly different from zero. Statistical allowance for temperature and humidity increased the magnitude of these slopes. Nitrogen dioxide never exceeded 40 ppb during the time of testing and averaged 13 ppb. Sulfur dioxide's highest measurement was 8 ppb and often was at the limit of detection. Neither NO2 nor SO2 was considered in the statistical modeling. Data were divided based on whether each subject had been exposed to levels of ozone in excess of the National Ambient Air Quality Standard (NAAQS) during the several hours previous to being tested. Exposures exceeding the NAAQS indicated a significant negative relationship between ozone and FEV1, FVC, and PEFR. Data for nonexceedance periods did not indicate this negative relationship for any of the three lung function parameters, but it could not be determined if this was due to an absence of an ozone effect or to a combination of the increased variability and decreased size of this data subset. These data indicate that lung function changes on a daily basis relate in a negative fashion to ambient ozone levels. The magnitude of the changes are small and are reversed as ambient ozone decreases.

Air Pollutants↗
PubMed1990

Respiratory responses of young asthmatic volunteers in controlled exposures to sulfuric acid aerosol.

Thirty-two asthmatic volunteers 8 to 16 yr of age, recruited through local schools and private physicians, were exposed in a chamber to clean air (control condition) and to sulfuric acid aerosol at a "low" concentration (46 +/- 11 micrograms/m3; mean +/- SD) and at a "high" concentration (127 +/- 21 micrograms/m3). Acid aerosols had mass median aerodynamic diameters near 0.5 microns with geometric standard deviations near 1.9. Temperature was 21 degrees C, and relative humidity was near 50%. Subjects were exposed with unencumbered oronasal breathing for 30 min at rest plus 10 min at moderate exercise (ventilation rate approximately 20 L/min/m2 of body surface). A subgroup (21 subjects) were exposed similarly to clean air and to "high" acid (134 +/- 20 micrograms/m3) with 100% oral breathing. Increased symptoms and bronchoconstriction were found after exercise under all exposure conditions. For the group, symptom and lung function responses were not statistically different during control and during acid exposures with unencumbered breathing or with oral breathing. By contrast, other investigators have reported statistically significant lung function disturbances in groups of young asthmatics exposed similarly with oral breathing. A minority of our subjects showed possibly meaningful excess bronchoconstriction with "high" acid exposure relative to control with both routes of breathing. This could be the result of chance, or it could suggest the existence of an acid-sensitive subpopulation of young asthmatics.

Adolescent↗
PubMed1989

Effect of droplet size on respiratory responses to inhaled sulfuric acid in normal and asthmatic volunteers.

We exposed groups of healthy and asthmatic volunteers to sulfuric acid aerosols with volume median droplet diameters of approximately 20, 10, and 1 microns, at nominal concentrations of 2,000 micrograms/m3, and exposed them similarly to aerosols of purified water as a control. Exposures lasted 1 h each, and included three 10-min periods of exercise (ventilation rate typically 40 to 45 L/min). Exposures occurred in randomized order 7 days apart. Temperature was 10 degrees C, relative humidity was approximately 100% in 20- and 10-microns (fog) exposures, and approximately 75 to 80% in 1-micron aerosol exposures. Healthy subjects showed no statistically significant changes in lung function or in bronchial reactivity to methacholine attributable to acid exposures. They showed significant increases in lower and upper respiratory irritant symptoms when exposed to 20- or 10-microns acid fog, but not when exposed to 1-micron acid aerosol. Asthmatics showed significant excess decreases in forced expiratory performance, increases in airway resistance, and increases in irritant symptoms during acid exposures, relative to control conditions. Lung function changes in asthmatics tended to increase with time during exposure; they did not vary significantly with acid droplet size. Symptoms in asthmatics were slightly worse with 10- or 20-microns fog as compared with 1-micron aerosol. In a few instances, symptoms and lung function decrements necessitated stopping exercise or terminating the exposure early. Thus, asthma is a risk factor for unfavorable physiologic response to sulfuric acid at occupational exposure concentrations. Large droplet size (i.e., fog) tends to exacerbate short-term symptomatic response, but we have not been able to demonstrate a consistent effect of droplet size on physiologic response.

Adult↗
PubMed1989

Experimental exposures of young asthmatic volunteers to 0.3 ppm nitrogen dioxide and to ambient air pollution.

Asthmatic volunteers aged 8 to 16 (N = 34) were exposed on separate occasions to clean air (control), to 0.30 ppm nitrogen dioxide (NO2) in otherwise clean air, and to polluted Los Angeles area ambient air on summer mornings when NO2 pollution was expected. Exposures lasted 3 hr, with alternating 10-min periods of exercise and rest. In ambient pollution exposures, 3-hr average NO2 concentrations ranged from 0.01 to 0.26 ppm, with a mean of 0.09 ppm. Ambient exposures did not significantly affect lung function, symptoms, or bronchial reactivity to cold air, relative to the control condition. Responses to 0.3 ppm NO2 exposures were equivocal. Asthma symptoms were more severe during 1-week periods before 0.3 ppm exposures, and lung function was decreased immediately before 0.3 ppm exposures, compared to other conditions. Lung function declined slightly during the first hour at 0.3 ppm, but improved over the remaining 2 hr. Compared to other conditions, symptoms were not increased during 0.3 ppm exposures, but were increased during 1-week periods afterward. These observations may reflect untoward effects of 0.3 ppm NO2, or may reflect chance increases in asthma severity prior to 0.3 ppm exposures.

Adolescent↗
PubMed1989

Acid fog: effects on respiratory function and symptoms in healthy and asthmatic volunteers.

Acidic air pollutants generally are dissolved in water droplets. Mean droplet diameter may range from more than 10 microns in dense fog to less than 1 micron at low relative humidity. Droplet size influences the deposition of inhaled acid within the respiratory tract and thus may influence toxicity. To help assess health risks from acid pollution, we performed controlled exposures of normal and asthmatic volunteers to sulfuric acid aerosols at nominal concentrations of 0 (control), 500, 1000, and 2000 micrograms/m3. Exposures lasted 1 hr with intermittent heavy exercise. Response was assessed by lung function tests and symptom questionnaires. Under foggy conditions (mean droplet size 10 microns, temperature 50 degrees F), no marked effects on lung function were found. However, both normal and asthmatic subjects showed statistically significant dose-related increases in respiratory symptoms. In a separate study, normal subjects exposed at 70 degrees F with mean droplet size 0.9 microns showed no marked effect on function or symptoms. Asthmatics showed dose-related decrements in forced expiratory performance and increases in symptoms, most obvious at 1000 and 2000 micrograms/m3. The different results of the two studies probably reflect an influence of droplet size, but further investigation is needed to confirm this. The aggregate results suggest that only mild, if any, short-term respiratory irritant effects are likely at acid concentrations attained in ambient pollution.

Acid Rain↗
PubMed1988

Laboratory study of asthmatic volunteers exposed to nitrogen dioxide and to ambient air pollution.

Adult volunteers with moderate to severe asthma (N = 59) underwent dose-response studies to assess their reactivity to nitrogen dioxide (NO2) in otherwise clean air. Exposure concentrations were 0.0 (control), 0.3 and 0.6 ppm. A subgroup (N = 36) also underwent exposures to Los Angeles area ambient air at times when NO2 pollution was expected. Concentrations of NO2 during ambient exposures were 0.086 +/- 0.024 ppm (mean +/- s.d.). All exposures took place in a movable chamber/laboratory facility. Each study lasted 2 hr, with alternating 10 min periods of exercise (mean ventilation rate 40 L/min) and rest. Lung function was measured prior to exposure and after 10 min, 1 hr and 2 hr of exposure. Symptoms were recorded prior to exposure, during exposure and for 1 week afterward. In some subjects bronchial reactivity to cold air was measured 1 hr after the end of exposure and again 24 hr later. Different exposure conditions were presented in randomized order, 1 week apart. No pollutant exposure produced statistically significant changes in lung function, symptoms, or bronchial reactivity, relative to clean air. Ambient air exposures produced the largest (still nonsignificant) mean changes in some lung function tests. Given the physiological and atmospheric variability, negative statistical results do not rule out a small unfavorable effect of ambient pollution on lung function. If any such effect occurred, it was not likely caused by NO2. Statistical results remained negative when the analysis was restricted to the 20 subjects with most severe lung dysfunction. In conclusion at least in the Los Angeles area, sensitivity to ambient concentrations of NO2 is not common, even among adult asthmatics with moderate to severe disease.

Adult↗
PubMed1988

Respiratory dose-response study of normal and asthmatic volunteers exposed to sulfuric acid aerosol in the sub-micrometer size range.

Twenty-one healthy and 21 asthmatic volunteers were exposed to respirable sulfuric acid aerosol (mass median particle diameter approximately 0.9 micron, geometric standard deviation 2.5) in a chamber at 21 degrees and 50% relative humidity. Measured sulfuric acid concentrations averaged 0, 380, 1060, and 1520 micrograms/m3 (in the occupational range, higher than concentrations observed in ambient air pollution). Exposures to different concentrations occurred in randomized order 1 week apart. They lasted 1 hr and included three 10-min periods of heavy exercise. Healthy volunteers showed no statistically significant changes in pulmonary function, airway reactivity to inhaled methacholine, or overall reporting of irritant symptoms which could be attributed to acid exposure. They did show a slight statistically significant (P less than .01) increase in cough with increasing acid concentration. At the two highest acid concentrations, asthmatics showed significant increases in irritant symptoms and decrements in pulmonary function, without significant changes in airway reactivity. Their function decrements appeared to increase with time during exposure. Previous studies in fog (10 degrees, median particle diameter approximately 10 micron) with similar concentrations of sulfuric acid showed more symptoms but less pulmonary function change, perhaps reflecting different sites of particle deposition in airways and/or different degrees of neutralization by airway ammonia. This and earlier evidence predicts little, if any, acute irritant response in short-term (1 hr or less) exposures to sulfuric acid at concentrations found in ambient air pollution.

Administration, Inhalation↗
PubMed1988

Repeated laboratory ozone exposures of volunteer Los Angeles residents: an apparent seasonal variation in response.

This study was intended to help explain individual differences in susceptibility to irritant effects of ozone (O3), by determining whether prior ambient O3 exposures and/or recent acute respiratory illness modified response to laboratory O3 exposures. Response was measured in terms of lung function changes and irritant symptoms. Initially, 59 adult volunteer Los Angeles area residents underwent screening exposures in spring, before the season of frequent high ambient O3 levels. Unusually responsive and nonresponsive individuals (N = 12 and 13 respectively) underwent followup exposures in autumn (late in the high-O3 season) and in winter (low-O3 season). All exposures were to 0.18 ppm O3 for 2 hr with intermittent heavy exercise at 31 degrees C and 35% relative humidity. Nonresponders tended to remain nonresponsive throughout. In fall, responders had lost much of their reactivity, as if they had "adapted" to summer ambient O3 exposures. They did not regain reactivity by winter. Clinical laboratory findings suggestive of acute respiratory illness did not appear to correlate with O3 response. Eight responders and 9 nonresponders underwent another followup exposure in spring, about 1 yr after screening. By that time most responders had regained their reactivity; individual function changes were significantly correlated with changes 1 yr earlier. These results suggest that response to O3 is a persistent individual characteristic, but can be modified by repeated ambient exposures.

Adult↗