Pre-exposure to ozone does not enhance or produce exercise-induced asthma

Human exposure to air contaminants in sports environments

The aim of this review was to investigate human exposure to relevant indoor air contaminants, predictors affecting the levels, and the means to reduce the harmful exposure in indoor sports facilities. Our study revealed that the contaminants of primary concern are the following: particulate matter in indoor climbing, golf, and horse riding facilities; carbon dioxide and particulate matter in fitness centers, gymnasiums, and sports halls; Staphylococci on gymnasium surfaces; nitrogen dioxide and carbon monoxide in ice hockey arenas; carbon monoxide, nitrogen oxide(s), and particulate matter in motor sports arenas; and disinfection by-products in indoor chlorinated swimming pools. Means to reduce human exposure to indoor contaminants include the following: adequate mechanical ventilation with filters, suitable cleaning practices, a limited number of occupants in fitness centers and gymnasiums, the use of electric resurfacers instead of the engine powered resurfacers in ice hockey arenas, carefully regulated chlorine and temperature levels in indoor swimming pools, properly ventilated pools, and good personal hygiene. Because of the large number of susceptible people in these facilities, as well as all active people having an increased respiratory rate and airflow velocity, strict air quality requirements in indoor sports facilities should be maintained.

Exercise-induced bronchospasm in children: comparison of FEV1 and FEF25-75% responses

The response of asthmatic children to exercise has usually been evaluated by forced expiratory volume in 1 sec (FEV(1)). We reasoned that other respiratory indexes derived from the forced vital capacity maneuver such as forced expiratory flow between 25-75% of vital capacity (FEF(25-75%)) would add significant information in the evaluation of the relationship between asthma severity and response to exercise. We studied 164 children with intermittent (n = 63), mild persistent (n = 30), moderate persistent (n = 40), and severe persistent asthma (n = 31). Subjects exercised for 6 min on a cycle ergometer at 80% of their maximum heart rate, and spirometry was performed before and 5, 10, and 20 min after exercise. There was good correlation between changes in FEV(1) and FEF(25-75%) after exercise (r = 0.60, P < 0.001 for intermittent asthma and r = 0.80, P < 0.001 for severe persistent asthma). The presence of a fall in both FEV(1) (>/=10%) and in FEF(25-75%) (>/=26%) when compared to a decrease in only one of these two indexes was significantly greater in children with more severe asthma (60.0% for intermittent asthma and 94.4% for severe persistent asthma, P = 0.022). FEF(25-75%) can decrease in response to exercise without changes in FEV(1), mainly in children with mild asthma. In the evaluation of the response to exercise in children with different asthma severities, more than one maximum expiratory flow-volume parameter should be used.

Exercise-induced bronchospasm in children: effects of asthma severity

The prevalence of exercise-induced bronchospasm (EIB) in asthmatic individuals has been reported to vary from 40% to 90%. There are, however, few studies addressing the effects of asthma severity on airway responsiveness to exercise. The purpose of the present study was to investigate the effects of asthma severity on EIB in children. We studied 164 children classified as having intermittent (n = 63), mild persistent (n = 30), moderate persistent (n = 40), and severe persistent asthma (n = 31) according to the Global Initiative for Asthma classification. Subjects exercised for 6 min on a cycle ergometer at 80% of their maximum heart rate, and spirometry was performed before and 5, 10, and 20 min after exercise challenge. The prevalence of EIB in children with moderate or severe persistent asthma was significantly greater than in children with intermittent asthma (p < 0.001). EIB-positive children with intermittent asthma exhibited smaller changes in FEV1 than children in the other three groups (p < 0.001). There was no significant relationship between baseline FEV1 and the decline in FEV1 after exercise. We conclude that the prevalence of EIB is greater in children with more severe asthma, and that the intensity of response to exercise is not consistently related to the clinical severity of asthma.

Relationship between acute ozone responsiveness and chronic loss of lung function in residents of a high-ozone community

We hypothesized that acute respiratory responsiveness to ozone predicts chronic lung injury from repeated exposure to ozone-containing air pollution. We tested this hypothesis in 164 middle-aged nonsmoking residents of an ozone-polluted community who underwent lung-function measurements during 1986 and 1987 (i.e., time 3). The time-3 study was a follow up of more comprehensive studies conducted in 1977-1978 (time 1) and in 1982-1983 (time 2). In contrast to the apparent rapid (i.e., approximately 60 ml/y) decline in lung-function measurements between times 1 and 2, our subjects showed little change in forced vital capacity (FVC) or forced expired volume in 1 s (FEV1.0) between times 2 and 3, and they experienced a normal decline between times 1 and 3. A subgroup (n = 45) underwent 2-h laboratory ozone exposures to 0.4 ppm ozone, accompanied by intermittent exercise, and they experienced mild acute reductions in FEV1.0 and FVC, but there was little change in bronchial responsiveness to methacholine. Individual acute responses to laboratory ozone were not correlated with individual long-term changes between times 1 and 3. In summary, the results did not support our initial hypothesis, and they did not confirm rapid function decline in nonsmokers chronically exposed to ozone-containing air pollution.

Cardiovascular effects of ozone exposure in human volunteers

We hypothesized that ozone (O3) exposure acutely affects cardiovascular hemodynamics in humans and, in particular, in subjects with essential hypertension. We studied 10 nonmedicated hypertensive and six healthy male adults. Each subject, after catheterization of the right heart and a radial artery, was exposed in an environmentally controlled chamber to filtered air (FA) on one day and to 0.3 ppm O3 on the following day for 3 h with intermittent exercise. Relative to FA exposure, O3 exposure induced no statistically significant changes in cardiac index, ventricular performance, pulmonary artery pressure, pulmonary and systemic vascular resistances, ECG, serum cardiac enzymes, plasma catecholamines and atrial natriuretic factor, and SaO2. The overall results did not indicate major acute cardiovascular effects of O3 in either the hypertensive or the control subjects. However, mean preexposure to postexposure changes were significantly (p < 0.02) larger with O3 than with FA for rate-pressure product (1,353 beats/min/mm Hg) and for heart rate (8 beats/min); these responses were not significantly different between the hypertensive and the control subjects. Significant O3 effects were also observed for mean FEV1 (-6%), and AaPO2 (> 10 mm Hg increase), which were not significantly different between the two groups. These results suggest that O3 exposure can increase myocardial work and impair pulmonary gas exchange to a degree that might be clinically important in persons with significant preexisting cardiovascular impairment, with or without concomitant lung disease.

Mechanisms of pollution-induced airway disease: in vivo studies

Several studies have investigated the effects of ozone, sulphur dioxide (SO2), and nitrogen dioxide (NO2) on lung function in normal and asthmatic subjects. Decreased lung function has been observed with ozone levels as low as 0.15 ppm-this effect is concentration dependent and is exacerbated by exercise. A number of lines of evidence suggest that the effect on lung function is mediated, at least in part, by neural mechanisms. In both normals and asthmatics, ozone has been shown to induce neutrophilic inflammation, with increased levels of several inflammatory mediators, including prostaglandin E2. However, in normal subjects, none of the markers of inflammation correlate with changes in lung function. The lung function changes in asthmatics may be associated with inflammatory effects; alternatively, ozone may prime the airways for an increased response to subsequently inhaled allergen. Indeed, an influx of both polymorphonucleocytes and eosinophils has been observed in asthmatic patients after ozone exposure. It has been suggested that the effect of ozone on classic allergen-induced bronchoconstriction may be more significant than any direct effect of this pollutant in asthmatics. SO2 does not appear to affect lung function in normal subjects, but may induce bronchoconstriction in asthmatics. Nasal breathing, which is often impaired in asthmatics, reduces the pulmonary effects of SO2, since this water-soluble gas is absorbed by the nasal mucosa. NO2 may also influence lung function in asthmatics, but further research is warranted. SO2 and NO2 alone do not seem to have a priming effect in asthmatics, but a combination of these two gases has resulted in a heightened sensitivity to subsequently inhaled allergen.

Attenuated response to repeated daily ozone exposures in asthmatic subjects

The development of attenuated response ("tolerance") to daily ozone (O3) exposures in the laboratory is well established in healthy adult volunteers. However, the capability of asthmatics to develop tolerance during multiday ozone exposures is unclear. We exposed 10 adult volunteers with mild asthma to 0.4 ppm O3 in filtered air for 3 h/d on 5 consecutive d. Two similar filtered-air exposures during the preceding week served as controls. Follow-up O3 exposures were performed 4 and 7 d after the most recent consecutive exposure. All exposures were performed in an environmental chamber at 31 degrees C and 35% relative humidity. The subjects performed moderate exercise (mean ventilation rate of 32 l/min) for 15 min of each half-hour. Responses were measured with spirometry and symptom evaluations before and after each exposure, and a bronchial reactivity test (methacholine challenge) was conducted after each exposure. All response measurements showed clinically and statistically significant day-to-day variation. Symptom and forced-expiratory-volume-in-1-s responses were similarly large on the 1st and 2nd O3 exposure days, after which they diminished progressively, approaching filtered air response levels by the 5th consecutive O3 day. This tolerance was partially lost 4 and 7 d later. Bronchial reactivity peaked after the first O3 exposure and remained somewhat elevated after all subsequent O3 exposures, relative to its control level following filtered-air exposures. Individual responses varied widely; more severe initial responses to O3 predicted less rapid attenuation. We concluded that asthmatics can develop tolerance to frequent high-level O3 exposures in much the same manner as normal subjects, although the process may be slower and less fully effective in asthmatics.

Obtaining information about susceptibility from the epidemiological literature

Whether people become ill after encountering environmental pollutants depends on the magnitude of their exposure and their capacity to respond. Exposure and intrinsic response capabilities vary within the population. Those that become ill when the general population remains largely unaffected are considered to be highly susceptible. The U.S. Environmental Protection Agency (USEPA), responsible for protecting the public from environmental pollutants, has developed risk assessment procedures to assist in evaluating the likelihood of health effects. However, the Agency's ability to evaluate the risk faced by highly susceptible populations is often hindered by the paucity of adequate health effects data. Response variability can be assessed with animal models and human epidemiological studies. Although animal models are useful when evaluating the effect of gender and developmental stage on susceptibility, inbred rodent strains underestimate the genetic and lifestyle-induced variability in susceptibility found in human populations. Epidemiological approaches are the preferred source of information on variability. This paper reviews the epidemiological literature from the perspective of a risk assessor seeking data suitable for estimating the risk to highly susceptible populations. Epidemiological approaches do not measure the full range of population response variability. Rather, "susceptibility factors" are evaluated either as risk factors or by focusing on the susceptible population, e.g. children. Susceptibility factors due to genetics, developmental stage, gender, ethnicity, disease state and lifestyle are most frequently encountered. Often, the information describing the health impact of the susceptibility factor is incomplete due to, (1) a failure to consider factors modifying susceptibility; (2) inadequate exposure data; (3) a failure to evaluate the health impact of the susceptibility factor. In addition, for a given exposure agent, several susceptibility factors may be relevant. While incomplete data describing susceptibility factors limits the opportunity for quantitative estimations of risk, available information can supplement qualitative evaluations and risk management.

Effect of Air Pollution in Asthma and Respiratory Allergy

Epidemiologic and controlled exposure studies of human volunteers have shown that exposure to a variety of pollutants induces asthma exacerbations. Interestingly, in the case of ozone, recent evidence suggests that this pollutant acts to enhance the effect of inhaled allergen in persons with asthma. These and other data also suggest that pollutants may influence lung function in persons with asthma by increasing airway inflammation. The interaction of pollutants and inhaled allergens and the effect of pollutant exposure on baseline airway inflammation may be a key mechanism of pollutant-induced exacerbation of asthma. Further study of this interaction, as well as interactions of multiple pollutants, will be crucial for rational development of intervention and regulatory strategies.

Are non-allergenic environmental factors important in asthma?

OBJECTIVE

To review the roles of viral respiratory tract infections, environmental tobacco smoke and air pollution in asthma.

DATA SOURCES

MEDLINE (1992-1995) searches were conducted for publications on asthma, environmental tobacco smoke, ozone, nitrogen dioxide and particulates.

STUDY SELECTION

Representative original experimental and epidemiological studies and reviews of viral infections in asthma.

DATA SYNTHESIS

Respiratory virus infections are the most common and important trigger of asthma attacks in children and probably also in adults. Their role in promoting development of asthma is not so clear. Exposure to environmental tobacco smoke is almost certainly responsible for some cases of childhood asthma, and can also trigger symptoms of bronchoconstriction in adults with asthma. Exposure to ozone or nitrogen dioxide is associated with symptoms, impaired lung function, bronchial hyperresponsiveness and hospital presentations for asthma. These pollutants may also act as cofactors in the development of allergen-specific bronchial hyperresponsiveness.

CONCLUSIONS

Research on preventing upper respiratory viral infections may reduce asthma morbidity. The move to non-smoking workplaces is welcome, but new interventions are needed to prevent young women taking up smoking and subsequently exposing their children. The ambient air quality guideline for ozone should be revised and a health-based guideline for respirable particulates introduced.

Comparative short-term health responses to sulfur dioxide exposure and other common stresses in a panel of asthmatics

We studied 14 unmedicated sulfur dioxide (SO2)-sensitive asthmatics to test the hypothesis that SO2 exacerbates asthma more than other everyday respiratory stressors. In Phase I, subjects underwent controlled exposures to 0.0, 0.5, and 1.0 ppm SO2 with light, medium, and heavy exercise (average ventilation 30, 36, and 43 l/min, respectively). Lung function, symptoms of asthma, and psychophysical (stamina) changes were measured. Function, symptom, and stamina responses correlated modestly. Increasing SO2 had stronger unfavorable effects than increasing exercise. In Phase II, subjects performed eight different physical tasks in SO2-free ambient air while symptoms and stamina were measured. Fast stair-climbing evoked symptoms similar to the effects of 0.5 ppm SO2/light exercise, while stamina reduction was comparable to 0.5 ppm SO2/heavy exercise. In Phase III, subjects recorded time-activity patterns, symptoms, and stamina during randomly selected intervals on a typical weekday and weekend day. Most reported activities were sedentary. Infrequent, strenuous Phase III exercise increased symptoms more than did 0.5 ppm SO2/light exercise, but with less effect on stamina. We conclude that for typical mild asthmatics, ten-minute SO2 exposures at concentrations > 0.5 ppm and ventilation > 30 l/min can cause short-term asthma manifestations more intense than those usually experienced from everyday stresses without SO2 exposure.

How Pollution and Airborne Allergens Affect Exercise

In brief Air pollution, airborne allergens, and changing weather conditions-alone or in combination-can hinder physical activity. In any active individual, high ozone levels can cause restrictive lung dysfunction, and high carbon monoxide levels can impair oxygen delivery. Sulfur dioxide worsens nasal symptoms in people who have allergies and causes bronchospasm in those who have asthma. Airway irritation from fine particulates can lead to bronchospasm. Atopic individuals suffer from the well-known effects of fungi and pollen. If a change in exercise routine or activity doesn't relieve symptoms, pharmacologic treatment may include antihistamines, immunotherapy, inhaled corticosteroids, and/or inhaled beta-₂ bronchodilators.

Air pollution and asthma: molecular mechanisms

Air pollution, in particular that generated by road traffic, is a matter of rising public concern and has been implicated in the worsening of asthma. In this article, the evidence that air pollutants (particularly sulphur dioxide, ozone and nitrogen dioxide) can affect the airways of asthmatic patients is reviewed, and the possible molecular mechanisms that may link air pollution to increased inflammation in the airways are discussed. Airway epithelial cells may respond to oxidant pollutants by the activation of transcription factors, such as nuclear factor kappa B, resulting in increased transcription of genes for certain cytokines, such as interleukin 8 and inflammatory enzymes, such as inducible nitric oxide synthase and cyclo-oxygenase.