Airway sensitivity of asthmatics to sulfur dioxide

Does Nitrogen Dioxide Exposure Increase Airways Responsiveness?

A number of reports have suggested that exposure to nitrogen dioxide (NO2) may cause increased airways responsiveness (AR). Twenty studies of asthmatics and five studies of healthy subjects exposed to NO2 were used to test this hypothesis using a simple method of meta-analysis. Individual data were obtained for the above studies and the direction of change in AR was determined for each subject. Only studies with available individual data were used. Subjects from these studies whose directional change in AR could not be determined were excluded. The fraction of positive responses (i.e. increased AR) was determined for all subjects within a group and tested for significance using a sign test. Data were also grouped according to NO2 concentration and by whether the exposure included exercise. There was an overall trend among asthmatics for AR to increase (60%) but this was primarily due to increased AR seen in resting exposures (70%). Among healthy subjects AR also increased with NO2 exposure but only at concentrations above 1.0 ppm. This analysis suggests that NO2 exposure causes increased airway responsiveness in healthy and asthmatic subjects but that exercise during exposure may modify this response in asthmatics.

Racial/Ethnic Disparities in Cumulative Environmental Health Impacts in California: Evidence From a Statewide Environmental Justice Screening Tool (CalEnviroScreen 1.1)

OBJECTIVES

We used an environmental justice screening tool (CalEnviroScreen 1.1) to compare the distribution of environmental hazards and vulnerable populations across California communities.

METHODS

CalEnviroScreen 1.1 combines 17 indicators created from 2004 to 2013 publicly available data into a relative cumulative impact score. We compared cumulative impact scores across California zip codes on the basis of their location, urban or rural character, and racial/ethnic makeup. We used a concentration index to evaluate which indicators were most unequally distributed with respect to race/ethnicity and poverty.

RESULTS

The unadjusted odds of living in one of the 10% most affected zip codes were 6.2, 5.8, 1.9, 1.8, and 1.6 times greater for Hispanics, African Americans, Native Americans, Asian/Pacific Islanders, and other or multiracial individuals, respectively, than for non-Hispanic Whites. Environmental hazards were more regressively distributed with respect to race/ethnicity than poverty, with pesticide use and toxic chemical releases being the most unequal.

CONCLUSIONS

Environmental health hazards disproportionately burden communities of color in California. Efforts to reduce disparities in pollution burden can use simple screening tools to prioritize areas for action.

Do group responses mask the effects of air pollutants on potentially sensitive individuals in controlled human exposure studies?

To establish primary National Ambient Air Quality Standards (NAAQS) for criteria air pollutants such as nitrogen dioxide (NO2), ozone (O3), and sulfur dioxide (SO2), US EPA relies in part on controlled human exposure studies. It has been suggested that evaluating average responses for all participants in these studies may not reflect the responses of sensitive participants in these studies. To evaluate this, we identified controlled exposure studies with multiple exposure concentrations or durations that provided individual-level lung function data. Based on individual lung function responses at specific exposure concentrations and the slope of individual concentration-response curves, we identified 12 participants out of a total of 208 participants in 12 studies who were potentially sensitive to O3, SO2, or sulfuric acid (H2SO4). We did not identify any participants sensitive to NO2. All of these participants were found to be potentially sensitive only at concentrations that were well above the NAAQS (SO2), above likely ambient concentrations (H2SO4), or at concentrations at which the study reported significant lung function effects for all participants (O3). Based on our analysis, average responses for all participants combined adequately reflect lung function responses for potentially sensitive study participants at concentrations in the range of the current NAAQS.

Associations between pollen counts, pollutants, and asthma-related hospital admissions in a high-density Indian metropolis

BACKGROUND

The seasonal pattern of asthma-related hospitalization has often been correlated with ambient allergen/pollutant levels.

OBJECTIVE

To examine the relationship between asthma-related hospital admissions (ARHA) and outdoor pollen, spore, and pollutant levels for adult patients in a densely populated Indian megacity Kolkata.

METHODS

ARHA data were obtained from two major teaching hospitals of the city. Pollen and spores causing allergic sensitization were identified by skin prick tests (SPTs) among respiratory allergic subjects (N = 1353). Outdoor concentrations of aeroallergens were determined using a Burkard sampler for five consecutive years (2004-2009). Levels of NO(2), SO(2), suspended particulate matters (SPMs), and respirable particulate matters (RPMs) were made available by West Bengal Pollution Control Board (WBPCB, Government of West Bengal). Poisson multivariate Poisson regression (with adjustments for overdispersion) was used to model the data. Results. We found that ARHA in Kolkata increased with predictable regularity in March and September, while remaining low in January and July. SPT showed highly positive skin reactions with grass/weed and palm pollens in respiratory allergic patients, while Aspergilli spores also evoked good sensitivity. In our regression model, the airborne pollen types, Cheno-Amaranthaceae and Cyperaceae, and the inorganic pollutant, SO(2) and RPM, were significantly associated with ARHA (p < .05).

CONCLUSION

ARHA in the megacity of Kolkata shows two seasonal peaks that can be correlated with outdoor grass/weed pollen and RPM concentrations. In contrast, the city's ambient fungal spore counts were not found to be significantly associated.

Motor vehicle air pollution and asthma in children: a meta-analysis

BACKGROUND

Asthma affects more than 17 million people in the United States;1/3 of these are children. Children are particularly vulnerable to airborne pollution because of their narrower airways and because they generally breathe more air per pound of body weight than adults, increasing their exposure to air pollutants. However, the results from previous studies on the association between motor vehicle emissions and the development of childhood wheeze and asthma are conflicting. Therefore, we conducted a meta-analysis to clarify their potential relationship.

METHODS

MEDLINE, Highwire, and The Cochrane Library databases were searched for relevant studies. Adjusted odds ratio (OR) with corresponding 95% confidence interval (CI) for the association between traffic air pollutants and wheeze or asthma were retrieved from individual studies and pooled to generate summary effect estimates (meta-OR) in STATA 11.1.

RESULTS

Nineteen studies were included in the meta-analysis. Exposure to nitrogen dioxide (meta-OR: 1.05, 95% CI: 1.00-1.11), nitrous oxide (meta-OR: 1.02, 95% CI: 1.00-1.04), and carbon monoxide (meta-OR: 1.06, 95% CI: 1.01-1.12) were positively associated with a higher prevalence of childhood asthma. Exposure to sulfur dioxide (meta-OR: 1.04, 95% CI: 1.01-1.07) was positively associated with a higher prevalence of wheeze in children. Exposure to nitrogen dioxide was positively associated with a higher incidence of childhood asthma (meta-OR: 1.14, 95% CI: 1.06-1.24), and exposures to particulate matter was positively associated with a higher incidence of wheeze in children (meta-OR: 1.05, 95% CI: 1.04-1.07).

CONCLUSIONS

Living or attending schools near high traffic density roads exposes children to higher levels of motor vehicle air pollutants, and increases the incidence and prevalence of childhood asthma and wheeze.

Effects of simulated downwind coal combustion emissions on pre-existing allergic airway responses in mice

CONTEXT

Coal-fired power plant emissions can contribute a significant portion of the ambient air pollution in many parts of the world.

OBJECTIVE

We hypothesized that exposure to simulated downwind coal combustion emissions (SDCCE) may exacerbate pre-existing allergic airway responses.

METHODS

Mice were sensitized and challenged with ovalbumin (OVA). Parallel groups were sham-sensitized with saline. Mice were exposed 6 h/day for 3 days to air (control, C) or SDCCE containing particulate matter (PM) at low (L; 100 μg/m³), medium (M; 300 μg/m³), or high (H; 1000 μg/m³) concentrations, or to the H level with PM removed by filtration (high-filtered, HF). Immediately after SDCCE exposure, mice received another OVA challenge (pre-OVA protocol). In a second (post-OVA) protocol, mice were similarly sensitized but only challenged to OVA before air/SDCCE. Measurement of airway hyperresponsiveness (AHR), bronchoalveolar lavage (BAL), and blood collection were performed ~24 h after the last exposure.

RESULTS

SDCCE significantly increased BAL macrophages and eosinophils in OVA-sensitized mice from the post-OVA protocol. However, there was no effect of SDCCE on BAL macrophages or eosinophils in OVA-sensitized mice from the pre-OVA protocol. BAL neutrophils were elevated following SDCCE in both protocols in nonsensitized mice. These changes were not altered by filtering out the PM. In the post-OVA protocol, SDCCE decreased OVA-specific IgG₁ in OVA-sensitized mice but increased levels of total IgE, OVA-specific IgE and OVA-specific IgG₁ and IgG(2a) in non-sensitized animals. In the pre-OVA protocol, SDCCE increased OVA-specific IgE in both sensitized and non-sensitized animals. Additionally, BAL IL-4, IL-13, and IFN-γ levels were elevated in sensitized mice.

CONCLUSION

These results suggest that acute exposure to either the particulate or gaseous phase of SDCCE can exacerbate various features of allergic airway responses depending on the timing of exposure in relation to allergen challenge.

A review of controlled human SO₂ exposure studies contributing to the US EPA integrated science assessment for sulfur oxides

Laboratory studies involving intentional and highly controlled exposures to air pollutants among groups of human volunteers provide valuable information related to the potential health effects of pollutants regulated under the US Clean Air Act. These controlled human exposure studies often provide biological plausibility for the associations between air-pollutant concentration and a given health endpoint observed in epidemiologic investigations. In some cases, results from human laboratory studies provide evidence of a relevant health effect at ambient or near-ambient concentrations and thus directly support the selection of air quality standard levels. In the recently completed review of the US National Ambient Air Quality Standards (NAAQS) for sulfur dioxide (SO₂), the US Environmental Protection Agency (EPA) concluded that short-term exposures to SO₂ are causally associated with an increase in respiratory morbidity. This determination was based in large part on findings from laboratory studies of controlled exposures to SO₂ among small groups of asthmatic individuals. The purpose of this review is to concisely present an overview of the evidence from controlled human exposure studies of SO₂-induced respiratory health effects following short-term exposures. While the majority of these studies were conducted over 20 years ago, the findings and insights gained from this work continues to play an integral role in evaluating the respiratory effects of ambient exposures to SO₂.

Effects of climatic changes and urban air pollution on the rising trends of respiratory allergy and asthma

Over the past two decades there has been increasing interest in studies regarding effects on human health of climate changes and urban air pollution. Climate change induced by anthropogenic warming of the earth's atmosphere is a daunting problem and there are several observations about the role of urbanization, with its high levels of vehicle emissions and other pollutants, and westernized lifestyle with respect to the rising frequency of respiratory allergic diseases observed in most industrialized countries.There is also evidence that asthmatic subjects are at increased risk of developing exacerbations of bronchial obstruction with exposure to gaseous (ozone, nitrogen dioxide, sulfur dioxide) and particulate inhalable components of air pollution.A change in the genetic predisposition is an unlikely cause of the increasing frequency in allergic diseases because genetic changes in a population require several generations. Consequently, environmental factors such as climate change and indoor and outdoor air pollution may contribute to explain the increasing frequency of respiratory allergy and asthma. Since concentrations of airborne allergens and air pollutants are frequently increased contemporaneously, an enhanced IgE-mediated response to aeroallergens and enhanced airway inflammation could account for the increasing frequency of allergic respiratory diseases and bronchial asthma.Scientific societies such as the European Academy of Allergy and Clinical Immunology, European Respiratory Society and the World Allergy Organization have set up committees and task forces to produce documents to focalize attention on this topic, calling for prevention measures.

Air pollution as a determinant of asthma among schoolchildren in Mohammedia, Morocco

The objective of the study was to investigate whether air quality in western Morocco is truly a significant risk factor in the development and exacerbation of respiratory diseases and, in particular, asthma. The continuous measurement of the mean concentrations of sulfur dioxide (SO(2)) in the air and the density of Total Suspended Particulates (TSP) for a period of four years was determined. Information on individual characteristics and indoor environments from 1318 children with an average age of 12 years was evaluated by questionnaire, completed by parents (assisted by professional investigators) and symptoms/diseases were medically diagnosed and reported. We have used the Student's t-test, Chi-square tests & odds ratios (ORs) with 95% confidence intervals (CI 95%) for estimates of the risk of asthma. The prevalence of asthma varies in a significant way according to the zone (chi(2) = 14.61, p < 0.05). Respiratory diseases (OR 6.27, 95% confidence interval [CI] 4.09-9.64, p < 0.0001), strongly polluted zone (OR 3.62, 95% CI 1.71-7.81, p < or = 0.0001) and infectious diseases (OR 3.29, 95% CI 1.99-5.47, p < 0.0001) are high risk factors for asthma. Air pollution is a determinant factor but is not the only factor increasing the risk of asthma in children; other factors such as respiratory diseases, infectious diseases, genetic and passive smoking present a high-risk threat.

Environmental risk factors and allergic bronchial asthma

The prevalence of allergic respiratory diseases such as bronchial asthma has increased in recent years, especially in industrialized countries. A change in the genetic predisposition is an unlikely cause of the increase in allergic diseases because genetic changes in a population require several generations. Consequently, this increase may be explained by changes in environmental factors, including indoor and outdoor air pollution. Over the past two decades, there has been increasing interest in studies of air pollution and its effects on human health. Although the role played by outdoor pollutants in allergic sensitization of the airways has yet to be clarified, a body of evidence suggests that urbanization, with its high levels of vehicle emissions, and a westernized lifestyle are linked to the rising frequency of respiratory allergic diseases observed in most industrialized countries, and there is considerable evidence that asthmatic persons are at increased risk of developing asthma exacerbations with exposure to ozone, nitrogen dioxide, sulphur dioxide and inhalable particulate matter. However, it is not easy to evaluate the impact of air pollution on the timing of asthma exacerbations and on the prevalence of asthma in general. As concentrations of airborne allergens and air pollutants are frequently increased contemporaneously, an enhanced IgE-mediated response to aeroallergens and enhanced airway inflammation could account for the increasing frequency of allergic respiratory allergy and bronchial asthma. Pollinosis is frequently used to study the interrelationship between air pollution and respiratory allergy. Climatic factors (temperature, wind speed, humidity, thunderstorms, etc) can affect both components (biological and chemical) of this interaction. By attaching to the surface of pollen grains and of plant-derived particles of paucimicronic size, pollutants could modify not only the morphology of these antigen-carrying agents but also their allergenic potential. In addition, by inducing airway inflammation, which increases airway permeability, pollutants overcome the mucosal barrier and could be able to "prime" allergen-induced responses. There are also observations that a thunderstorm occurring during pollen season can induce severe asthma attacks in pollinosis patients. After rupture by thunderstorm, pollen grains may release part of their cytoplasmic content, including inhalable, allergen-carrying paucimicronic particles.

Childhood asthma hospitalizations and ambient air sulfur dioxide concentrations in Bronx County, New York

The association between asthma hospitalizations and ambient sulfur dioxide (SO2) concentrations was examined in a case-control study in Bronx County, New York. Cases comprised 2629 children aged 0-14 yr who were admitted to hospitals for asthma. There were 2236 controls who were admitted for reasons other than asthma. Daily ambient SO2 concentrations were categorized into quartiles of both average and maximum levels and various exposure windows (i.e., day of admission and 1-, 2-, and 3-d lags). Cases were exposed to higher daily average concentrations of SO2 than controls. The authors compared the highest exposure quartile with the lowest, and the odds ratios were 1.66, 1.90, 2.05, and 2.21 (all p < 0.01 for same-day, 1-, 2-, and 3-d lags, respectively), with a similar finding for daily SO2 maximum exposure. The results suggest a consistent positive association between SO2 exposure and hospitalizations for childhood asthma.

The effect of sulphurous air pollutant exposures on symptoms, lung function, exhaled nitric oxide, and nasal epithelial lining fluid antioxidant concentrations in normal and asthmatic adults

AIMS

To explore the effects in normal and asthmatic adults of exposure to 200 ppb sulphur dioxide (SO2) and 200 microg/m3 and 2000 microg/m3 aerosols of ammonium bisulphate (AB) and sulphuric acid (SA) (MMD 0.3 microm).

METHODS

Exposures were placebo controlled, for one hour at rest, double blind in random order. DeltaFEV1 was the primary outcome; secondary outcomes included symptoms, ventilation, exhaled nitric oxide (NO) concentrations, and nasal lavage fluid ascorbic (AA) and uric acid (UA) concentrations.

RESULTS

There were no significant changes in spirometry or symptoms with any exposure in either group. SO2 exposure was associated with an increased respiratory rate relative to air exposure in the asthmatic group (SO2: 958.9 breaths/hour; air: 906.8 breaths/hour) but the mean volume breathed did not differ significantly (SO2: 318.8 litres; air: 311.4 litres). AB exposures were associated with a significant rise in [NO] in the asthmatic (+1.51 ppb, and +1.39 ppb), but not in the normal group. Mean pre- and post-exposure [AA] tended to be higher in the normal than in the asthmatic group. Within each group, [AA] did not change significantly with any exposure. Post-exposure [UA] were greater than pre-exposure concentrations for all exposures, significantly so in the normal group for all exposures except SO2. There were no significant differences in the mean change in [UA] for any exposure relative to air.

CONCLUSIONS

The pollutant exposure concentrations employed in this study were generally much greater than ambient. It is unlikely that short lived exposures at lower concentrations would show significant effects, but effects of longer term lower concentration exposures cannot be ruled out.

Genetic polymorphisms as biomarkers of sensitivity to inhaled sulfur dioxide in subjects with asthma

BACKGROUND

Individuals with asthma are sensitive to inhaled sulfur dioxide (SO2); decrements in pulmonary function occur after exposure to low concentrations even for a short duration of time. There is a great amount of interindividual variation in response to SO2.

OBJECTIVE

It was our objective to determine whether one of the following polymorphism locations linked with asthma is associated with the bronchial hyperresponsiveness to SO2 observed in some asthmatic patients: the beta2-adrenergic receptor, interleukin-4 (IL-4) receptor alpha subunit, Clara cell secretory protein (CC16), TNF-alpha gene promoter, and first intron of the lymphotoxin alpha (LT-alpha) gene.

METHODS

Subjects were volunteers with physician-diagnosed asthma requiring regular asthma medication. Spirometry was performed before and after a 10-minute exposure to 0.5 ppm SO2. Subjects were classified as SO2 responders if forced expiratory volume in 1 second (FEV1) decreased > or = 12%. DNA obtained from buccal cell samples was analyzed for genetic polymorphisms.

RESULTS

Of the 62 subjects (21 male and 41 female), 13 had a 12% or greater decrement in FEV1 after SO2 exposure (range + 19% to -49%). Response to SO2 was associated with the wild-type allele of the TNF-alpha promoter polymorphism (12 of 12 SO2 responders versus 28 of 46 nonresponders; P < .05) but with no other polymorphisms. Medication category and atopic status showed no association with SO2 sensitivity.

CONCLUSIONS

The wild-type allele of the TNF-alpha promoter polymorphism may be associated with mechanisms of asthmatic sensitivity to inhaled SO2.

Point source sulphur dioxide peaks and hospital presentations for asthma

OBJECTIVE

To examine the effect on hospital presentations for asthma of brief exposures to sulphur dioxide (SO2) (within the range 0-8700 micrograms/m3) emanating from two point sources in a remote rural city of 25,000 people.

METHODS

A time series analysis of SO2 concentrations and hospital presentations for asthma was undertaken at Mount Isa where SO2 is released into the atmosphere by a copper smelter and a lead smelter. The study examined 5 minute block mean SO2 concentrations and daily hospital presentations for asthma, wheeze, or shortness of breath. Generalised linear models and generalised additive models based on a Poisson distribution were applied.

RESULTS

There was no evidence of any positive relation between peak SO2 concentrations and hospital presentations or admissions for asthma, wheeze, or shortness of breath.

CONCLUSION

Brief exposures to high concentrations of SO2 emanating from point sources at Mount Isa do not cause sufficiently serious symptoms in asthmatic people to require presentation to hospital.

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.

Air pollution: brown skies research

Direct information on the health effects of air pollution in humans relies mainly on chamber studies and epidemiological studies. Although chamber studies have limitations they allow the acute effects of individual pollutants to be studied in well characterised subjects under controlled conditions. Most chamber studies have shown relatively small falls in lung function and relatively small increases in bronchial reactivity at the concentrations of ozone, SO2, and NO2 that occur even during high pollution episodes in the UK. The possible exception is SO2 where sensitive asthmatic patients may show a greater response at concentrations that are seen from time to time in certain areas and in proximity to power stations. There is no convincing evidence of potentiation between pollutants in chamber studies. Epidemiological studies are more difficult to carry out and require considerable epidemiological and statistical expertise to deal with the main problem-confounding by other factors. Although the health effects seen with current levels of pollution are small compared with those seen in the 1950s and close to the limits of detection, this should not be interpreted as being unimportant. A small effect may have large consequences when the population exposed is large (the whole population in this case). Recent data suggest that particles have more important health effects than the pollutant gases that have been studied. Much of this information comes from the USA though the findings are probably applicable in the UK. More information is needed on the size of the health effects that occur during the three types of air pollution episodes seen in this country and the relative contributions of particles, pollutant gases, pollen, and other factors such as temperature. Research into air pollution declined in the UK following the introduction of the Clean Air Acts; it is now increasing again following pressure from certain individuals and ginger groups, including the British Lung Foundation, and its potential importance is recognised by the Department of Health. This article has concentrated on the acute effects of air pollution episodes, though the long term effects of acute episodes of air pollution and chronic high levels of pollutants is equally, if not more, important. Roger Altounyan had severe chest-disease attributed to asthma and personal pollution (cigarette smoke). But did the smog episodes in Manchester in the 1950s or subsequent vehicle related pollution play a part and did they interact with the bronchial challenges he underwent over the years (estimated at 3000)? Air pollution is a product of the way that society chooses to live. Obtaining an accurate picture of the extent to which current levels of air pollution cause acute and chronic effects on health is important if sensible choices are to be made by individuals and society about the processes contributing to air pollution. It is also important for patients with or at risk of developing cardiorespiratory disease.

Effects of air pollution on symptoms and peak expiratory flow measurements in subjects with obstructive airways disease

BACKGROUND

Evidence from laboratory studies suggests that air pollution can produce bronchoconstriction and respiratory symptoms in selected subjects, but the relevance of these findings to exposure to natural pollution is unclear. This study was performed to determine whether air pollution at typical levels found in the UK has demonstrable effects on respiratory function and symptoms in subjects with airways disease.

METHODS

Seventy five adult patients with diagnoses of asthma or chronic obstructive pulmonary disease (COPD) were studied for a period of four weeks during which they kept records of their peak expiratory flow (PEF) rates, symptoms (wheeze, dyspnoea, cough, throat and eye irritation), and bronchodilator use. Thirty six patients in whom the provocative dose of methacholine causing a 20% fall in FEV1 was below 12.25 mumol were classified as reactors. Ambient air pollution was measured with absorption spectroscopy.

RESULTS

There were modest but significant increases in PEF variability, bronchodilator use, and wheeze with increasing sulphur dioxide levels; bronchodilator use, dyspnoea, eye irritation, and minimum PEF readings were related to ozone levels. In the subgroup of reactors falls in mean and minimum peak flow and increases in wheeze, dyspnoea, and bronchodilator use were associated with increases in levels of both sulphur dioxide and ozone. Some associations were seen with pollution levels on the same day, but for others the pollution effects appeared to be delayed by 24 or 48 hours. Pollution levels did not breach the WHO guide levels during the course of the study.

CONCLUSIONS

Increases in environmental levels of ozone and sulphur dioxide are associated with adverse changes in peak flow measurements and both ocular and respiratory symptoms in subjects with obstructive airways disease. Although the peak flow and symptom changes were modest, they occurred at pollution levels below current WHO guide levels.

Inhaled A23187 produces a preferential sensitization to substance P

We examined the effect of A23187-induced lung injury on airway responses to a variety of bronchoconstrictive aerosols in conscious guinea pigs. Guinea pigs were exposed to aerosolized A23187 or vehicle for 12 min or until labored breathing began. Animals were allowed to recover for 24 h, and then they were challenged with inhaled histamine, leukotriene D4 (LTD4), platelet-activating factor (PAF), or substance P. Eight minutes after start of the bronchoprovocative aerosol, the guinea pigs were killed and excised lung gas volume (ELGV) measurements were used as an index of in vivo airway obstruction. No differences in ELGV dose-response curves to LTD4 were seen in A23187- and vehicle-exposed animals. A23187 exposure produced small increases in both histamine and PAF sensitivity. However, A23187 caused a much more pronounced leftward shift in the dose-response to substance P. Coadministration of the neutral endopeptidase inhibitor, thiorphan, did not reduce the A23187-related airway responses to substance P. Histologic evaluation of A23187-treated lungs revealed peribronchiolar inflammation, bronchiolar epithelial injury, and mild alveolitis. We conclude that A23187 treatment produces differential airway responses to bronchoactive agents, with a preferential sensitization to substance P.

Relationship between the airway response to inhaled sulfur dioxide, isocapnic hyperventilation, and histamine in asthmatic subjects

To determine whether bronchoconstriction induced by sulfur dioxide can be predicted by the airway response to inhaled histamine, we exposed on two days 46 patients with asthma to air or 0.5 ppm SO2. The exposure protocol consisted of 10 min of tidal breathing followed by 10 min of isocapnic hyperventilation at a rate of 30 l/min. Airway response was measured before (baseline) and after hyperventilation in terms of specific airway resistance, SRaw. Exposure to air increased baseline mean (SD) SRaw from 6.27 (2.12) to mean (SD) maximum post-hyperventilation SRaw of 9.10 (4.38) cmH2O*s (P less than 0.0001). Exposure to SO2 increased mean (SD) baseline SRaw from 6.93 (3.29) to mean (SD) maximum post-hyperventilation SRaw of 18.21 (18.69) cmH2O*s (P less than 0.0001). Mean (SD) effect of SO2 defined as difference between maximum post-hyperventilation SRaw after SO2 versus air was 9.11 (16.14) cm H2O*s. When evaluated individually, 26 and 34 of the 46 patients showed an airway response to hyperventilation of air and SO2, respectively. Airway response to histamine was determined as the histamine concentration necessary to increase specific airway resistance by 100%, PC100SRaw. The airway response after SO2 and PC100SRaw showed a weak but significant correlation (R = -0.48), whereas the responses to hyperventilation and SO2 did not correlate. We suggest that the mechanisms by which histamine and SO2 exert their bronchomotor effects are different and that in asthmatic patients the risk of pollutant-induced asthmatic symptoms can be poorly predicted by histamine responsiveness.

Comparison of the effects of inhaled corticosteroids on the airway response to histamine, methacholine, hyperventilation, and sulfur dioxide in subjects with asthma

To investigate whether inhaled steroids modulate the airway response to different bronchoconstrictive stimuli, we studied 25 subjects with mild asthma with a double-blind, noncrossover design to compare the effect of a 3-week treatment with salbutamol (0.2 mg, four times a day [q.i.d.]) and placebo (N = 11) to the effect of salbutamol (0.2 mg q.i.d.) and inhaled beclomethasone dipropionate (BDP, 0.5 mg q.i.d.) (N = 14). Airway response to histamine and methacholine was assessed as the provocative concentration (in milligrams per milliliter) necessary to increase the specific airway resistance (SRaw) (in centimeters of H2O times second) by 100% (PC100 SRaw). Airway response to hyperventilation of air and to hyperventilation of 0.75 ppm of sulfur dioxide (SO2) was determined as the provocative ventilation (in liters per minute) necessary to increase SRaw by 75% (PV75 SRaw). Challenges were performed on separate days before and after treatment, and salbutamol inhalation was withheld at least 6 hours before each challenge. Salbutamol and placebo did not change perchallenge baseline SRaw nor did they have any significant effect on the airway response to the stimuli. Salbutamol and BDP decreased the mean prechallenge baseline SRaw (SEM) from 7.7 (0.37) to 5.9 (0.28) (p less than 0.01) and significantly (p less than 0.01) increased geometric mean (SEM) PC100 SRaw for histamine from 0.5 (1.42) to 0.9 (1.53) mg/ml; for methacholine, from 0.2 (1.47) to 0.5 (1.51) mg/ml; and mean (SEM) PV75 SRaw for hyperventilation of air from 51.8 (2.32) to 58.4 (1.86) L/min. In contrast, the change of PV75 SRaw during hyperventilation of SO2 from 26.2 (2.29) to 31.4 (3.30) L/min was not significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid fog-induced bronchoconstriction. The role of hydroxymethanesulfonic acid

Hydroxymethanesulfonate (HMSA), the bisulfite (HSO3-) adduct of formaldehyde (CH2O), is a common constituent of California acid fogs. HMSA, most stable in a fog pH range of 3 to 5, dissociates at 6.6, the pH of the fluid lining human airways. The dissociation of inhaled HMSA should theoretically generate sulfur dioxide and CH2O, both of which have bronchoconstrictor potential. Thus, we hypothesized that HMSA may have a specific bronchoconstrictor effect independent of its strength as an acid. To determine whether HMSA has such an effect, 19 subjects with mild to moderate asthma were studied using two different protocols. Initially, a mouthpiece study was performed in which 9 subjects, on 2 separate days, inhaled five aerosols containing either sequentially increasing concentrations (0, 30, 100, 300, and 1000 microM) of HMSA in 50 microM sulfuric acid (H2SO4) or 50 microM H2SO4 alone. The subjects inhaled each aerosol for 3 min during tidal breathing at rest. Specific airway resistance (SRaw) was measured before and after each 3-min exposure. There were no significant differences in the mean changes in SRaw among the various aerosol exposures. To confirm this lack of bronchoconstrictor effect of HMSA, we then performed a chamber study in which 10 freely breathing, intermittently exercising subjects were exposed to fog containing either 1 mM HMSA in 5 mM H2SO4 or 5 mM H2SO4 alone for 1 h. SRaw was measured before, during, and at the end of the 1-h exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Short-term exposure to 0.3 ppm nitrogen dioxide does not potentiate airway responsiveness to sulfur dioxide in asthmatic subjects

Whether short-term exposure to low levels of nitrogen dioxide (NO2) enhances airway responsiveness in asthmatic subjects is controversial. Because it is well established that asthma is associated with increased airway responsiveness to another common air pollutant, sulfur dioxide (SO2), we examined whether short-term exposure of asthmatic subjects to 0.3 ppm NO2 potentiates airway responsiveness to inhaled SO2. We exposed nine subjects with clinically stable asthma to 0.3 ppm NO2 or filtered air in an environmental room for 30 min on 2 separate days at least 1 wk apart in a double-blind, randomized fashion. A questionnaire about common symptoms related to inhaled irritants was completed before and immediately after each exposure. Each subject exercised (60 to 80 W) on a cycloergometer during the first 20 min of each exposure. We measured specific airway resistance (SRaw) and FEV1/FVC before, 5 min after, and 1 h after completion of the air or NO2 exposure. The single-breath nitrogen test (SBN2) was also performed before and 1 h after completion of the air or NO2 exposures and closing volume was determined; subsequently, SO2 dose-response curves (0.25 to 4.0 ppm) were performed via a mouthpiece. Each dose of SO2 was inhaled at a minute ventilation of 20 L/min for 4 min and was doubled until SRaw increased by at least 8 U above baseline. The dose of SO2 required to provoke an increase in SRaw of 8 U above baseline was determined by linear interpolation from the dose-response curve (PD8Uso2).(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary effects of sulfur dioxide exposure and ipratropium bromide pretreatment in adults with nonallergic asthma

In this study we examined the potential short-term effect of sulfur dioxide (SO2) on total respiratory resistance and forced expiratory volume in patients with nonallergic asthma. A group of nine adult subjects with nonallergic asthma, 55 years of age or older, were exposed to SO2 at 0, 0.5, and 1.0 ppm for 20 minutes at rest followed by 10 minutes during light-moderate exercise. The measures of pulmonary function assessed were FEV1, specific total respiratory resistance (SRT), and maximal expiratory flow rates at 50% (Vmax50) and 75% (Vmax75) of expired vital capacity. Measurements were made before exposure to SO2 (baseline), postresting exposure, postexercising exposure, and at 30 minutes thereafter (recovery). Repeat measure analysis of variance revealed a statistically significant dose-response effect of SO2 inhalation on FEV1 (p = 0.008), SRT (p = 0.033), Vmax50 (p = 0.017), and Vmax75 (p = 0.048). Eight subjects had repeat exposure to SO2 at 1.0 ppm after treatment with either placebo or ipratropium bromide, 60 micrograms by metered-dose inhaler. Inpratropium bromide treatment, compared to placebo treatment, resulted in a statistically significant improvement in all baseline measures of pulmonary function: FEV1 (p = 0.017), SRT (p = 0.027), Vmax50 (p = 0.018), and Vmax75 (p = 0.035). However, this drug did not significantly alter the proportionate change in pulmonary function caused by SO2 inhalation in these subjects. These findings indicate that adults with nonallergic asthma are sensitive to short-term low-level SO2 exposure and that treatment with 60 micrograms of ipratropium bromide causes significant bronchodilation but does not protect, completely, these patients from the effect of SO2 inhalation.