Dose-response study of asthmatic volunteers exposed to nitrogen dioxide during intermittent exercise

Twenty-one mildly asthmatic volunteers were exposed to 0, 0.3, 1.0, and 3.0 ppm nitrogen dioxide (NO2) in purified background air in an environmental control chamber. Exposures were separated by 1-wk periods and occurred in random order. Each lasted 1 hr and included three 10-min bouts of moderately heavy exercise (mean ventilation rate 41 L/min). Exposure temperature was near 22 degrees C and relative humidity near 50%. Specific airway resistance and maximal forced expiratory performance were measured preexposure, after the initial exercise, and near the end of exposure. Bronchial reactivity was assessed immediately following exposure, by normocapnic hyperventilation with subfreezing air. Symptoms were recorded on questionnaires before, during, and for 1-wk after each exposure. Exercise induced significant bronchoconstriction regardless of NO2 level. No statistically significant untoward response to NO2 was observed at any exposure concentration. This negative finding agrees with our previous results, but contrasts with findings elsewhere of respiratory dysfunction after exposure to 0.3 ppm. The discrepancy is presently unexplained, but it may relate to different severity of asthma in different subject groups.

A dose-response study of healthy, heavily exercising men exposed to ozone at concentrations near the ambient air quality standard

Twenty-four healthy, well-conditioned young adult male volunteers, free of asthma or clinical respiratory allergies, were exposed to purified air containing ozone (O3) at 0.16, 0.14, 0.12, 0.10, 0.08, and 0.00 part per million (ppm). Exposures were separated by 2-week intervals, occurred in random order, and lasted 2 hours each. Temperature was 32 +/- 1 degree C and relative humidity was 38 +/- 3%, simulating Los Angeles area smog conditions. Subjects exercised 15 minutes of each half hour, attaining ventilation rates averaging 68 L/min (approximately 35 L/min per m2 body surface area). Lung function was measured pre-exposure and after 1 hr and 2 hr of exposure. Airway responsiveness to a cold-air challenge was measured immediately following the 2-hr exposure. Symptoms were recorded before, during, and for one-week periods following exposures. For the group as a whole, no meaningful untoward effects were found except for a mild typical respiratory irritant response after 2 hr exposure to 0.16 ppm O3. Two individual subjects showed possible responses at 0.14 ppm, and one of them also at 0.12 ppm. In comparison to some previous investigations, this study showed generally less response to O3. The comparative lack of response may relate to the favorable clinical status of the subjects, the pattern of exercise during exposure, or some other factor not yet identified.

Controlled exposure of volunteers with chronic obstructive pulmonary disease to nitrogen dioxide

Twenty-two volunteers with chronic obstructive pulmonary disease were exposed to nitrogen dioxide at 0.0, 0.5, 1.0, and 2.0 ppm in a controlled environment chamber. Exposure lasted 1 hr and included two 15-min exercise periods, during which the mean ventilation rate was roughly 16 L/min. Pulmonary mechanical function was evaluated pre-exposure, after initial exercise, and at the end of exposure. Blood oxygenation was measured by ear oximetry pre-exposure and during the second exposure period. Symptoms were recorded during exposures and for 1-wk periods afterward. No statistically significant changes in symptom reporting could be attributed to nitrogen dioxide exposure at any concentration, compared to the 0.0 ppm control condition. Measures of pulmonary mechanics showed either no significant changes, or small and equivocal changes. Arterial oxygen saturation showed marginal improvement with exercise, regardless of nitrogen dioxide concentration.

Potential risks to human respiratory health from "acid fog": evidence from experimental studies of volunteers

Observations of high acidity (pH as low as 1.7) in fogwater collected in polluted areas have provoked concern for public health. Effects of exposure to acidic pollutants have not been studied under foggy conditions; thus there is no directly relevant information from which to estimate the health risk. Indirectly relevant information is available from numerous studies of volunteers exposed to "acid fog precursors" under controlled conditions at less than 100% relative humidity. The effect of fog in modifying responses to inhaled acidic pollutants is difficult to predict: depending on circumstances, fog droplets might either increase or decrease the effective dose of pollutants to the lower respiratory tract. Fog inhalation per se may have unfavorable effects in some individuals. Sulfur dioxide is known to exacerbate airway constriction in exercising asthmatics, at exposure concentrations attainable in ambient air. Nitrogen dioxide has shown little untoward respiratory effect at ambient concentrations in most studies, although it has been suggested to increase bronchial reactivity. Sulfuric acid aerosol has shown no clear effects at concentrations within the ambient range. At somewhat higher levels, increased bronchial reactivity and change in mucociliary clearance have been suggested. Almost no information is available concerning nitric acid.

Respiratory effects of photochemical oxidant air pollution in exercising adolescents

Healthy volunteers 12 to 15 yr of age (46 boys, 13 girls) were exposed to purified air and to smoggy Los Angeles ambient air on different occasions. The studies were performed in random order approximately 2 wk apart. They included 1 h of continuous bicycle exercise (mean ventilation, 32 L/min) plus brief warm-up and cool-down periods. Symptoms and forced expiratory performance were recorded preexposure in purified air, immediately postexposure, and after 1 h recovery in purified air. Mean exposure temperature was 32 degrees C, and mean relative humidity was 45%. In ambient exposure, pollutant concentrations averaged 0.144 ppm for ozone and 153 micrograms/m3 for total suspended particulates. Group mean FEV1 decreased during ambient exposure (p less than 0.01) and only partially recovered during the following 1 h. Unlike adults studied previously, this subject group reported no significant increase in respiratory symptoms accompanying changes in FEV1. Adolescents may be less aware of early respiratory irritation by oxidants and thus more at risk from ambient exposures than are adults.

Effects of exposure to 4 ppm nitrogen dioxide in healthy and asthmatic volunteers

Healthy and asthmatic volunteer subjects (N = 25 and N = 23, respectively) were exposed twice each to purified air (control) and to 4 ppm nitrogen dioxide (NO2) in a controlled-environment chamber. Exposures lasted 75 min, and included 15 min each of light exercise (ventilation rate near 25 L/min) and heavy exercise (near 50 L/min). Compared to control, NO2 exposure produced no statistically significant untoward effects on airway resistance, symptoms, heart rate, skin conductance, or self-reported emotional state in normal or asthmatic subjects. Exercise was associated with significantly (P less than .001) increased airway resistance in both subject groups, although the increase in normals was small. In both groups, systolic blood pressure showed small but significant (P less than .01) decreases with NO2 exposure, compared to control. This effect, if real, may relate to formation of a vasodilating nitrite or nitrate from inhaled NO2. The lack of respiratory response contrasts with previous findings elsewhere; at present, this inconsistency is unexplained.

Controlled exposure to a mixture of SO2, NO2, and particulate air pollutants: effects on human pulmonary function and respiratory symptoms

Exposure of 20 volunteers to sodium chloride (NaCl) aerosol or to a mixture containing NaCl plus irritant particles (zinc ammonium sulfate) and irritant gases (nitrogen dioxide and sulfur dioxide) produced no significant decrements in pulmonary function. There was a slight tendency for respiratory symptoms to be greater during the exposure to the mixture than during exposure to the NaCl aerosol alone; the differences were not statistically significant. The pollutant concentrations studied approximated worst-case ambient levels observed in the Los Angeles basin.

Effects of heat and humidity on the responses of exercising asthmatics to sulfur dioxide exposure

Twenty-two asthmatic young adult volunteers, predetermined to be reactive to sulfur dioxide (SO2) with exercise at normal room temperature, were studied to document short-term effects of SO2 exposure under hot conditions, both humid and dry. For comparison, similar exposures were conducted at mild temperatures. All subjects were exposed in an environmental control chamber to all possible combinations of 2 atmospheric conditions (purified air and 0.6 ppm SO2), 2 temperatures (near 21 and 38 degrees C), and 2 levels of relative humidity (near 20 and 80%). Exposures involved 5 min of heavy exercise (target ventilation rate, 50 L/min) plus brief warm-up and cool-down periods. Body plethysmographic measurements and symptom questionnaire interviews were administered before and at the end of each exposure. Response was expressed in terms of change in airway size or change in intensity of symptoms during exposure. Atmospheric condition showed the most marked and significant overall effect on physiologic responses; temperature and humidity effects were also significant. High temperature and high humidity tended to mitigate the bronchoconstriction produced by 0.6 ppm SO2 exposure: group mean specific airway resistance approximately tripled at 21 degrees C and low humidity, but increased by less than 40% at 38 degrees C and high humidity. Temperature and humidity affected symptoms less consistently than physiologic responses, but in general, symptom responses paralleled physiologic responses.

Combined effect of sulfur dioxide and cold in exercising asthmatics

Twenty-four asthmatic volunteers were exposed to 0, 0.3, and 0.6 ppm sulfur dioxide (SO2) in purified background air at each of three temperatures--21 degrees, 7 degrees, and -6 degrees C--in a controlled-environment chamber. Relative humidity was approximately 80%. Exposures consisted of 5 min heavy exercise periods plus brief warmup and cooldown periods. Airway resistance, thoracic gas volume, and symptoms were measured immediately before and after exposure. For the group, increasing SO2 concentration and decreasing temperature were associated with statistically significant unfavorable effects on airway resistance and respiratory symptoms, as expected from previous findings. Effects of SO2 and cold usually appeared to combine in an additive or less-than-additive fashion; there was little evidence of synergism. Individuals' response patterns were variable: a few suggested synergism, but others suggested a mitigating effect of cold on the bronchoconstrictive response to SO2.

Respiratory responses of humans exposed to an aerosol-gas pollutant mixture: multivariate contrast of a complex atmosphere to clean air and sodium chloride aerosol controls

Data from a group of 20 subjects with normal baseline pulmonary function, who were exposed for 2 h to a test atmosphere containing a complex mixture of pollutants, have been contrasted with data from two other groups exposed to presumably non-toxic control atmospheres. Group 1 was exposed to clean air, group 2 was exposed to clean air containing sodium chloride aerosol at 270 micrograms m-3, and group 3 was exposed to the complex atmosphere containing sodium chloride (332 micrograms m-3) and zinc ammonium sulfate (23 micrograms m-3) aerosols plus nitrogen dioxide (0.5 ppm) and sulfur dioxide (0.5 ppm). These atmospheres (ranked according to the presumed relative toxicities of the components; clean air = 0, sodium chloride = 1, complex mixture = 2) were contrasted using multiple regression and partial correlation analyses. The effects of exposure to the complex gas-aerosol mixture on forced expiratory performance were not significantly different from those observed in subjects exposed to clean air or to sodium chloride aerosol.

Time course of exercise-induced bronchoconstriction in asthmatics exposed to sulfur dioxide

Young adult asthmatic volunteers (N = 17) were exposed to 0.75 ppm sulfur dioxide (SO2) for 3-hr periods, exercising vigorously for the first 10 min and resting thereafter. Specific airway resistance (SRaw) and symptoms were recorded preexposure, immediately postexercise, and after 1, 2, and 3 hr of exposure. Symptoms and SRaw were significantly increased after exercise, relative to preexposure measurements. Group mean SRaw and symptom increases were no longer significant at 1 hr. In a few individuals, effects may have persisted for 2 hr or more. On separate occasions, comparable exposures were conducted, and forced expiratory spirometry was performed preexposure and postexercise, in addition to the other tests. Inclusion of spirometry did not significantly affect the other results. Spirometry and SRaw showed nearly equal significance in changes postexercise. Thus, in general, asthmatics' bronchoconstriction induced by exercise in SO2 seems to reverse quickly with rest, even if SO2 exposure continues. Spirometry may be useful for studying pollution-induced bronchoconstriction when SRaw measurements are impractical.

Asthmatics' responses to 6-hr sulfur dioxide exposures on two successive days

Asthmatic volunteers (N = 14) aged 18 to 33 yr with documented sensitivity to sulfur dioxide (SO2) were exposed in a chamber to 0.6 ppm SO2 for 6-hr periods on 2 successive days. Similar exposures to purified air, 1 wk later or earlier, served as controls. Subjects exercised heavily (target ventilation rate 50 L/min) for 5 min near the beginning of exposure (early exercise) and for an additional 5 min beginning after 5-hr of exposure (late exercise). At all other times, they rested. Body plethysmographic measurements and symptom questionnaires were administered pre-exposure, after each exercise period, and hourly during rest. Bronchoconstriction and lower respiratory symptoms were observed during or immediately following exercise--to a slight extent with clean air, and to a more marked extent with SO2. Bronchoconstriction and symptoms were modestly less severe on the second day of SO2 exposure than on the first day, but there were no meaningful differences in response between early and late exercise periods on either day.

Comparative effects of sulfur dioxide exposures at 5 degrees C and 22 degrees C in exercising asthmatics

Either airway cooling or sulfur dioxide (SO2) can induce bronchoconstriction in many asthmatics. Whether these two stresses act synergistically is a question with important public health implications. Eight young adult asthmatic volunteers were exposed to SO2 at 0.0, 0.2, 0.4, and 0.6 ppm, during 5 min heavy exercise at 5 degrees C, both with high (approximately 85%) and with low (approximately 50%) relative humidity. Physiologic response increased with increasing SO2 concentration but did not vary significantly with humidity. Symptom response was marginally greater at low than at high humidity. Twenty-four asthmatics were exposed similarly to clean air and to 0.6 ppm SO2, at 5 degrees C and also at 22 degrees C, always at high relative humidity. For this group, physiologic and clinical responses to SO2 (in excess of responses to clean air) were highly significant, regardless of temperature. The mean excess responses at 5 degrees compared with those at 22 degrees C were not statistically significant in clean air or SO2. Thus, moderate cold stress exacerbated the untoward response to SO2 only slightly and inconsistently in these asthmatic subjects.

Effects of 0.2 ppm nitrogen dioxide on pulmonary function and response to bronchoprovocation in asthmatics

To study the respiratory effects of nitrogen dioxide (NO2) at ambient concentrations, we exposed 31 asthmatic volunteers to purified air (control) and to 0.2 ppm NO2 for 2-h periods with light intermittent exercise. Bronchial reactivity (loss of forced expiratory performance in response to graded doses of methacholine chloride aerosol) was determined postexposure, using a newly developed apparatus that allowed accurate quantitation of methacholine dose. Forced expiratory performance, total respiratory resistance, and symptoms were also recorded immediately pre- and postexposure (prior to methacholine challenges). No significant direct effect of NO2 exposure on forced expiratory function or total respiratory resistance was observed. Symptoms showed a small significant (p less than 0.05) excess in purified air relative to NO2 exposures. Individual responses to methacholine varied greatly. About two-thirds of the subjects showed greater response after NO2 than after purified air, but the mean excess response was small. Mean changes attained significance in some but not all applicable statistical tests. Thus we cannot conclude unequivocally that NO2 exposure increased bronchial reactivity in this group, although there was some tendency in that direction.

Controlled clinical studies of air pollutant exposure: evaluating scientific information in relation to air quality standards

In controlled clinical studies, volunteers are deliberately exposed to specific air pollutants under conditions simulating ambient exposures, and health-related responses are documented. Studies of the health risks of air pollution need to be scientifically rigorous and clearly relevant to "real-world" pollution exposures. Their results should be confirmed by independent replication if they are to be used as a basis for air quality regulations. Well-designed controlled clinical studies readily meet these criteria, and complement the other methods of scientific risk assessment--animal toxicology and epidemiology. Clinical studies, toxicology, and epidemiology all have provided important information about air pollution health effects. A better understanding of the interrelationships of findings from these different fields is needed.

Response to ozone in volunteers with chronic obstructive pulmonary disease

Twenty-eight volunteers with chronic obstructive pulmonary disease were exposed to 0.0, 0.18, and 0.25 ppm ozone in purified air for 1-hr periods with light intermittent exercise, with exposure conditions presented in random order at 1-month intervals. No statistically significant changes attributable to ozone were found in forced expiratory performance or percent oxyhemoglobin (measured near the beginning and end of each exposure). No ozone-related changes in clinical status were found by interviews that included the time for 1 wk before to 1 wk after each exposure, except that a moderate increase in lower respiratory symptoms was reported by nonsmokers in 0.18 ppm exposures only. Thus, a slight decrement in hemoglobin saturation with ozone exposure (reported in two previous studies of chronic obstructive pulmonary disease subjects) may not be a common occurrence under typical ambient exposure conditions.

Respiratory effects of 0.75 ppm sulfur dioxide in exercising asthmatics: influence of upper-respiratory defenses

To determine the influence of mouthpiece breathing on respiratory responses to sulfur dioxide (SO2), 23 young adult asthmatic volunteers were exposed in a chamber to 0.75 ppm SO2 during heavy exercise, once with breathing unencumbered and once while they wore noseclips and mouthpieces. These conditions (more severe than in typical ambient exposures) were deliberately chosen to produce significant physiological and clinical responses. Similar exposures to clean air served as controls. Exposure studies were separated by 1-week intervals and order was randomized. The protocol consisted of 10 min on a bicycle ergometer (mean load 650 kg-m/min, mean ventilation 40 liter/min), preceded and followed by response testing (body plethysmography, symptom questionnaires, and forced expiratory function tests; the last were performed only postexposure). During clean-air exposures, specific airway resistance (SRaw) and symptoms increased significantly, but no meaningful differences between mouthpiece breathing and unencumbered breathing were observed. Exposures to SO2 under these relatively severe conditions produced greater increases in SRaw than clean-air exposures regardless of the mode of breathing, but the excess increase was significantly greater with mouthpiece than with unencumbered breathing. Symptom changes and postexposure forced expiratory function showed qualitatively the same pattern of decrements with SO2 ad did SRaw, but the excess responses attributable to mouthpiece breathing did not attain statistical significance. Mouthpiece breathing can compromise upper-respiratory defenses against SO2 to the extent that responses are greater than with more natural breathing. The mode of breathing should be taken in account when applying laboratory human exposure data to air-quality risk assessment.

Respiratory effects of sulfur dioxide in heavily exercising asthmatics. A dose-response study

Twenty-three asthmatic volunteers 19 to 31 yr of age were exposed to 0 (control), 0.2, 0.4, and 0.6 ppm sulfur dioxide (SO2) in random order at 1-wk intervals. Exposures took place in a controlled-environment chamber at 23 degrees C and 85% relative humidity; they included 5 min heavy exercise (mean minute volume, 48 L) plus time for postexercise physiologic testing. Body plethysmography (preexposure and end-exposure), spirometry (end-exposure only), and symptom questionnaires (covering the exposure period and the following week) all showed highly significant trends toward increased response with increasing SO2 concentration. Pairwise statistical comparisons showed substantial, highly significant, changes at 0.6 ppm, relative to control. Fewer and smaller significant changes were found at 0.4 ppm. At 0.2 ppm, no significant physiologic changes were found, but increases in symptoms during exposure were possibly significant. Symptom reports 1 day and 1 wk postexposure showed no significant variation related to SO2 level, i.e., exposure-related symptoms apparently reversed in less than 1 day.

Laboratory evaluation of a disposable half-face mask for protection against ozone

The ability of disposable half-face masks containing activated carbon to protect against inhaled ozone (O2) (nominal experimental exposure concentration, 0.5 ppm) was tested using a specially designed mechanical device simulating the breathing of a moderately exercising human, and then tested further by 18 volunteers exposed to O2 in a controlled-environment chamber for 2 h with intermittent mild exercise. As a control experiment, masks containing no activated carbon were tested similarly. On the mechanical device, carbon-impregnated masks removed 96 to 98% of ambient O3, whereas masks with no carbon removed 32 to 37%. Volunteers experienced typical respiratory irritation and temporary loss of forced expiratory function during O3 exposures when they wore the masks without carbon. These untoward effects were substantially reduced when masks containing carbon were worn. Volunteers tolerated the half-masks reasonably well, although some complained of discomfort. Disposable masks may be of significant benefit in protecting sensitive people from O2 exposures that they cannot readily avoid by other means.

Short-term respiratory effects of 0.12 ppm ozone exposure in volunteers with chronic obstructive pulmonary disease

Twenty-five volunteers with chronic obstructive pulmonary disease of mild to moderately severe degree underwent 1-h exposures to 0.12 ppm ozone (O2) in purified air with intermittent mild exercise. Their responses were assessed in terms of forced expiratory performance, ear oximetry, and reported symptoms. Control studied consisted of similar exposures to purified air alone. Control studies were separated from O2 exposures by 1 month, and the order was randomized. All studies took place in a controlled-environment chamber, and were preceded by approximately 1 h of rest in a purified-air environment. No significant disturbances in forced expiratory performance or symptoms attributable to O2 exposure were found. A slight but significant tendency to decreased arterial hemoglobin oxygen saturation (SaO2) during exercise in O2 was observed. The decrement in SaO2 with O2 relative to clean air (mean 1.3%) was near the limit of resolution of the ear oximeter test and was detected by signal averaging, thus its physiologic or clinical significance is uncertain.