Ronald M. Bailey

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.

Exposures of human volunteers to a controlled atmospheric mixture of ozone, sulfur dioxide and sulfuric acid

Nineteen human volunteers with normal pulmonary function and no history of asthma were exposed on two separate days to clean air and to an atmospheric mixture containing ozone (O3), 0.37 ppm, sulfur dioxide (SO2), 0.37 ppm, and sulfuric acid aerosol (B2SO4), 100 micrograms/m3. Subjects were exposed under carefully controlled conditions for two hours. During this period, the subjects alternately exercised for 15 minutes, at a level calculated to double minute ventilation, and rested for 15 minutes. The experimental goal was to determine whether the presence of the copollutants, H2SO4 and SO2, would significantly enhance the irritant potential of ozone, or cause decrements in pulmonary function on the order of 10 - 20 percent. Statistical analysis of the group averaged data suggested that the mixture may have been slightly more irritating to the subjects than was O3 alone. A large percentage of the subjects exhibited small decrements in pulmonary function. The group averaged FEV1.0 (forced expiratory volume in one second) on the exposure day was depressed 3.7 percent from the control value. One might expect O3 alone to depress FEV1.0 by about 2.8 percent under similar exposure conditions.

Effect of ammonium nitrate aerosol on human respiratory function and symptoms

Abstract Volunteers, 20 normal and 19 asthmatic, were exposed to clean air (sham) and to ammonium nitrate (NH 4 NO 3 ) aerosol (exposure) under conditions which simulated a “worstcase” ambient pollution episode. The arosol concentration was nominally 200 μg/m 3 with a mass median aerodynamic diameter (MMAD) of 1.1 μm and a geometric standard deviation (σg) of 3.3. Exposures lasted 2 hr with intermittent exercise and heat stress. No substantial alterations in pulmonary function or overall reported symptoms attributable to the NH 4 NO 3 exposure were found for either subject group. Possibly meaningful pulmonary function changes or symptom increases were seen in a few individuals, but these showed no obvious pattern and may well have been chance occurrences.

Respiratory effects of mixed nitrogen dioxide and sulfur dioxide in human volunteers under simulated ambient exposure conditions

Abstract Normal and asthmatic volunteers (N = 24 and 19, respectively) were exposed to mixed nitrogen dioxide (NO2) and sulfur dioxide (SO2) in purified background air in an environmental chamber under conditions simulating an ambient pollution episode. The NO2 concentration was 0.5 ppm; the SO2 concentration was 0.5 ppm for normals and 0.3 ppm for asthmatics. Exposures lasted 2 hr and included intermittent exercise and heat stress. Control studies consisted of similar exposures to purified air alone. The mixed pollutant gases may have reacted chemically in the exposure chamber, but no appreciable amounts of sulfate or nitrate aerosol were detected there. Group mean lung function changes during exposure generally were not significantly different from control for normals or for asthmatics. Symptoms reported by the normal group showed a small significant overall increase during pollutant exposure and later the same day relative to the corresponding control periods; the asthmatics showed a small significant increase later in the day but not during exposure. The increased symptom reporting showed little consistency from subject to subject: there were small increases for most individual symptom categories evaluated, none of them statistically significant. The results are not sufficient to establish whether this slight and nonspecific clinical response should be attributed to the pollutant mixture or to some other aspect of the exposure protocol.

Respiratory responses of young adult asthmatics to sulfur dioxide exposure under simulated ambient conditions

Twenty-four young adult asthmatic volunteers were exposed to 0, 0.25, and 0.50 ppm SO/sub 2/ in random order at 1-week intervals. Exposures, conducted in a controlled-environment chamber at 23/sup 0/C and 90+% relative humidity, lasted 1 hr and incorporated alternating 10-min periods of moderate exercise (mean exercise ventilation about 27 liters/min) and rest. Airway resistance was measured before exposure, after the first exercise period, and near the end of exposure. Forced expiratory performance was measured after the final airway resistance measurement. Exposure-relatable symptoms were recorded before, during, and after exposure periods. None of these measures of response showed statistically significant variation attributable to SO/sub 2/, although small significant increases in resistance attributable to exercise were found. These negative results contrast with previous positive findings in asthmatics exposed to SO/sub 2/ via mouthpiece. The differences may relate to effects of mouthpiece breathing on respiratory defenses, or to interindividual variations in bronchial reactivity to SO/sub 2/.

Human respiratory responses to an aerosol containing zinc ammonium sulfate

Abstract Twenty-one normal volunteers and 19 volunteers with asthma were exposed in an environmental control chamber to a polydisperse aerosol of zinc ammonium sulfate (ZnSO 4 ·(NH 4 ) 2 SO 4 )—a model of ambient metallic sulfate aerosols derived from trace metals in fossil fuels—at a nominal concentration of 20 μg/m 3 . As a model of the background ambient particulate burden, polydisperse sodium chloride aerosol at a nominal concentration of 300 μg/m 3 was added to the chamber atmosphere during control as well as exposure studies. Exposure temperature was 20°C and relative humidity was 85%, simulating weather conditions typical of fall/winter ambient pollution episodes. Exposure and control studies were performed on separate days, separated by about 3 weeks, in random order under double-blind conditions. Exposure periods lasted 2 hr and included intermittent light exercise. Lung function and symptoms were evaluated before and at the end of the exposure or control period. Symptom reports showed no significant variation attributable to zinc ammonium sulfate exposure. Group mean lung function measures showed a few significant changes possibly attributable to the sulfate exposure, but these were small and inconsistent. It was concluded that zinc ammonium sulfate produced minimal or no short-term respiratory effects observable under the conditions of the experiment.

Human exposure to ferric sulfate aerosol: effects on pulmonary function and respiratory symptoms

Twenty normal and 18 asthmatic human volunteers were exposed to ferric sulfate aerosol at a nominal concentration of 75 microgram/m3 (equivalent to 20 microgram iron/m3). The concentration and particle size distribution (2 micron mass median aerodynamic diameter; geometric standard deviation of 3) were selected to simulate worst case ambient conditions. Ferric sulfate was chosen for study because it is toxic, it is a respiratory system irritant, and increased use of coal and high sulfur fuel oils will lead to increased concentrations of iron and sulfate in ambient air. A double-blind protocol was followed in which each subject was exposed on two days, separated by about a three week period. The subjects were exposed to clean air (sham) on one day and to ferric sulfate aerosol on the other (exposure); the order of exposure was selected randomly. Neither the subjects nor the staff performing the clinical testing were informed as to the nature of the atmosphere on any given day. Pulmonary function tests were performed immediately before (pre) and after (post) each 2 hr sham or exposure period; this protocol included intermittent exercise. Pre- and post-exposure symptom score interviews were also administered. On the average, the two groups of subjects did not exhibit significant pre- to post-changes in total respiratory system resistance, forced expiratory flow/volume performance, and single breath nitrogen washout parameters. None of the subjects reported more than slight changes in symptoms during exposure. Five individuals showed small but significant decremental trends in pulmonary function; however, nine subjects tended to improve after exposure.

Sulfate aerosol generation and characterization for controlled human exposures

Carefully controlled human exposures to ammonium sulfate, ammonium bisulfate, and sulfuric acid aerosols were performed to provide valid data concerning effects of potentially harmful atmospheres at “worst case” ambient and possibly industrial levels. The aerosols were produced by a specially designed generator, based upon the Babington nebulization principle. Volunteer human subjects were exposed to nominal sulfate aerosol concentrations of 100 µg/m3 (mass median aerodynamic diameter [MMAD] of 0.3 µ. and a geometric standard deviation of approximately 2.9) at 31.1°C (88°F), 40% relative humidity, in a 62.3 m3 (2200 ft3) chamber. The chamber was continuously supplied with air at a flow rate of 14 m3/min (500 ft3/min) which was well mixed with the existing chamber air to assure that no concentration gradients existed within the subject exposure zone. Real-time monitoring of aerosol mass and size was performed by a computer-controlled electrical aerosol size analyzer/optical particle counter system. The tot...

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.