Oral and oronasal breathing during continuous exercise produce similar responses to ozone inhalation

Breathing route has a profound effect on sulfur dioxide-induced pulmonary function response in human subjects. There is comparatively little evidence of the effects of oral, nasal, and oronasal breathing on ozone (O3)-induced responses in humans. In this study, six young adult males were exposed on five occasions to 0.40 parts per million (ppm) O3 while exercising continuously at one of two workloads (minute ventilation, VE, of approximately 30 and 75 l/min). The VE exposure time product was similar for all protocols. Four exposures were delivered randomly with a Hans-Rudolph respiratory valve attached to a silicone facemask, with breathing route effected with and without noseclip. A 2 x 2 analysis of variance revealed no statistically significant differences (p less than .05) across conditions in pulmonary function, exercise ventilatory pattern, or subjective symptoms responses. The fifth exposure, delivered via the same respiratory valve with mouthpiece, but without facemask, revealed significantly greater forced expiratory volume in 1 s (FEV1.0) impairment than that observed for the respiratory valve, facemask with noseclip exposure (-20.4% and -15.9%, respectively). The latter suggests partial O3 reactivity to the facemask and clean shaven facial surface of the subjects, although reduced oral scrubbing by mouthpiece-induced bypassing of the oral vestibule might account, in part, for this difference. Recent O3 uptake evidence from another laboratory, however, supports our conclusion that breathing route during moderate and heavy continuous exercise does not affect acute physiologic responses to 0.40 ppm O3.     

Effects of Ozone Exposure: A Comparison between Oral and Nasal Breathing

Mode of inhalation, by nose or by mouth, as a determinant of pulmonary toxicity to acute inhalant exposure has beem investigated incompletely. This communication addresses whether there are significant differences in toxic pulmonary responses to acute ozone (O₃) exposure between differing modes of inhalation (nasal vs. oral breathing). Changes in the results of pulmonary function tests and symptomatology of healthy young adults were compared following both exclusive nose and exclusive mouth breathing during a 30-min exposure to approximately 0.4 ppm O₃ under conditions of moderate continuous exercise. In this single-blind, randomized, crossover study, no significant differences in either the results of pulmonary function tests or in symptomatology were found between the two modes of inhalation.     

Exposure-effect relationship of selected pulmonary function measurements in subjects exposed to ozone

Summary Healthy adult male volunteer subjects were exposed to 0.15, 0.3, 0.45 and 0.5 ppm ozone (O₃) with and without intermittent light exercise. The results suggest that the subject's level of exercise during exposure is considerably related to the magnitude of changes in lung function and the occurrence rate of respiratory symptoms at any given O₃ concentration, and that among healthy subjects there is a considerable range of reactivity to O₃ exposure. A level of 0.15 ppm O₃ with intermittent light exercise produced a significant decrease of specific airway conductance in most subjects and coughing during deep inspiration in five of 15 subjects, while a level of 0.5 ppm O₃ produced fewer effects when the subject did not exercise. The nonsmoker is more reactive to O₃ than the smoker. The subject's level of exercise during exposure and his smoking habit are two important factors in evaluating the exposure-effect relationship of O₃.     

Respiratory effects of 2-hr exposure to 1.0 ppm nitric oxide in normal subjects

Eight adult healthy male volunteers were exposed to 1.0 ppm nitric oxide (NO) with intermittent light exercise for 2 hr. No one showed any symptoms during NO exposure. A small, but significant, decrease of specific airway conductance was observed in half of the subjects. As a group, a significant reduction of the percentage increase of maximal expiratory flow at 50% of forced vital capacity while breathing a HeO₂ gas mixture as compared with air was observed among various pulmonary function tests. These results suggested that some physiological responses to NO exposure might be observed in some subjects when performing exercise.     

Monitoring Intracellular Redox Changes in Ozone-Exposed Airway Epithelial Cells

Background: The toxicity of many xenobiotic compounds is believed to involve oxidative injury to cells. Direct assessment of mechanistic events involved in xenobiotic-induced oxidative stress is not easily achievable. Development of genetically encoded probes designed for monitoring intracellular redox changes represents a methodological advance with potential applications in toxicological studies.Objective: We tested the utility of redox-sensitive green fluorescent protein (roGFP)–based redox sensors for monitoring real-time intracellular redox changes induced by xenobiotics in toxicological studies.Methods: roGFP2, a reporter of the glutathione redox potential (E_GSH), was used to monitor E_GSH in cultured human airway epithelial cells (BEAS-2B cells) undergoing exposure to 0.15–1.0 ppm ozone (O₃). Cells were imaged in real time using a custom-built O₃ exposure system coupled to a confocal microscope.Results: O₃ exposure induced a dose- and time-dependent increase of the cytosolic E_GSH. Additional experiments confirmed that roGFP2 is not directly oxidized, but properly equilibrates with the glutathione redox couple: Inhibition of endogenous glutaredoxin 1 (Grx1) disrupted roGFP2 responses to O₃, and a Grx1-roGFP2 fusion protein responded more rapidly to O₃ exposure. Selenite-induced up-regulation of GPx (glutathione peroxidase) expression–enhanced roGFP2 responsiveness to O₃, suggesting that (hydro)peroxides are intermediates linking O₃ exposure to glutathione oxidation.Conclusion: Exposure to O₃ induces a profound increase in the cytosolic E_GSH of airway epithelial cells that is indicative of an oxidant-dependent impairment of glutathione redox homeostasis. These studies demonstrate the utility of using genetically encoded redox reporters in making reliable assessments of cells undergoing exposure to xenobiotics with strong oxidizing properties.     

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 SO₂ in random order at 1-week intervals. Exposures, conducted in a controlled-environment chamber at 23°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 SO₂, although small significant increases in resistance attributable to exercise were found. These negative results contrast with previous positive findings in asthmatics exposed to SO₂ via mouthpiece. The differences may relate to effects of mouthpiece breathing on respiratory defenses, or to interindividual variations in bronchial reactivity to SO₂.     

Overt and latent cardiac effects of ozone inhalation in rats: evidence for autonomic modulation and increased myocardial vulnerability

Background: Ozone (O₃) is a well-documented respiratory oxidant, but increasing epidemiological evidence points to extrapulmonary effects, including positive associations between ambient O₃ concentrations and cardiovascular morbidity and mortality.Objective: With preliminary reports linking O₃ exposure with changes in heart rate (HR), we investigated the hypothesis that a single inhalation exposure to O₃ will cause concentration-dependent autonomic modulation of cardiac function in rats.Methods: Rats implanted with telemeters to monitor HR and cardiac electrophysiology [electrocardiography (ECG)] were exposed once by whole-body inhalation for 4 hr to 0.2 or 0.8 ppm O₃ or filtered air. A separate cohort was tested for vulnerability to aconitine-induced arrhythmia 24 hr after exposure.Results: Exposure to 0.8 ppm O₃ caused bradycardia, PR prolongation, ST depression, and substantial increases in atrial premature beats, sinoatrial block, and atrioventricular block, accompanied by concurrent increases in several HR variability parameters that were suggestive of increased parasympathetic tone. Low-O₃ exposure failed to elicit any overt changes in autonomic tone, heart rhythm, or ECG. However, both 0.2 and 0.8 ppm O₃ increased sensitivity to aconitine-induced arrhythmia formation, suggesting a latent O₃-induced alteration in myocardial excitability.Conclusions: O₃ exposure causes several alterations in cardiac electrophysiology that are likely mediated by modulation of autonomic input to the heart. Moreover, exposure to low O₃ concentrations may cause subclinical effects that manifest only when triggered by a stressor, suggesting that the adverse health effects of ambient levels of air pollutants may be insidious and potentially underestimated.     

Rocket Propellants

The effects of photochemical air pollution on respiratory function of Tokyo elementary school children were investigated. Nine types of environmental factors were continuously recorded. Seven categories of respiratory function tests were performed on 20 normal 11-year-old children once a week from June to December 1972, as a general rule. The correlation coefficients between respiratory function measurements and each of the environmental factors were calculated. The maximum expiratory flow rate ([Vdot] max) showed high correlation with the largest number of environmental factors.

Among environmental factors, temperature highly affected various respiratory function tests. The O₃ was significantly associated with airway resistance (Raw) or specific airway conductance (Gaw/Vtg), NO or NO₂ with [Vdot] max, and temperature with Raw, Gaw/Vtg, and [Vdot] max.

Two subjects among all subjects were considered as the reactors to the environmental factors.     

Cardiovascular adjustments to carbon monoxide exposure during rest and exercise in dogs

Cardiovascular, respiratory, and metabolic measurements were made on dogs at rest and during 30 minutes of exercise at either 6.4 km/hour, 10% grade, or 8.0 km/hour, 16% grade, following the bolus administration of CO for 1 or 2 minutes, or room-air breathing mixtures. During rest and exercise elevated mean blood HbCO levels (6 to 21%) reduced the arterial and mixed venous oxygen contents and saturations, and mixed venous P_O2 levels. Arterial-mixed venous oxygen differences were reduced during exercise as a result of CO administration. Elevated blood HbCO levels had a minimal or no effect on other cardiovascular, respiratory, and metabolic parameters. During work the reductions in a-v?_O2 differences were not offset by appropriate increases in cardiac outputs.     

Effects of ozone exposure: a comparison between oral and nasal breathing

Mode of inhalation, by nose or by mouth, as a determinant of pulmonary toxicity to acute inhalant exposure has been investigated incompletely. This communication addresses whether there are significant differences in toxic pulmonary responses to acute ozone (O3) exposure between differing modes of inhalation (nasal vs. oral breathing). Changes in the results of pulmonary function tests and symptomatology of healthy young adults were compared following both exclusive nose and exclusive mouth breathing during a 30-min exposure to approximately 0.4 ppm O3 under conditions of moderate continuous exercise. In this single-blind, randomized, crossover study, no significant differences in either the results of pulmonary function tests or in symptomatology were found between the two modes of inhalation.     

Health effects of short-term inhalation of nitrogen dioxide and ozone mixtures.

The effects of single and multiple daily 3-hour exposures to nitrogen dioxide (NO₂) and ozone (O₃) mixtures on the resistance to streptococcal pneumonia were investigated. The concentrations of NO₂ ranged from 1.5 to 5.0 ppm, and those of O₃, from 0.05 to 0.5 ppm. The effect of a single exposure to the mixture was additive, whereby the excess mortality rates were equivalent to those induced by the inhalation of each individual pollutant. The ability to clear inhaled bacteria from the lungs was diminished in mice exposed to the NO₂O₃ mixtures for 3 hours. This impairment was manifested by the increased frequency of isolation of Streptococcus from the lungs for up to 6 days after the respiratory challenge. Excess mortalities observed after 20 daily 3-hour exposures suggested that a synergistic effect might be present upon repeated inhalation of pollutant mixtures, that made them more effective in reducing resistance to respiratory infection. The results emphasize the need for the establishment of primary air quality standards for short-term NO₂ exposures.     

Effect of 0.62 ppm NO2 on cardiopulmonary function in young male nonsmokers

Cardiopulmonary and metabolic responses of three groups, each consisting of five adult males (aged 20–25), were determined before, during, and after a 2-hr exposure to 0.62 ± 0.12 ppm NO₂ at 25°C and 45% RH. The three groups exercised during exposure at 40% of V?_{O2 max} for either 15, 30, or 60 min for Groups A, B, and C, respectively. During the exercise periods the ventilation was about 33 liter/min, a fourfold increase over the resting level. There were no physiologically significant cardiovascular, metabolic, or pulmonary function changes which could be attributed to exposure to this level of NO₂ (0.62 ppm). There were no differences between the groups in their response despite the fact that Groups A and B received more NO₂ as a result of 28% and 84% greater ventilations, respectively.     

The effect of controlled ozone exposure on human lymphocyte function

The effects of ozone (O₃) on cell-mediated immunity were studied in 16 human subjects exposed to 1176 μg/m³ O₃ (0.6 ppm) for 2 hr in an environmentally controlled exposure chamber. Venous blood samples were taken before and immediately after controlled air and O₃ exposures, as well as at 72 hr, 2 and 4 weeks, and at one random time at least 1 month after treatment. The relative frequency of T lymphocytes in blood and the in vitro blastogenic response of lymphocytes to phytohemagglutinin (PHA), concanavalin A (Con A), pokeweed mitogen (PWM), and Candida albicans were determined. During the course of the experiment, no statistically significant changes were observed in the number of T lymphocytes that form spontaneous rosettes with sheep erythrocytes. The response of T lymphocytes to PHA was significantly reduced (P < 0.05) in samples taken at 2 and 4 weeks following O₃ exposure. Normal response to PHA was observed at 2 months post-O₃ exposure. No statistically significant changes in lymphocyte responses to Con A. PWM, or Candida were seen. These results show that one 2 hr exposure of humans to 0.6 ppm O₃ may lead to a transient suppression of the PHA-stimulated blastogenic transformation of peripheral blood lymphocytes. The data indicate that the blastogenic response to PHA of human lymphocytes is exquisitely sensitive to O₃ exposure and could serve as a bioassay for evaluating subtle changes in cellular immunity induced by O₃ and possibly other pollutants.     

Changes of cardiac and respiratory rhythm in non- and tracheostomized rats exposed to nitrogen dioxide

Cardiac and respiratory changes in non- and tracheostomized rats were examined during exposure to 20 ppm of NO₂ for 150 min. The abnormal respiratory pattern consisted of rapid shallow breathing, deep breathing, and apnea, and the bradyarrhythmias were observed in the tracheostomized rats during exposure. Also, similar changes were seen in the nontracheostomized rats. A decrease in the heart rate (HR) was observed in both non- and tracheostomized rats. The decrease in HR was depressed by atropine injection, and the abnormal respiratory patterns were almost abolished by this drug. It was suggested, from these results, that the cardiac and respiratory abnormalities could be induced without the irritation to upper respiratory tracts, and that the vagal efferent pathway had an important role in the appearance of the abnormalities during exposure.     

Ozone exposure, adaptation, and changes in lung elasticity.

In rabbits, the left lung (LL) was compressed by a unilateral pneumothorax to prevent ventilation while the right lung (RL) was exposed to ozone (O₃) (2 ± 0.2 or 5± 0.4 ppm) for 3 hr. Following the exposure, the LL was reexpanded. One week later the lungs were exposed bilaterally to higher concentrations of O₃ (16 ± 2.2 or 19 ± 0.4 ppm) for 3 hr. The animals were then killed and the two lungs were excised, weighed, and subjected to volume/pressure measurements. The previously exposed RL was found to be less edematous, but also less distensible than the paired LL. In addition, the LL showed increases in wet and dry weights below what would be expected from its single direct exposure to O₃. The findings indicate that while the reduction in edema formation associated with adaptation or tolerance to O₃ occurs mostly on a local basis, a part of the tissue response of the respiratory system to O₃, as evidenced by the changes in weight of the LL, may be mediated systemically. The possible relation between the reduction in edema formation and altered distensibility of the RL is discussed.     

Protein accumulation in lung lavage fluid following ozone exposure

Accumulation of protein in lung lavage fluid was used as an indicator of pulmonary damage following exposure of guinea pigs to O₃. Exposure of animals to 510, 1000, or 1960 μg/m³ (0.26, 0.51, or 1.0 ppm) of O₃ for 72 hr resulted in significantly elevated levels of lavage fluid protein when compared to that of air controls. This effect was not observed in animals exposed to 196 μg O₃/m³ (0.10 ppm). When exposure time was reduced to 3 hr, the O₃-induced protein accumulation in lavage fluids was undetectable unless the time of lavage was delayed 10–15 hr following the exposure. Under these conditions, elevated protein content was seen in lung lavage fluids obtained from animals exposed to O₃ ranging from 510 to 1470 μg O₃/m³ (0.26-0.75 ppm) and a dose relationship between the amount of protein accumulation in the lung and the concentration of O₃ to which the animals were exposed was observed. Vitamin C deficiency did not enhance this O₃-induced lesion in guinea pigs. The dose relationship has also been confirmed by polyacrylamide gel electrophoresis of the lavage fluids. Lung lavage fluid protein content in animals exposed to 353 μg O₃/m³ (0.18 ppm) for 8 hr/day for 5 or 10 consecutive days was not different from that of air controls.     

Study of respirator effect on nasal-oral flow partition

Factors affecting worker tolerance of respiratory personal protective devices are inadequately understood. This study evaluates whether respirator-type loads affected the switch from nasal to oral breathing. Eleven healthy subjects were studied under progressive exercise conditions, using a respirator full-face mask with inspiratory resistance (I), pressure breathing (P) (10 cm H₂O end-expiratory pressure), or no load (N). A rapid-response thermistor was used to determine whether flow was predominantly oral or nasal. Both P and I increased the percentage of time that breathing was predominantly oral. The effect was most pronounced at higher exercise levels. The percentage of mouth breathing appeared to be closely related to the expiratory time. This study suggests that nasal-oral flow partitioning should be considered as a possible determinant of respirator tolerance. Am. J. Ind. Med. 32:408–412, 1997. © 1997 Wiley-Liss, Inc.     

Experimental suppression of tolerance to ozone and of cross-tolerance (NO2O3) in rats by actinomycin D and colchicine

Rats were initially exposed to 2 ppm ozone or 16–20 ppm NO₂ for 3 hr in order to induce a certain tolerance to ozone during 3 days after the initial exposure. After the initial exposure, the y were intraperitoneally administered actinomycin D or colchicine at a scheduled interval. Twenty-four hours after the administration, the induction of tolerance was assayed by the response of lung weight to challenge exposure to 5.6 ppm ozone for 3 hr. Either actinomycin D or colchicine administered immediately after the initial exposure suppressed the induction of tolerance (O₃O₃) and of cross-tolerance (NO₂O₃), while the tolerance was not suppressed by the inhibitors administered 12 to 24 hr following the initial exposure. Normal tolerance to ozone was induced 12 to 24 hr after the initial exposure. It was thus shown that the induction of tolerance could not be suppressed by the inhibitors administered after the lungs became fully tolerant; we tentatively interpret these results to suggest that no tolerance is induced without pulmonary cell proliferation stimulated by the initial exposure.     

Protective effects of dietary -tocopherol in rats exposed to toxic levels of ozone and nitrogen dioxide

The effect of dietary α-tocopherol at various levels, especially in the range 0–45 mg/kg, on the acute toxicity of O₃ and NO₂ to rats was studied. The highest level of α-tocopherol was 1500 mg/kg of diet in combination with ascorbic acid, dl-methionine and butylated hydroxytoluene; the level of O₃ ranged from 0.7 to 16 ppm and NO₂ from 20 to 25 ppm; and various exposure periods were used. α-Tocopherol alone and in combination with the other antioxidants exerted a protective effect in rats exposed to O₃ and NO₂ as measured by acute toxicity and animal weight change. During 1 ppm O₃ exposure voluntary activity decreased, while at lower levels of O₃ (0.7–0.8 ppm) α-tocopherol protection against lipid peroxidation in the lung, as measured by endogenous lung thiobarbituric acid reactants, was a reciprocal function of the logarithm of dietary α-tocopherol. Extracts of lung tissue from animals exposed to O₃ and O₂ showed no increase in fluorescent products associated with lipid peroxidation.     

Response of Cats to Inhaled Mixtures of SO2 and SO2-NaCl Aerosol in Air

Twenty healthy, adult male cats were lightly anesthetized with pentobarbital (Nembutal) sodium and tracheotomized; respiration was maintained by pump, Medical-grade breathing air, with or without sulfur dioxide alone or in combination with sodium chloride aerosol was delivered in predetermined exposure sequencer Pulmonary flow resistance and lung compliance were evaluated. Pollutants were also delivered via endotracheal catheter or face mask, or both. Approximately 20 ppm of SO₂ in air was required to evoke a significant change in pulmonary flow resistance in “reactors.” The majority of animals showed no response to this concentration of SO₂ either alone or with NaCl aerosol (10 mg/cu m). An increased frequency of significant changes in pulmonary flow resistance was suggested when pollutants were delivered via endotracheal catheter or face mask. All alterations in parameters of response were reversible shortly after exposure ceased.