Lupe M. Valencia

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.

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 volun teers, free of asthma or clinical respiratory allergies, were exposed to purified air containing ozone (03) 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° 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 (∼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, dur ing, 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 03. 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 03. The comparative lack of response may relate to the favorable clinical status of the subjects, the pattern of exercise dur ing exposure, or some other factor not yet identified.

Respiratory dose-response study of normal and asthmatic volunteers exposed to sulfuric acid aerosol in the sub-micrometer size range.

Twenty-one healthy and 21 asthmatic volunteers were exposed to respirable sulfuric acid aerosol (mass median particle diameter approximately 0.9 pm, geometric standard deviation 2.5) in a chamber at 21° and 50% relative humidity. Measured sulfuric acid concentrations averaged 0, 380, 1060, and 1520 μg/m3 (in the occupational range, higher than concentrations observed in ambient air pollution). Exposures to different concentrations occurred in randomized order 1 week apart. They lasted 1 hr and included three 10-min periods of heavy exercise. Healthy volunteers showed no statistically significant changes in pulmonary function. airway reactivity to inhaled methacholine, or overall reporting of irritant symptoms which could be attributed to acid exposure. They did show a slight statistically significant (P <. 01) increase in cough with increasing acid concentration. At the two highest acid concentrations, asthmatics showed significant increases in irritant symptoms and decrements in pulmonary function, without significant changes in airway reactivity. Their function decrements appeared to increase with time during exposure. Previous studies in fog (10°, median particle diameter approximately 10 urn) with similar concentrations of sulfuric acid showed more symptoms but less pulmonary function change, perhaps reflecting different sites of particle deposition in airways and/or different degrees of neutralization by airway ammonia. This and earlier evidence predicts little, if any, acute irritant response in short-term (1 hr or less) exposures to sulfuric acid at concentrations found in ambient air pollution.

Short-Term Respiratory Effects of Photochemical Oxidant Exposure in Exercising Children

To assess the short-term respiratory effects of photochemical oxidant pollution in children, 66 volunteers—33 boys and 33 girls aged 8 to 11—were exposed in a movable laboratory to polluted Los Angeles area ambient air and to purified air as a control. Exposures lasted one hour, during which subjects exercised continuously at roughly 50 percent of maximal oxygen consumption. Forced expiratory function and symptoms were evaluated prior to and at the end of exposure. The mean ozone concentration in ambient exposures was 0.113 ppm, reflecting an unusually mild pollution season. As a group, the subjects showed no statistically significant untoward responses to ambient air in comparison to purified air, and no significant differences in response between sexes. Nevertheless, regression analyses of individual data indicated a significant (p < 0.05) trend toward forced expiratory dysfunction with increasing ambient ozone concentrations. When the regression analyses were expanded to include older children and adul...

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.

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.

Controlled exposures of volunteers with chronic obstructive pulmonary disease to sulfur dioxide.

Twenty-four volunteers with chronic obstructive pulmonary disease (COPD) were exposed to sulfur dioxide (SO2) at 0, 0.4, and 0.8 ppm in an environmental control chamber. Exposures lasted 1 hr and included two 15-min exercise periods (mean exercise ventilation rate 18 liter/min). Pulmonary mechanical function was evaluated before exposure, after initial exercise, and at the end of exposure. Blood oxygenation was measured by ear oximetry before exposure and during the second exercise period. Symptoms were recorded throughout exposure periods and for 1 week afterward. No statistically significant changes in physiology or symptoms could be attributed to SO2 exposure. Older adults with COPD seem less reactive to a given concentration of SO2 than heavily exercising young adult asthmatics. This may be due to lower ventilation rates (i.e., lower SO2 dose rates) and/or to lower airway reactivity in the COPD group.