Replicated Dose-Response Study of Sulfur Dioxide Effects in Normal, Atopic, and Asthmatic Volunteers

Abstract

To help assess respiratory health risks from sulfur dioxide (SO2) air pollution, we studied 24 normal, 21 atopic, 16 minimal/mild asthmatic, and 24 moderate/severe, medication-dependent asthmatic subjects classified according to history, lung function, allergy skin tests, serum IgE level, and airway reactivity to methacholine. All were exposed in a chamber (21 degrees C, 50% humidity) to 0.0, 0.2, 0.4, and 0.6 ppm SO2 in random order at 1-wk intervals; then exposures were repeated to test consistency of response. The 1-h exposures included three 10-min exercise periods (ventilation approximately 40 L/min). Physiologic response was measured early (approximately 15 min) and late (approximately 55 min) in exposure. Symptoms were evaluated during exposure and for 1 wk afterward. Normal and most atopic subjects showed little response at these SO2 levels. A few atopic subjects and many asthmatics developed bronchoconstriction and respiratory symptoms, but most were able to maintain their exercise. Effects were not markedly different between early and late measurements, nor between the first and second round of studies; however, late and second-round responses appeared slightly more favorable. No statistically significant effect of SO2 on symptoms was found 1 day or 1 wk after exposure. Minimal/mild asthmatics showed, on the average, slight responses at 0.0 ppm (attributable to exercise) and increasing responses at increasing SO2 concentrations. Moderate/severe asthmatics reacted more at 0.0 ppm, but their increments in response with increasing SO2 concentration were roughly similar to those of minimal/mild asthmatics. Thus, responses to SO2 per se were not strongly dependent on clinical severity of asthma, nor on SO2 exposure history during previous weeks.

The effect of sulphur dioxide exposure on indices of heart rate variability in normal and asthmatic adults

“…At higher concentrations than employed in this study, SO 2 is a powerful bronchoconstrictor, i.e. at concentrations of around 400 ppb in asthmatics [5] and at concentrations w1,000 ppb in normal subjects [4]. Such effects in normal subjects can be completely abolished with anticholinergic drugs, but are only partially reversed in subjects with asthma.…”

“…Normal subjects vary considerably in their response to this gas, most responding to concentrations of 4,000±5,000 ppb [4], but no effects have been recorded in normal individuals exposed to concentrations <1,000 ppb [5]. Bronchoconstriction in asthmatic subjects occurs at lower concentrations, changes in lung function being detectable at concentrations of 400 ppb when exposures are combined with exercise [5]. The mechanisms producing bronchoconstriction in humans are relatively poorly understood, but are thought to involve stimulation of irritant receptors in the upper airway [6].…”

Health Risks of Short-term S02Exposure to Exercising Asthmatics

“…In all probability, asthmatics living near the power plants exhibit a wide range of clinical severity. Recent data 18 indicate that our assumption that all asthmatics are "mild" did not introduce significant bias since the data show only slightly greater responses from moderate-to-severe asthmatics. Confining the risk analysis to asthmatics is likely to have been reasonable, because the experimental data indicate far lower sensitivity among normal subjects to either SO2 or exercise-induced bronchoconstriction.…”

Characterization of Road Traffic Emissions in a Densely Populated Residential Area of Kuwait

“…Individuals suffering from asthma, chronic lung disease, or chronic heart disease are the most sensitive to ambient SO 2 levels exceeding 2000 ppb (greater than 4 x 10 16 inhaled molecules). Concentrations of SO 2 ranging from 0 to 80 ppb (0 to 1.6 x 10 15 inhaled molecules) are expected to be safe since no health effects are expected to be experienced by healthy people (Linn, Avol, Penc, Shamoo, & Hackney, 1987). The calculated average inhaled SO 2 molecules expressed in Table 3 are considerably lower than the ones computed above.…”