TIME-ACTIVITY PATTERNS AND DIURNAL-VARIATION OF RESPIRATORY STATUS INA PANEL OF ASTHMATICS - IMPLICATIONS FOR SHORT-TERM AIR-POLLUTION EFFECTS

To understand the short-term health risks to people from air pollution exposure, we investigated time-activity patterns and temporal variati on of the respiratory status in 49 asthmatic Los Angeles area resident s 18-50 years old. During the summer (May-September) and winter (Novem ber-March), subjects measured their lung function two to four times da ily at home for one week periods, and every hour recorded their sympto ms, medication, and activity hourly in diaries. Almost all subjects re corded heart rates (HR), which were converted to ventilation rate (VR) estimates using individual laboratory exercise data. Most subjects' l ung function and symptoms varied diurnally, and were worst in early mo rning. For subjects with clinically mild asthma, diurnal forced expire d volume in 1 sec (FEV1) changes averaged 7%, verseus 12% in those wit h moderate symptoms, and 18% in severely asthmatic subjects. Lung func tion was similar in summer and winter, but symptoms and medication use decreased in winter. In the aggregate, subjects reported spending 75% of waking hours indoors at self-rated slow activity and 11% in vehicl es. HR records usually corroborated reports of medium or fast activity . Mean estimated VR at slow, medium, and fast activity was 19, 37, and 61 L/min for men, and 16, 24, and 32 L/min for women. Outdoor fast ac tivity, representing the greatest vulnerability to outdoor pollution, occupied approximately 0.2% of waking hours (2 min/day on average); ou tdoor medium activity occupied about 2% of waking hours (19 min/day on average). Estimated cumulative ventilation was higher than that of pr evious healthy panels because of asthmatics' higher VR at slow activit y. If these activity patterns are typical, asthmatics may be especiall y vulnerable to pollutants with effects dependent on cumulative inhale d dose. Effects dependent on high inhaled dose rates over a short peri od, e.g., sulfur dioxide effects, would be unlikely, except perhaps fo r uncommonly active individuals in uncommonly polluted areas.