EFFECT OF 3 HOURS PASSIVE SMOKE EXPOSURE IN THE EVENING ON AIRWAY TONE AND RESPONSIVENESS UNTIL NEXT MORNING

To study the effect of environmental tobacco smoke (ETS) exposure in t he evening on nocturnal changes in airway tone and responsiveness, 17 subjects with mild asthma (mean +/- SD age, 26 +/- 5 years, FEV(1)% pr ed., 89 +/- 14%) were exposed to either ambient air (sham) or ETS (20 ppm CO) for 3 h (7:00 to 10:00 p.m.). Seven subjects had a history of ETS-induced respiratory symptoms. Spirometry was performed 2 h before exposure (5:00 p.m.), every 30 min during exposure, and at 11:00 p.m., 3:00 a.m., and 7:00 a.m. The provocative concentrations of methacholi ne necessary to decrease FEV(1) by 20%, PC(20)FEV(1), were assessed at 5:00 p.m., 11:00 p.m., 3:00 a.m., and 7:00 a.m. Compared with pre-exp osure measurements, mean FEV(1) values during and after ETS exposure w ere significantly lower than with sham exposure = 0.013 and 0.026). Th is effect, however, was due to a significant response in single indivi duals. The higher bronchial responsiveness after ETS than after sham e xceeded one doubling concentration in 4, 5, and 4 patients at 11:00 p. m., 3:00 a.m., and 7:00 a.m., respectively. The opposite effect was ob served in 2, 2, and 2 patients, respectively. There was no statistical ly significant mean effect of ETS on airway responsiveness during nigh t; however, there was significant heterogeneity in individual response s (P = 0.0002). Patients with and without a history of ETS-induced sym ptoms did not show different responses to experimental ETS exposure. I n conclusion, our data suggest that in single adult subjects with mild asthma, acute exposure to ETS in the evening can produce a deteriorat ion of airway tone and responsiveness during the night, with wide inte rindividual variability in the response.