Two conditions were compared: heating with a low-[NO.sub.x] unflued gas heater and heating with a flued gas heater.
Subjects who had a flued gas heater were assumed not to have an unflued gas heater, 'Geometric mean and geometric 95% range are shown.
Mean daily in-class temperature between 0900 and 1500 hours was 20.9[degrees]C on days when the unflued gas heater was operating and 20.5[degrees]C on days when the flued gas heater was operating (difference adjusted for random effects 0.4[degrees]C; 95% CI, 0.0-0.8, p = 0.07).
However, when the analysis was limited to days and schools in which heater use was [greater than or equal to] 30%, morning [FEV.sub.1] was 0.03 L (95% CI, 0.003-0.057, p = 0.03) higher during the period of exposure to the unflued gas heater. Similarly, in this subgroup, evening PEF was 5.2 L/min (95% CI, 1.0-9.3, p = 0.01) higher during operation of the unflued gas heater.
There was no evidence of any decrement in lung function attributable to unflued gas heater exposure when the analysis was restricted in this way.
Analysis of lung function measures recorded during in-school testing on Thursday or Friday of each study week revealed that the unflued gas heater was associated with a small increase in [FEV.sub.1] [0.03 L (95% CI, 0.01-0.05), p = 0.01] compared with the flued gas heater.
In the subgroup with current asthma, eNO concentrations were 3.7 ppb higher during exposure to the unflued gas heater than during exposure to the flued gas heater (95% CI, -0.5 to 7.9, p = 0.08).
The overall daily prevalence of wheeze in the morning was 4.9% during periods of exposure to the low-[NO.sub.x] unflued gas heater and 4.4% during exposure to flued gas heater (Table 5).