Histamine challenge in asthmatics at 07.00-12.00-17.00 and 22.00 h.

Nine adult asthmatics were challenged with histamine four times during the same day, at 07.00, 12.00, 17.00 and 22.00 h. A dose of histamine, which had induced a fall in FEV1 greater than 20%, when inhaled a few days before the study day, was used. The baseline values before the inhalations varied through the day. FEV1 was on average 1.9 liter at 07.00, 2.2 l. at 12.00, 2.2 l. at 17.00 and 2.0 l. at 22.00 h. The average decrease in per cent from the baseline after the inhalation of histamine was 27% at 07.00, 33% at 12.00, 29% at 17.00 and 28% at 22.00 h. A statistically significant difference in baseline FEV1 was measured during the day, but no statistically significant difference was found in the percentage decrease in FEV1 after inhalation of histamine, when measured at 07.00, 12.00, 17.00 and 22.00 h.