The protocol used for this challenge is that described in detail by Smith and Anderson with some modifications. In brief, it was as follows. The saline aerosol was generated by a large volume ultrasonic nebulizer (Mist02gen 143A, Timeter Somerset, Penn) and patients inhaled the aerosol at their resting ventilation rate through a large two-way valve (Hans Rudolph No. 2700, Kansas City, MO). The airway response was measured using FEV,. The FEV, was measured in duplicate (Minato Autospirometer AS 500, Osaka, Japan) before challenge and 60 to 90 s after each exposure to the aerosol. The initial exposure to 4.5 percent saline aerosol was 30 s and this time was doubled to 8 min and then repeated, (1, 2, 4, 8, 8, 8 min) until at least a 20 percent reduction in FEV, was recorded or the aerosol had been inhaled for a cumulative time of 31.5 min. buy tavist online
The canister and tubing (but not the valve) of the nebulizer was weighed before and after the challenge. The total dose of aerosol delivered to the inspiratory port of the valve was divided by the total time of exposure to obtain the delivered dose per exposure.
The reduction in FEV, was expressed as a percentage of the value for FEV, measured immediately before the challenge (percent fall in FEV,). This value was plotted in relation to the dose of 4.5 percent saline aerosol delivered.
The sensitivity of the aerosol was calculated using the dose of 4.5 percent aerosol required to induce a 20 percent fall in FEV, (PD20). When the fall in FEV, was less than 20 percent but greater than 6.1 percent, the PD20 was taken as the maximum dose of aerosol delivered. When the fall in FEV, was equal to or less than the mean value of 6.1 percent observed in normal subjects the PD20 was taken as 60 ml. This value of 60 ml was taken as an estimate because the greatest volume delivered during the challenge was 56 ml.
Because a 20 percent fall in FEV, was not documented on all occasions after treatment the dose-response slope (DRS), an index of reactivity, was also calculated. This was done by taking the final percent fall in FEV, and dividing by the dose of aerosol which caused that fall. On the four occasions out of 54, the percent fall in FEV, was zero and a value of 1 percent was assigned to calculate DRS. From our laboratory data, the mean value for DRS for 65 normal subjects with a percent fall in FEV, greater than zero (95 percent confidence intervals [Cl]) is 0.225 (0.18-0.27).
The geometric mean and 95% Cl for the PD20 and DRS were calculated and compared on the five occasions using analysis of variance. Where a difference was found, a Student’s t test for paired values was used to assess the level of significance which was taken as p < 0.05. Values for the FEV, measured on each test day were compared using analysis of variance. Fold change in sensitivity (PD20) and reactivity (DRS) to 4.5 percent saline aerosol was calculated by taking the antilog of the mean of the differences of the log values for PD20 and DRS. The fold changes reported compare each visit with visit 1.