The Bronchial Response, but not the Pulmonary Response to Inhaled Methacholine Is Dependent on the Aerosol Deposition Pattern: Experimental Days
Methacholine was mixed with 500 MBq “mTc-DTPA and diluted with saline solution to reach the intended concentration of methacholine and a final volume of 3 ml. The relationship between the amount of radioactivity and methacholine was fixed for each individual in the two experiments. The aerosol was inhaled by tidal breathing, which was maintained during 3 min, and the inhaled doses of methacholine required to induce a 50 percent decline from the baseline values of sGaw were empirically found to correspond to around 150 percent of the cumulated doses of methacholine, found in the individual titration studies. After inhalation of the radiolabeled aerosol, an image of the radioactivity deposited within the lung was made with a gamma camera (see below), and the data were stored on disk. The stored data were then used for analyses of deposited radioactivity in defined regions of interest (see below) and for comparison of the total count rate recorded over the chest during the first and the second experimental days. canadian health mall
The patients returned for the second experiment within 3 weeks after the first one, and the individually chosen doses of radio-labeled methacholine, used in the first experiment, were nebulized by a jet nebulizer producing small particles (MAD 2, Astra, Sweden; MMAD s=2.5 mт). To further ascertain a peripheral lung-distribution pattern, delivery of a bolus of the aerosol was achieved by connecting a dosimeter (Spira electro 2, Inhalation dosimeter, Finland) equipped with a flow regulator to the inhalation circuit. The inhalation flow was set to 0.5 L/s. To achieve comparable lung doses of methacholine in the two separate experiments, the aerosols were inhaled until the total count rates recorded over the chest by the gamma camera were similar to that recorded during the first experimental day.