The Bronchial Response, but not the Pulmonary Response to Inhaled Methacholine Is Dependent on the Aerosol Deposition Pattern: Radionuclide Imaging
The radioactivity deposited in the lungs was recorded by means of a gamma-camera (Picker SX300, Nuclear Diagnostics, United States). Data were recorded in a 64X64 matrix, and the total activity as well as counts per pixel were recorded in areas corresponding to the lung fields. Regions of interest were defined and selected from the stored images. The regions corresponded to the lower part of trachea and the main bronchi, as well as to two equally large areas of each of the two peripheral lung fields (each 6X10 pixels). The mean counts per pixel were recorded and the areas were postulated to represent radioactivity per tissue unit in central or peripheral airways. A penetration index was formed according to previously published principles by calculating a ratio between the number of counts per pixel in the regions of interest corresponding to the peripheral airway or the trachea and central bronchi. An example of a recorded image is given in Figure 1.
The lung function variables were assessed at baseline before the bronchial challenge, and immediately after, 30 min, and 120 min after the inhalation of the radio-labeled methacholine. Measurement of sGaw was chosen as an estimate of the responses exerted by the central airways, instead of forced expiratory volumes, to avoid interference with lung volume history. canadian neighbor pharmacy online
Specific Airway Conductance (sGaw): This was assessed by a constant volume body plethysmograph (Jager Masterlab Bodypl-ethysmograph, Germany) during tidal breathing. Previously published reference values were used.
Ventilation Perfusion Relationship: Arterial blood gases and ventilation-perfusion relationship (Va/Q) were postulated to be sensitive to functional changes in the peripheral sections of the airways. Va/Q was assessed by the multiple inert gas elimination technique. Arterial blood and expired gas samples were collected and inert gas concentrations were analyzed by gas chromatography. The dispersions of the perfusion and ventilation on different Va/Q ratios are expressed as the logarithmic SD of the perfusion and ventilation distribution, respectively (log SDQ and log SDV). Log SDQ and log SDV are thereby expressing the degree of overall ventilation-perfusion mismatch.
Blood Gas Analyses: Two milliliters of arterial blood was withdrawn for determination of oxygen and carbon dioxide tensions (PaC>2 and РаСОг) and pH in each measurement. Standard electrode techniques were used for the analyses (Model ABL 2, Radiometer, Denmark).
Figure 1. Example of an image recorded over the lung of one of the patients after inhalation of identical doses of radio-labeled methacholine deposited preferentially in the central (a) or the peripheral (b) airways.