The Bronchial Response, but not the Pulmonary Response to Inhaled Methacholine Is Dependent on the Aerosol Deposition Pattern: Comment
Similar to the conditions reported there, we postulated that mixing of the two water-soluble compounds, methacholine and DTPA, was homogeneous, both in the nebulizing chamber and in the separate aerosol particles. We, therefore, assumed that the differences in amounts of methacholine deposited within the various sections of the airways were proportional to the differences in counts per pixel recorded by the gamma camera over the corresponding regions. The surface area facing the air is much larger in the peripheral than in the central parts of the airways, and, consequently, the local drug concentration per unit area of the peripheral airway mucosa would be much lower. Furthermore, only the surface area of trachea and central airways may be similar in the two experiments, while the recipient surface area of the peripheral parts of the airways may vary largely dependent on a number of factors, such as transient airway constriction and mucous plugging. Comparisons of local drug concentrations on mucous membranes via estimations by means of the method we used, therefore, may be hazardous, at least when performed in the peripheral airways. Buy Flovent Inhaler
Ventilation perfusion relationships (ie, log SDQ) and arterial oxygenation (РаОг) were also affected by the methacholine provocation, but, in contrast to sGaw, there was no difference in the response whether the deposition was in central or peripheral airways. This may appear surprising, since it is generally held that gas exchange impairment is caused mainly by peripheral airway dysfunction. However, canine experiments on airway occlusion by means of balloon catheters and beads implanted in the bronchial tree have shown that the Va/Q mismatch becomes more severe with a larger obstructed airway. This may indicate that hypoxic pulmonary vasoconstriction is more effective the smaller the region of lung involved.