Laser-Doppler measurement of tracheal mucosal blood flow: Comparison with tracheal arterial flow

Blood flow in the tracheal mucosa (Q̇m) has been measured by laser-Doppler flowmetry in anesthetized sheep and dogs. The values have been compared with tracheal arterial inflow (Q̇tr) by use of an electromagnetic flow probe and with tracheal arterial perfusion pressure (Ptr) produced by mechanical perfusion. Changes in blood flow were caused by injections of methacholine, phenylephrine, and histamine into the perfusion circuit. These interventions produced a range of measurements for each animal. Correlations of Q̇m against Q̇tr were significant in two of five animals (R = 0.03-0.03); correlations of Q̇m against Ptr were significant in two of four animals (R = 0.56-0.96). Percent changes in Q̇tr were generally much larger than those of Q̇m, and there was considerable variability between Q̇m and either Q̇tr or Ptr. Q̇m reflected the same vascular changes as Ptr or Q̇tr in 28 interventions and showed an opposing change in 4 cases. In 11 interventions, changes measured by Ptr or Q̇tr were not reflected by any changes in Q̇m. Thus qualitative changes in tracheal perfusion measured with these methods were usually the same; quantitatively the three methods showed great differences. These differences may reflect different regulatory mechanisms in various components of the tracheal vasculature or different technical aspects of the methods used.