Passive Exhalation Technique Correlates with Esophageal Balloon Measurements of Respiratory Mechanics in Beagle Pups

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Abstract
We correlated respiratory system mechanics measured by passive exhalation technique with pulmonary mechanics assessed by esophageal balloon technique to determine the ability of each to detect histamine-aerosol-induced changes in conductance and compliance. Eight beagle pups were anesthetized with chloralose and mechanically ventilated 6 times over a 2-wk period of an acute canine parainfluenza II infection. Measurements of respiratory mechanics were obtained by both methods after aerosol challenge with 5 breaths of saline and after each of 9 increasing doses of histamine. Pulmonary conductance and static compliance of the lung were measured by the esophageal balloon method. The rate constant of the respiratory system was calculated by computer-assisted analysis of passive exhalation. Static compliance of the respiratory system was measured after 2 s of apnea, and conductance of the respiratory system was calculated as compliance multipled by rate constant. Paired data were obtained on 349 measurements. As expected, both conductance and complicance decrease significantly (p < 0.05) after histamine aerosol challenge by both techniques. Rate constant did not change significantly by either method. The 2 techniques were highly correlated (p < 0.001) for conductance (r = 0.76), compliance (r = 0.94), and rate constant (r = 0.66). We conclude that analysis of respiratory mechanics using the passive exhalation method correlates well with esophageal balloon data. Furthermore, passive exhalation techniques are technically simple and can detect changes in respiratory mechanics associated with histamine challenges.

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