Effect of Pulmonary Edema on Tracheal Diameter

Abstract

Background: Though it is well known that cardiogenic and noncardiogenic pulmonary edema can cause changes in lung mechanics, actual alterations in tracheal diameter have not been described. Objective: To evaluate the effects of pulmonary edema induced by increased left atrial pressure (cardiogenic) and Perilla ketone (PK; noncardiogenic) on tracheal diameter in chronically instrumented awake sheep. Methods: We investigated the effects of two mechanistically distinct types of pulmonary edema on tracheal diameter in chronically instrumented awake sheep. Cardiogenic pulmonary edema (analogous to congestive heart failure in humans) was induced by increasing left atrial pressure (↑P_LA) by inflating the balloon on a Foley catheter positioned in the mitral valve annulus to cause partial obstruction to flow across the valve (n = 18). Noncardiogenic pulmonary edema (increased pulmonary microvascular permeability pulmonary edema analogous to the acute respiratory distress syndrome in humans) was produced by the intravenous administration of PK (n = 11). Lateral chest radiographs (CXRs) were scored by a standardized 5-point scoring system for the severity of pulmonary edema, and tracheal diameter was measured at a fixed location in the carina. Three radiologists, blinded to sheep identification number and experimental protocol, evaluated the radiographs independently at different points in time for edema severity and tracheal diameter. The sheep were sacrificed immediately after the final CXR, and wet/dry lung weight ratio (W/D ratio) was determined. Results: Both ↑P_LA and PK were associated with statistically significant tracheal narrowing (↑P_LA: 20.3 ± 0.6 to 15.1 ± 0.9 mm; PK: 20.2 ± 0.6 to 14.1 ± 1.4 mm). Tracheal narrowing correlated with the severity of the pulmonary edema determined radiographically (↑P_LA: r = –0.69, p < 0.01; PK: r = –0.62, p < 0.01) and by W/D ratio (↑P_LA: r = –0.64, p < 0.05; PK: r = –0.54, p < 0.05). Conclusions: We conclude that tracheal narrowing occurs in sheep models of both cardiogenic and noncardiogenic pulmonary edema and that the degree of narrowing correlates with the severity of the edema.