Quantification of lung microvascular injury with ultrasound

Quantification of water and solute exchange rates across the lung microvascular barrier (LMB) may be an important early-warning indicator of pulmonary microvascular diseases such as acute respiratory distress syndrome. Our objective was to determine the degree to which osmotic water movement across the LMB induced by injection of hypertonic solutions of NaCl and glucose could be detected downstream from the lung with a specialized ultrasonic velocity (USV) transducer manufactured by Transonic Systems. We hypothesized that mathematical modeling of the osmotic transients (OT) would yield estimates of osmotic exchange parameters that were sensitive to microvascular injury. Two groups of six dogs were studied under baseline conditions and after injury with high dose (HD) or low dose (LD) oleic acid. Osmotic conductances (sigmaK(1), sigmaK(2)), and volumes (V(1), V(2)) of two extravascular spaces were estimated by fitting the mathematical model to the OT data. HD results (mean +/- standard error) indicated a significant decrease (by paired t test) in sigmaK(1) from 1.59 +/- 0.09 to 1.04 +/- 0.015 [ml h(-1) (mosm/l)(-1) g(-1) WLW)], an increase in sigmaK(2) from 0.20 +/- 0.08 to 0.32 +/- 0.12 [ml h(-1) (mosm/l)(-1) g(-1)], and a significant increase in V2 from 23.26 +/- 2.51 to 78.0 +/- 15.23 (ml) for NaCl injections. LD V2 estimated from NaCl increased significantly from 21.57 +/- 2.15 to 37.59 +/- 2.36 (ml), sigmaK2 increased from 0.09 +/- 0.03 to 0.17 +/- 0.04 and no significant change in sigmaK(1) was found. Baseline glucose sigmaK(1), sigmaK(2), and V1 in the LD series were 2.08 +/- 0.18, 0.64 +/- 0.19 [ml h(-1) (mosm/l)(-1) g(-1)] and 13.08 +/- 1.89 (ml), respectively, and did not change significantly with injury. We conclude that OT data measured by USV is a sensitive and informative indicator of LMB osmotic properties, and may be useful for quantification of LMB permeability changes due to acute injury. We further conclude that V(1) represents microvascular endothelial volume and V(2) is an estimate of interstitial volume.