Lung water measurement by nuclear magnetic resonance: Correlation with morphometry

Estimates of lung water content obtained from nuclear magnetic resonance (NMR) and morphometric and gravimetric measurements were compared in normal and experimentally injured rats. Average lung water density (<(rho)over bar>(H2O)) was measured by an NMR technique in excised unperfused rat lungs (20 normal lungs and 12 lungs with oleic acid-induced edema) at 0 (full passive deflation) and 30 cmH(2)O lung inflation pressure and in vivo (4 normal rats and 8 rats with lung injury induced by oleic acid or rapid saline infusion). The <(rho)over bar>(H2O) values were compared with morphometric measurements of lung tissue volume density (V-v) obtained from the same lungs fixed at corresponding liquid-instillation pressures. A close correlation was observed between <(rho)over bar>H2O and V-v in normal and injured excised lungs [correlation coefficient (r) = 0.910, P < 0.01]. In vivo <(rho)over bar>(H2O) was also closely correlated with V-v (r = 0.897, P < 0.01). The correlation coefficients between <(rho)over bar>H2O and gravimetric lung water content (LW(Gr)) were lower in the excised lung group (r = 0.663 and 0.692, respectively, for <(rho)over bar>H2O at 0 and 30 cmH(2)O lung inflation pressure, P < 0.01) than in the in vivo study (r = 0.857, P < 0.01). Our results indicate that NMR techniques, which are noninvasive and nondestructive, provide reliable estimates of lung water density and that the influence of lung inflation on <(rho)over bar>H2O is important (compared with the effect of lung water accumulation in lung injury) only in the presence of deliberately induced very large variations in the lung inflation level.