Alveolar air-tissue interface and nuclear magnetic resonance behavior of lung.
Inflated lungs are characterized by a short nuclear magnetic resonance (NMR) free induction decay (rapid disappearance of NMR signal), likely due to internal (tissue-induced) magnetic field inhomogeneity produced by the alveolar air-tissue interface. This phenomenon can also be detected using temporally symmetric and asymmetric NMR spin-echo sequences; these sequences generate a pair of NMR images from which a difference signal (delta) is obtained (reflecting the signal from lung water experiencing the air-tissue interface effect). We measured delta in normal excised rat lungs at inflation pressures of 0-30 cmH2O for asymmetry times (a) of 1-6 ms. Delta was low in degassed lungs and increased markedly with alveolar opening when measured at a = 6 ms (delta 6 ms); delta 6 ms varied little during the rest of the inflation-deflation cycle. Delta 1 ms (a = 1 ms) did not vary significantly on inflation and deflation. Measurements of delta at a = 3 and 5 ms generally lay between those of delta 1 ms and delta 6 ms. These findings, which are consistent with theoretical predictions, suggest that measurements of delta at appropriate asymmetry times are particularly sensitive to alveolar opening and may provide a means of distinguishing alveolar recruitment from alveolar distension in the pressure-volume behavior of the lung.
Cutillo
A G
AG
Department of Internal Medicine, University of Utah, Salt Lake City.
Ganesan
K
K
Ailion
D C
DC
Morris
A H
AH
Durney
C H
CH
Symko
S C
SC
Christman
R A
RA
D000388:Air; D000818:Animals; D001834:Body Water / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D008176:Lung Volume Measurements; D009682:Magnetic Resonance Spectroscopy; D011312:Pressure; D011650:Pulmonary Alveoli / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains