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To the Editor:—
The problem that Dr. Ream presents has not been solved to everyone's satisfaction at the present time. There are certainly profound anatomical changes in the lung bases in mitral stenosis, but the mechanisms by which these anatomic changes occur are not readily defined. If the response of the pulmonary bed is differentially under active vascular control, this cannot be readily demonstrated. It is likely that these changes take considerable time to evolve and that venous pressure reasonably plays a role in the development of these anatomical changes. Certainly, in a normal lung, there is absent apical perfusion in the seated or erect position but this does not result in profound anatomic changes in the basal portions of the lung. The distribution of pulmonary blood flow is gravity dependent, and this can be demonstrated readily by the observations of pulmonary blood flow distribution during acceleration in which the
Steiner SH, Quinn JL. Cardiovascular Hemodynamics. JAMA. 1968;204(8):742. doi:10.1001/jama.1968.03140210098038