Previous studies in humans have shown that gravity has little influence on the distribution of lung blood flow while changing posture from supine to prone. This study aimed to evaluate the maximal influence of posture by comparison of regional lung blood flow in the upright and head-down posture in 8 healthy volunteers, using a tilt table. Regional lung blood flow was marked by i.v. injection of macroaggregates of human albumin labeled with 99mTc or 113mIn, in the upright and head-down posture respectively, during tidal breathing. Both radiotracers remain fixed in the lung after administration. The distribution of radioactivity was mapped using quantitative SPECT corrected for attenuation and scatter. All images were obtained supine during tidal breathing. A shift from upright to the head-down posture caused a clear redistribution of blood flow from basal to apical regions. We conclude that posture plays a role for the distribution of lung blood flow in upright humans, and that the influence of posture, and thereby gravity, is much greater in the upright and head-down posture than in horizontal postures. However, the results of the study demonstrate that lung structure is the main determinate of regional blood flow and gravity is a secondary contributor to the distribution of lung blood flow in the upright and head-down positions.
- Inverse upright
- tilt table
- Copyright © 2015, Journal of Applied Physiology