Heart volume during short-term head-down tilt (-6 degrees) in comparison with horizontal body position

The immediate effect of head-down tilt (5 min., -6 degrees) on heart volume was investigated in nine healthy male volunteers. Heart volumes were determined by the X-ray method of Kahlstorf and Rohrer as modified by Musshoff and Reindell. Biplane chest orthodiagrams were taken after 5 min of rest in a prone horizontal position (control values) and 5 min after tilting the examination table into a -6 degrees head-down tilt position. After 5 min head-down tilt, cardiac volumes had increased significantly (+ 5.2%). The results indicate that head-down tilt leads to an immediate increase in heart volume, which is similar in terms of elapsed time to results of immersion experiments conducted by other researchers, but not in terms of percent of increase.