Kirsch KA, J Merke, H Hinghofer-Szalkay
Fluid volume distribution within superficial shell tissues along body axis during changes of body posture in man. The application of a new miniature plethysmographic method
Pflügers Arch. 1980; 383: 195-201
In up to six different sites along the body axis during tilting manoeuvres, volume shifts into or out of superficial tissues were followed with a newly developed miniature plethysmograph.
A region was localized where no or only minor volume changes during the tilt table experiments occurred. This region is identical with the Hydrostatic Indifferent Point (HIP) being localized below the apex of the heart in the upper third of abdominal vena cava. Above the HIP fluid is drained out off the tissues during assumption of upright posture whereas below the HIP fluid volume is pooled.
The volume changes occurred in two phases. Within the first 5 s in the cephalad parts of the body a rapid decrease occurred, thereafter the volume remained unchanged or even increased; below the HIP within the first 5 s a large volume increase was followed by a slow continuous volume increment.
The functional peculiarities of the low pressure system as a whole were visible studying only superficial shell tissues of the body with the non invasive miniature plethysmographic technique.