Very rapid net transcapillary fluid absorption from skeletal muscle and skin in man during pronounced hypovolaemic circulatory stress

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Abstract
High levels (11-120 cmH2O) of lower body negative pressure (LBNP) were used in male volunteers (n=7) to produce pronounced hypovolaemic circulatory stress in an attempt to reveal the potential in man for compensatory absorption of extravascular fluid from skeletal muscle and skin as studied in the upper arm by plethysmographic technique. LBNP evoked clear-cut hypovolaemic symptoms or even accidental syncope as well as a marked tachycardia response and a significant fall in systolic blood pressure. In the studied arm there was concomitantly a very rapid net transcapillary absorption of extravascular fluid into the circulation at an average rate of 0.35 ml min-1 100 ml-1 soft tissue during 5 min of LBNP exposure. These data demonstrate an amazingly great potential to increase plasma volume by ''autotransfusion'' of fluid from tissue to blood, as may be visualized by extrapolation of the data from the arm to apply to the whole mass of skeletal muscle and skin in the body. The observed absorption rate would then correspond to a total fluid gain of no less than 700 ml within a period no longer than 5 min. At present, however, there is no evidence to indicate that such impressive fluid volumes can be rapidly transferred from the extra- to the intravascular space after actual blood loss.