Large capillary fluid permeability in skeletal muscle and skin of man as a basis for rapid beneficial fluid transfer between tissue and blood

Abstract

Our previous studies strongly indicate that the capillary filtration coefficient (CFC) in skeletal muscle and skin of man is much larger than previously believed, or about 0.050 ml min-1 100 ml-1 mmHg-1. The hypothesis that this large capillary fluid permeability is a factor of primary importance for plasma volume control was approached. Experimental hypovolaemia induced by lower body negative pressure (LBNP of 70-95 cmH2O) was associated with a rapid net fluid gain from the studied upper arm into the circulation of 0.17 ml min-1 100 ml-1 tissue. The transcapillary driving force for this fluid transfer, probably caused by adrenergic adjustment of vascular resistance, with a decline of capillary pressure, was relatively small, or 1.7 mmHg on average. CFC was instead very high during LBNP, increasing from a control value of 0.054 +/- 0.004 (SE) to no less than 0.097 +/- 0.007 ml min-1 100 ml-1 mmHg-1, probably reflecting an increased number of effectively perfused capillaries. It is suggested that the large capillary fluid permeability in skeletal muscle and skin of man, with large tissue mass and fluid reservoir, may be of great functional importance for plasma volume control after blood loss and also in other (patho)physiological situations. As demonstrated, it can thus permit rapid transfer of large fluid volumes into the circulation and, perhaps of special importance, with only small transcapillary driving force (capillary pressure decline).(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced capillary hydraulic conductivity in skeletal muscle and skin in Type I diabetes: a possible cause for reduced transcapillary fluid absorption during hypovolaemia

“…The piston recorder was placed in an airtight plastic box, in which a defined and stable negative pressure could be applied and transmitted through the piston to the plethysmograph. Thus, this experimental setup allowed changes in tissue volume to be measured simultaneously with the application of negative pressure in the plethysmograph [3].…”

“…After the discontinuation of negative pressure, arm volume gradually returned to baseline within 20 min. After 30 min, central hypovolemic circulatory stress with a concomitant sympathetic stimulation was instituted with the aid of LBNP (60 cm H 2 0), during which CFC (CFC LBNP ) was measured in the arm [3]. The LBNP was applied when the upper arm volume was stable and was maintained for 13 min.…”

“…The LBNP was continued after the CFC manoeuvre for an additional 5 min now with atmospheric pressure in the arm plethysmograph and then discontinued. The change in the transcapillary fluid absorption slope created by the applied negative pressure in the plethysmograph was divided by the applied negative pressure in the plethysmograph and was taken as CFC LBNP [3]. The transmural driving force was calculated from the fluid absorption curve after CFC LBNP divided by CFC LBNP .…”

“…The CFC and blood volume capacitance responses in the upper arm were measured using a volumetric technique [3]. The air-filled plethysmographs we used were cylindrical, 8 cm long and made of 3.5 mm thick transparent plastic.…”

“…This fluid shift has been shown to have a major effect on early plasma volume restitution during rapidly started hypovolaemic circulatory stress [2,3]. The fluid absorption is caused by a sympathetic a-mediated and b-mediated decrease in capillary pressure and is enhanced by a concomitant increase in capillary surface area available for fluid transfer [3±5].…”