Dynamics of the plasma-interstitial fluid distribution and transcapillary pressure difference.

The relationship between the effective intracapillary pressure and the effective pericapillary pressure following blood withdrawal and retransfusion was studied. Change in the effective pericapillary pressure was estimated from the transcapillary pressure difference determined from the amount of transcapillary fluid shift and the effective intracapillary pressure. The estimated alteration in the effective intracapillary pressure ranged from 1 to 7 mmHg in blood withdrawal and retransfusion (15% of estimated blood volume). The transcapillary pressure difference, or effective pressure gradient for fluid movement between intracapillary and pericapillary space, was within about 0.5 mmHg when the whole body filtration coefficient obtained by us was used. The effective pericapillary pressure closely followed the effective intracapillary pressure. In other words, change in intracapillary pressure elicits a rapid shift of vascular or interstitial fluid and the effective pericapillary pressure equilibrates rapidly with the intracapillary pressure.