Arterial hematocrit and separation of cells and plasma in the dog kidney

Abstract

With the indicator-dilution technique, the mean transit times of cells (t_r) labeled with Cr⁵¹ and of plasma (t_pl) labeled with T-1824 or as human albumin-I¹³¹ decrease as the arterial hematocrit (Hct) decreases. The regression equations are: t_r = 0.0388 Hct + 1.73 and t_pl = 0.0596 Hct + 1.69. The separation of cells and plasma labels, as measured by the difference of the mean transit times (Δt), is also related to the hematocrit. Δt = 0.00895 Hct + 0.269. There is an excess plasma label volume of distribution per 100 g kidney, ΔV_pl, which may be intra- or extravascular. ΔV_pl = Q_rΔt (1 - Hct), where Q_r is blood flow per 100 g kidney. ΔV_pl is independent of t_r and of Hct. However, ΔV_pl increases with Q_r. ΔV_pl = 0.127 Q_r + 1.79. The hypothesis that the separation of cells and plasma results from transcapillary passage of the plasma labels is consistent with but is not established by the data.