The ratio of body haematocrit to venous haematocrit in open heart surgery and estimation of the blood volume in the large and small vessels.

Double tracer blood volume technique revealed in open heart surgery patients a wide variability of Fcells-value in about 11 per cent of cases investigated, from the "normal" 0.91 value. The possible calculational error of blood volume measurements by single-isotopic--haematocrit methods in the normal or subnormal LVH-ranges point to the superiority of plasma volume determinations in the calculation of the total blood volume. The calculation of the volume of the blood-component actually not-labelled during single-isotopic--haematocrit procedures can be so highly inaccurate because of the hidden deviation of Fcells-value, that such misleading arithmetics has no real value and therefore should be omitted. Estimation of the large vessel and small vessel volumes and haematocrits in patients showed a rough 70 per cent---30 per cent distribution of the circulating blood volume between large and small vessels and an LVH tosmall vessel haematocrit ratio of 2:1 to 2:1.5. This offers a possibility to divide the circulating blood volume into a haemodynamically active (large vessel area) and a metabolically active (small vessel area) part, which can have important diagnostic and prognostic implications.