Blood volume and hematocrit in various organs in newborn piglets

Plasma volume and red cell mass of various organs in piglets aged 24 hr (n = 7) and 7 (n = 6), and 14 (n = 6) days were measured using 99mTc-labeled albumin and 51Cr-labeled red blood cells. Organ activities were counted in a whole-body counter. Blood volume and hematocrit were calculated. The blood volumes in microliters/g varied markedly between various organs. The lowest blood volumes at 24 hr of age were found in skin (21.9 +/- 5.0 microliter/g), brain (33.3 +/- 8.4), and skeletal muscle (35.5 +/- 7.4). The highest values at this age were noted in liver (670.0 +/- 89.1), lung (533.8 +/- 80.7), spleen (332.0 +/- 82.8), and kidney (300.6 +/- 55.5). Blood volumes of about 150 microliters/g were observed in heart muscle and thyroid gland and those of about 100 microliters/g in thymus and gastrointestinal tract. The total blood volume was 100.2 +/- 3.9 microliters/g at 24 hr and remained unchanged during the first 2 wk of life. A significant decrease in relative blood volume with growth was noted in liver and lung (P less than 0.01), and in skeleton (P less than 0.05). The blood volume, contained in the great vessels outside the organs, increased from 29.5 +/- 5.5% of total blood volume at 24 hr to 31.2 +/- 5.7% at 7 days and to 38.2 +/- 7.5% at 14 days of life. The total body-venous hematocrit ratio was about 0.84. Accordingly, tissue hematocrits of most organs were below the venous hematocrit. Only in spleen was the tissue/venous hematocrit ratio (TH/VH) higher than 1.0. TH/VH of brain, gastrointestinal tract, thyroid gland, and thymus approached unity. The lowest TH/VH was found in kidney (0.54 +/- 0.08 at day 1). In skin, the TH/VH decreased from 0.98 +/- 0.10 to 0.82 +/- 0.07 during the first 2 wk of life.