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  • Title: Effects of hemorrhagic hypotension on cerebral blood flow and perfused capillaries in newborn pigs.
    Author: Anwar M, Agarwal R, Rashduni D, Weiss HR.
    Journal: Can J Physiol Pharmacol; 1996 Feb; 74(2):157-62. PubMed ID: 8723028.
    Abstract:
    We examined the effect of hemorrhagic hypotension on cerebral blood flow and perfused capillaries in newborn pigs, 2-10 days old. Cerebral blood flow was measured by using radioactive microspheres, perfused capillaries were determined by infusing a plasma marker, fluorescein isothiocyanate (FITC) - dextran (molecular mass 147,000 Da), and total capillaries were determined by staining with alkaline phosphatase. Rapid removal of 66 +/- 16 mL of blood resulted in a fall in mean blood pressure from 68 +/- 6 to 31 +/- 4 mmHg (1 mmHg = 133.3 Pa), an increase in heart rate from 137 +/- 18 to 240 +/- 34 beats/min, and a drop in arterial pH from 7.33 +/- 0.05 to 7.23 +/- 0.07. PCO2 was controlled by mechanical ventilation (36 +/- 4 mmHg before hemorrhage and 35 +/- 5 mmHg after hemorrhage) and PO2 remained stable (89 +/- 11 mmHg before hemorrhage and 94 +/- 10 mmHg after hemorrhage). Blood flow (n = 9) did not fall significantly in any brain region after hemorrhage. The percentage of perfused capillaries/mm2 (control, n = 7, hemorrhage, n = 6) was reduced in all brain regions during hypotension (cortex from 72 +/- 8 to 57 +/- 8%, cerebellum from 75 +/- 10 to 52 +/- 10%, and medulla from 76 +/- 8 to 51 +/- 9%). Similar results were seen for perfused capillary surface area We conclude that hemorrhagic hypotension resulted in a variable blood flow response with no significant reduction in cerebral blood flow but a reduction in perfused capillary number and surface area in all brain regions studied. We speculate that decreased capillary perfusion may be a contributing factor in diffuse neuronal injury after severe hemorrhagic hypotension.
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