title: Effects of hemorrhagic hypotension on cerebral blood flow and perfused capillaries in newborn pigs.
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.
authors.affiliation: Department of Pediatrics, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway 08854-5635, USA.
authors.forename: M
authors.initials: M
authors.lastname: Anwar
authors.forename: R
authors.initials: R
authors.lastname: Agarwal
authors.forename: D
authors.initials: D
authors.lastname: Rashduni
authors.forename: H R
authors.initials: HR
authors.lastname: Weiss
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002196:Capillaries / Q000503:physiopathology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006439:Hemodynamics / Q000502:physiology; D006470:Hemorrhage / Q000150:complications / Q000503:physiopathology*; D007022:Hypotension / Q000209:etiology / Q000503:physiopathology*; D008297:Male; D008833:Microcirculation; D013552:Swine