No abstract

Regional and total gastrointestinal (GI) blood flow, O2 delivery, and whole-gut O2 extraction and O2 consumption were measured before and 30, 60, and 120 min after feeding in nonanesthetized, awake 2-day-old piglets. Cardiac output and blood flow to kidneys, heart, brain, and liver were also determined. Blood flow was measured using the radiolabeled microsphere technique. In the preprandial condition, total GI blood flow was 106 +/- 9 ml X min-1 X 100 g-1, while O2 extraction was 17.2 +/- 0.9% and O2 consumption was 1.99 +/- 0.19 ml O2 X min-1 X 100 g-1. Thirty minutes after slow gavage feeding with 30 ml/kg artificial pig milk, O2 delivery to the GI tract and O2 extraction rose significantly (P less than 0.05) by 35 +/- 2 and 33 +/- 2%, respectively. The increase in O2 delivery was effected by a significant increase in GI blood flow, which was localized to the mucosal-submucosal layer of the small intestine. O2 uptake by the GI tract increased 72 +/- 4% 30 min after feeding. Cardiac output and blood flow to non-GI organs did not change significantly with feeding, whereas arterial hepatic blood flow decreased significantly 60 and 120 min after feeding. The piglet GI tract thus meets the oxidative demands of digestion and absorption by increasing local blood flow and tissue O2 extraction.

ABSTRAm. The acute effects of normoxemic hypocarbia and hypercarbia were examined in six newborn piglets. Brain blood flow was maintained during hypocarbia until extremely low Paco2 ( 4 5 mm Hg) levels were achieved at which time total brain and cerebral blood flow decreased significantly from baseline values. Blood flow to the thalamus, cerebellum and brain stem was unchanged from baseline conditions during hypocarbia. This suggests that the newborn brain is relatively insensitive to moderate degrees of hypocarbia. Extreme hypocarbia (Paco, e l 5 mm Hg) was associated with a significant increase in heart rate, accompanied by a significant decrease in mean arterial blood pressure; however, cardiac output was not significantly different from baseline determinations. Hypercarbia with normoxemia was associated with significant increases in total brain blood flow, with greater blood flow to the brain stem, cerebellum, and thalamus than to the cerebrum. The percentage of cardiac output received by the brain was also significantly increased, although total cardiac output was unchanged. This demonstrates that the newborn cerebral vasculature is sensitive to hypercarbia and that regional differences in sensitivity may account for the greater increments in blood flow to the caudal portions of the brain than that to the cerebrum. (Pediatr Res 18:1132-1136, 1984) Hyperventilation to extremely low Paco2 levels has been advocated as a form of therapy for pulmonary vasospasm in the human neonate (7,22). Hyperventilation has also been used in adults as a method of restoring autoregulation of the brain blood flow following brain injury (21). In the adult, there is no further reduction in cerebral blood flow below carbon dioxide tensions of approximately 20 mm Hg, presumably because ischemia induces metabolic changes in the brain that ovemde the C02 control of the cerebral vasculature (3,10,26 species whose brain maturation differs significantly from that of the term human neonate. The maturation of the newborn piglet brain is comparable to a human infant of 36-38 wk gestation (6, 23). Therefore, we utilized the newborn piglet to assess the acute effects of variations in Paco2 on brain blood flow and cardiac output, with a comparison of regional blood flow within the brain and the percentage of cardiac output received by the brain during hypo-and hypercarbia. MATERIALS AND METHODSSix, 1-to 4-day-old farm-bred piglets were subjects of this study. All piglets remained with the sows until the morning of the study. The weight of the piglets was 1.52 & 0.42 kg (mean +. SD).surgical procedures. All surgical procedures were performed under nitrous oxide inhalation anesthesia with local anesthesia using 1% xylocaine. A tracheotomy was performed and the piglets were ventilated with a pressure-limited Amsterdam infant ventilator using a gas mixture of 70% nitrous oxide and 30% oxygen. Polyvinyl catheters (OD127 ID86) were placed in the left axillary artery, abdominal aorta via the femoral artery and inferior vena cava via the femoral ...