Brain blood flow and ventilatory response to hypoxia in sedated newborn piglets

To evaluate the relationship between brain blood flow and ventilatory response to hypoxia, seventeen sedated, spontaneously breathing newborn piglets were studied. Minute ventilation (VE) was measured by pneumotachograph, cardiac output by thermodilution and total brain and brain stem blood flows with radiolabeled microspheres. Measurements were performed while the animals were breathing room air and after 10 min of hypoxia induced by breathing 10% O2. Two patterns of ventilatory response to hypoxia were observed in the study animals. All animals increased VE during the 1st min of hypoxia, but nine (mean +/- SD; age 5 +/- 1.3 d; wt 1828 +/- 437 g) sustained increased VE after 10 min of hypoxia (increases VE group). The remaining eight animals (age 5 +/- 1.2 d; wt 1751 +/- 168 g) had decreased VE at 10 min of hypoxia to values less than their room air baseline (decreases VE group). The decrease in PaO2 during hypoxia was similar in both groups, however the PaCO2 decreased significantly only in the increases VE group. Although cardiac output increased significantly during hypoxia in both groups, the values during normoxia and hypoxia were lower in the decreases VE group (p less than 0.001). Arterial blood pressure increased significantly during hypoxia only in the increases VE group. The increase in total brain and brain stem blood flows with hypoxia was similar in both groups, despite the two different patterns of ventilatory response to hypoxia. These data suggest that in this animal model the distinct patterns of ventilatory response to hypoxia are not related to the changes in total brain or brain stem blood flows that occur during hypoxia.