Effect of hyperventilation on oxygenation of the brain cortex of newborn piglets

Abstract

A new phosphorescence imaging method (Rumsey et al. Science Wash. DC 241: 1649-1651, 1988) has been used to continuously monitor the PO2 in the blood of the cerebral cortex of newborn pigs. A window was prepared in the skull and the brain superfused with artificial cerebrospinal fluid. The phosphorescent probe for PO2, Pd-meso-tetra(4-carboxyphenyl)porphine, was injected directly into the systemic blood. The phosphorescence of the probe was imaged, and the lifetimes were measured using flash illumination and a gated video camera. The PO2 in the blood of the veins and capillary beds of the cortex was calculated from the lifetimes. Systemic blood pressure was continuously monitored while the systemic arterial PCO2, PO2, and blood pH were measured periodically. The PO2 in the blood was quantitated for 60- to 200 microns2 regions within the image (from a total field of approximately 3 mm diam). The PO2 in the microvasculature was not uniform across the viewing field but increased or decreased in each region independently of the other regions. Thus at any point in time the PO2 in a region could be substantially above or below the average value. During hyperventilation, which lowered arterial PCO2 and increased pH of the blood, the average PO2 decreased in proportion to the decrease in arterial PCO2. For example, hyperventilation, which decreased arterial PCO2 from its normal value of 40 Torr to 10 Torr, caused a rapid (within 5 min) decrease in PO2 in the blood of capillaries and veins to approximately one-third of normal.

Fetal Hypercapnia and Cerebral Tissue Oxygenation: Studies in Near-Term Sheep

“…In addition, in the management of the premature infant "permissive hypercapnia" with mild respiratory acidosis has been anticipated to reduce the risk of periventricular leukomalacia (10,28). In contrast, accumulating evidence suggests the adverse neurologic consequences of hypocapnia, explained in part by cerebral vasoconstriction and increasing Hb O 2 affinity (21,29,30). In accordance with these findings, in the immature rat Vannucci and co-workers (31) have shown that hypercapnic (PaCO 2 ϭ 54 torr) cerebral hypoxia-ischemia was more neuroprotective than normocapnic hypoxia-ischemia, and hypocapnic hypoxia-ischemia was associated with more severe brain damage than that which is normocapnic.…”

Noninvasive measurement of microvascular and interstitial oxygen profiles in a human tumor in SCID mice.

“…Wilson and coworkers (17)(18)(19) recently pioneered a phosphorescence technique and obtained macroscopic, twodimensional images (12,000 anm x 8000 pm) of Po2 in normal and tumor tissue of anesthetized animals. We have used this technique to obtain Po2 values in single microvessels and the interstitial Po2 distribution at known distances from blood vessels with higher spatial resolution (1wl5 pm).…”

“…We report here a noninvasive microscopic approach based on a modified Algire chamber preparation in severe combined immunodeficient (SCID) mice (21) and oxygen-dependent phosphorescence quenching (17)(18)(19)43) to measure Po2 in the microvascular and interstitial space of a human tumor xenograft. Blood flow and Po2 were measured with and without anesthesia in animals breathing air or carbogen.…”

Untitled

“…Knowing that hypocapniamediated vasoconstriction is maintained in hypoxic-ischemic encephalopathy raises concerns that low PCO 2 may accentuate secondary brain injury, not only by reducing cerebral perfusion, but by reducing O 2 delivery, increasing neuronal energy demands and DNA fragmentation, and depleting neuronal energy stores [4][5][6][7]. Indeed newborn animal models demonstrate that hypocapnia reduces cerebral blood flow following asphyxia and is associated with greater brain injury than observed in either eucapnic or hypercapnic animals [8,9].…”