Acute Cerebral Ischaemia: Concurrent Changes in Cerebral Blood Flow, Energy Metabolites, pH, and Lactate Measured with Hydrogen Clearance and³¹P and¹H Nuclear Magnetic Resonance Spectroscopy. II. Changes during Ischaemia

Abstract

Summary: CBF has been measured with the hydrogen clearance technique in the two cerebral hemispheres of the gerbil under halothane anaesthesia. This has been correlated with changes in local pH, tissue lactate, and phosphorus energy metabolites measured in the same an imals with lH and 31p nuclear magnetic resonance spec troscopy. We demonstrate a threshold flow value for the The metabolic changes that are associated with reduced CBF have been extensively studied by many workers (Siesj6, 1978). When the flow falls sufficiently, there is a decline in high-energy phos phates, an increase in inorganic phosphate (P), an increase in lactate, and a decline in pH, and the time courses of these changes in acute ischaemia have been well documented in a number of animal models. However, much remains to be learned about the precise relationship between flow, energy consumption, and metabolic state. For example, can we define a critical threshold value of flow at which the energy status of the brain tissue becomes impaired, and how does this relate to thresholds for brain function? The results of Eklof and Siesj6Received December 11,1986; accepted February 20,1987 394 metabolic changes associated with energy failure at a level similar to the values previously reported for elec trical failure and tissue water accumulation, but higher than that associated with breakdown of extracellular po tassium homeostasis.

Assessment of Postischemic Cerebral Energy Metabolism in Cat by 31P NMR: The Cumulative Effects of Secondary Hypoxia and Ischemia

“…2), consistent with a finding in gerbil by Naritomi et al (1988), before there was an appreciable decline in the ATP. Thus, in contrast to the previous indirect conclusion of Crockard et al (1987), it seems that EEG activity does not fail be cause energy in the form of ATP is not available.…”

Alterations in Cerebral Blood Flow and Phosphorylated Metabolites in Piglets during and after Partial Ischemia

“…min-' -100 g-' was associated with failure to maintain control levels of cerebral high energy metabolites. This CBF is higher than the critical flow threshold for energy failure in adult animals of other species such as gerbils (13,14). When expressed as a relative reduction in CBF, energy failure in piglets occurs at similar flow decrements as in adult rats (10) and gerbils (14).…”

“…Recently combined CBF and 31P NMR measurements have established that the flow threshold for energy failure is in the range of 12-20 ml . min-' -100 g-I in adult gerbils ( 13,14).…”

Acute Cerebral Ischaemia: Concurrent Changes in Cerebral Blood Flow, Energy Metabolites, pH, and Lactate Measured with Hydrogen Clearance and31P and1H Nuclear Magnetic Resonance Spectroscopy. III. Changes following Ischaemia

“…This can be attributed to a distribution of pH; the effect is most apparent in the spectrum obtained after 7 min of recovery, when the Pi linewidth would correspond to a pH range of �0.5 units. This pH distribution could reflect a mixture of effects, including tissue heterogeneity, variability between the different animals, and pH changes occurring during the course of the 2-min spectral acquisitions [for further discussion of the effects of tissue heter ogeneity, see Crockard et al (1987)]. Thus, the ab solute differences in pH «0.2 pH units) between the NMR data and the data of Smith et al (1986) are small and not unexpected, given the different methodologies; in fact, the NMR measurements tend to validate the indirect, calculated pH data.…”