Relationship of somatosensory evoked potentials and cerebral oxygen consumption during hypoxic hypoxia in dogs.

Abstract

The effects of hypoxic hypoxia on cerebral hemodynamics and somatosensory evoked potential (SEP) were studied in 10 pentobarbital anestheteized dogs. Cerebral blood flow (CBF) was measured using the venous outflow technique and cerebral oxygen consumption (CMRO2) was calculated from the arterio-cerebro-venous oxygen difference times CBF. SEP was evaluated by percutaneous stimulation of an upper extremity nerve and was recorded over the contralateral somatosensory cortex. The latencies of the initial negative wave (N1), second positive wave (P2) and the amplitude of the primary complex (P1N1) were measured. Animals were breathed sequentially with oxygen concentrations of 21, 10, 6, 5, and 4.5% for five minutes each. Animals were returned to room air breathing when the amplitude of the SEP decreased to less than 20% of control and were observed for 30 minutes following reoxygenation. Severe hypoxia (4.5% O2) increased CBF to 200% of control, decreased CMRO2 to 45% of control, decreased amplitude and increased latency of SEP. Following reoxygenation, as CMRO2 increased toward control, latency of SEP decreased and amplitude increased and CBF returned to baseline within 30 min. During hypoxia and reoxygenation, the latencies of N1 and P2 and the amplitude of P1N1 were correlated with CMRO2 in individual animals. We conclude that changes in SEP amplitude and latency reflect changes in CMRO2 despite high CBF during rapidly progressive hypoxic hypoxia and following reoxygenation.

Effect of lidocaine on somatosensory evoked response and cerebral blood flow after canine cerebral air embolism.

“…We therefore refer the amplitude measurement from the latency of the baseline peak to the next most negative peak; this amplitude has been shown to correlate with cerebral blood flow of 0.1-0.2 ml/g tissue per minute 1617 and with the metabolic rate of glucose utilization. 18 The loss of amplitude of the SSEP also correlates with poor prognosis for clinical recovery after stroke in primates. 19 After clipping the rat middle cerebral artery, SSEP amplitude correlates better with white matter edema; this may be due to the pattern of collateral flow in those models and would not apply to the situation of multiple microemboli.…”

Somatosensory Evoked Potential and Brain Water Content in Post-Asphyxic Immature Piglets

“…In group 4, cerebral blood flow was measured by the radio labeled microsphere technique, and cerebral O 2 consumption was calculated using sagittal sinus O 2 content measurements as previously described (18,19). SEP (Cadwell Quantum 84, Cadwell Laboratory, Kennewick, WA, and Nicolet Spirit Evoked Potential System, Nicolet Instrument Corp. , Madison, WI) were measured as previously described (5,6,20) . Measurements were made simultaneously with blood sampling.…”

“…Depressed SEP amplitude may be associated with impaired cortical neuronal generators of evoked potentials. During the onset of ischemia or severe hypoxemia, alterations in SEP occur at criticall y low levels of cerebral blood flow and oxygen delivery (3,4) that correlate with inability to maintain cerebral oxygen consumption (5,6). In addition to being a sensitive indicator of anoxia in somatosensory cortex, SEP is also influenced by subcortical above baseline.…”

Cerebral Tolerance of Hypoxia in Growth-Retarded and Appropriately Grown Newborn Guinea Pigs

“…Evoked potentials have been used to detect and quantify changes during hypoxia (27)(28)(29) and in growth-retarded infants (1 1, 12). We used the amplitude of the contralateral primary response as the measure of functional cerebral integrity.…”

“…This could reflect an adaption to the process of growth retardation which is also indicated by the ability of the growthretarded human fetus and neonate to adapt its circulation favoring the brain (3 1). SEP has been shown to closely reflect CMRO2 in hypoxic hypoxia (28,29). When multiple regression analysis was applied the SEP response to hypoxia was shown to be dependent on weight but not on blood pressure.…”