Exogenous endothelin-1 improves microvascular oxygen balance during focal cerebral ischemia in the rat

Local O2 Balance in Cerebral Ischemia-Reperfusion Improved during Pentobarbital Compared with Isoflurane Anesthesia

BACKGROUND

Most anesthetics affect cerebral blood flow and metabolism. We compared microregional O2 balance in cerebral ischemia-reperfusion during pentobarbital and isoflurane anesthesia.

METHODS

After 1 hour of middle cerebral artery occlusion and a 2-hour reperfusion under isoflurane (1.4%, n = 14) or pentobarbital (50 mg/kg, n = 14) anesthesia in rats, regional cerebral blood flow using (14)C-iodoantipyrine autoradiography, microregional arterial and venous O2 saturation (20-60 μm in diameter) using cryomicrospectrophotometry, and the size of cortical infarct were determined.

RESULTS

Ischemia-reperfusion decreased the average cortical venous O2 saturation in both pentobarbital and isoflurane groups (P < .0001), which was higher (P < .05) with pentobarbital despite a similar average regional cerebral blood flow and O2 consumption. The heterogeneity of venous O2 saturation reported as a coefficient of variation (100 × standard deviation/mean) was smaller (P < .005) with pentobarbital than that with isoflurane (7.5 versus 16.1). The number of veins with low venous O2 saturation (<50%) was smaller (P < .005) with pentobarbital (5 of 80 versus 24 of 80). The percentage of cortical infarct in total cortex was smaller with pentobarbital (5.2 ± 2.5% versus 12.3 ± 2.6%, P < .001).

CONCLUSIONS

In the cerebral ischemic-reperfused cortex, the average venous O2 saturation was higher, and its heterogeneity and the number of veins with low O2 saturation were smaller under pentobarbital than isoflurane anesthesia. This improvement in microregional O2 balance with pentobarbital was accompanied by the reduced cortical infarct. Our data suggest that the neurologic outcome could vary during cerebral ischemia-reperfusion depending on the anesthetics used.

Effects of dexmedetomidine on microregional O2 balance during reperfusion after focal cerebral ischemia

BACKGROUND

This study was performed to determine whether there is an association between microregional O2 balance and neuronal survival in cerebral ischemia-reperfusion using dexmedetomidine, an α2-adrenoreceptor agonist and a sedative.

METHODS

Rats were subjected to 1 hour middle cerebral artery occlusion and a 2-hour reperfusion. During reperfusion, normal saline (n = 14) or dexmedetomidine 1 μg/kg/minute (n = 14) was infused intravenously. At 2 hours of reperfusion, regional cerebral blood flow using (14)C-iodoantipyrine autoradiography, microregional arterial and venous (20-60 μm in diameter) O2 saturation (SvO2) using cryomicrospectrophotometry, and the size of cortical infarction were determined.

RESULTS

Ischemia-reperfusion decreased microregional SvO2 (52.9 ± 3.7% vs. 61.1 ± .6%, P < .005) with increased variation or heterogeneity (P < .0001) with similar regional cerebral blood flow and O2 consumption. Dexmedetomidine during reperfusion decreased the heterogeneity of SvO2 that was analyzed with an analysis of variance (P < .01) and reported as coefficient of variation (100 × standard deviation/Mean) (11.8 vs. 16.4). The number of veins with O2 saturation less than 50% decreased with dexmedetomidine (13/80 vs. 27/81, P < .01). The percentage of cortical infarct in total cortex was smaller with dexmedetomidine (8.3 ± 2.2% vs. 12.6 ± 1.5%, P < .005).

CONCLUSIONS

In the cerebral ischemic reperfused cortex, dexmedetomidine decreased the heterogeneity of SvO2 and the number of small veins with low O2 saturation suggesting improved microregional O2 supply/consumption balance. The improvement was accompanied by the reduced size of cortical infarction.

Cerebral Ischemia and Reperfusion Increases the Heterogeneity of Local Oxygen Supply/Consumption Balance

Background and Purpose—

After cerebral vessel blockage, local blood flow and O 2 consumption becomes lower and oxygen extraction increases. With reperfusion, blood flow is partially restored. We examined the effects of ischemia-reperfusion on the heterogeneity of local venous oxygen saturation in rats in order to determine the pattern of microregional O 2 supply/consumption balance in reperfusion.

Methods—

The middle cerebral artery was blocked for 1 hour using the internal carotid approach in 1 group (n=9) and was then reperfused for 2 hours in another group (n=9) of isoflurane-anesthetized rats. Regional cerebral blood flow was determined using a C 14 -iodoantipyrine autoradiographic technique. Regional small vessel arterial and venous oxygen saturations were determined microspectrophotometrically.

Results—

After 1 hour of ischemia, local cerebral blood flow (92±10 versus 50±10 mL/min per 100 g) and O 2 consumption (4.5±0.6 versus 2.7±0.5 mL O 2 /min per 100 g) decreased compared with the contralateral cortex. Oxygen extraction increased (4.7±0.2 versus 5.4±0.3 mL O 2 /100 mL) and the variation in small vein (20–60 μm) O 2 saturation as determined by its coefficient of variation (=100×SD/mean) increased (5.5 versus 10.5). With 2 hours of reperfusion, the blood flow decrement was reduced and O 2 consumption returned to the value in the contralateral cortex. Oxygen extraction remained elevated in the ischemic-reperfused area and the coefficient of variation of small vein O 2 saturation increased further (17.3).

Conclusions—

These data indicated continued reduction of O 2 supply/consumption balance with reperfusion. They also demonstrated many small regions of low oxygenation within the reperfused cortical region.

RBC velocities in single capillaries of mouse and rat brains are the same, despite 10-fold difference in body size

Employing high-speed camera laser-scanning confocal microscopy with RBC-tracking software, we previously showed that RBC velocities in intraparenchymal capillaries of rat cerebral cortex are distributed over a wide range. In the present work, we measured RBC velocities in mice, whose body weights are less than one-tenth of that of rats. In an isoflurane-anesthetized mouse, a cranial window was opened in the left temporo-parietal region. Intravenously administered FITC-labeled RBCs were automatically recognized and tracked frame-by-frame at 500fps, and the velocities of all RBCs recognized were calculated with our Matlab-domain software, KEIO-IS2. Among 15241 RBCs detected in the ROI in 21 mice, 1655 were identified as flowing in capillaries. The velocities of these RBCs ranged from 0.15 to 8.6mm/s, with a mean of 2.03+/-1.42mm/s. A frequency distribution plot showed that RBC velocities were clustered at around 1.0mm/s, tailing up to 8.6mm/s, and 59% of the RBCs in capillaries showed velocities within the range of 0.5 to 2.0mm/s. Unexpectedly, these characteristics of RBC velocities in mice were very similar to those of rats, despite differences in RBC diameter (6.0 vs. 6.5microm), body size (25 vs. 327g), heart rate (461 vs. 319bpm) and arterial blood pressure (86 vs. 84mmHg). We speculate that physical factors relating to oxygen exchange may constrain general RBC velocity in capillaries to a certain range for optimum oxygen exchange, regardless of species.