Methodological Requirements for Accurate Measurements of Brain and Body Temperature during Global Forebrain Ischemia of Rat

Abstract

Summary:The methodological requirements for accurate measurements of brain and body temperature during brain ischemia have been validated in Wistar rats submit ted to 30 min of four-vessel occlusion. During ischemia, brains were exposed to three different temperature pro files: spontaneous cooling from 36 to 31°C (n = 10), con stant hypothermia at 30°C (n = 19), and constant normo thermia at 36°C (n = 21). Direct and indirect brain tem perature recordings were carried out by placing fine thermocouples (200 !-Lm diameter) into the striate nucleus, the temporal muscle, and the epidural space. Body tem perature was measured with a flexible thermocouple in serted at various depths into the rectum. Accurate mea surements of body temperature required insertion of the The severity of brain damage after global cere brocirculatory arrest is markedly affected by slight variations of brain temperature (Busto et a!., 1987(Busto et a!., , 1989a. Investigations of ischemic injury, therefore, require precise measurements of brain temperature, particularly for the evaluation of pharmacological intervention (Buchan and Pulsinelli, 1990;Corbett et a!., 1990). A methodological problem associated with such measurements is the placement of the temperature probes. Measurements on the surface of the brain require exposure of the cortex and are greatly affected by changes in ambient temperature. Insertion of the probe into the brain produces a pen etrating lesion that may affect the ischemic injury (Takahata and Shimoji, 1986; Mushiroi et aI., 1989 817rectal probe to a depth of at least 6 cm; lesser insertion resulted in an underestimation of up to 6°C, Accurate estimates of brain temperature were obtained in all three experimental conditions by recording of the epidural tem perature. The temperature in the temporal muscle, by contrast, differed from the brain temperature by up to 2°C, depending upon the experimental condition and the duration of ischemia. We therefore suggest that indirect measurements of brain temperature during ischemia are carried out in the epidural space in order to avoid misin terpretations of temperature-sensitive pathological changes.

Theoretical simulation of temperature distribution in the brain during mild hypothermia treatment for brain injury

“…Temperature difference in the superficial brain tissue can be up to 20 °C, so that the cerebral cooling is not uniform. This agrees well with the experimental observation that large temperature variations exist in the brain tissue (KULUZ et el., 1992;MIYAZAWA and HOSSMANN, 1992). Our theoretical simulation also predicts that the thickness of the brain tissue layer with temperature variations was approximately 17 mm in both adults and infants, it agrees well with the direct intraoperative measurements showing that the brain tissue temperature is essentially the same at 20 mm beneath the cortical surface (STONE et el., 1997).…”

“…During surface cooling, ambient or brain surface temperature will produce an artifact in the brain temperature measurement if the probe is placed in the superficial region. Furthermore, it has been shown that the temporal muscle temperature underestimated brain temperature by as much as 4 °C during global forebrain ischaemia of rats (KULUZ et al, 1992;MIYAZAWA and HOSSMANN, 1992). Temporal and spatial temperature gradients in the brain during hypothermia depend on heat convection due to blood flow, heat conduction through the tissue and metabolic heat generation in the heat balance.…”

Time course of the apparent diffusion coefficient after cerebral infarction

“…For rat brain Miyazawa and Hossman [33] report that 15 min after occlusion of all cerebral arteries temperature declines 3-4°C. This drop of temperature induces ADC reduction of 30×10 -8 cm 2 /s to 40×10 -8 cm 2 /s [33]. Nevertheless reduction of ADC in the contralateral hemisphere in our study was significantly higher (100×10 -8 cm 2 /s).…”

Hypothermia Attenuates the Loss of Hippocampal Microtubule-Associated Protein 2 (MAP2) following Traumatic Brain Injury

“…Temperature was monitored continuously with a thermistor probe im planted in the temporalis muscle, a location that accu rately reflects intracerebral temperature (Busto et al, 1987). Although recent studies have demonstrated that indirect brain temperature measurements may underesti mate direct brain temperature under ischemic conditions (Miyazawa and Hossmann, 1992), we have previously demonstrated a strong correlation between temporalis muscle temperature and intracerebral temperature in this (nonischemic) fluid percussion injury model (Jiang et aI., 1991). All surgical procedures were performed under complete anesthesia induced by 2% isoflurane in a 2: 1 mixture of N20/02.…”