Mismatch recovery of regional cerebral blood flow and brain temperature during reperfusion after prolonged brain ischemia in gerbils

The influence of body temperature on tissue stiffness, blood perfusion, and water diffusion in the mouse brain

While hypothermia of the brain is used to reduce neuronal damage in patients with conditions such as traumatic brain injury or stroke, little is known about how temperature affects the biophysical properties of in vivo brain tissue. Therefore, we measured shear wave speed (SWS), apparent diffusion coefficient (ADC), and cerebral blood flow (CBF) in the mouse brain at different body temperatures to investigate the relationship between temperature and tissue stiffness, water diffusion, and blood perfusion in the living brain. Multifrequency magnetic resonance elastography (MRE), diffusion-weighted imaging (DWI), and arterial spin labeling (ASL) were performed in seven mice while increasing and recording body temperature from hypothermia (28-30 °C) to normothermia (36-38 °C). SWS, ADC, and CBF were analyzed in regions of whole brain, cortex, hippocampus, and diencephalon. Our results show that SWS decreases while ADC and CBF increase from hypothermia to normothermia (whole brain SWS: -6.2%, ADC: +34.0%, CBF: +80.2%; cortex SWS: -10.1%, ADC: +30.9%, CBF: +82.4%; all p > 0.05). We found a significant inverse correlation between SWS and both ADC and CBF in all analyzed regions except diencephalon (whole brain SWS-ADC: r = -0.8, p < 0.005; SWS-CBF: r = -0.84, p < 0.005; cortex SWS-ADC: r = -0.74, p < 0.05; SWS-CBF: r = -0.65, p < 0.05). These results show that in vivo brain stiffness is inversely correlated with temperature, extracellular water mobility, and microvascular blood flow. Regional differences indicate that cortical areas are more markedly affected by hypothermia than central regions such as diencephalon. Temperature should be considered as a confounder in elastographic measurements, especially in preclinical settings. STATEMENT OF SIGNIFICANCE: Hibernating mammals lower their body temperature and metabolic activity. A hypothermic state can also be induced for medical purposes to reduce the risk of neural damage in patients with neurological disease or injury. However, little is known how physical soft-tissue properties of the in-vivo brain such as water diffusion, blood perfusion or mechanical parameters correlate with each other when temperature changes. Our study demonstrates for the first time that those quantitative imaging markers are tightly linked to changes in body temperature. While water diffusion and blood perfusion are reduced during hypothermia, brain stiffness significantly increases, suggesting that multiparametric quantitative MRI should be used for the noninvasive assessment of brain metabolic activity.

Portable system for monitoring of regional cerebral oxygen saturation during prehospital cardiopulmonary resuscitation: a pilot study

Aim

We aimed to create a system for monitoring of regional cerebral oxygen saturation (rSO ₂) in patients with prehospital cardiopulmonary arrest and clarify the changes in rSO ₂ during cardiopulmonary resuscitation.

Methods

We measured rSO ₂ in cardiopulmonary arrest patients who were transferred by the emergency response vehicle of Nagasaki University Hospital. We developed a portable rSO ₂ monitor (HAND ai TOS), which is small enough to carry during prehospital treatment. The sensor is attached to the forehead of the patient and monitors rSO ₂ continuously during treatment and transfer.

Results

No difficulties were experienced in monitoring rSO ₂ during patient treatment and transfer. Median time (interquartile range) from the emergency medical service call to emergency response vehicle arrival was 15.0 min (11.0-19.5 min). Median rSO ₂ on emergency response vehicle arrival at the scene was 46.3% (44.0-48.2%) (n = 9; median age, 74.0 years; four men, five women). Median rSO ₂ showed significant increase within 5 min after return of spontaneous circulation (n = 6, 46.6% versus 58.7%, P < 0.05). There was no significant increase in rSO ₂ during prehospital cardiopulmonary resuscitation until return of spontaneous circulation was established.

Conclusions

We developed an rSO ₂ monitoring system for use during prehospital cardiopulmonary resuscitation. The monitoring system showed a significant increase in rSO ₂ after return of spontaneous circulation, whereas there was no significant increase in rSO ₂ during cardiopulmonary resuscitation after intubation but before return of spontaneous circulation.

Ischemic pretreatment delays ischemic brain vasospasm injury in gerbils

Three experiments were conducted for the present study. First, to elucidate the mechanism and functional significance underlying ischemic vasoconstriction, we investigated the relationship between arteriolar constriction and tissue energy metabolism during bilateral common carotid artery occlusion in gerbils. Second, to identify differences in the postischemic recovery of physiologic parameters between short and prolonged brain ischemia, we measured changes in regional cerebral blood flow, microvessel diameter, brain temperature, and electrophysiologic response. Third, to explore the physiological mechanism of ischemic tolerance, we studied vascular response and intracerebral oxygenation states after acute global ischemia with and without pretreatment by mild ischemic stress. Here, we identify one of the physiologic mechanisms of the ischemic tolerance caused by brief ischemic pretreatment.

Age-dependent brain temperature decline assessed by diffusion-weighted imaging thermometry

Brain metabolism declines with age, but cerebral blood flow (CBF) is less age dependent. We therefore hypothesized that the brain temperature would decline with age, and measured the temperatures of the lateral ventricles in healthy volunteers. Diffusion-weighted imaging (DWI) data from 45 healthy volunteers [mean (± standard deviation) age, 30.6 ± 8.66 years; range, 19-56 years] were used for this study. The temperature of water molecules is directly related to the diffusion coefficient, so that the temperature of cerebrospinal fluid can be measured using DWI. Temperature was calculated using the equation, T ( °C) = 2256.74/ln(4.39221/D) - 273.15, where D is the diffusion coefficient. The lateral ventricles were manually extracted by an experienced neuroradiologist on b(0) images. The mean ventricular temperature was determined from the distribution function of the temperature of all selected voxels. The mean lateral ventricular temperature in healthy volunteers showed a linear decrease with age (correlation coefficient R(2)  = 0.8879; p < 0.01), presumably caused by an asynchronous decline in brain metabolism and CBF. DWI-based thermometry demonstrates that ventricular temperature declines with the normal aging process. Further study is warranted to define the relationships between temperature, metabolism and circulation.