Effect of cooling and re-warming on cerebral and whole body electrical impedance

Temperature and Frequency Dependence of Human Cerebrospinal Fluid Dielectric Parameters

Accurate human cerebrospinal fluid (CSF) dielectric parameters are critical for biological electromagnetic applications such as the electromagnetic field modelling of the human brain, the localization and intensity assessment of electrical generators in the brain, and electromagnetic protection. To detect brain damage signals during temperature changes by electrical impedance tomography (EIT), the change in CSF dielectric parameters with frequency (10 Hz-100 MHz) and temperature (17-39 °C) was investigated. A Debye model was first established to capture the complex impedance frequency and temperature characteristics. Furthermore, the receiver operating characteristic (ROC) analysis based on the dielectric parameters of normal and diseased CSF was carried out to identify lesions. The Debye model's characteristic fc parameters linearly increased with increasing temperature (R2 = 0.989), and R0 and R1 linearly decreased (R2 = 0.990). The final established formula can calculate the complex impedivity of CSF with a maximum fitting error of 3.79%. Furthermore, the ROC based on the real part of impedivity at 10 Hz and 17 °C yielded an area under the curve (AUC) of 0.898 with a specificity of 0.889 and a sensitivity of 0.944. These findings are expected to facilitate the application of electromagnetic technology, such as disease diagnosis, specific absorption rate calculation, and biosensor design.

Understanding the Full Spectrum of Organ Injury Following Intrapartum Asphyxia

Birth asphyxia is a significant global health problem, responsible for ~1.2 million neonatal deaths each year worldwide. Those who survive often suffer from a range of health issues including brain damage-manifesting as cerebral palsy (CP)-respiratory insufficiency, cardiovascular collapse, and renal dysfunction, to name a few. Although the majority of research is directed toward reducing the brain injury that results from intrapartum birth asphyxia, the multi-organ injury observed in surviving neonates is of equal importance. Despite the advent of hypothermia therapy for the treatment of hypoxic-ischemic encephalopathy (HIE), treatment options following asphyxia at birth remain limited, particularly in low-resource settings where the incidence of birth asphyxia is highest. Furthermore, although cooling of the neonate results in improved neurological outcomes for a small proportion of treated infants, it does not provide any benefit to the other organ systems affected by asphyxia at birth. The aim of this review is to summarize the current knowledge of the multi-organ effects of intrapartum asphyxia, with particular reference to the findings from our laboratory using the precocial spiny mouse to model birth asphyxia. Furthermore, we reviewed the current treatments available for neonates who have undergone intrapartum asphyxia, and highlight the emergence of maternal dietary creatine supplementation as a preventative therapy, which has been shown to provide multi-organ protection from birth asphyxia-induced injury in our preclinical studies. This cheap and effective nutritional supplement may be the key to reducing birth asphyxia-induced death and disability, particularly in low-resource settings where current treatments are unavailable.

A new method of noninvasive brain-edema monitoring in stroke: cerebral electrical impedance measurement

OBJECTIVE

To explore the primary regularity of cerebral electrical impedance (CEI) change in healthy people, patients with intracerebral hemorrhage (ICH) and patients with cerebral infarction (CI).

METHODS

CEI of 200 healthy volunteers, 78 patients with ICH and 51 patients with CI were measured by noninvasive brain-edema monitor. The results of perturbative index (PI) converted from CEI were compared with the volumes of infarction, hematoma and surrounding edema, which were calculated by image analysing system according to MRI or CT scan.

RESULTS

(1) In the normal groups, PI in the left and right sides of cerebral hemispheres was respectively 7.98 +/- 0.95 and 8.02 +/- 0.71, and there was no significant difference between the two sides (p>0.05). (2) In the patients with ICH, PI of the hematoma side initially was lower than the other side, but then increased and finally exceeded that of the other side. The average transitional time was 19.67 +/- 11.52 hours. Perturbative index of the hematoma side after the transitional time was much higher than before the transitional time in the same patients (7.79 +/- 0.75 versus 7.09 +/- 0.72) (p<0.001). The volumes of peri-hematoma edema were also significantly larger after the transitional time than before (24.32 +/- 12.86 versus 13.33 +/- 6.12) (p<0.05). There was a positive correlation between the PI of hematoma side and the volumes of peri-hematoma edema (p<0.01). (3) In the patients with arterothrombotic cerebral infarction, PI in the infarct side was higher than that in the opposite side 3-5 days after onset (8.93 +/- 1.89 versus 8.58 +/- 1.61) (p<0.001), and PI of the infarct side had a positive correlation with the volume of infarction (p<0.001). (4) The sensitivity of PI was high when the volumes of lesions were >20 ml or the position of them were located in the basal ganglia, but was low when the volumes were <20 ml or the position near the midline.

CONCLUSION

CEI may be a useful parameter for noninvasively monitoring the change of brain edema and hematoma in stroke at bedside. It could be a good complement to CT and MRI.

Bioelectrical impedance analysis for assessment of fluid status and body composition in neonates--the good, the bad and the unknown

BACKGROUND/OBJECTIVES

There is a critical need for improved technologies to monitor fluid balance and body composition in neonates, particularly those receiving intensive care. Bioelectrical impedance analysis meets many of the criteria required in this environment and appears to be effective for monitoring physiological trends.

SUBJECT/METHODS

The literature regarding the use of bioelectrical impedance in neonates was reviewed.

RESULTS

It was found that prediction equations for total body water, extracellular water and fat-free mass have been developed, but many require further testing and validation in larger cohorts. Alternative approaches based on Hanai mixture theory or vector analysis are in the early stages of investigation in neonates.

CONCLUSIONS

Further research is required into electrode positioning, bioimpedance spectroscopy and Cole analysis in order to realise the full potential of this technology.

Ordinary surface ECG electrodes accurately reflect cardiac electric activity at hypothermia

BACKGROUND

It has been claimed that needle electrodes can be a useful means to detect weak ECG signals in cases of accidental hypothermia.

METHODS

Four pigs were cooled by immersion in ice water, followed by direct cooling of the blood through an extracorporeal circulation system until the core temperature was lowered to 12 degrees C and surface-measured ECG indicated asystole. Following cooling, the pigs were rewarmed and weaned from extracorporeal circulation if possible. ECG and interelectrode impedance were measured between surface electrodes, needle electrodes and electrodes sewn to the epicardium during the cooling and rewarming procedure.

RESULTS

Needle and surface electrodes showed exactly the same ECG whatever the temperature of the skin or the core was. The impedance varied only slightly with temperature and could not explain the disappearance of surface ECG. The QRS wave amplitude showed the greatest sensitivity to temperature, disappearing completely before the P-wave disappeared. The P-wave showed the least sensitivity, and was the last wave to disappear, indicating that the sinus node is the most resistant part of the heart to cooling. Between 19 and 17 degrees C, a commercial monitor indicated asystole although P-waves could be seen in the ECG and atrial contractions could be visually observed on the heart.

CONCLUSION

Surface electrodes had a similar high accuracy to indicate electric activity as needle electrodes. Higher amplification and reduction of the timebase made it possible to detect ECG in a situation where asystole was indicated by commercial monitors.

Effects of deep hypothermic circulatory arrest with retrograde cerebral perfusion on electroencephalographic bispectral index and suppression ratio

OBJECTIVE

No systematic study has been conducted to investigate effects of deep hypothermic circulatory arrest (DHCA) on electroencephalographic bispectral index (BIS) and suppression ratio (SR). Thus, the effects of DHCA were evaluated on BIS and SR.

DESIGN

A prospective clinical study.

SETTING

University hospital (single institute).

PARTICIPANTS

Twenty consecutive patients undergoing thoracic aortic surgery using DHCA under narcotics-sevoflurane anesthesia.

INTERVENTIONS

BIS and SR were monitored during cardiopulmonary bypass, simultaneously with nasopharyngeal temperature (NPT).

MEASUREMENTS AND MAIN RESULTS

BIS decreased to 0 with induction of deep hypothermia and rose again with rewarming, although rates of BIS changes in response to cooling and rewarming varied widely among patients. Typically, BIS decreased slowly until NPT reached 26 degrees C during cooling and then it began to decrease rapidly and reached 0 at 17 degrees C, in inverse proportion to SR, which increased rapidly with deep hypothermia and reached 100% at 17 degrees C. When SR was 50% or more, BIS was determined by SR according to the expression: BIS = 50-SR/2. With rewarming, BIS rose again and returned to precooling baseline levels. Time to the beginning of the BIS recovery significantly correlated with duration of DHCA.

CONCLUSIONS

With induction of deep hypothermia, BIS decreased in a biphasic manner to 0 at rates varying among patients. With rewarming, BIS rose again at rates extremely widely varying among patients. The rate of BIS recovery was related to duration of DHCA. BIS may be capable of conveniently tracing suppression and recovery of a part of cerebral electrical activity before, during, and after DHCA.

The role of noninvasive monitoring of cerebral electrical impedance in stroke

OBJECTIVE

To explore the change regularity of cerebral electrical impedance (CEI) in the healthy people and patients with intracerebral hemorrhage (ICH) and ischemic stroke.

METHODS

CEI of 100 healthy volunteers, 52 patients with ICH and 33 patients with ischemic stroke was measured by noninvasive Brain-Edema Monitor. The results of perturbative index (PI) converted from CEI were compared with the volume of infarction, hematoma and surrounding edema, which calculated by image analyzing system according to MRI or CT.

RESULTS

In the normal groups, PI in the left and right sides of cerebral hemispheres was respectively 7.76 +/- 0.75 and 7.79 +/- 0.58, and there was no significant difference between the two sides (P > 0.05). In the patients with ICH, PI in the hematoma side decreased and was lower than the other side, and then increased gradually, finally exceeded that of the other side. The average "cross" time was (16.25 +/- 8.96) h. It showed that the volume of hematoma was no obvious change before and after the "cross" time [(31.25 +/- 21.59) vs (37.59 +/- 27.57)] (P > 0.05). However, the volume of peri-hematoma edema was significantly larger after the "cross" time than before the "cross" time [(26.35 +/- 13.96) vs (14.68 +/- 5.30)] (P < 0.05). There was a positive correlation between the PI of hematoma side and the volume of peri-hematoma edema (r = 0.8811, P < 0.01). In the patients with arterothrombotic cerebral infarction, PI in the infarct side had a positive correlation with the volume of infarction (r = 0.8496, P < 0.01).

CONCLUSIONS

CEI is a stable physical parameter reflecting the electrical character of human brain tissue. It is useful for monitoring edema and hematoma in stroke.