新生猪不同程度脑缺氧与脑功能、脑损伤关系的近红外光谱研究

Correlation of brain hypoxia at different degrees with brain function and brain damage investigated using near infrared spectroscopy

目的通过检测不同程度缺氧时新生猪脑氧合的变化,研究脑缺氧程度-脑功能-脑损伤之间的规律。方法对15只新生猪检测脑组织血氧饱和度(Regional oxygen saturation,rSO_2),给新生猪机械通气吸入低浓度氧,造成脑 rSO_2不同进行分组。实验过程监测生理参数、脑电,脑损伤后72 h 进行海马 CA1区光镜及电镜检查。结果在缺氧至脑 rSO_2>40%的小猪组,缺氧后平均动脉压(Mean arterial pressure,MAP)为(56±0.00)mm Hg(1 mm Hg=0.133 kPa),血乳酸(2.3±1.2)mmol/L,脑电变化不明显,脑组织光镜、电镜无明显改变。在缺氧至脑 rSO_230%～40%时,MAP 为(73±8)mm Hg,血乳酸增高至(8.2±3.9)mmol/L,脑电观察的脑功能发生改变,但缺氧后有所恢复,脑组织光镜有缺血性改变,电镜表现为海马 CA1区神经元线粒体损伤。当缺氧至脑 rSO_2<30%时,MAP 为(35±0.00)mmHg,血乳酸增高至(12±2)mmol/L,脑电观察脑功能受损,部分在缺氧后难以恢复,光镜下细胞有空泡形成,破碎,海马 CA1区神经元线粒体严重损伤。结论在不同程度的缺氧下,当脑至 rSO_2 30%～40%时,新生猪出现脑损伤,当 rSO_2<30%,出现严重的脑损伤;rSO_2越低,脑功能、脑损害越重;无创近红外光谱检测到的脑组织 rSO_2可以在脑缺氧过程中反映脑损伤及损伤的程度。

Objective To study correlation of brain hypoxia of different degrees with brain function and damage. Methods The brain regional oxygen saturation （ rSO2 ） was determined by using a non-invasive near infrared spectroscopy （NIRS） technique in 15 piglets; the piglets were subjected to inhale 3% - 11% oxygen-nitrogen mixed gas through mechanical ventilation for 30 min. The piglets were divided into groups according to the level of brain rSO2（i.e. 〈30%, 30% -35%, 35% - 40%, and 40% - 50%）, and the data were compared with those of the control group （ rSO2 〉 60% ）. Changes of brain function were detected through amplitude and frequency of EEG waves and signal complexity. The piglets were sacrificed via decapitation 72 h after brain damage, and then histopathological and ultrastructural examinations were performed on cerebral cortex and hippocampal CA1 area. Results In the group with rSO2 〉 40%, the mean arterial pressure （MAP） after hypoxia was （56±0.00）mm Hg（ 1 mm Hg =0.133 kPa） , the blood lactic acid （LA） was （2.3± 1.2） mmol/L, the EEG findings were within normal range, and there was no change in brain tissue ultrastructure. In the group with brain rSO2 = 30% -40% , the MAP was （73±8 ） ram Hg, the LA was （8.2±3.9） mmol/L, the EEG waves showed decreased amplitude, frequency and complexity, but restored to some extent after hypoxia. The brain tissue ultrastructure showed damages to the cerebral cortex and neuron mitochondria at hippocampal CA1 area. In the group with brain rSO2 〈 30% , the MAP waa （35±0） ram Hg, the LA was （12±2 ） mmol/L, the EEG showed decreased amplitude, frequency, and complexity of signals compared with those of the normal control group, and was difficult to restore after hypoxia in some of the piglets ; the brain tissue ultrastructure appeared to be similar to the changes seen with high-degree swollen cerebral cortex and neuron mitochondria at.hippocampal CA1 area. Conclusion Different degrees of hypoxia had different influence on brain function and brain damage. The lower the brain rSO2, the more severe the damages to the brain and its function. The rSO2 of brain tissues detected with noninvasive NIRS can reflect brain injury and its severity during cerebral anoxia.