Speziali G, Russo P, Davis D A, Wagerle L C
Department of Cardiothoracic Surgery, Temple University School of Medicine, Philadelphia, Pennsylvania 19134.
J Surg Res. 1994 Jul;57(1):80-4. doi: 10.1006/jsre.1994.1114.
Hypothermia is the major factor influencing autoregulatory properties of the cerebral circulation in human infants undergoing hypothermic cardiopulmonary bypass. The present investigation evaluated the effect of decreased temperature on the contractility of isolated middle cerebral arteries obtained from newborn lambs. Reducing bath temperature from 37 to 21 degrees C caused a temperature-dependent increase in contractile tension, achieving 1.32 +/- 0.09 g above resting tension (0.75 g). Pretreatment with nonselective (alpha 1 and alpha 2) alpha-adrenoceptor antagonist, phentolamine (10(-5) M), with an inhibitor of nitric oxide synthase, NG-nitro-L-arginine methyl ester hydrochloride (10(-4) M), and with a cyclooxygenase inhibitor, indomethacin (10(-5) M), did not affect the contractile response to a decrease in bath temperature from 37 to 21 degrees C. Furthermore, cerebral arteries were responsive to both norepinephrine (constriction) and sodium nitroprusside (relaxation) and the sensitivity of cerebral arteries to the sympathetic neurotransmitter norepinephrine appears to be enhanced at low temperatures. We postulate that direct cerebral vasoconstriction and enhanced adrenergic contractility may be responsible for increased cerebrovascular resistance during and after hypothermic cardiopulmonary bypass with possible ischemic cerebral injury and neurological sequelae.
体温过低是影响接受低温体外循环的人类婴儿脑循环自动调节特性的主要因素。本研究评估了温度降低对从新生羔羊获取的离体大脑中动脉收缩性的影响。将浴温从37℃降至21℃会导致收缩张力随温度依赖性增加，比静息张力（0.75g）高出1.32±0.09g。用非选择性（α1和α2）α-肾上腺素能受体拮抗剂酚妥拉明（10^(-5)M）、一氧化氮合酶抑制剂盐酸N-硝基-L-精氨酸甲酯（10^(-4)M）和环氧化酶抑制剂吲哚美辛（10^(-5)M）进行预处理，并不影响对浴温从37℃降至21℃的收缩反应。此外，大脑中动脉对去甲肾上腺素（收缩）和硝普钠（舒张）均有反应，并且在低温下大脑中动脉对交感神经递质去甲肾上腺素的敏感性似乎增强。我们推测，直接的脑血管收缩和增强的肾上腺素能收缩性可能是低温体外循环期间及之后脑血管阻力增加的原因，可能导致缺血性脑损伤和神经后遗症。
