Nakajima Yasufumi, Takamata Akira, Ito Tomoyuki, Sessler Daniel I, Kitamura Yoshihiro, Shimosato Goshun, Taniguchi Satoshi, Matsuyama Hiroki, Tanaka Yoshifumi, Mizobe Toshiki
Department of Anesthesiology, Kyoto Prefectural University of Medicine, Kawaramachi Hirokoji, Kamigyo-ku, Kyoto 602-8566, Japan.
Anesth Analg. 2002 Jun;94(6):1646-51, table of contents. doi: 10.1097/00000539-200206000-00053.
We recently reported that baroreceptor-mediated reflexes modulate thermoregulatory vasoconstriction during lower abdominal surgery. Accordingly, we examined the hypothesis that postural differences and the related alterations in baroreceptor loading similarly modulate the thermogenic (i.e., shivering) response to hypothermia in humans. In healthy humans (n = 7), cold saline was infused IV (30 mL/kg at 4 degrees C) for 30 min to decrease core temperature. Each participant was studied on 2 separate days, once lying supine and once sitting upright. Tympanic membrane temperature and oxygen consumption were monitored for 40 min after each saline infusion. The decrease in core temperature upon completion of the infusion in the upright posture position was 1.24 degrees C +/- 0.07 degrees C, which was significantly greater than the 1.02 degrees C +/- 0.06 degrees C seen in the supine position. The core temperature was reduced by 0.59 degrees C +/- 0.07 degrees C in the upright position but only by 0.37 degrees C +/- 0.05 degrees C in the supine position when the increase in oxygen consumption signaling thermogenic shivering occurred. Thus, the threshold temperature for thermogenesis was significantly less in the upright than the supine position. The gain of the thermogenic response did not differ significantly between the positions (363 +/- 69 mL. min(-1). degrees C(-1) for upright and 480 +/- 80 mL. min(-1). degrees C(-1) for supine). The skin temperature gradient was significantly larger in the upright than in the supine posture, suggesting that the peripheral vasoconstriction was augmented by upright posture. Plasma norepinephrine concentrations increased in response to cold saline infusion under both conditions, but the increase was significantly larger in the upright than in the supine posture. Baroreceptor unloading thus augments the peripheral vasoconstrictor and catecholamine response to core hypothermia but simultaneously reduces thermogenesis, which consequently aggravated the core temperature decrease in the upright posture.
Upright posture attenuates the thermogenic response to core hypothermia but augments peripheral vasoconstriction. This divergent result suggests that input from the baroreceptor modifies the individual thermoregulatory efferent pathway at a site distal to the common thermoregulatory center or neural pathway.
我们最近报道，在腹部下部手术期间，压力感受器介导的反射调节体温调节性血管收缩。因此，我们检验了以下假设：姿势差异以及压力感受器负荷的相关改变同样会调节人类对体温过低的产热（即寒战）反应。在健康人类（n = 7）中，静脉输注冷盐水（4℃时30 mL/kg）30分钟以降低核心体温。每位参与者在2个不同的日子接受研究，一次仰卧，一次直立坐着。每次输注盐水后监测鼓膜温度和耗氧量40分钟。直立姿势输注结束时核心体温的下降为1.24℃±0.07℃，显著大于仰卧位时的1.02℃±0.06℃。当表示产热寒战的耗氧量增加时，直立位核心体温降低0.59℃±0.07℃，而仰卧位仅降低0.37℃±0.05℃。因此，直立位产热的阈值温度显著低于仰卧位。产热反应的增益在不同姿势之间无显著差异（直立位为363±69 mL·min⁻¹·℃⁻¹，仰卧位为480±80 mL·min⁻¹·℃⁻¹）。直立位皮肤温度梯度显著大于仰卧位姿势，表明直立姿势增强了外周血管收缩。在两种情况下，冷盐水输注后血浆去甲肾上腺素浓度均升高，但直立位的升高显著大于仰卧位姿势。因此，压力感受器卸载增强了外周血管收缩剂和儿茶酚胺对核心体温过低的反应，但同时减少了产热，从而加剧了直立位时核心体温的下降。
直立姿势减弱了对核心体温过低的产热反应，但增强了外周血管收缩。这种不同的结果表明，来自压力感受器的输入在共同体温调节中枢或神经通路远端的位点改变了个体体温调节传出通路。
