Maher J T, Manchanda S C, Cymerman A, Wolfe D L, Hartley L H
Am J Physiol. 1975 Feb;228(2):477-81. doi: 10.1152/ajplegacy.1975.228.2.477.
Previous studies have shown that exposure to high altitude results in an initial increase in heart rate, followed by a return to sea-level values within several days; circulating catecholamines rise progressively during this time. Nine conscious dogs were studied in normoxia (N) and after 10 days' exposure to 445 torr (CH). The mean (plus or minus SE) hematocrit was higher in CH (50 plus or minus 2 vs. 42 plus or minus 1%) while Pa-o2 (53 plus or minus 1 vs. 97 plus or minus 2 torr) and PaCO2 (27 plus or minus 1 vs. 35 plus or minus 1 torr) were lower than in N. A 3.5-fold increase in plasma norepinephrine above the N value was found in CH. Arterial pH, heart rate (HR), and mean femoral arterial pressure (MAP) did not differ significantly in N and CH. Isoproterenol (ISO), 0.5 mug/kg iv, produced an average increase in HR of 92 plus or minus 9 beats/min in N, but only 66 plus or minus 8 beats/min in CH (P smaller than .02). Reduction in MAP after ISO were similar. Pretreatment with propranolol, 0.15 mg/kg iv, reduced HR equally in N and CH without affecting MAP, but diminished the HR response to ISO significantly more in CH than in N. The attenuated chronotropic response to beta-adrenoceptor stimulation following chronic hypobaric hypoxia suggests a relative cardiac refractoriness secondary to an increased level of sympathetic activity.
先前的研究表明，暴露于高海拔地区会导致心率最初升高，随后在几天内恢复到海平面值；在此期间，循环中的儿茶酚胺会逐渐升高。对9只清醒的狗在常氧环境（N）下以及暴露于445托（CH）环境10天后进行了研究。CH组的平均（±标准误）血细胞比容更高（50±2 vs. 42±1%），而动脉血氧分压（Pa - o2）（53±1 vs. 97±2托）和动脉血二氧化碳分压（PaCO2）（27±1 vs. 35±1托）低于N组。发现CH组血浆去甲肾上腺素比N组的值增加了3.5倍。动脉pH值、心率（HR）和平均股动脉压（MAP）在N组和CH组之间没有显著差异。静脉注射异丙肾上腺素（ISO）0.5μg/kg，在N组中使HR平均增加92±9次/分钟，但在CH组中仅增加66±8次/分钟（P<0.02）。ISO注射后MAP的降低情况相似。静脉注射普萘洛尔0.15mg/kg预处理，在N组和CH组中对HR的降低作用相同，且不影响MAP，但在CH组中比在N组中更显著地减弱了对ISO的HR反应。慢性低压低氧后对β - 肾上腺素能受体刺激的变时反应减弱表明，继发于交感神经活动水平升高的相对心脏不应性。
