急性缺氧性缺氧时心脏功能的改变

F_(IO_2)(吸入气氧浓度)为12.35、9.87及7.7l％,分别吸入10、8及5min时,心功能呈代偿性增强改变。F_(IO_2)为9.37％、吸入20min时心功能的变化趋势与9.87％8min时仍基本相同。继发性缺二氧化碳对缺氧引起的心功能代偿性增强,在一定程度上起抵消作用。F_(IO_2)为9.87％时的缺氧程度约相当于18km高空加压供氧总压值为15.3kPa(115mmHg)时的缺氧。单纯从缺氧因素考虑,将总压值由常用的17.3kPa(130mmHg)降低为15.3kPa是可允许的。

EFFECTS OF ACUTE HYPOXIC HYPOXIA ON CARDIAC FUNCTION

Cardiac unction changed compensatively during breathing in mixed gas containing 12.35% oxygen (for 10 min), 9.87 % oxygen (for 8 min), or 7.71% oxygen (for 5 min). cardiac output and cardiac work increased; Heather index and ejection fraction rose; isovolumic contraction time, preejection period index and Q-Z interval index shortened; preejection period/left ventricular ejection time ratio diminished; and left ventricular ejection time index lengthened. The variational tendency of the cardiac function when fraction of oxygen in the inspiratory air was 9.37% for 20 min was nearly the same as that when fraction of oxygen in the inspiratory air was 9.87% for 8 min. The changes of cardiac function while fraction of carbon dioxide in the alveolar air was kept at 4.5% for 8 min by means of hyperventi-lation were contrary to that induced by hypoxia and, therefore, in certain degree had a countervailing effect on the latter. The degree of hypoxia induced by inhaling mixed gas containing 9.87% oxygen was about equal to that occurred during positive pressure breathing at the altitude of 18 km with total oxygen pressure of 15.3 kPa. The preliminary conclusion from the result may be that it is permissible to decrease the total oxygen pressure from 17.3 kPa to 15.3 kPa when only hypoxia is taken into consideration.