Hershenson M B, O'Rourke P P, Christakis D A, Coopes B J, Crone R K
Department of Anaesthesia, Harvard Medical School, Boston, Massachusetts.
Pediatr Res. 1990 Aug;28(2):101-5. doi: 10.1203/00006450-199008000-00005.
Past studies have found that total-body O2 extraction during hypoxia was less in 1-wk-old lambs than in older animals. It was proposed that reduced O2 extraction was secondary to suppression of growth-related oxygen consumption (VO2) in tissues such as skeletal muscle, bone, kidney, and skin, rather than a defect in peripheral O2 use. To determine the capacity of immature skeletal muscle to extract O2, we isolated the hind limb circulation of eight ketamine-anesthetized, 7- to 18-d-old lambs exposed to stagnant hypoxia by inflation of a right atrial balloon catheter. Femoral arterial and venous PO2, PCO2, pH, Hb concentration, O2 saturation, and femoral arterial blood flow (Q) were measured and hind limb O2 delivery (DO2), extraction ratio, and VO2 calculated. Individual critical levels of DO2 below which VO2 was dependent on O2 supply were determined by dual-line best-fit regression analysis. In six of eight animals, VO2 was clearly independent of supply until DO2 reached critically low levels. However, O2 extraction during extreme hypoxia appeared submaximal (baseline O2 extraction ratio, 0.22 +/- 0.06; at critical levels of DO2, 0.51 +/- 0.11; at the lowest level of Q, 0.64 +/- 0.15). When 2,4-dinitrophenol, an uncoupler of oxidative phosphorylation, was administered to four additional lambs exposed to stagnant hypoxia, O2 extraction below critical levels of DO2 increased from 0.48 +/- 0.15 to 0.79 +/- 0.10 (p less than 0.001, unpaired t test). These data suggest that initial limitations in O2 extraction were a result of the suspension of O2-consuming processes, not an irreversible defect in peripheral O2 use.
以往的研究发现，1周龄羔羊在缺氧期间的全身氧摄取量低于年龄较大的动物。有人提出，氧摄取减少是由于骨骼肌、骨骼、肾脏和皮肤等组织中与生长相关的氧消耗（VO2）受到抑制，而不是外周氧利用存在缺陷。为了确定未成熟骨骼肌摄取氧的能力，我们对8只氯胺酮麻醉、7至18日龄的羔羊进行了实验，通过右心房球囊导管充气使其暴露于停滞性缺氧状态，分离其后肢循环。测量股动脉和静脉的PO2、PCO2、pH、血红蛋白浓度、氧饱和度以及股动脉血流量（Q），并计算后肢氧输送量（DO2）、摄取率和VO2。通过双线性最佳拟合回归分析确定VO2依赖于氧供应的个体临界DO2水平。在8只动物中的6只中，直到DO2达到极低水平之前，VO2明显不依赖于氧供应。然而，在极端缺氧期间的氧摄取似乎未达到最大值（基线氧摄取率为0.22±0.06；在临界DO2水平时为0.51±0.11；在最低Q水平时为0.64±0.15）。当对另外4只暴露于停滞性缺氧的羔羊给予氧化磷酸化解偶联剂2,4-二硝基苯酚时，低于临界DO2水平的氧摄取从0.48±0.15增加到0.79±0.10（p<0.001，未配对t检验）。这些数据表明，最初氧摄取的限制是氧消耗过程暂停的结果，而不是外周氧利用的不可逆缺陷。
