这样是否改动太大？

Maintenance of constant oxygen consumption in the face of reduced delivery can only be achieved at the expense of a reduction in mixed venous saturation, as a result of increased extraction of oxygen from the arterial blood. This has been clearly demonstrated in both acute (Fig. 24.1, D) and sustained anaemia.2A reduction in the oxygen content of mixed venous blood curtails the ability of the anaemic patient to encroach on a useful reserve of oxygen, which is an important response to exercise. Reduction of haemoglobin to 100 g.L21 resulted in a curtailment of oxygen consumption attained at maximal exercise from the control values of 3.0 L.min21 (normalized to 70 kg body weight) down to 2.5 L.min21 in the acute stage, and 2.1 L.min21 after 14 days of sustained anaemia.The increase in cardiac output required for the same increase in oxygen consumption was greater in the anaemic state, and cardiac output at maximal oxygen consumption was slightly less than under control conditions. Maximal exercise in the anaemic state resulted in a reduction of mixed venous oxygen saturation to the exceptionally low value of 12%, compared with control values of 23% during maximal exercise with a normal haemoglobin concentration.

为了在氧输送减少的情况下保持氧消耗恒定，组织对动脉血氧摄取量增加， 因此混合静脉血氧饱和度降低，这在急性贫血(图24.1，D)和慢性贫血中都得到了证实²。在贫血者中，混合静脉血氧含量作为运动时氧气的重要储备被提前消耗。对于一个体重70Kg的人来说，如果血红蛋白下降至100g/L，急性贫血者其运动时的最大耗氧量从3.0L/min降至2.5L/min，而持续14天的慢性贫血者更会低至2.1L/min (图24.2) ²。贫血者提升相同耗氧量所需要增加的心排血量相较正常人更大，当达到最大耗氧量时其心排血量略低于正常人。血红蛋白浓度正常者在剧烈运动时混合静脉血氧饱和度约为正常值的23%，而在贫血者中可低至12%。

这两句话的翻译，其实核心意思是一样的，但我总觉得改写太大，是不是不大好，尤其第一句，语气给省略了

第1句应这么：面对氧输送下降，维持耗氧量恒定只能以降低混合静脉氧饱和度为代价，这是动脉血氧摄取增加所致。

第2句应这么：贫血患者中，混合静脉血氧含量下降削弱了贫血患者动用氧储备的能力，这对于运动很重要。