In the giraffe with a total height of 5 m., the heart is at a height of about 2.5 m., and it would be extremely interesting to know just how the giraffe avoids the development of filtration oedema in its long legs.
There can be little doubt that fishes swimming rapidly do not make respiratory movements at all, but obtain the necessary ventilation of the gills simply by opening the mouth.
In many organisms, including man, the mechanical respiration and the circulation of the blood are 'regulated' so as to correspond to the demand of the moment.
Muscles do not use oxygen at a constant rate.
The affinity of blood or pure haemoglobins for oxygen is a complex phenomenon, depending upon a number of conditions, the most important of which are temperature and hydrogen ion concentration.