Similitude in the cardiorespiratory responses to exercise across vertebrates

The anatomy of the heart and the respiratory organs differs enormously amongst vertebrates, and the absolute rates of oxygen uptake - both at rest and exercise - are several-fold higher in the endothermic birds and mammals when compared to fish, amphibians and reptiles (all ectothermic). Despite these large differences, all vertebrates can elevate the rate of oxygen consumption by 5-10 times when engaging in physical exercise. The increased oxygen delivery is attained by increasing the convective flows (i.e. increased ventilation and cardiac output) as well as increased extraction of oxygen from the blood leading that widens the arterial-venous oxygen concentration difference with an extraction of approximately 90%. All members of all vertebrate classes appear to exhibit some diffusive limitation for oxygen in the gills or lungs, whereas arterial PCO2 tends to decrease due to hyperventilation.