Grubb B, Jorgensen D D, Conner M
J Exp Biol. 1983 May;104:193-201. doi: 10.1242/jeb.104.1.193.
Cardiovascular variables were studied as a function of oxygen consumption in the emu, a large, flightless ratite bird well suited to treadmill exercise. At the highest level of exercise, the birds' rate of oxygen consumption (VO2) was approximately 11.4 times the resting level (4.2 ml kg-1 min-1). Cardiac output was linearly related to VO2, increasing 9.5 ml for each 1 ml increase in oxygen consumption. The increase in cardiac output is similar to that in other birds, but appears to be larger than in mammals. The venous oxygen content dropped during exercise, thus increasing the arteriovenous oxygen content difference. At the highest levels of exercise, heart rate showed a 3.9-fold increase over the resting rate (45.8 beats min-1). The mean resting specific stroke volume was 1.5 ml per kg body mass, which is larger than shown by most mammals. However, birds have larger hearts relative to body mass than do mammals, and stroke volume expressed per gram of heart (0.18 ml g-1) is similar to that for mammals. Stroke volume showed a 1.8-fold increase as a result of exercise in the emus, but a change in heart rate plays a greater role in increasing cardiac output during exercise.
对鸸鹋（一种大型、不会飞的平胸鸟类，非常适合跑步机运动）的心血管变量作为耗氧量的函数进行了研究。在最高运动水平时，鸟类的耗氧率（VO2）约为静息水平（4.2毫升·千克⁻¹·分钟⁻¹）的11.4倍。心输出量与VO2呈线性相关，耗氧量每增加1毫升，心输出量增加9.5毫升。心输出量的增加与其他鸟类相似，但似乎比哺乳动物的更大。运动期间静脉血氧含量下降，从而增加了动静脉血氧含量差。在最高运动水平时，心率比静息心率（45.8次·分钟⁻¹）增加了3.9倍。静息时平均比每搏输出量为每千克体重1.5毫升，这比大多数哺乳动物的要大。然而，相对于体重而言，鸟类的心脏比哺乳动物的更大，每克心脏的每搏输出量（0.18毫升·克⁻¹）与哺乳动物的相似。鸸鹋运动时每搏输出量增加了1.8倍，但心率变化在运动期间增加心输出量方面起更大作用。
