Thomas D P, Fregin G F
J Appl Physiol Respir Environ Exerc Physiol. 1981 Apr;50(4):864-8. doi: 10.1152/jappl.1981.50.4.864.
The purpose of this study was to measure cardiovascular, respiratory, and metabolic responses to graded treadmill exercise in the horse. A five-stage treadmill test up to 90% of predicted maximal heart rate was administered to five sedentary horses. The highest measured level of exercise produced a sixfold increase in cardiac output and a 41% elevation of stroke volume over standing values. Left ventricular, arterial, and right atrial pressures as well as the maximal time derivative of left ventricular pressure were all elevated during exercise. Under the same two conditions hematocrit (Hct) increased from 33 +/- 2 to 47 +/- 1%, oxygen uptake (VO2) from 1.1 +/- 0.1 to 32.7 +/0 2.1 1.min-1, and respiratory exchange ratio (RQ) increased from 0.83 +/- 0.02 to 0.96 +/- 0.01. In addition, three of the horses were willing to trot at a sixth stage (14 km.h-1, 11.5% grade), which elicited a VO2 of 39.8 +/- 0.31.min-1 and an RQ of 0.98 +/- 0.01. In response to the sympathetic stimulation of exercise, the horse is able to elevate Hct, hemoglobin, and oxygen-carrying capacity by emptying the spleen, thus increasing total circulating red blood cells by as much as 50%. This enabled three of the five horses used in the present study to increase aerobic metabolism almost 40-fold above resting or twice that seen in humans. Therefore, in the horse "blood-boosting" is an efficient mechanism for increasing aerobic metabolism. This finding lends further support to the view that the oxygen transport system limits maximal aerobic capacity in humans.
本研究的目的是测定马在分级跑步机运动中的心血管、呼吸和代谢反应。对五匹久坐不动的马进行了一项五阶段跑步机测试，运动强度最高达到预测最大心率的90%。所测的最高运动水平使心输出量增加了六倍，每搏输出量比站立时的值升高了41%。运动期间，左心室、动脉和右心房压力以及左心室压力的最大时间变化率均升高。在相同的两种条件下，血细胞比容（Hct）从33±2%增加到47±1%，摄氧量（VO₂）从1.1±0.1增加到32.7±2.1 ml·min⁻¹，呼吸交换率（RQ）从0.83±0.02增加到0.96±0.01。此外，其中三匹马愿意在第六阶段（14 km·h⁻¹，坡度11.5%）小跑，此时VO₂为39.8±0.3 ml·min⁻¹，RQ为0.98±0.01。为应对运动引起的交感神经刺激，马能够通过排空脾脏来提高Hct、血红蛋白和携氧能力，从而使循环中的红细胞总数增加多达50%。这使得本研究中使用的五匹马中的三匹马的有氧代谢比静息时增加了近40倍，是人类的两倍。因此，在马中，“血液增强”是增加有氧代谢的一种有效机制。这一发现进一步支持了氧气运输系统限制人类最大有氧能力的观点。
