Pelletier N, Leith D E
Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan 66506, USA.
J Appl Physiol (1985). 1995 Feb;78(2):654-62. doi: 10.1152/jappl.1995.78.2.654.
Thoroughbred horses (TB) have no ventilatory response to added CO2 during near-maximal exercise. To see whether that reflects mechanical limits to ventilation or the control of breathing, we examined the effects of varying inspired O2 fraction (0.16, 0.21, or 0.30) in five normal TB standing quietly and galloping at 10 and 14 m/s on a level treadmill. We measured gas exchange (O2 consumption and CO2 production) and ventilation with a flow-through mask system. We also measured PO2, PCO2, and O2 contents in arterial and mixed venous blood and calculated cardiac output by using the Fick equation. Low inspired O2 fraction (0.16 vs. 0.21) had significant effects in TB galloping at 14 m/s. Arterial PO2 then was 38 Torr compared with 56 Torr for horses on air. Tidal volume and minute ventilation were 20% greater than their corresponding values on air, which were 12 liters and 1,475 l/min, respectively, whereas respiratory frequency did not change. O2 consumption and CO2 production were unchanged, but alveolar ventilation was 6% greater, despite increased alveolar and physiological dead spaces, so arterial PCO2 was lower (45 vs. 50 Torr on air). Thus, hypoxia was an effective stimulus to breathing, and minute ventilation was not mechanically limited in TB breathing air at the speeds studied.
纯种马（TB）在接近最大运动强度时对额外的二氧化碳没有通气反应。为了探究这是反映了通气的机械限制还是呼吸控制，我们在水平跑步机上，对五匹正常的纯种马在安静站立以及以10米/秒和14米/秒的速度奔跑时，研究了不同吸入氧分数（0.16、0.21或0.30）的影响。我们使用流通面罩系统测量气体交换（氧气消耗和二氧化碳产生）和通气情况。我们还测量了动脉血和混合静脉血中的氧分压、二氧化碳分压和氧含量，并使用菲克方程计算心输出量。低吸入氧分数（0.16对比0.21）对以14米/秒速度奔跑的纯种马有显著影响。此时动脉氧分压为38托，而呼吸空气的马匹为56托。潮气量和分钟通气量比它们在呼吸空气时相应的值分别大20%，呼吸空气时潮气量和分钟通气量分别为12升和1475升/分钟，而呼吸频率没有变化。氧气消耗和二氧化碳产生没有改变，但尽管肺泡和生理死腔增加，肺泡通气量仍增加了6%，因此动脉二氧化碳分压更低（呼吸空气时为50托，此时为45托）。因此，低氧是呼吸的有效刺激因素，在所研究的速度下，纯种马呼吸空气时分钟通气量没有受到机械限制。
