Koterba A M, Kosch P C, Beech J, Whitlock T
Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville 32610.
J Appl Physiol (1985). 1988 Jan;64(1):337-46. doi: 10.1152/jappl.1988.64.1.337.
To investigate the mechanism underlying the polyphasic airflow pattern of the equine species, we recorded airflow, tidal volum, rib cage and abdominal motion, and the sequence of activation of the diaphragm, intercostal, and abdominal muscles during quiet breathing in nine adult horses standing at rest. In addition, esophageal, abdominal, and transdiaphragmatic pressures were simultaneously recorded using balloon-tipped catheters. Analysis of tidal flow-volume loops showed that, unlike humans, the horse at rest breathes around, rather than from, the relaxed volume of the respiratory system (Vrx). Analysis of the pattern of electromyographic activities and changes in generated pressures during the breathing cycle indicate that the first part of expiration is passive, as in humans, with deflation toward Vrx, but subsequent abdominal activity is responsible for a second phase of expiration: active deflation to below Vrx. From this end-expiratory volume, passive inflation occurs toward Vrx, followed by a second phase of inspiration: active inflation to above Vrx, brought about by inspiratory muscle contraction. Under these conditions the abdominal muscles appear to share the principal pumping duties with the diaphragm. Adoption of this breathing strategy by the horse may relate to its peculiar thoracoabdominal anatomic arrangement and to its very low passive chest wall compliance. We conclude that there is a passive and active phase to both inspiration and expiration due to the coordinated action of the respiratory pump muscles responsible for the resting adult horse's biphasic inspiratory and expiratory airflow pattern. This unique breathing pattern perhaps represents a strategy of minimizing the high elastic work of breathing in this species, at least at resting breathing frequencies.
为了研究马属动物多相气流模式的潜在机制，我们记录了9匹成年静立休息马在安静呼吸时的气流、潮气量、胸廓和腹部运动，以及膈肌、肋间肌和腹肌的激活顺序。此外，使用带气囊导管同时记录食管、腹部和跨膈压。潮气流速-容量环分析表明，与人类不同，静息状态下的马围绕呼吸系统的松弛容积（Vrx）呼吸，而非从该容积开始呼吸。对呼吸周期中肌电图活动模式和产生压力变化的分析表明，与人类一样，呼气的第一部分是被动的，向Vrx方向放气，但随后的腹部活动导致了呼气的第二阶段：主动放气至Vrx以下。从这个呼气末容积开始，向Vrx方向发生被动充气，随后是吸气的第二阶段：由吸气肌收缩导致的主动充气至Vrx以上。在这些情况下，腹肌似乎与膈肌共同承担主要的泵血功能。马采用这种呼吸策略可能与其独特的胸腹解剖结构以及极低的被动胸壁顺应性有关。我们得出结论，由于负责成年静息马双相吸气和呼气气流模式的呼吸泵肌肉的协同作用，吸气和呼气均存在被动和主动阶段。这种独特的呼吸模式可能代表了该物种在静息呼吸频率下将高弹性呼吸功降至最低的一种策略。
