Douse M A, Mitchell G S
Department of Comparative Biosciences, University of Wisconsin, Madison 53706.
Respir Physiol. 1992 Jan;87(1):77-90. doi: 10.1016/0034-5687(92)90101-2.
The episodic breathing pattern in many reptiles consists of two or more clustered breaths separated by variable non-ventilatory periods. This pattern is commonly postulated to result from oscillations in lung and/or blood PO2 or PCO2 via chemoreceptor feedback. We tested this hypothesis by monitoring breathing pattern in: (1) awake, undisturbed alligators and (2) sedated alligators (approx. 25 mg/kg pentobarbital, i.p.; 3 days prior to data collection). In sedated alligators, measurements were made: (1) before and after bilateral cervical vagotomy, a procedure that removes peripheral arterial chemoreceptors, CO2-sensitive intrapulmonary chemoreceptors and pulmonary stretch receptors (n = 6); and (2) during unidirectional ventilation (UDV) at high flow rates (greater than 2 L/min), thereby minimizing oscillations in lung and blood PO2 and PCO2 (n = 6). Measurements on sedated alligators were made at 30 and 20 degrees C in each of these conditions. In awake, undisturbed alligators, breathing was typically episodic with 2-7 breaths/cluster, although the pattern was easily altered (increased breaths/cluster) by even seemingly minor disturbances. In sedated alligators, episodic breathing was still evident after vagotomy, but only at increased inspired CO2; at 5% CO2 four of six alligators exhibited episodic breathing consisting of 2-3 breaths/cluster interspersed with occasional single breaths. An episodic breathing pattern was also evident during UDV; at low levels of CO2, 2-4 breaths/cluster interspersed with occasional single breaths were evident in four alligators, while two had 6-8 breaths/cluster. Increasing CO2 in the UDV gas stream generally increased the number of breaths/cluster. After vagotomy, all six alligators could manifest an episodic breathing pattern during UDV in at least one CO2 condition (greater than 2 breaths/cluster interspersed with occasional single breaths). The episodic breathing pattern was very labile, sometimes changing to single breaths without apparent cause. The results suggest: (1) episodic breathing requires neither feedback from vagal sensory receptors nor oscillations in respiratory gases; and (2) changes in arterial PCO2 modulate, but do not initiate episodic breathing. Episodic breathing in alligators may be due to complex interactions of higher brain structures with the central rhythm generator.
许多爬行动物的间歇性呼吸模式由两个或更多成组的呼吸组成，中间间隔着长短不一的非通气期。这种模式通常被认为是通过化学感受器反馈，由肺部和/或血液中的氧分压（PO2）或二氧化碳分压（PCO2）的振荡引起的。我们通过监测以下动物的呼吸模式来验证这一假设：（1）清醒、未受干扰的短吻鳄；（2）注射镇静剂的短吻鳄（腹腔注射约25mg/kg戊巴比妥；在数据收集前3天）。对于注射镇静剂的短吻鳄，测量在以下情况下进行：（1）双侧颈迷走神经切断术前和术后，该手术会去除外周动脉化学感受器、对二氧化碳敏感的肺内化学感受器和肺牵张感受器（n = 6）；（2）在高流速（大于2L/min）的单向通气（UDV）过程中，从而使肺部和血液中的PO2和PCO2的振荡最小化（n = 6）。在上述每种情况下，对注射镇静剂的短吻鳄在30摄氏度和20摄氏度时进行测量。在清醒、未受干扰的短吻鳄中，呼吸通常是间歇性的，每组有2 - 7次呼吸，尽管即使是看似轻微的干扰也很容易改变这种模式（每组呼吸次数增加）。在注射镇静剂的短吻鳄中，迷走神经切断术后间歇性呼吸仍然明显，但仅在吸入二氧化碳增加时出现；在5%二氧化碳的情况下，六只短吻鳄中有四只表现出间歇性呼吸，每组由2 - 3次呼吸组成，偶尔穿插单次呼吸。在单向通气期间间歇性呼吸模式也很明显；在低二氧化碳水平下，四只短吻鳄中明显可见每组2 - 4次呼吸，偶尔穿插单次呼吸，而另外两只每组有6 - 8次呼吸。在单向通气气流中增加二氧化碳通常会增加每组呼吸的次数。迷走神经切断术后，所有六只短吻鳄在至少一种二氧化碳条件下（每组呼吸次数大于2次，偶尔穿插单次呼吸）的单向通气期间都能表现出间歇性呼吸模式。间歇性呼吸模式非常不稳定，有时会无明显原因地转变为单次呼吸。结果表明：（1）间歇性呼吸既不需要迷走感觉感受器的反馈，也不需要呼吸气体的振荡；（2）动脉血二氧化碳分压的变化调节但不启动间歇性呼吸。短吻鳄的间歇性呼吸可能是由于高级脑结构与中枢节律发生器的复杂相互作用所致。
