Hicks J W, Wang T
Department of Ecology and Evolutionary Biology, University of California, Irvine 92697, USA.
Physiol Zool. 1998 Jan-Feb;71(1):1-14. doi: 10.1086/515892.
This study describes the integrated cardiovascular response of instrumented turtles to acute anoxic exposure (approximately 2 h) and also determines the factors that regulate these responses. Trachemys scripta were chronically implanted with ultrasonic blood flow probes for the measurement of total pulmonary and systemic blood flows and heart rate. In addition, catheters were implanted into the right aortic arch for the measurement of systemic blood pressure, arterial blood gases, and pH. Animals were free to swim within an aquarium but could only breathe within a small chamber located at the surface. Cardiovascular variables were continuously monitored during normoxia, 2 h of anoxia, and during recovery at normoxia. In addition, some animals were treated with atropine or epinephrine during the anoxic exposure. During the onset of nitrogen breathing there was an increase in ventilation frequency, heart rate, pulmonary blood flow, and systemic blood flow and the development of a net left-to-right cardiac shunt. These changes lasted up to 1 h, followed by bradycardia (heart rate was reduced by 50% from control values) and the development of a large net right-to-left shunt (approximately 80% of the total cardiac output). These changes lasted the duration of the anoxic exposure and were rapidly reversed on return to a normoxic environment. Injections of epinephrine during anoxia had no effect on heart rate, pulmonary blood flow, or systemic blood flow. In contrast, injection of atropine during anoxia resulted in an increase in the heart rate and systemic blood flow, suggesting that the anoxic cardiac response is partially mediated through cholinergic mechanisms.
本研究描述了植入仪器的乌龟对急性缺氧暴露（约2小时）的综合心血管反应，并确定了调节这些反应的因素。将红耳龟长期植入超声血流探头，以测量总肺血流量、全身血流量和心率。此外，将导管植入右主动脉弓，以测量全身血压、动脉血气和pH值。动物可在水族箱内自由游动，但只能在位于水面的小室内呼吸。在常氧、缺氧2小时以及恢复到常氧期间，持续监测心血管变量。此外，一些动物在缺氧暴露期间接受了阿托品或肾上腺素治疗。在开始呼吸氮气时，通气频率、心率、肺血流量和全身血流量增加，并且出现了从左到右的净心脏分流。这些变化持续长达1小时，随后出现心动过缓（心率比对照值降低50%）以及出现大量从右到左的净分流（约占心输出量的80%）。这些变化在缺氧暴露期间持续存在，并在恢复到常氧环境后迅速逆转。缺氧期间注射肾上腺素对心率、肺血流量或全身血流量没有影响。相反，缺氧期间注射阿托品导致心率和全身血流量增加，这表明缺氧时的心脏反应部分是通过胆碱能机制介导的。
