Cardiac Output (CO), Stroke Volume (SV) and Heart Rate (HR) in exercising rats

Abstract

Exercise requires augmented blood flow to skeletal muscle. Increased blood flow is delivered by redistribution of blood flow and by increased CO caused by increases in both SV and HR. The purpose of this study was to determine the effects of two different levels of exercise on volumetric CO, SV and HR in untrained rats. Male Sprague Dawley rats exposed to a Columbus Instruments 5/6 treadmill and trained to run for brief period of time. Animals were instrumented with a 2.5SL transit time flow probe (Transonic Systems Inc.) on the ascending aorta for determination of CO. After a recovery period of at least 1 week, rats were again exposed to the treadmill. On the day of testing, animals were attached to the flow meter by a thether. 15 min. of homecage baseline CO were determined using IOX software (1000Hz, 1 min. averages). Animals were transferred to the treadmill and allowed to acclimate for 15 min. Subjects then were exercised at 15 or 30 m/min for 10 min. After a 15 min rest, the animals were exposed to the alternate level of exercise. All values are expressed as χ±sem. Under homecage baseline conditions, CO = 74±7 ml/m, HR=392±23 bpm, and SV=181±17 μl/m. With onset of exercising at 15m/min all parameters increased to an initial peak then dropped slightly over the remaining exercise period. Average hemodynamic values were: CO 107±11, HR=504±19 and SV=198±16. At 30 m/min all parameters increased and remained level throughout the exercise at: CO=123±11, HR=540±16 and SV=213±15. These studies demonstrate that increasing levels of treadmill exercise are maintained by increasing levels of CO in the rat. Both SV and HR are instrumental in achieving this increase.