Saeid Changiz Ashtiani, Saeid Khameneh, Hamid Salimi Khaligh,
Volume 2, Issue 7 (Summer 1999)
Abstract
Arterial baroreflexes are the most important mechanism of cardiovascular control. These reflexes compared with other reflexes act so rapidly that can respond to rapid blood pressure changes during daily activities. In this study we have assessed the cardiac responses of cardiac baroreflexes dynamic exercise , and compared the results with acute response during rest exercise. It was 50% of calculated maximum force. Experiments were performed on 12 young male healthy sedentary volunteers isometric exercise(protocol B) and dynamic exercise (protocol C). In order to stimulate the carotid baroreceptors neck suction device Eckberg model was used , ECG were taken continuously during experiment. In protocol A (control group) after stimulation the cardiac cycle (R-R interval) from baseline reached to acute responses in the first beat induction baseline in the forth beat P<0.003 and in the protocol C reached acute response compared with baseline in the eighth beat after induction P<0.001. If the observed acute responses during test are compared and concluded that shorting R-R interval in response to isometric due to vagal withdrawal combined with an subtle sympathetic stimulation. This phenomenon is observed more strongly in dynamic exercise.
Saeid Changizi Ashtiyani , Saeid Khameneh, Hamid Salimi Khaligh ,
Volume 3, Issue 2 (Summer 2000)
Abstract
Arterial baroreflexes are the most important mechanism of cardiovascular system that can respond to rapid blood pressure changes during everyday activities. In this study we have assessed adaptive responses of carotid baroreflexes during isometric & dynamic exercise and compared the results with acute response during rest. The applied work loud in dynamic exercise was 100 watts and in isometric exercise it was 50% of calculated maximum force. Experiments were performed on 12 young male healthy sedentary volunteers aged between 21-28. This study was done in three exercises. In all three protocles, adaptation process during stimulation was assessed by studying of beat to beat R-R interval of ECG. In order to stimulate the carotid baroreceptors neck suction device Eckberg model was used and duration of stimulation was 10 seconds. ECG was taken carefully. Examination of adaptive process during stimulation showed maximal response achieved in resting state is statistically significant compared with that of isometric and dynamic exercise respectively (P<0.038, P<0.007). where as, comparison of adaptive response of rest state with isometric exercise and dynamic exercise was not statistically significant. There is no significant relation between maximal and adaptative response in dynamic and isometric exercises, although in general adaptative process in resting state compared with isometric and dynamic exercise was more pronounced. This observation confirmed that Vagal withdrawal with alimited degree of sympathic stimulation are challenged in this phenomenon. In other words the Sa response to vagal stimulation is related by sympathic stimulation.
