Why the arterial blood pressure increases during exercise? -A role of muscle mechanoreflex-

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EXPERIMENT I. To examine whether the cerebrum is essential for producing the rapid cardiovascular adjustment at the beginning at overground locomotion, we examined heart rate (HR), mean arterial blood pressure (MAP), and integrated electromyogram (iEMG) of the forelimb triceps brachialis muscle during locomotion in freely-moving decerebrate cats. Two to four days after decerebration surgery performed at the level of precollicular-premammillary body, the animals would spontaneously produce overground locomotion supporting body weight. HR began to increase immediately before the onset of iEMG, and MAP began to rise almost simultaneously with the iEMG onset. Their increases in HR and MAP(24 * 3 bpm and 22 * 4 mmHg) were sustained during locomotion. Sinoaortic denervation (SAD) did not affect the abrupt changes in HR and MAP at the beginning of locomotion (0-4 s from the onset of iEMG), whereas SAD had a contrasting effect during the subsequent period, a decrease in the HR response (9 * 1b … More pm) and an increase in the MAP response (30 * 3 mmHg). These results suggest that the cerebrum an the rostral part of the diencephalon are not essential for producing the rapid cardiovascular adjustment at the beginning of spontaneous overground locomotion. The arterial baroreflex does not contribute this rapid adjustment but play an important role in regulating the cardiovascular responses during the later period of spontaneous locomotion.EXPERIMENT II. To examine the role of a sudden load change on the cardiovascular adjustments during the bicycling exercise. Fifteen healthy female volunteers performed the same bicycling exercise which included one abrupt change of load-up or load-down under three different conditions in which the preliminary instructions about the load change given verbally before the bicycling exercise were no, true or false. The true and false instructions both produced anticipatory increases in HR and MAP observed 30 s before the onset of the load change, whereas no instruction did not alter them. After the onset of load-up or load-down, the cardiovascular responses to true instruction were more rapid than to other instructions. These results suggest that preliminary instructive preparation for voluntary exercise could modify the cardiovascular adjustment to the abrupt load changes. Less