KINETICS OF HEART-RATE AND CATECHOLAMINES DURING EXERCISE IN HUMANS - THE EFFECT OF HEART DENERVATION

To elucidate the role of factors other than the nervous system in heart rate (f(c)) control during exercise, the kinetics of f(c) and plasma catecholamine concentrations were studied in ten heart transplant recipients during and after 10-min cycle ergometer exercise at 50 W. The f(c) did not increase at the beginning of the exercise for about 60 s. Then in the eight subjects who completed the exercise it increased following an exponential kinetic with a mean time constant of 210 (SEM 22) s. The two other subjects were exhausted after 5 and 8 min of exercise during which f(c) increased linearly. At the cessation of the exercise, f(c) remained unchanged for about 50 s and then decreased exponentially with a time constant which was unchanged from that at the beginning of exercise. In the group of eight subjects plasma noradrenaline concentration ([NA]) increased after 30 s to a mean value above resting of 547 (SEM 124) pg . ml-1, showing a tendency to a plateau, while adrenaline concentration ([A]) did not increase significantly. In the two subjects who became exhausted an almost linear increase in [NA] occurred up to about 1,300 pg . ml-1 coupled with a significant increase in [A]. During recovery an immediate decrease in [NA] was observed towards resting values. The values of the f(c) increase above resting levels determined at the time of blood collection were linearly related with [NA] increments both at the beginning and end of exercise with a similar slope, i.e. about 2.5 beats . min-1 per 100 pg . ml-1 of [NA] change. These findings would seem to suggest that in the absence of heart innervation the increase in f(c) depends on plasma [NA].