MIDDLE CEREBRAL-ARTERY BLOOD VELOCITY AND PLASMA-CATECHOLAMINES DURING EXERCISE

During dynamic exercise. mean blood velocity (V-mean) in the middle ce rebral artery (MCA) demonstrates a graded increase to work rate and re flects regional cerebral blood flow. At a high work rate. however. vas oactive levels of plasma catecholamines could mediate vasoconstriction of the MCA and thereby elevate V-mean at a given volume flow. To eval uate transcranial Doppler-determined V-mean at high plasma catecholami ne levels. seven elite cyclists performed a maximal performance test o n a bicycle ergometer. Results were compared with those elicited durin g five incremental exercise bouts and during rhythmic handgrip when pl asma catecholamines are low. During rhythmic handgrip the V-mean was e levated by 21 +/- 3% (mean +/- SE). which was not statistically differ ent from that established during moderate cycling. However, at the hig hest submaximal and maximal work intensities on the bicycle ergometer. V-mean increased by 31 +/- 3% and 48 +/- 4%. respectively. and this w as significantly higher compared to handgrip (P < 0.05). During maxima l cycling. plasma adrenaline increased from 0.21 +/- 0.04 nmol L(-1) a t rest to 4.18 +/- 1.46 nmol L(-1). and noradrenaline increased from 0 .79 +/- 0.08 to 12.70 +/- 1.79 nmol L(-1). These levels were 12- to 16 -fold higher than those during rhythmic handgrip (adrenaline: 0.34 +/- 0.03 nmol L(-1); noradrenaline: 0.78 +/- 0.05 nmol L(-1)). The increa se in V-mean during intense ergometer cycling conforms to some middle cerebral artery constriction elicited by plasma catecholamines. Such a n influence is unlikely during rhythmic handgrip compared with low int ensity cycling.