Mean flow velocity in the right common carotid artery before and after maximal exercise

The effect of exercise on mean flow velocity (MFV) in the right common carotid artery (RCC) was studied using pulsed Doppler ultrasound. MFV was measured at rest and at 2 minutes intervals after a 6 minute rowing ergometer test. Age-related maximum heart rate of 190 +/- 10 beats.min-1, maximum respiratory rate of 60 +/- 5 breaths.min-1, and postexercise lactate level of greater than 8 mmol.l-1 were the criteria used to define maximal exercise. The control group comprised 13 healthy, active males, mean age 19.8 years, with 19 healthy oarsmen, mean age 19.9 years, in the exercise group. At rest, MFV in the RCC was found to be 18.6 +/- 5.6 and 16.4 +/- 6.3 cm.min-1 in the control and exercise groups respectively. After exercise, MFV decreased to 21% of its resting value and remained significantly reduced (posthoc tests, Newman Keuls at alpha = 0.01) until 14-16 minutes of recovery. Mean systemic arterial pressure (MSAP) remained within normal limits. Mean age-related maximum heart rate was 182 +/- 3 beats.min-1, respiratory rate 58 +/- 3 breaths.min-1, and postexercise serum lactate 20.2 +/- 3.5 mmol.l-1 which satisfied the criteria for maximal exercise. In this group of young males, MFV in the RCC decreased markedly after maximal exercise and remained significantly reduced for a long period. This sustained reduction in MFV has not previously been described and is most likely due to vasoconstriction in distal cerebral resistance arterioles mediated by hypocapnia and autonomic activity.