CHANGES IN CAROTID BLOOD-FLOW AND ELECTROCARDIOGRAM IN HUMANS DURING AND AFTER WALKING ON A TREADMILL

Blood flow velocity in the common carotid artery and the electrocardio gram were measured simultaneously by telemetry in seven male subjects during 20-min walking on a treadmill at an exercise intensity correspo nding to a mean oxygen uptake of 26.0 (SD 2.9) ml.kg(-1) min(-1). The mean cardiac cycle was shortened from 0.814 (SD 0.103) s to 0.452 (SD 0.054) s during this exercise. Of this shortening, 73% was due to shor tening of the diastolic period and 27% to shortening of the systolic p eriod. In the relatively small shortening of the mean systolic period [from 0.377 (SD 0.043) s to 0.268 (SD 0.029) s], the isovolumetric con traction time was shortened by 56%. During exercise, the heart rate (f (c)) increased by 79.4% [from 74.3 (SD 9.3) beats.min(-1) to 133.3 (SD 14.8) beats.min(-1)]and the peak blood velocity (S-1) in the common c arotid artery increased by 56.1% [from 0.82 (SD 0.10) m.s(-1) to 1.28 (SD 0.11) m.s(-1)]. After exercise, the S-1 decreased rapidly to the r esting level. The f(c) decreased more slowly, still being higher than the initial resting level 5 min after exercise. The diastolic velocity wave and the end-diastolic foot decreased during exercise. The blood flow rate in the carotid artery increased transiently by 13.5% at the beginning of exercise [from 5.62 (SD 0.63) ml.s(-1) to 6.38 (SD 0.85) m. s(-1)] and by 26.5% at the end of the exercise period [from 5.62 (S D 0.63) ml.s(-1) to 7.11 (SD 1.34) ml.s(-1)]. The increase of blood fl ow in the carotid artery at the onset of exercise may have been mainly related to cerebral activation, and partly to an increase of blood fl ow to the skin of the head. The physiological significance for cerebra l function of the increase of blood flow in the artery after the end o f exercise is unknown.