Middle cerebral artery blood velocity during running: interactions of heart and stride impact rates

Abstract

Vertical movement during running or treadmill exercise generates complex aortic blood pressure waveforms that are developed by the interactions of the cardiac and foot impact pressure pulses (>120bpm). Heart rate (HR) and stride rate (SR) can be synchronized in and out of phase with beat frequencies (difference in the HR and SR). Large variations in phasic aortic pulse pressures (40–120 mmHg) occur during running. Transcranial Doppler (TCD) measures dynamic middle cerebral artery blood velocity (CBFv), an index of hemispheric cerebral blood flow. Due to technical limitations, CBFv during running has not been reported. We hypothesized that running would significantly modulate CBFv. We used a 2 MHz TCD and a form fitting headset to minimize motion artifact in 5 healthy subjects (26 ±8SD) during: upright rest; walking (4 mph, no vertical motion); and running (7 mph, 4–5 inch vertical motion). The resting and walking waveforms were similar to reported ergometer waveforms. Running CBFv waveforms were similar to reported pressure waveforms and exhibited beat frequencies with a range of maximal and minimal CBFv. During in phase HR and SR periods, CBFv was 78±8 cm/s. Out of phase CBFv was 56±6 cm/s (p<0.05). Preliminary data suggest that CBFv is significantly modulated by the convolution of HR and SR during running. Dynamic cerebral blood flow may depend on the mode of exercise, and it could be optimized by timing of stride rate.