Assessment of Cerebral Blood Flow Velocity by Transcranial Doppler Ultrasound During Maximal Bicycle Ergometry

Abstract

0165 Transcranial Doppler Ultrasonography (TCD) is a functional technique to noninvasively insonate cerebral arteries to monitor changes in mean cerebral blood flow velocity (mBFV). To date research has demonstrated both an increase and decrease in mBFV with dynamic exercise. PURPOSE: This study was conducted to evaluate the changes in mBFV through the middle cerebral artery (MCA) at varying intensities during upright cycle ergometry. METHODS: Fifteen (Male = 9, Female = 6) healthy, young (23.7±4.1 yr) participants volunteered for this study. Mean height and weight were 175.3 cm (±9.1) and 72.3 kg (±10.6), respectively. Participants underwent a stepwise bicycle protocol starting at 50 watts and increasing 25 watts every 2 minutes until maximal exertion. The mBFV was continuously monitored in the left MCA by TCD through a 2-MHz probe attached to Mark IV headgear. Partial pressure of end-tidal carbon dioxide (PETCO2), mean arterial pressure (MAP), and mBFV were assessed at rest, light intensity (LI: 30% VO2max), moderate intensity (MI: 60% VO2max), and VO2max. Data were analyzed using one-way repeated measures ANOVA with Bonferoni's post hoc analysis and are reported as mean±SEM. RESULTS: The main effect of exercise was significant for mBFV (P = 0.001), PETCO2 (P<0.001), and MAP (P<0.001). There was no change from rest to LI (52.2±2.6 vs. 56.7±3.2 cm/sec), however there was a significant increase from rest to MI (63.9±3.5 cm/sec, P = 0.001), and LI to MI (P = 0.01), thereafter mBFV decreased significantly from MI to VO2max (55.9±3.2 cm/sec, P = 0.01) with no difference between rest and VO2max or LI and VO2max. The PETCO2 followed a similar pattern as mBFV increasing significantly from rest to LI (32.5±1.2 vs. 38.4±0.6 mmHg, P<0.001), rest to MI (41.7±0.8 mmHg, P<0.001), and LI to MI (P<0.001) then decreasing slightly from MI to VO2max (38.5±1.7 mmHg, P = 0.08). There was no difference between LI and VO2max, however VO2max values were significantly elevated from rest (P = 0.01). Although no difference was found in MAP from rest to LI, there was a significant increase from rest to MI (89.5±1 vs. 102±2 mmHg, P<0.001), LI to MI (P = 0.001), MI to VO2max (109±2 mmHg, P = 0.001), and rest to VO2max (P<0.001). CONCLUSION: These data demonstrate an increase in mBFV during dynamic exercise up to 60% VO2max after which mBFV decreases to levels equivalent to those at rest. Both MAP and PETCO2, the primary regulators of cerebral blood flow, increased with workload up to 60% VO2max where MAP continued to rise and PETCO2 declined similarly to what we observed in mBFV.