Different blood flow responses to dynamic exercise between internal carotid and vertebral arteries in women

The blood flow regulation in vertebral system during dynamic exercise in humans remains unclear. We examined the blood flow responses in both the internal carotid artery (QICA) and vertebral artery (QVA) simultaneously during graded dynamic exercise by Doppler ultrasound to evaluate whether cerebrovascular responses to exercise were similar. In the semisupine position, 10 young women performed a graded cycling exercise at three loads of 30, 50, and 70% of peak oxygen uptake (VO2peak) for 5 min for each workload. Mean arterial pressure, heart rate, and cardiac output increased progressively with three workloads (P<0.01). The end-tidal partial pressure of CO2 (PetCO2) in the expired gas increased from the resting level (P<0.01) at 30 and 50% VO2peak. The PetCO2 at 70% VO2peak (43.2±1.6 Torr) was significantly lower than that at 50% VO2peak (45.3±1.4 Torr). In parallel with the changes in PetCO2, QICA increased from resting level by 11.6±1.5 and 18.4±2.7% at 30 and 50% VO2peak (P<0.01), respectively, and leveled off at 70% VO2peak. In contrast, QVA did not show a leveling off and increased proportionally with workload: 16.8±3.1, 32.8±3.6, and 39.5±3.4% elevations at the three exercise loads, respectively (P<0.01). With increasing exercise load, the cerebrovascular resistance in internal carotid artery increased (P<0.01), while cerebrovascular resistance in vertebral artery remained stable during exercise. The different responses between QICA and QVA in the present study indicate a heterogenous blood flow and cerebrovascular control in the internal carotid and vertebral systems during dynamic exercise in humans.