Blood Flow Pattern in the Middle Cerebral Artery in Relation to Indices of Arterial Stiffness in the Systemic Circulation

Abstract

BACKGROUND: The brain is perfused at high-volume flow throughout systole and diastole. We explored the association of blood flow in the middle cerebral artery (MCA) with the pulsatile components of blood pressure in the systemic circulation and indices of arterial stiffness. METHODS: We enrolled 334 untreated subjects (mean age, 50.9 years; 45.4% women) who had been referred for ambulatory blood pressure monitoring to Ruijin Hospital, Shanghai, China. We measured the MCA pulsatility index (PI) by transcranial Doppler ultrasonography. The indices of arterial stiffness included pulse pressure (brachial (bPP) and central (cPP) measured at the office and 24-h ambulatory (24-h PP)) and carotid-femoral (cf-PWV) and brachial-ankle (ba-PWV) pulse wave velocity. Effect sizes, expressed per 1 s.d., were adjusted for sex, age, heart rate, and mean pressure. RESULTS: Women had faster MCA blood flow than men (68.0 vs. 58.3 cm/s), but lower PI (75.4 vs. 82.3%; P < 0.001). The five arterial stiffness indices were intercorrelated (r ≥ 0.37; P < 0.001). PI increased (P ≤ 0.045) with bPP (+6.78%), cPP (+5.56%), 24-h PP (+7.58%), cf-PWV (+1.59%), and ba-PWV (+3.46%). In explaining PI variance, bPP ranked first (partial r(2) = 0.25), 24-h PP second (0.20) and cPP third (0.14). In models including both cf-PWV and ba-PWV, only the latter was significant (-0.19%; P = 0.84 vs. +3.54%; P < 0.001). In models including both bPP and ba-PWV, only the former contributed to PI variance (+6.98%; P < 0.001 vs. -0.24%; P = 0.78). CONCLUSION: MCA blood flow is closely associated with the pulsatile pressure in the systemic circulation, which depends on arterial stiffness as measured by PWV.