Effect of apolipoprotein E genotype on cerebral autoregulation during cardiopulmonary bypass

Background and Purpose - The presence of the apolipoprotein E ε4 (apoE4) allele has been associated with cognitive decline after cardiac surgery. We compared autoregulation of cerebral blood flow (CBF), cerebral metabolic rate for oxygen (CMRO₂), and arterial-venous oxygen content difference [C(A-V)O₂], during cardiopulmonary bypass (CPB) in patients with and without the apoE4 allele to help define the mechanism of association with cognitive decline. Methods - One hundred fifty-four patients underwent coronary artery bypass grafting with CPB, nonpulsatile flow, and α-stat management. CBF was measured by using ¹³³Xe washout methods. C(A-V)O₂, CMRO₂, and oxygen delivery were calculated. Pressure-flow autoregulation was tested by using 2 CBF measurements at stable hypothermia: the first at stable mean arterial pressure (MAP) and the second 15 minutes later, when MAP had increased or decreased ≥20%. Metabolism-flow autoregulation was tested by varying the temperature and measuring the coupling of CBF and CMRO₂. Results - In patients with (n=41) or without (n=113) the apoE4 allele, there were no differences in CBF, CMRO₂, C(A-V)O₂, pressure-flow and metabolism-flow autoregulation corrected for age, gender, non-insulin-dependent diabetes, hemoglobin, CPB time, and temperature. Conclusions - We conclude that apoE genotype does not affect global CBF and oxygen delivery/extraction during CPB, which suggests that other mechanisms are responsible for the apoE isoform-related neurocognitive dysfunction seen in patients undergoing CPB.