Effect of apolipoprotein E genotype on cerebral autoregulation during cardiopulmonary bypass

Background and Purpose-The presence of the apolipoprotein E epsilon4 (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)O-2], 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 gr afting with CPB, nonpulsatile flow, and ct-stat management. CBF was measure d by using Xe-133 washout methods. C(A-V)O-2, CMRO2, and oxygen delivery we re calculated. Pressure-flow autoregulation was tested by using 2 CBF measu rements at stable hypothermia: the first at stable mean arterial pressure ( MAP) and the second 15 minutes later, when MAP had increased or decreased g reater than or equal to 20%. Metabolism-flow autoregulation was tested by v arying 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)O-2, pressure-flow and metabolism- flow autoregulation corrected for age, gender, non-insulin-dependent diabet es, hemoglobin, CPB time, and temperature. Conclusions-We conclude that apoE genotype does not affect global CBF and o xygen delivery/extraction during CPB, which suggests that other mechanisms are responsible for the apoE isoform-related neurocognitive dysfunction; se en in patients undergoing CPB.