Newman M F, Croughwell N D, Blumenthal J A, White W D, Lewis J B, Smith L R, Frasco P, Towner E A, Schell R M, Hurwitz B J
Department of Anesthesiology, Duke Heart Center, Durham, NC.
Circulation. 1994 Nov;90(5 Pt 2):II243-9.
Age is a predictor of cognitive dysfunction after cardiac surgery, but the mechanism is unknown. The purpose of our study was to determine whether age-related decrements in cognition are associated with cerebral blood flow (CBF) autoregulation during cardiopulmonary bypass (CPB).
Cognitive function testing was completed before surgery and before hospital discharge in 215 patients undergoing elective coronary artery bypass grafting (CABG) surgery. The battery consisted of seven tests with nine measures designed to evaluate memory, mood changes, and visuomotor speed and function. Pressure-flow and metabolic-flow cerebral autoregulation during hypothermic cardiopulmonary bypass were determined using the 133Xe clearance CBF method and radial artery and jugular bulb effluent to calculate cerebral metabolic rate (CMRO2) and cerebral AV difference (C[AV]O2). Pressure-flow autoregulation was tested by using two CBF measurements at stable hypothermia: one at stable mean arterial pressure (MAP) and the second 15 minutes later when MAP had increased or decreased > or = 20%. Metabolism-flow autoregulation was tested by varying the temperature (CMRO2) and measuring the coupling of CBF and CMRO2. Individual patient autoregulation was correlated with changes in cognitive measures. Cognitive performance declined in 6 of 9 measures after CABG surgery. Age predicted cognitive decline in 7 of 9 measures; short-term memory showed the greatest effect of age. Pressure-flow autoregulation during hypothermic CPB showed a small but significant (P < .0001) effect of pressure on CBF. There was no effect of age on the slope of CBF response to changes in MAP (pressure-flow autoregulation). There was a major effect of temperature on CBF during CPB (P < .0001). Coupling CBF and CMRO2 with changing temperature was unaffected by age. Changes in cognition were not associated with measures of cerebral autoregulation. However, increasing C(AV)O2 is associated with cognitive deficits in 5 of 9 measures; these associations were independent of age.
Increased age predisposes to impaired cognition after cardiac surgery. This decline in cognitive function in the elderly is not associated with age-related changes in cerebral blood flow autoregulation. The association of increased oxygen extraction with decline in some measures of cognitive function suggests that an imbalance in cerebral tissue oxygen supply, which is unrelated to age, contributes to acute cognitive dysfunction after cardiac surgery. Cognitive dysfunction after CPB in the elderly cannot be explained by impaired CBF autoregulation.
年龄是心脏手术后认知功能障碍的一个预测因素，但其机制尚不清楚。我们研究的目的是确定与年龄相关的认知能力下降是否与体外循环（CPB）期间的脑血流量（CBF）自动调节有关。
对215例行择期冠状动脉旁路移植术（CABG）的患者在手术前及出院前完成认知功能测试。测试组合包括七项测试，共九个指标，旨在评估记忆力、情绪变化以及视觉运动速度和功能。采用133Xe清除法测量CBF，并利用桡动脉和颈静脉球流出液计算脑代谢率（CMRO2）和脑动静脉氧差（C[AV]O2），以此确定低温体外循环期间的压力-流量和代谢-流量脑自动调节。通过在稳定低温状态下进行两次CBF测量来测试压力-流量自动调节：一次在稳定平均动脉压（MAP）时，另一次在15分钟后MAP升高或降低≥20%时。通过改变温度（CMRO2）并测量CBF与CMRO2的耦合来测试代谢-流量自动调节。将个体患者的自动调节与认知指标的变化进行关联分析。CABG手术后9个指标中的6个认知表现下降。9个指标中的7个，年龄可预测认知功能下降；短期记忆受年龄影响最大。低温CPB期间压力-流量自动调节显示压力对CBF有微小但显著（P <.0001）的影响。年龄对CBF对MAP变化的反应斜率（压力-流量自动调节）无影响。CPB期间温度对CBF有主要影响（P <.0001）。随着温度变化耦合CBF与CMRO2不受年龄影响。认知变化与脑自动调节指标无关。然而，C(AV)O2升高与9个指标中的5个认知缺陷相关；这些关联独立于年龄。
年龄增加易导致心脏手术后认知功能受损。老年人认知功能的这种下降与脑血流量自动调节的年龄相关变化无关。氧摄取增加与某些认知功能指标下降之间的关联表明，与年龄无关的脑组织氧供应失衡导致了心脏手术后的急性认知功能障碍。老年患者CPB后的认知功能障碍不能用CBF自动调节受损来解释。
