BACKGROUND Linear models cannot capture nonlinear associations when the relationships between cognition and risk factors vary across risk levels. We demonstrate a method of modelling nonlinear associations using the example of blood pressure (BP) and memory. METHODS We measured memory and BP (in mm Hg) annually for 10 years in a population-based cohort (N=1982) aged 65+. We evaluated the relationship between BP and memory at the same time points using both linear mixed models and generalized additive mixed models with smoothing splines, adjusting for relevant covariates. RESULTS Linear mixed models found no significant associations. Generalized additive mixed models detected different associations between BP and memory across baseline BP categories (normotensive, hypertensive, hypotensive). Among normotensives, systolic blood pressure (SBP)/diastolic blood pressure (DBP) around 140/80 was associated with the highest, while SBP/DBP around 110/60 was associated with the lowest, predicted memory scores. Among hypertensives, SBP/DBP around 130/85 was associated with the highest, while SBP/DBP around 150/65 was associated with the lowest, predicted memory scores. Among hypotensives, no significant association was found. Among both normotensives and hypertensives, a DBP >75 was associated with better memory. CONCLUSIONS By modelling nonlinear associations, we showed that the relationship between BP and memory performance varied by baseline BP among normotensives and hypertensives.

中文翻译：

---

血压和记忆：纵向研究中非线性效应建模的新方法。


背景技术当认知和风险因素之间的关系随风险水平变化时，线性模型无法捕获非线性关联。我们以血压 (BP) 和记忆为例演示了一种非线性关联建模方法。方法 我们在 65 岁以上人群（N=1982）中每年测量记忆力和血压（以毫米汞柱为单位），为期 10 年。我们使用线性混合模型和具有平滑样条的广义加性混合模型评估同一时间点的 BP 和记忆之间的关系，并调整相关协变量。结果线性混合模型没有发现显着的关联。广义相加混合模型检测了跨基线血压类别（正常血压、高血压、低血压）的血压和记忆之间的不同关联。在血压正常的人中，收缩压 (SBP)/舒张压 (DBP) 大约 140/80 与最高相关，而 SBP/DBP 大约 110/60 与最低预测记忆得分相关。在高血压患者中，SBP/DBP 大约 130/85 与最高预测记忆得分相关，而 SBP/DBP 大约 150/65 与最低预测记忆得分相关。在低血压中，没有发现显着的关联。在血压正常和高血压患者中，DBP >75 与更好的记忆力相关。结论 通过建立非线性关联模型，我们发现血压与记忆表现之间的关系因血压正常者和高血压者的基线血压而异。