Methods
We tried to conduct and report this meta-analysis in comply with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)16.
Literature search
We searched PubMed, Cochrane library, Web of Science, China National Knowledge Infrastructure(CNKI), Wanfang, China Biology Medicine disc (CBM), and Weipu database for the study on the association between blood pressure variability and cognitive function. The search terms included ”blood pressure variability” OR ”BPV” OR ”ambulatory blood pressure” and ”cognitive function” ”OR ”cognitive functioning”. The search was carried out by combining subject words and free words. Retrieval time limit was from the date of establishment of each database to July 15, 2021.
Inclusion and exclusion criteria
The inclusion criteria for this meta-analysis were: Study type: a publicly published case-control study on blood pressure variability and cognitive function; Research population: patients aged 18 to 80 years old and diagnosed with essential hypertension; Control: CI group and no CI group; The outcome indicators included blood pressure et al; Language: Chinese or English article. The exclusion criteria of this meta-analysis were: patients with severe cardiovascular diseases and other major diseases; articles that repeatedly publish or use the same data; studies with incomplete data.
Literature screening and data extraction
Two researchers independently searched and screened relevant documents. The search results were imported into Endnote for double-checking, and then the initial screening was carried out based on the abstracts of the literature to eliminate irrelevant or unusable documents. After completion, the researchers collected and recorded following information, including the author, publication year, country, age, sample size, outcome indicators, findings.
Quality Evaluation
The type of studies included in this meta-analysis was case-control study, so it was scored according to the Newcastle-Ottawa Scale (NOS) Literature Quality Evaluation Scale17. The full scale of the scale was 10 points. The evaluation items mainly included three items: population selection, comparability, and exposure. If the quality score was less than 5, it indicated a high risk of bias and needs to be excluded. Disagreements in the evaluation results were resolved through further discussion.
Statistical processing
We used RevMan 5.3 for data meta-analysis. Relevant indicators were visually displayed in forest plots, and funnel plots were used to detect the populations. Continuous variables were represented by the mean difference (MD) and its 95% confidence interval (CI). If I2≤50% or P>0.10, the heterogeneity of the study was small, and the fixed-effects model was adopted; if I2>50% or P ≤0.10, the random-effects model was adopted. P<0.05 indicated the differences between two groups were statistically different.