Visit-to-Visit Variability in Blood Pressure Is Related to Late-Life Cognitive Decline

Qin B, Viera AJ, Munther P, et al.
Hypertension 2016;68:106-113

Background

The investigations of cognitive disorders in relation to blood pressure (BP) are commonly focussed on mean BP levels in contrast to the variability between visit-to-visit BP measurements. However, over the last 5 years evidence has accumulated that visit-to-visit BP variability may not be a random phenomenon or simply an unimportant measurement artefact, but may instead provide information on pathological processes and it can be relevant for prognosis [1,2].

Although evidence demonstrated that midlife hypertension is a risk factor for cognitive decline, its association with late-life hypertension is less clear. Nor is it known whether visit-to-visit variability in BP is associated with a faster rate of cognitive decline in a general population of older adults.

Therefore, this study examined the association between visit-to-visit variability in BP and cognitive decline among a sample of community-dwelling Chinese men and women (n=976, age ≥55yrs) that were included in the China Health and Nutrition Survey (CHNS) which is an ongoing longitudinal open cohort study from 1989 onwards. In 3 waves (1997, 2000 and 2004), CHNS used identical cognitive screening items that were verified by telephone.

Main results

Systolic blood pressure (SBP)

• A higher SD of SBP was associated with older age, higher urbanisation index, lower education and physical activity, having a history of stroke or diabetes mellitus, and taking antihypertensive medication.
• Mean SBP was progressively higher with increased SD of SBP (r=0.33).
• No significant association was seen between mean change in SBP and global cognitive decline (= total score of all cognitive screening items, lowest vs. highest tertile of SD of SBP, β=-0.13, P=0.09).
• The adjusted rate of global cognitive decline associated with the middle (9.30-15.00 mmHg) and highest (≥15.01 mmHg) tertile of SD of SBP was faster by -0.13 and -0.27 points per year respectively (95% CI: -0.33 to 0.06 and -0.47 to -0.07 respectively), compared to the lower tertile (<9.30 mmHg, P trend = 0.008).
  For verbal memory scores this was -0.018 for the middle and -0.041 for the highest tertile of SD of SBP (95% CI: -0.051 to 0.015 respectively -0.075 to -0.008, P trend =0.02).
• The associations were not dependent on age.

Diastolic blood pressure (DBP)

• Age significantly modified the association between DBP variability and cognitive decline (P=0.01).
• For those aged ≥65 yrs, a higher SD of DBP was associated with a history of myocardial infarct, but not with cognitive decline.
• Higher mean DBP and antihypertensive medication, stratified for age, were associated with increased SD of DBP (association with mean DBP r=0.14 for participants <65 yrs and 0.09 for those ≥65 yrs).
• Among adults aged <65 yrs, the adjusted rate of global cognitive decline for the middle and highest tertile of SD of SBP was faster by -0.29 respectively -0.29 points per year (95% CI: -0.53 to -0.05 for both), compared to the lower tertile (P trend = 0.02).
• There was a difference in the association between residual variation of DBP and global cognitive declines (highest vs. lowest tertile; β=-0.27, 95% CI: -0.51 to -0.03, P trend = 0.04), suggesting the relation is possibly because of the DBP fluctuation instead of the systematic pattern over time
  
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Conclusion

Higher visit-to-visit variability in SBP was associated with a faster decline of global cognitive function and to a lesser extent of verbal memory over a mean follow-up of 5 years. This was also true for DBP for adults of 55-64 years of age. In contrast, no association between mean SBP or DBP with cognitive change over time was observed.

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References

1. Muntner P, Joyce C, Levitan EB, Holt E, Shimbo D, Webber LS, Oparil S, Re R, Krousel-Wood M. Reproducibility of visit-to-visit variability of blood pressure measured as part of routine clinical care. J Hypertens. 2011;29:2332–2338. doi: 10.1097/HJH.0b013e32834cf213.
2. Rothwell PM, Howard SC, Dolan E, O’Brien E, Dobson JE, Dahlöf B, Sever PS, Poulter NR. Prognostic significance of visit-to-visit variability, maximum systolic blood pressure, and episodic hypertension. Lancet. 2010;375:895–905. doi: 10.1016/S0140-6736(10)60308-X