Discussions
Long-term hypertension can cause cerebral arteriosclerosis and cerebral
blood circulation disorders, cause brain tissue function damage, and is
related to cognitive dysfunction31. This meta-analysis
has included thirteen case-control studies on the correlation between
blood pressure variability and cognitive function, and the quality of
the included literature is high. The synthesized outcomes have showed
that the increase in blood pressure coefficient of variation is
correlated with cognitive dysfunction, and cognitive function is also
correlated with 24-hour blood pressure standard deviation and average
blood pressure, but there is no correlation with the morning peak of
blood pressure. The increase of blood pressure variability will increase
the risk of cognitive dysfunction and adversely affect the prognosis of
hypertensive patients32. It is worth noting that the
large heterogeneity of the analysis indicators in this study may be
related to the sample size and age or the inconsistent follow-up time of
each study. Therefore, the results of this meta-analysis should be
treated with cautions.
Short-term and long-term blood pressure variability are independently
related to the development, progression, and severity of heart, blood
vessel, and kidney damage, and are associated with an increased risk of
cardiovascular events and death33,34. Blood pressure
variability has been considered that it has a better predictive effect
on cardiovascular events than the average blood pressure [20].
Cognitive dysfunction covers the entire progression from mild cognitive
impairment to dementia, and it is also a major problem in the prevention
and treatment of hypertension complications. There has been a large
amount of evidence in the past that hypertension is the most common risk
factor for cognitive impairment, and recent
studies35,36 has shown that blood pressure variability
has a close clinical relationship with cognitive function. At present,
the mechanism between blood pressure variability and cognitive function
is not clear, but some scholars believe that it may be related to the
white matter. Blood pressure variability is related to target organ
damage, including white matter that has nothing to do with the 24-hour
average blood pressure value, leading to the occurrence of white matter
hyperintensity, and white matter lesions are the inducing conditions for
cognitive impairment37. The presence of high-strength
lesions and cavities around the ventricles of the elderly with
asymptomatic hypertension suggests the relationship between diurnal
blood pressure changes and cerebrovascular injury, and cerebrovascular
injury will further accelerate the progress of cognitive dysfunction,
which is also a common predictor of stroke8.
Previous study38 has showed that increased systolic
blood pressure and increased sleep systolic pressure variability were
related to the aggravation of brain atrophy. The aggravation of cerebral
arteriosclerosis and cerebral arterial remodeling caused by long-term
systolic hypertension may be related to the disorder of brain
autoregulation39. It leads to a decrease in cerebral
blood flow and aggravation of brain atrophy, which leads to a decline in
cognitive function40. Recent
studies41,42 have shown that increased blood pressure
variability is associated with stroke and advanced carotid artery
remodeling, and carotid artery remodeling can lead to cognitive
impairment. The absolute dynamic systolic blood pressure level
especially during sleep and the decrease in night systolic blood
pressure are important indicators of brain volume and cognitive
function. Based on the above results, it is believed that chronic
ischemia caused by hypertension may cause the interruption of the day
and night changes in blood pressure through the damage of the brain’s
self-regulatory function, and then the blood pressure does not drop
during sleep43. Previous
studies44,45 have found that systolic blood pressure
variability is more predictive of cognitive dysfunction than systolic
blood pressure. It’s been reported that through community experiments
that higher blood pressure variability is related to the decline in
cognitive function of patients assessed by simple mental status
examination46. Although the systolic blood pressure
variability cannot predict whether the risk of dementia in the overall
population increases, it is not found in the subgroup of individuals
without a history of cardiovascular disease47. The
systolic blood pressure variability is positively correlated with the
risk of dementia48. Previous
studies49,50 have reported that high or low blood
pressure will lead to cognitive dysfunction. The above conclusions are
consistent with the analysis results of this research. Therefore, it is
speculated that blood pressure variability reflects the degree of
cognitive decline to a certain extent, and can be used as an important
clinical reference index in the prognosis of middle-aged and elderly
hypertensive patients51,52.
Several limitations in this present meta-analysis should be concerned.
Firstly, most included studies were reported from China, therefore
population and region biases may be existed, future studies from
different region and populations should be conducted. Secondly, studies
have reported that cognitive impairment is related to factors such as
pulse pressure index and ankle brachial index. Due to the limitations of
the included research data, we cannot further analyze and discuss the
correlation of these indicators. Future research should be further
conducted to elucidate the correlation between blood pressure related
indicators and CI.