The paper reviewed here is ‘Relationships between 24-hour blood pressures, subcortical ischemic lesions and cognitive impairment’ by Kim and colleageus and freely available here.
In the introduction, the authors give a very interesting overview of the relationship between blood pressure and subcortical lesions. In particular they focus on the nocturnal blood pressure as there is typically a diurnal cycle with a drop in blood pressure during the night – the so-called dipping phenomenon (and hyperdipping depending on the magnitude of the drop). They discuss some of the evidence of risk associations with non-dipping. They also discuss subcortical vascular mild cognitive impairment (SvMCI).
In the study, the researchers compared 24-hour BP values in controls, people with Subcortical Vascular Dementia (SVaD) and people with SvMCI. People with SVaD and SvMCI were recruited from a memory clinic in Seoul, Korea while the controls were recruited from a cardiology centre again in Seoul. I wasn’t clear on how SvMCI was diagnosed and thought it might have been a complex judgement. There are details given in the paper and the authors do acknowledge the difficulties in attributing cognitive impairment to a subcortical vascular cause but they state that other causes have been excluded. Nevertheless the MRI scans in themselves would not be suitable for detecting amyloid plaques that would be present in an AD (although they have looked specifically for other markers of AD pathology on the MRI). Blood pressures were obtained using ambulatory blood pressure monitoring and a 3 Tesla MRI scanner was used for the MRI scans and they use a specific protocol to assess the images for vascular lesions. Cardiovascular risk factors were identified in the participants. The Seoul neuropsychological screening battery was used and a breakdown of this screening instrument is given in the paper. They also state that the
There were a number of exclusion criteria although this didn’t affect the final numbers too much (89 included with SVaD or SvMCI initially and 79 after exclusion). On looking through the methodology and results, I noticed that there were a large number of comparisons being used and the researchers were also using the Tukey’s test – which is used in a post-hoc analysis. The researchers described their main findings as an increased systolic blood pressure variability in the SVaD group compared to the SvMCI group as well as an ‘disruption’ of the nocturnal BP rhythm in the SVaD and SvMCI groups. The researchers themselves note that this is not a prospective study and that the SvMCI diagnosis was made in the ‘absence’ of established criteria for SvMCI. While these were potentially interesting findings, I noted the post-hoc analysis and would be interested to see a larger replication study, prospective in design and using these results to inform the primary outcome measures in the next study.
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