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Reference: Li, 2007
Cohort: Adult Changes in Thought-Group Health Cooperative
Risk Factor: Blood Pressure


Average Follow-up Time Detail
All participants were members of the Group Health Cooperative HMO in the Seattle, WA area and were 65 years old or older at baseline. Recruitment and baseline assessments of participants occurred in 1994-1996. Participants who were dementia-free at baseline were followed biennially for approximately 8 years.

The study authors reported stratified results based on age at baseline. This entry reflects consideration of the approximately 150 participants who were 85+ years old at baseline.

Exposure Detail
"At enrollment and at each biennial follow-up examination, a trained nurse or technician measured BP using standardized techniques. After subjects sat at rest for at least 5 minutes, systolic BP (SBP) was taken as point of first hearing the Korotkoff sound and diastolic BP (DBP) as the point of disappearance of the Korotkoff sound. Two BP measurements were taken 5 minutes apart, and the average of the two readings was used for the analysis. ... The majority of invalid BP measurements were due to inability of experienced examiners to obtain BP measurements. For example, they could not hear the Korotkoff sound when taking BP. A few cases had extremely high or low values that were most likely due to error. The plausible range of SBP was defined as 70 to 260 mmHg and DBP as 40 to 160 mmHg."

Age Detail
The authors stratified results by age at baseline, with age categories chosen to provide sufficient numbers within groups. This entry summarizes the results for those over 85 years old.

Screening and Diagnosis Detail
Screening Method:
CASICognitive Abilities Screening Instrument (Teng 1994)

AD Diagnosis:
NINCDS ADRDA National Institute of Neurological and Communicative Diseases and Stroke/Alzheimer's Disease and Related Disorders Association Criteria (McKhann 1984)

Total dementia definition: DSM-IV criteria for dementia due to any cause.

"Those with CASI scores less than 86 underwent a standardized dementia diagnostic evaluation, including a physical and neurological examination by a study neurologist (JDB), geriatrician (WM), or internist (EBL) and a 1-hour battery of neuropsychological tests. Relevant laboratory tests and brain computed tomography or magnetic resonance imaging studies were performed, or results were obtained from Group Health Cooperative records. Diagnoses were assigned by consensus of experts using Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, criteria for dementia26 and the National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer Disease and Related Disorders Association criteria for AD.27 Dementia due to any cause and probable AD were used as outcome measurements. Vascular dementia and multi-infarct dementia were not analyzed as separate outcomes in these analyses because of the lack of sensitive and reliable diagnostic criteria28,29 and because there were few individuals who appeared to have pure vascular dementia.30

Participants with new onset of dementia underwent at least one annual follow-up examination for verification of dementia status and assessment of cognitive decline. The point of dementia onset was defined by convention as halfway between the date of the prior screening or examination and the date of diagnosis."

Covariates & Analysis Detail
Analysis Type:
Cox proportional hazards regression

"Because of its relationship to dementia and AD risk, age was used as the time axis.31 Data were left-truncated at the age of study entry. … To assess the association between BP and dementia beyond the effects of other vascular factors, models were also constructed including history of coronary heart disease, cerebrovascular disease, diabetes mellitus, and use of antihypertensive medications. … To assess whether the effect of BP on subsequent dementia or AD risk varied by age, separate models were constructed for each of three age groups at entry: 65 to 74, 75 to 84, and 85 and older. These age categorizations were chosen to provide sufficient numbers in each group to permit analyses while dividing the population to examine whether effects were consistent across age groups. To determine the statistical significance of the variation of the BP–dementia association according to age, likelihood ratio tests were used to compare models including all participants (i.e., non-age stratified) with and without terms for the interaction between BP categories and age at entry as a continuous variable."

AD Covariates:
Aage
Eeducation
Ggender
APOE4APOE e4 genotype
RErace/ethnicity

TD Covariates:
Aage
Eeducation
Ggender
APOE4APOE e4 genotype
RErace/ethnicity