Optimizing Blood Pressure May Impact Brain Health

When MRI scans are conducted on elderly people, global brain atrophy (reduction of brain volume) is a common finding.1 Elderly people with brain atrophy tend to perform more poorly on neuropsychological testing and may be at increased risk for developing Alzheimer’s disease. Besides age, no definite risk factor has been identified for brain atrophy. The researchers for this study investigated the possible relationship between blood pressure levels and brain atrophy.

Patients with either a high diastolic blood pressure (above 85 mmHg) or with a low diastolic blood pressure (below 65 mmHg) had more cortical atrophy than patients with a diastolic blood pressure level between 65 and 74 mmHg. Diastolic blood pressure is the ‘bottom number’ of the blood pressure measurement. Meanwhile, systolic blood pressure (the ‘top number’) did not appear to be related to the degree of cortical atrophy. The researchers concluded that both high and low diastolic blood pressure levels are associated with more global brain atrophy.

This study utilized data collected from the Rotterdam Scan Study, which was designed to investigate determinants and consequences of brain abnormalities on magnetic resonance imaging (MRI) of the elderly. The Rotterdam Scan Study was conducted between 1995 and 1996, and included 1904 subjects aged 60-90 in strata of age (5 years) and gender from two population cohort studies. The researchers in this blood pressure study excluded 187 subjects because they had dementia, were blind, or had MRI contraindications at the time of selection. Of the remaining 1717 eligible patients, 63% (n=1077) gave informed consent and a cerebral MRI scan was obtained. The patients who agreed to complete the MRI scan were on average younger and healthier than those who refused to participate. The study population was divided into two cohorts, and 513 subjects from one of these cohorts (59%) had historical blood pressure data from 20 years before the MRI.

Measurements for both exams included two blood pressure measurements in a seated position, with the average of the values being used. The researchers had no concurrent blood pressure values on 6 of the patients who had MRI scans. The patients all showed their prescribed medications to a physician for coding. Antihypertensive medications and oral antidiabetic medication or insulin were classified according to the Anatomic-Therapeutic-Chemical index. The physician also asked the patients about smoking habits (current, never, or former) and calculated a pack years value by multiplying the number of cigarettes smoked per day by the number of years the person smoked and then dividing this value by 20. Body mass index (BMI) was also evaluated by taking a height and weight measurement and calculating the measure (BMI= weight / (height squared)). Also, T1, T2, and axial proton density weighted MRI scans were made with a slice thickness of 5mm to 6mm and an interslice gap of 20%. Two experienced raters scored the cortical atrophy measures independent of one another and blinded to all other clinical characteristics. They used a 4-point rating scale based on the size of the gyri and sulci from 0 (no cortical atrophy) to 3 (severe cortical atrophy) at five regions (frontal, parietal, temporal and occipital lobes, and the insular region) and the sum of these five regions was calculated.

The degree of cortical atrophy was significantly higher with increasing age and more pronounced in men than in women. Patients that used antihypertensive medications in late life, but not mid- life had more pronounced cortical atrophy, age, and gender adjusted difference. Patients with a high diastolic blood pressure level (85-90mmHg and above 90mmHg) had more cortical atrophy than patients with a diastolic blood pressure level between 65 and 74mmHg. Also, patients with a diastolic blood pressure level of 65mmHg had more cortical atrophy than patients with a diastolic blood pressure level between 65 and 74mmHg. This u-shaped distribution of the association between diastolic blood pressure level and degree of cortical atrophy was statistically significant and remained significant after adjustments for diabetes, BMI, and white matter lesions. The results were similar for users and non-users of antihypertensive medications. Concurrent systolic blood pressure level was not related to the degree of cortical atrophy and systolic blood pressure levels 20 years before the MRI were also not associated with the degree of cortical atrophy later in life. On average, the patients exhibited very little decline in diastolic blood pressure over 20 years. However, a steeper decline in diastolic blood pressure was associated with significantly more cortical atrophy compared to a stable blood pressure level over time. Patients with a decline of more than 10mmHg in diastolic blood pressure had more cortical atrophy than patients with a stable blood pressure over time. The researchers concluded that both high and declining diastolic blood pressure levels were associated with more global brain atrophy on MRI.

 

  1. Heijer T, Skoog I, Oudkerk M, et al. Association between blood pressure levels over time and brain atrophy in the elderly. Neurobiology Aging. 2003; 24:307‐313.