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Aging, Neuropsychology, and Cognition: A Journal on Normal and Dysfunctional Development Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/nanc20

Relationship between 24-Hour Ambulatory Blood Pressure and Cognitive Function in Healthy Elderly People Iris B. Goldstein , David Shapiro , Asenath La Rue & Don Guthrie Published online: 09 Aug 2010.

To cite this article: Iris B. Goldstein , David Shapiro , Asenath La Rue & Don Guthrie (1998) Relationship between 24-Hour Ambulatory Blood Pressure and Cognitive Function in Healthy Elderly People, Aging, Neuropsychology, and Cognition: A Journal on Normal and Dysfunctional Development, 5:3, 215-224, DOI: 10.1076/anec.5.3.215.611 To link to this article: http://dx.doi.org/10.1076/anec.5.3.215.611

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Aging, Neuropsychology, and Cognition 1998, Vol. 5, No. 3, pp. 215-224

1382-5585/98/0503-215$12.00 © Swets & Zeitlinger

Relationship between 24-Hour Ambulatory Blood Pressure and Cognitive Function in Healthy Elderly People* Iris B. Goldstein1, David Shapiro1, Asenath La Rue2, and Don Guthrie1 1Department

of Psychiatry and Biobehavioral Sciences, University of California, Los Angeles, and 2Department of Psychiatry, University of New Mexico

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ABSTRACT This study explored the relationship between cognitive function and blood pressure (BP) in 84 women and 64 men, aged 55–79. Assessments were made of casual BP, 24-hour ambulatory BP, and cognitive function. Participants had no evidence of any health disorders, were taking no medication, and were primarily normotensive. By means of principal components analysis, the number of variables was reduced to three BP components of Level, Wake Variability, and Sleep Variability and four cognitive components of Psychomotor Speed/Cognitive Flexibility, Attention, Verbal Memory, and Short-term/Working Memory. Elevated ambulatory BP (level and variability) was associated with difficulties in Attention and Shortterm/Working Memory. The fact that increased risk of poorer cognitive function may be related to BP in an elderly population with relatively low BP means that even moderate elevations in BP may be cause for concern.

In general, BP level is inversely related to cognitive performance, with hypertensive individuals performing more poorly than their normotensive counterparts on neuropsychological tests, particularly in areas of memory, attention, and abstract reasoning (see reviews in Elias, Cobb, White, & Wolf, 1995; Elias & Robbins, 1991; Kalra, Jackson, & Swift, 1994; Waldstein, Manuck, Ryan, & Muldoon, 1991). While most of these findings occurred in young and middleaged populations, investigations of elderly participants reported mixed findings (Farmer et al., 1987; Scherr, Hebert, Smith, & Evans, 1991; Starr, Whalley, Inch, & Schering, 1993; Wallace et al., 1985; Wilkie & Eisdorfer, 1985). In addition, individuals with elevations in BP during midlife exhibited lowered cognitive functioning in old age (Elias et al., 1995; Laurner, Masaki, *

Petrovich, Foley, & Havlik, 1995; Swan, Carmelli, & La Rue, 1996). The current study explored the relationship between cognitive function and BP in unmedicated, healthy, active, elderly participants with no evidence of previous BP, cardiac, psychological, or neurological problems. The focus was on 24-hour ambulatory measures. Ambulatory BP was recorded because of findings that it has an advantage over clinic measures in the diagnosis of hypertension and the evaluation of antihypertensive treatment, is a more sensitive measure of cardiovascular and peripheral vessel target organ damage, and is a better predictor of cardiovascular morbidity and mortality (Mancia, 1990; Rion et al., 1985). Both BP level and variability were related to target organ damage (Frattola, Parati, Cuspidi, Albini, & Mancia, 1993; Mere-

This research was supported by Research Grant AG-11595 from the National Institute on Aging. The computer program used to process the activity data was developed by Timothy F. Elsmore, Activity Research Services, San Diego, CA. Address correspondence to: Iris B. Goldstein, UCLA Department of Psychiatry, 760 Westwood Plaza, Los Angeles, CA 90095-1759, USA. Telephone: (310) 825-8897. Fax: (310) 825-6792. E-mail: [email protected]. Accepted for publication: August 10, 1998.

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dith, Perloff, Mancia, & Pickering, 1995; Palatini et al., 1992). In addition, ambulatory BP was superior to standard BP techniques in predicting future cerebrovascular disease (i.e., lacunae and periventricular hyperintensities; Kawamoto et al., 1991; Shimada, Kawamoto, Matsubayashi, & Ozawa, 1990). We concluded that 24-hour BP would show a relationship to cognitive performance as well. The utilization of the ambulatory monitor allowed us not only to measure BP while participants were awake and during sleep but enabled us to explore BP variability during each of these time periods. In a pilot study of 36 healthy, elderly, normotensive men and women, we found that performance on some neuropsychological tests was significantly correlated with ambulatory BP level and variability during periods of sleep and wake but not with casual blood pressure. Consequently, we predicted that in a comparable healthy population with relatively low BP our findings would be similar. That is, individuals in the higher range of ambulatory BP and those who displayed greater BP level and variability would exhibit decrements in cognitive performance.

METHOD Participants Participants were recruited by media advertisements and from senior centers in Los Angeles. From a total of 1,154 people inquiring about the study, telephone screening revealed that 187 were not interested and 758 did not meet the criteria. Fifty-nine people were dropped after the medical exam, and two were later dropped for noncompliance. The final sample consisted of 84 women and 64 men aged 55–79, mean (SD) = 66.2(5.85) years. Racial composition of the group was as follows: 114 Caucasians, 20 Asian Americans, 12 African Americans, and 2 Latinos. All were healthy and leading an active community life. Ninety-six participants were retired, and 52 were employed fulltime. Only five participants were smokers. Elevations in casual BP were restricted to 10 participants: Two participants had isolated systolic hypertension, systolic BP (SBP) 151–152 mmHg and diastolic BP (DBP) 71–75 mmHg; one participant had moderate hypertension (165/103 mmHg); and seven participants had mild hypertension (SBP 140–155 mmHg, DBP 85–93 mmHg) (The sixth report, 1997) . The remainder of participants were within the normotensive range. Casual and ambulatory BP, neuropsychological test scores, and other participant characteristics are given in Table 1.

Table 1. Characteristics of Sample of 148 Men and Women.

a

Variables

Mean (SD)

Education (years) Self-rated Exercise (hours per week)a Body Mass Index (kg/m2) Blood Pressure Casual Blood Pressure (mmHg) Wake Blood Pressure (mmHg) Sleep Blood Pressure (mmHg) Wake Blood Pressure Variability (mmHg) Sleep Blood Pressure Variability (mmHg) Neuropsychological Tests Digits Forward (number) Digits Backward (number) Auditory Consonant Trigrams (number correct) California Verbal Learning Test (number correct) Trails A (time in s) Trails B (time in s) Digit Symbol (number correct) Benton Visual Retention Test (number correct)

15.5 (5.8) 10.3 (8.4) 24.6 (2.9)

Includes moderate to brisk exercise.

118.8 (14.2)/72.4 (8.7) 126.3 (11.7)/74.0 (6.5) 109.8 (12.9)/62.1 (7.3) 13.8 (3.0)/10.7 (2.9) 9.6 (3.2)/7.5 (2.5) 7.9 (2.3) 6.7 (2.3) 44.5 (8.9) 11.0 (2.8) 35.9 (11.7) 84.3 (28.7) 53.2 (11.0) 7.1 (1.5)

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All participants gave informed consent, with approval obtained from the Human Subjects Protection Committee. Eligible individuals underwent medical examinations and were scheduled to begin ambulatory BP monitoring a few days later. They were studied during two 24-hour time periods, on weekdays, about a week apart. The neuropsychological test battery was given about two days after the first ambulatory session.

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Procedures Medical Evaluation and Screening Initial screening excluded individuals with evidence of any serious current or prior illness, a history of drug or alcohol abuse, head injury, obesity (BMI > 30 kg/m2), prior psychiatric illness, and those taking medications influencing either the cardiovascular or central nervous system. We also excluded anyone having first degree relatives with Alzheimer’s, schizophrenia, or Huntington’s chorea. All participants were fluent in English. On their first visit, participants signed a consent form and underwent a physical and mental status examination by the project physician. This included a complete health history, 12-lead electrocardiogram, urinalysis, and blood chemistry panel. Exclusion criteria included neurological (e.g., history of cerebrovascular accident, Parkinson’s disease, or any serious involvement of the central nervous system), cardiovascular (e.g., congestive heart failure, myocardial infarction, history of coronary disease, atrial fibrillation or symptomatic ventricular arrhythmias), respiratory (e.g., symptomatic bronchospastic diseases), renal (e.g., elevated creatinine or proteinurea), endocrine, and major psychiatric or other disorders, either past or present. An oral glucose tolerance test was used to detect and exclude people with mild diabetes (fasting glucose of > 115 mg/dL, or a glucose > 200 mg/dL after one hour or > 114 mg/dL after two hours of a glucose tolerance test with 75 grams of glucose). Exclusions were made on the basis of the medical examination, laboratory findings, and participants’ medical history. The Mini-Mental State Exam (MMSE; Folstein, Folstein, & McHugh, 1975) was used to screen out cognitive disorders and as a possible covariate in the data analysis. Except for two people with scores of 26, the remainder of our sample scored between 27 and 30. Participants scoring > 5 on the short form of the Geriatric Depression Scale (Sheikh & Yesavage, 1986; Yesavage, 1986) were also excluded. The Brief Symptom Inventory (Derogitis & Spencer, 1982) screened out individuals with possible psychiatric symptoms. The Spielberger Trait Anxiety

217

Scale (Spielberger, Gorsuch, & Lushene, 1970) was administered for use as a covariate in later analyses. In order to determine that BP and cognitive changes were not influenced by sleep disturbances, the Epworth Sleepiness Scale was administered to assess the presence of sleep disorders. This scale was found to significantly distinguish normal individuals from patients with sleep disorders (i.e., sleep apnea syndrome) identified by polysomnography (Johns, 1991). The scale was utilized along with other indexes of sleep quality (see below). Ambulatory monitoring The Accutracker II (Suntech Medical Instruments, Raleigh, NC) was used for 24-hour ambulatory BP monitoring. It has been employed widely in clinical and research studies and has established reliability and validity (Jyothinagaram, Watson, & Padfield, 1990; White, Lund-Johansen, McCabe, & Omvik, 1989). After the participant was seated for 5 minutes and just prior to the ambulatory monitor hook-up, three successive casual readings were taken according to standard assessments (The sixth report, 1997). The laboratory assistant then applied the cuff of the ambulatory monitor to the nondominant arm. On each measurement occasion, single readings of SBP and DBP were obtained. The ambulatory recorder was programmed to operate 3 times an hour on a random schedule during waking hours and once an hour during sleep, the latter based on the participant’s estimates of time of going to sleep and awakening. Participants were given a diary to use with each cuff inflation and were instructed to indicate the following: the time, their location, their activity, and their posture. Actual time of wake and sleep was also noted in the participant’s diary. On the basis of the participant’s information, indexes of quality of sleep, number of times awakened, and number of hours slept were obtained. One week later the procedures were repeated during a second session. Ambulatory data were first edited for artifacts based on Accutracker reading codes (insufficient electrocardiogram or Korotkoff sounds) and extreme values (greater than 200/120 or less than 70/40 mmHg). Editing was done by set rules (Goldstein, Jamner, & Shapiro, 1992). Far outside values were excluded by the stem-and-leaf program of Systat (Evanston, IL). Ambulatory measures for SBP and DBP included (a) means of wake and sleep and (b) variability of the readings in these periods using the standard deviation. Classification of each reading as wake or sleep was based on diary entries and postsession reports. Only nighttime sleep values were included in the

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sleep category and daytime wake values in the wake category. Data for the two days were averaged together to provide single indexes for subsequent analysis. Activity monitor In order to adjust for differences in activity and account for it in the analyses, we utilized the actigraph (Mini-Motionlogger, Ambulatory Monitoring Inc., Ardsley, NY), an electronic activity monitor worn like a watch (Van Egeren, 1991). Movement was recorded on a 24-hour basis along with ambulatory BP. Activity levels were recorded in one-minute intervals (Shapiro & Goldstein, 1998). The activity monitor was used to confirm the differentiation of sleep from wake and to assess the contribution of activity to our findings. However, activity was found to account for a very small amount of the BP effects (Shapiro & Goldstein, 1998) and was not used as a covariate in any final analyses. Neuropsychological Measures The aim in selecting neuropsychological tests was to provide a relatively brief and focused set of clinically relevant cognitive tasks tapping comparatively independent abilities. Highest priority was given to areas of attention and working memory, learning and recall of new information (secondary memory), and speeded tests that place demands on cognitive flexibility or other frontal lobe functions (Boone et al., 1992; Farmer et al., 1990; Matsubayashi, Shimada, Kawamoto, & Ozawa, 1992; Waldstein et al., 1991; Wallace et al., 1985). (1) Digit Span (total number of digits recalled) is composed of two tests. Digit Span Forward is a measure of simple, passive attention; Digit Span Backward measures dual attentional tracking (Wechsler, 1981). (2) Auditory Consonant Trigrams (ACT; total number of correct responses) is useful as a measure of working memory (i.e., the ability to sustain information in short-term memory while other cognitive operations are performed) and divided attention (Peterson & Peterson, 1959; Stuss et al., 1985). (3) The California Verbal Learning Test (CVLT; total number of words correctly recalled) is a test of verbal learning and memory (Delis, Kramer, Kaplan, & Ober, 1987). Since all the subtests were highly intercorrelated, we selected one subtest, long-term delayed recall, as a dependent measure.

(4) The Trail Making Test (total amount of time to complete each task) consists of Trails A which provides an index of visuospatial scanning, simple sequencing, and psychomotor speed, and Trails B which adds the additional requirement of repeated switching of attention between two series (Reitan, 1958). (5) Wechsler Adult Intelligence Scale – Revised (WAIS-R) Digit Symbol (total number of correct responses) involves several cognitive and perceptual-motor functions, including attention, visuoperceptual and visuoconstructive ability, sequencing, and short-term memory (Wechsler, 1981). (6) The Benton Visual Retention Test (BVRT; total number correct) evaluates immediate memory and visuoperceptual-visuographic functions (Sivan, 1991). Data Analysis Using standard methodology, we computed separate principal component analyses (followed by varimax rotation) of the 10 BP and 8 cognitive variables to reduce the dimensionality of the data. The principal components were used in our primary data analyses. We then used multiple linear regression to predict cognitive component scores from BP component scores. Age, gender, and education were used as covariates (control variables). We also looked at individual BP and cognitive variables to illustrate which cognitive test scores were associated with the effects derived from the principal components analysis. On the basis of the distribution of each SBP and DBP measure (casual, wake, sleep, wake variability, sleep variability) participants were divided into upper and lower thirds. The sizes of the groups varied slightly because groups were divided so that there would be no overlapping BP scores. The two extreme groups were compared in a series of Analysis of Variance (ANOVA) tests using the neuropsychological measures as dependent variables. Since the ANOVAs were not used for inference, the p values were used as guidelines only. We included the following variables in both the regression and ANOVA models: age, gender, education, activity, alcohol intake, anxiety (Spielberger scores), and sleep measures (Epworth Sleepiness Scale, quality of sleep, number of times awakened, number of hours slept). In order to rule out cognitive problems identifiable by the MMSE, the score on this test was also used as a covariate in the analyses.

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RESULTS In the principal components analysis three BP components accounted for a total of 75% of the multidimensional variance; they appeared to represent: (a) BP level (casual, wake, and sleep SBP and DBP; (b) BP wake variability (SBP, DBP); and (c) BP sleep variability (SBP, DBP). Four components accounted for 78% of the variance in cognitive scores: (a) Psychomotor Speed/Cognitive Flexibility (Trails A and B, Digit Symbol); (b) Attention (Digit Span Forward and Backward); (c) Verbal Memory (CVLT); and (d) Short-term/Working Memory (ACT and BVRT). Correlations between the component scores and the individual BP and cognitive variables are shown in Tables 2 and 3. Since only age, education, and gender significantly altered our findings and were statistically significant as predictors in one or more of the four cognitive components, they were used as covariates in the final regression and ANOVA models. Our findings remained the same whether the 10 hypertensive individuals were left in or removed from the analyses. Since they were otherwise healthy and their BP elevations small, they were left in all of the analyses. Multiple Regression The components of Psychomotor Speed/Cognitive Flexibility and Verbal Memory were not significantly related to BP (see Table 4). For Attention, although none of the BP components

was significant individually, the combination of BP level, wake variability, and sleep variability added 5.4% additional variance beyond that accounted for by age, gender, and education, F(3, 141) = 2.77, p = .044. For Short-term/Working Memory, the three BP components added 7.1% to the variance, F(3, 141) = 3.80, p = .012, with both BP wake and sleep variability having significant standardized regression coefficients. ANOVA The results of the ANOVAs mirrored the multiple regression findings. See Table 5 for significant findings (F and p values) and BP values for the High and Low groups. As with the regression analyses, there were no significant effects for the tests involved with Psychomotor Speed/ Cognitive Flexibility (Trail Making, Digit Symbol) and long-term Verbal Memory (CVLT). Significant findings were as follows. 1. Individuals with low DBP variability during wake recalled more numbers during tests of attention (Digit Span Forward and Backward) than those exhibiting high variability. 2. Compared to the high SBP group individuals with low SBP during wake had significantly more correct responses on the ACT (working memory). 3. Low SBP variability during wake and low DBP variability during wake and sleep were associated with a higher number of correct responses on the BVRT (short-term visual memory).

Table 2. Correlations Between Blood Pressure Component Scores and Individual Blood Pressure Variables. BP variables DBP Wake SBP Wake SBP Casual DBP Sleep SBP Sleep DBP Casual DBP Wake SD SBP Wake SD DBP Sleep SD SBP Sleep SD

BP Level .85 .84 .81 .81 .78 .77 .07 .12 .06 .11

BP Wake Variability .14 .22 .22 –.15 .02 .02 .92 .87 .07 .11

BP Sleep Variability –.04 .24 .06 .18 .32 –.14 –.04 .28 .86 .84

Note. BP = blood pressure; SBP = systolic blood pressure; DBP = diastolic blood pressure. N = 148.

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Table 3. Correlations Between Cognitive Component Scores and Individual Cognitive Variables.

Cognitive variables

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Trails A Digit Symbol Trails B Digits Forward Digits Backward CVLT (long-term) Benton Visual Retention Test Auditory Consonant Trigrams

Pychomotor Speed/ Cognitive Flexibility –.84 .78 –.71 .19 .14 .16 .46 –.08

Attention –.16 .01 –.41 .87 .80 .03 –.03 .44

Verbal Memory .05 .18 –.20 –.09 .14 .96 .14 .15

Short-term/ Working Memory –.08 .15 –.04 .03 .26 .18 .74 .74

Note. Except for Trails A and Trails B, higher scores on tests indicate better performance. N = 48. CVLT = California Verbal Learning Test.

DISCUSSION The use of ambulatory recordings allowed us to obtain data over longer time periods, during both waking and sleep states, as well as gain information on BP variability. Recent studies indicated that there is a close relationship between target organ damage (cardiovascular and cerebrovascular) and ambulatory BP level and variability (Frattola et al., 1993; Meredith et al., 1995; Palatini et al., 1992). Moreover, we found greater BP variability during waking in participants with increased white matter hyperintensities of the brain (Goldstein, Bartzokis, Hance, & Shapiro, 1998). The present paper shows that BP variability was the single most consistent variable relating to cognitive data in this sample of predominantly normotensive older adults. From studies of casual BP it appears that there may be multiple pathophysiological mechanisms involved in associations between elevated BP and poorer cognitive performance. Persistently elevated BP may disrupt cerebral perfusion, which in turn could affect metabolism or lead to atrophy, increased white matter lesions, or lacunar infarcts (Chimowitz, Awad, & Furlan, 1989). Individuals with hypertension are likely to show signs of brain atrophy due to an interaction of age and elevated BP (Strassburger et al., 1997). All of these brain changes have been linked to cognitive impairments (Boone et al., 1992; Bowen, Barker, Loewenstein,

Sheldon, & Duara, 1990; DeCarli et al. 1995; Matsubayashi et al., 1992). Although elevations in BP have been associated with impairments in brain and cognitive function, little is known about the mechanisms underlying BP variability. We do know that increased variability has been related to a higher prevalence of hypertensive target organ damage (Frattola et al., 1993; Palatini et al., 1992). It has been suggested that the cardiovascular damage may be due to the fact that blood vessels are more susceptible to intermittent than to continuous levels of stress, although a direct cause-effect relationship has not been established (Coca, 1994). Central nervous system impairment and decrements in cognitive performance may also be the result of intermittent stress. Some investigators (Mancia, Di Rienzo, Grassi, & Parati, 1995) feel that increases in BP variability with both age and hypertension may be due to a decline in baroreflex sensitivity, resulting in an inability of the baroreceptors to exert their ‘‘antioscillatory’’ influence on BP. In previous studies, BP measures were most closely associated with measures of attention, working memory, and immediate recall of nonverbal material (Elias, Wolf, D’Agostino, Cobb, & White, 1993; Waldstein et al., 1991). These functions are influenced by multiple brain regions, including frontal-subcortical circuits that can be affected by subcortical white matter changes and by infarction in midbrain and sub-

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Table 4. Multiple Regression of Cognitive Components Using Covariates and Blood Pressure Components.

Components

Predictors

Psychomotor Speed/ Cognitive Flexibility

Age Gender Education BP Level BP Wake Variability BP Sleep Variability Age Gender Education BP Level BP Wake Variability BP Sleep Variability Age Gender Education BP Level BP Wake Variability BP Sleep Variability Age Gender Education BP Level BP Wake Variability BP Sleep Variability

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Attention

Verbal Memory

Short-term/ Working Memory

Standardized regression coefficient

Standard error

p

–.384 –.096 .082 .064 –.079 –.026 –.062 –.020 .153 –.131 –.153 .120 .065 –.449 .164 .074 –.066 –.016 –.108 –.057 .008 –.043 –.210 –.199

.092 .061 .075 .080 .082 .084 .090 .090 .084 .084 .086 .088 .086 .086 .079 .080 .082 .088 .088 .088 .082 .082 .084 .087

.0001 .223 .303 .428 .335 .757 .495 .825 .071 .123 .077 .177 .450 .0001 .041 .357 .420 .082 .222 .521 .923 .601 .014 .023

Cumulative % R2

16.0 16.9 2.9 8.3a 16.7 17.5 5.0 12.1a

Note. Higher scores on tests indicate better performance. For gender 1 = female, 2 = male. N = 148. Independent variables are entered in 2 stages: covariates followed by BP components. R2 is reported for covariates, then for the covariates and BP components. Standardized regression coefficient estimates are based on the full 6-variable regression model. a Additional variance over and above covariates due to BP factors significant at p < .05.

cortical structures. The pattern of cognition/BP associations observed in our study is consistent with prior findings. The BP components (Table 4) accounted for a significant amount of variance (above that due to age, gender, and education) for an Attention dimension and for a Shortterm Working Memory dimension. Not only were our results found primarily with BP variability, but these findings were in persons with good general health, relatively low BP levels, and no apparent cognitive deficits. It appears that both BP level and variability play a role in cognition, but in elderly people with relatively low BP, variability may be the primary marker of cognitive function.

The present findings also showed that the dimensions of Verbal Memory and of Psychomotor Speed and Cognitive Flexibility were not significantly related to BP. Verbal memory deficits have been reported in some studies comparing hypertensive and normotensive individuals (Waldstein et al., 1991). However, within the current sample, differences may emerge with time if BP values reach abnormal levels or if BP variability increases still further. Regarding psychomotor speeded tasks, their high within-group variability may have made it difficult to detect small differences in such a healthy sample (Waldstein et al., 1991). Although our findings on the relationship between high BP variability and decreased cogni-

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Table 5. Significant Neuropsychological Test Score Differences Based on High and Low Blood Pressure (BP) Groups.

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Test scores Digit Span Forward (number of digits) High DBP Wake SD (> 11.6 mmHg) Low DBP Wake SD (< 9.3 mmHg) Digit Span Backward (number of digits) High DBP Wake SD (> 11.6 mmHg) Low DBP Wake SD (< 9.3 mmHg) Auditory Consonant Trigrams (total correct) High SBP Wake (> 129 mmHg) Low SBP Wake (< 120 mmHg) Benton Visual Retention Test (total correct) High SBP Wake SD (> 14.9 mmHg) Low SBP Wake SD (< 12.0 mmHg) Benton Visual Retention Test (total correct) High DBP Wake SD (> 11.6 mmHg) Low DBP Wake SD (< 9.3 mmHg) Benton Visual Retention Test (total correct) High DBP Sleep SD (> 8.4 mmHg) Low DBP Sleep SD (< 6.4 mmHg)

n

BP value (SD)

Cognitive score (SD)

F and p for cognitive differences

51 48

13.9 (2.3) 7.8 (1.1)

7.1 (2.0) 8.7 (2.4)

F(1, 94) = 11.74, p = .001

51 48

13.9 (2.3) 7.8 (1.1)

6.1 (2.1) 7.6 (2.2)

F(1, 94) = 10.82, p = .001

52 49

139.3 (8.1) 114.7 (4.2)

42.2 (7.7) 46.8 (7.9)

F(1, 96) = 7.58, p = .007

51 48

17.1 (2.0) 10.8 (0.9)

6.7 (1.5) 7.6 (1.3)

F(1, 93) = 8.15, p = .005

51 48

13.9 (2.3) 7.8 (1.1)

6.8 (1.5) 7.5 (1.5)

F(1, 94) = 4.24, p = .042

51 50

10.2 (1.4) 4.9 (1.2)

6.7 (1.5) 7.4 (1.5)

F(1, 96) = 5.08, p = .026

Note. Cognitive scores were adjusted for age, education, and gender. BP cut-off scores are included. SBP = systolic blood pressure; DBP = diastolic blood pressure.

tive performance were found for only a few cognitive tests, these results were based on prior hypotheses. The results of this study should be interpreted in the context of the specific population sampled. This was a relatively homogeneous sample of healthy people who were primarily nonsmokers and exercised frequently. None had ever been diagnosed with a major health disorder, and laboratory tests were within the normal range. One only needs to compare the average casual BP of this group (120/72 mmHg) with the general population mean of individuals between the ages of 55 and 74 years (140/83 mmHg; Drizd, Dannenberg, & Engel, 1986) to see that the present study is concerned with a select sample of participants with low BP. Studies of the elderly that demonstrated a relationship between cognitive performance and elevated casual or clinic BP generally utilized hypertensive participants (Wallace et al., 1985; Wilkie & Eisdorfer, 1971) and/or studied very large samples (Elias et al., 1993; Starr et al., 1993; Wallace et al., 1985). The fact that healthy elderly individuals with relatively low BP may show cognitive changes in relation to BP vari-

ability means that even moderate elevations in BP may be cause for concern. Effective and early control of BP may do much to delay or even prevent the onset of changes in the brain as well as deterioration of cognitive function. It has been predicted that decreasing DBP by 2 mmHg would lead to a 17% decrease in hypertension and a 15% drop in the risk of stroke and transient ischemic attacks (Cook et al., 1995). There has been very little focus on BP variability. Current drugs can significantly lower casual BP but are not always effective in maintaining 24-hour control and do almost nothing to regulate variability (Meredith et al., 1995). Our data suggest that it may be important to control BP variability, as well as level. To summarize, cognitive function and BP were studied in healthy, unmedicated men (n = 64) and women (n = 84), aged 55–79 years. Assessments were made of casual BP, 24-hour ambulatory BP, and cognitive function. Elevated ambulatory BP (level and variability) was related to Attention and to Short-term/Working Memory. Results were independent of age, gender, and education. The fact that increased risk

AMBULATORY BLOOD PRESSURE AND COGNITION

of poorer cognitive function may be related to BP in an elderly population with relatively low BP means that even moderate elevations in BP may be cause for concern.

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