Journal of Gerontological Nursing

Assessment 

Resting and Reactive Blood Pressure

Lorraine Frazier, RN, DSN, NP-C

Abstract

Predictors of Ambulatory Blood Pressure in Older Adults with Hypertension

Blood pressure management is important in older adults to decrease mortality and morbidity. This study examines methods of measuring and interpreting blood pressure.

Abstract

Predictors of Ambulatory Blood Pressure in Older Adults with Hypertension

Blood pressure management is important in older adults to decrease mortality and morbidity. This study examines methods of measuring and interpreting blood pressure.

Hypertension affects more than 50 million Americans and is the main contributor to cardiovascular disease, stroke, and renal failure (Beevers & MacGregor, 1999). Effective blood pressure (BP) management is important in older adults with hypertension to decrease mortality and morbidity, but full BP control in this population is not a common achievement (Sega et al., 1997). To achieve better BP management in older adults with hypertension, traditional methods of measuring and interpreting BP should be revisited (Frazier, 2000).

Traditional "static" BP measurement consists of BP assessment while the patient is at rest. However, "dynamic" BP can be measured in the patient's own environment with ambulatory BP monitoring. Ambulatory BP monitoring captures the effect of environmental stressors by recording BP patterns throughout a 24-hour period allowing the calculation of a 24-hour mean BP and calculation of BP load, the percent of hypertensive BP readings over 24 hours (Prisant, 1995). This is significant because 24-hour mean BP represents the "true " BP of the patient better than does a static BP measurement (Moore, Krakoff & Phillips, 1997). In addition, a BP load greater than 40% is predictive of target organ damage (Prisant, 1995). Although ambulatory BP monitoring provides an accurate assessment for BP management, the time and expense required for ambulatory monitoring limit its use as a routine screening method.

The author undertook the current study to examine three methods of BP measurement - two clinical (resting BP and BP reactivity to a speech protocol) and one ambulatory (24-hour BP). The author wanted to determine the ability of resting BP, pulse pressure (PP) (i.e., difference between systolic and diastolic BP), and BP reactivity to predict 24-hour mean BP and BP load in a population of older adults who are medicated and hypertensive, and have cardiovascular disease. Both the BP reactivity protocol and ambulatory BP monitoring were used to capture the influence of the sympathetic nervous system on BP readings in response to the environment. The investigator hypothesized that reactive BP taken during the speech protocol would be better than resting BP in predicting 24-hour BP and be better than resting BP in predicting BP load.

CONCEPTUAL FRAMEWORK

The Model for Hypertension Development and Assessment (HDA) (Figure) served as the framework for the study (Frazier, 2000). The HDA model depicts increasing risk of hypertension with age and focuses on the older adult (50 and older). High BP is affected by the interactions of genetics, physiology, responses to the environment, and lifestyle factors that have increasing influence as one ages (Ellsworth, Hallman, & Boerwinkle, 1997; Hallman, Ellsworth, & Boerwinkle, 1997; Lynch, 1985; Weder & Schork, 1994). The HDA model emphasizes factors affecting hypertension risk in the older adult, focuses on BP assessment, and depicts the strong influence of sympathetic activity in risk factors of hypertension development. The HDA model will be used as a guide for the discussion focusing on physiology, response to the environment, and BP assessment (static and dynamic BP measurements).

PHYSIOLOGY

The physiology of BP in older adults who are hypertensive is complex. Arterial restructuring (which results from the arterial stiffening of aging) and increased resistance each affect BP measurements differently. With increased arterial stiffness, diastolic BP remains constant or falls below normal, and systolic BP increases, causing an increased PP (Franklin & Weber, 1994).

With increased resistance, systolic and diastolic BP increase. In adults older than age 50 (unlike in younger individuals), PP measured at the brachial artery may accurately reflect arterial stiffness in large arteries located in the central part of the body. This is because, unlike younger healthy arteries with PP lower in the central arteries compared with the peripheral arteries, stiffened arteries in older adults result in a greater increase in PP in the central arteries than in peripheral PP (Franklin & Weber, 1994). This results in a similar PP throughout the arterial system (Safar, 1996).

The restructuring of the arterial walls results in dynamic BP changes. Blood pressure reactivity increases as thickened arteries, resulting from chronic hypertension and aging, become hyperresponsive to sympathetic discharge in response to the environment (Julius & Nesbitt, 1996).

RESPONSE TO ENVIRONMENT

All BP measurement methods capture the patient's context or response to immediate environment (Thomas, Liehr, DeKeyser, & Friedmann, 1993). Static BP captures BP responses to the clinical environment, ambulatory BP captures BP responses to the patient's natural environment, and BP reactivity captures BP response to a controlled stressor.

Resting Blood Pressure

Static BP taken in the clinic reveals in some patients a "white coat" effect - an increased reaction of a patient's BP reading to a clinic environment. This phenomenon is present among all age groups, but older adults and individuals with hypertension are particularly affected. In a study measuring BP adaptation to the environment in patients ages 23 to 82 years, van Boxtel, Gaillard, van Es, Jolies, and de Leeuw (1996) found after 15 minutes of taking BP every 5 minutes, no further BP decrease was observed. The decrease during the adaptation period of both the systolic and diastolic BP was more pronounced with age, indicating an increase of the white coat effect in older adults. Furthermore, they argued the observed effect of age would be intensified in a clinical setting (particularly in hypertensive patients), thus emphasizing the importance of allowing an adequate adaptation period with the increasing age of the patient.

Although static BP measures BP at rest, research supports the ability of static BP to predict dynamic BP (24-hour ambulatory BP) in adolescents and young adults (Linden & Con, 1993; Leininger et al., 1999). No studies report the ability of static BP to predict 24-hour ambulatory BP in older hypertensive adults who, unlike younger individuals, have an increase of BP variability to environmental stressors.

Twenty-four-hour Blood Pressure

Ambulatory BP measures BP response to the environmental stressors of daily life, which increase with age (van Boxtel et al., 1996). When 24-hour ambulatory BP response to environment contributes to a BP load greater than 40%, end organ damage can result. White, Dey, and Schulman (1989) reported an association between BP load, recorded by ambulatory BP measurements over 24 hours, and left ventricular hypertrophy in patients ages 23 to 72 years (mean age, 47 years). Systolic and diastolic 24-hour loads greater than 40% were good predictors of left ventricular hypertrophy, approximately 60% to 90%, and BP loads less than 40% were an indication of low prevalence of hypertensive heart disease. It is, therefore, important to assess ambulatory BP mean and load for BP management in older adults who are hypertensive.

Figure. Model for hypertension development and assessment (HDA). Note: From "Factors influencing blood pressure: Development of a risk model," by L. Frazier, 2000. Journal of Cardiovascular Nursing, 75(1), p. 63. Copyright 2000 by Aspen. Reprinted by permission.

Figure. Model for hypertension development and assessment (HDA). Note: From "Factors influencing blood pressure: Development of a risk model," by L. Frazier, 2000. Journal of Cardiovascular Nursing, 75(1), p. 63. Copyright 2000 by Aspen. Reprinted by permission.

Blood Pressure Reactivity

In a study measuring BP reactivity to mental stress in patients with mean age of 47 ± 7 years with atherosclerosis, Krai et al. (1997) found "hot responders" (top quartile of change in diastolic and systolic BP) were more likely than other individuals to have ischemia associated with increased cardiovascular reactivity during exercise. These individuals demonstrated "response specificity," a term specifying the autonomic response is consistent for the individual across different stressor stimuli (Pickering & Gerin, 1990).

If the response in individuals is consistent across stressors, it can be hypothesized that older patients who are hypertensive (i.e., having increased BP reactivity in a clinic BP reactivity protocol) may have:

* A propensity for having a high BP load in their own environment over the course of a 24-hour period.

* A predisposition to increased morbidity and mortality.

BLOOD PRESSURE ASSESSMENT

Resting Blood Pressure Measurement

Static BP measurement (a single BP measurement taken at one point of time or the average of two readings in a clinical setting) fails to depict the variability of BP, while ambulatory BP monitor readings expose BP variability caused by physiologic factors, response to the environment, and lifestyle factors (Neutel, 1996). Pulse pressure, which is reflective of the compliance of the large arteries, has been recognized as an important cardiovascular risk factor (Van Bortel & Spek, 1998).

Twenty-four-hour Blood Pressure Measurement

Ambulatory BP is used as a research tool to study BP variation as individuals perform their normal daily activities. However, despite the expense involved, over the past 30 years this tool has evolved from a research instrument to a usable clinical measure (Pickering & O'Brien, 1991). If the number of BP measurements is at least 30, the sampling distribution approximates a normal curve. This increases the confidence that the measured mean BP represents the true BP of the client (Moore et al., 1997). Sleep-wake cycles have to be determined to measure BP load from ambulatory BP data. This is done through the use of activity monitors and diaries.

Blood Pressure Reactivity Measurement

Another way to evaluate BP is by determining the patient's reactivity to controlled stressors in a clinical setting over a short, structured time period to measure BP reactivity. Because of the positive relationship of ambulatory measures to end organ damage, there has been an interest in predicting ambulatory BP with BP reactivity laboratory protocols. However, the use of laboratory BP reactivity change scores (the deduction of baseline BP from tasklevel BP) (Linden & Con, 1993) for prediction of ambulatory BP has shown mixed results.

The speech task stressor has most consistendy produced predictive results with young adults. A speech task has not been used in a BP reactivity protocol to predict 24-hour ambulatory BP in older adults who are hypertensive.

Table

TABLE 1DESCRIPTIVE STATISTICS (N = 45)

TABLE 1

DESCRIPTIVE STATISTICS (N = 45)

The purpose of this study was to compare three methods of BP assessment to establish which measure would be most predictive of 24-hour mean BP and BP load. The methods are:

* Resting BP.

* Pulse pressure.

* Blood pressure taken during a BP-reactivity speech protocol.

METHODS

Sample

Patients 50 years or older who were participating in Phase II (structured outpatient program of exercise, counseling, and education) and Phase III (continuation of rehabilitation after patients reach their initial goals) cardiac rehabilitation at two outpatient cardiac rehabilitation centers in the southeastern United States were reviewed for the use of anti-hypertensive medications. English-speaking individuals treated with anti-hypertensives were invited to participate in the study. Both genders and all ethnic groups, married, widowed, or divorced, were included in the study (Table 1). Each patient had a history of coronary artery disease and was actively participating in cardiac rehabilitation.

Excluded from the study were patients with a diagnosis of congestive heart failure, or an arrhythmia or cardiomyopathy. Patients having undergone valve replacement surgery, or having an implanted defibrillator device were also excluded. Those in the sample had a mean age of 64.6 ± 8.5 years.

Included in the study were 45 patients who completed both the BP reactivity and ambulatory BP monitor protocol. Body mass index (BMI), the most commonly used index of overweight and obesity derived by dividing weight in kilograms by height in square meters, was calculated for each patient. The average BMI of the sample was 29.2 ± 5.8, which is overweight according to the World Health Organization (WHO). The WHO classifies a BMI greater than 25 as associated with being overweight, and a BMI of 25 or less with nonoverweight (Guo et al., 2000).

The average years of hypertension diagnosis was 15.3 ± 12.9 years. Anti-hypertensive medications taken by the sample included one or a combination of calcium channel blockers, beta-blockers, alpha-blockers, diuretics, or ACE inhibitors.

Table

TABLE 2BLOOD PRESSURE REACTIVITY PROTOCOL

TABLE 2

BLOOD PRESSURE REACTIVITY PROTOCOL

PROCEDURES

Each patient made an appointment to participate in the protocol. After 5 minutes of rest, the patient's BP was taken by a sphygmomanometer, the BP reactivity protocol was performed, and the patient was given instructions on ambulatory BP monitor and fitted with an ambulatory monitor and an actigraph to wear over 24 hours in the patient's own environment. A diary and instructions on its use were also provided.

Resting BP

Blood pressure was taken using a sphygmomanometer after 5 minutes of rest in a comfortable chair and repeated in 2 minutes as outlined by the American Heart Association (AHA) (Grim, 1999). Resting BP was the average of these two BP readings.

Blood Pressure Reactivity Protocol

The 26-minute BP reactivity protocol is depicted in Table 2. Each patient was seated in a comfortable chair in a small, private room. Blood pressure was taken using a Dinamap (GE Medical Systems, Fairfield, CT) every 2 minutes throughout the protocol except during talking, when pressures were taken every minute. During the normal talking period, the patient was asked to talk for 2 minutes in response to the request, "Please describe a typical day for you from beginning to end." This question was thought to be non-stressful because it was non-personal.

During the health talking period, the patient was asked to talk for 2 minutes in response to the question, "How have you felt over the past 3 months?" This question was thought to be stressful because talking about one's health is personal and requires the patient to think about negative life events. The order-of-talking series was randomly assigned using a table of random numbers.

Ambulatory Blood Pressure Monitoring

After the BP reactivity protocol, the patient was fitted with the BP cuff of the ambulatory BP monitoring device. The Motionlogger® actigraph (Ambulatory Monitoring, Inc., Ardsley, NY) was applied to the other wrist to track activity. The instruments are synchronized so specific time intervals of actigraph and ambulatory BP readings could be linked for data analysis.

Five actigraph readings at 1minute intervals immediately before the BP reading were used to control for activity with each BP measurement. The ambulatory BP monitor was programmed to take a reading every 30 minutes. The patient was provided with a diary and asked to make an entry about the patient's activity and posture on every waking BP measurement.

MEASUREMENTS

Confounding Variables

Many factors affect BP. The more stable qualities of gender, age, weight, and height for BMI computation and ethnicity were recorded on recruitment using self-report. Activity was recorded by both actigraph and diary.

Reactive BP change

The data used to determine reactive BP change was computed using Dinamap BP readings recorded during the BP reactivity protocol. Three reactive systolic BP and diastolic BP scores were calculated for each patient - the average of the normal, health, and total talking blood pressures recorded during the BP reactivity protocol. Reactive BP change was the change score derived by subtracting the average of the third and fourth quiet blood pressures from Period 3 of Series I of the BP reactivity protocol from the average of the health talking blood pressures and from the average of the normal talking blood pressures and from the average of the combined talking blood pressures.

Twenty-four-hour BP Mean

The 24-hour mean BP is the average of the total number of ambulatory BP readings.

Twenty-four-hour BP Load

The BP load is the percentage of ambulatory blood pressures greater than 140/90 mm Hg when awake and greater than 120/80 mm Hg when asleep (White, Dey & Schulman, 1989).

Pulse Pressure

Resting PP is the difference between systolic and diastolic pressures (Chobanian, 1983). Pulse pressure was calculated from resting BP measurements taken according to the AHA guidelines.

INSTRUMENTS

Dinamap

A Dinamap 1846SX, an oscillometric device, was used to measure BP during the BP reactivity protocol. The Dinamap's validity has been documented by comparing the Dinamap with intra-artenal BP readings (Ramsey, 1979).

Ambulatory Blood Pressure Monitor

A Spacelabs 90207 (Spacelabs Medical Inc., Redmond, WA) ambulatory monitor was used to collect the data for calculating 24-hour mean BP and BP load. This monitor is an oscillometric ambulatory BP monitor device, and was selected for its size (12.2 oz., with batteries), its quiet operation, and its reported validity, when compared to intra-arterial and sphygmomanometer readings (White, Lund-Johansen, & Omvik, 1990).

Actigraph

The Motionlogger actigraph, a large wrist- watch-like device, was used for this study to simultaneously record the activity of the patients during the 24-hour ambulatory BP monitoring period. The Motionlogger is highly reliable and valid in adults and children (Mason & Redeker, 1993). The actigraph collected and stored data on patient activity as a continuous time series, providing discrimination between waking and sleeping blood pressures.

Diary

Each patient used a pocketsize diary, adapted from one developed by Van Egeren and Madarasimi (1998), to record ratings of posture and activity coinciding with each BP measurement. The diary consisted of a simple checklist on which the patient would check the time of day, position (e.g., sitting, lying, standing), and activity (e.g., watching TV, reading, talking, walking, eating, using the phone, drinking caffeine, smoking, alcohol).

RESULTS

Data Analysis

Microsoft Access software (Redmond, WA) was used to prepare and merge the data, and to compute BP load. Blood pressure readings were examined in the context of the patient diary data (e.g., activity, position) at the time of the BP measurement and checked through the activity monitor to indicate whether or not the patient was asleep. Ambulatory BP data was reviewed, and the values that produced a Spacelabs error code were removed from consideration in the BP analysis. (The errors were most likely caused by patient movement during the BP reading.)

Table

TABLE 3DESCRIPTIVES OF MEAN BLOOD PRESSURE VARIABLES

TABLE 3

DESCRIPTIVES OF MEAN BLOOD PRESSURE VARIABLES

Ambulatory BP data were subjected to restricted maximum likelihood estimation to allow for missing some observations during the 24hour measurement period. The mixed-effects model for repeated measurements (Laird & Ware, 1982) was applied to analyze the 24-hour BP profile and test for relationships between the ambulatory BP measurements and the independent variables. The variables included resting BP; resting PP; activity; BMI; socioeconomic status; position (e.g., sitting, standing, reclining); and the reactive change scores of normal, health, and total talking. The BP load data were log-transformed and regression-analysis-applied using the independent variables of resting PP and resting systolic BP and the reactive change scores of normal talking, health talking, and total talking.

FINDINGS

The means and standard deviations of resting BP; 24-hour mean BP; total, health, and normal talking BP; talking and quiet BP; and change scores are presented in Table 3.

Analysis To Address Hypothesis

The two hypotheses of the study were:

* Reactive BP will be better than static BP (resting BP or PP) in predicting 24-hour BP.

* Reactive BP will be better than static BP (resting BP or PP) in predicting BP load.

Each hypothesis proposed the reactivity scores derived from the total of the combined talking would be a better predictor than the reactivity scores derived from either health or normal talking alone.

Hypothesis I

The first hypothesis was analyzed using a mixed model to quantify the extent to which reactive BP, resting BP, and PP predicted 24-hour BP (systolic BP and diastolic BP). Results of the preliminary analysis of adding the position factor and the Hollingshead Index to activity and BMI in repeated measurement indicated position p = .0001) was a significant predictor of ambulatory BP, while the Hollingshead Index (p = .0864) factors were not. The Hollinghead's Four Factor Index estimates a social status score for the individual based on the four factors of education, occupation, sex, and marital status (Hollingshead, 1975). The position factor was added to the model. Weighted regression analysis was applied to address this specific aim, adjusting the weight according to the number of BP measurements for each patient.

The change scores of normal talking (p = .6800), health talking (p = .0907), and total talking [p = .4081) were not significant predictors of 24hour systolic BP when added to a model using resting PP, resting systolic BP, activity, BMI, and position. Resting pulse pressure and resting systolic BP were significant predictors of 24-hour systolic BP in each of the three models using a different reactive change score. The significance levels of the resting systolic BP using each of the three mixedeffects models are p = .0003 in the model using normal talking, p = .0002 in the model using health talking, and p = .0003 in the model using total talking. The significance levels of resting PP using each of the three mixed-effects models are ? = .0106 in the model using normal talking,/) = .0348 in the model using health talking, and p = .0224 in the model using total talking.

Hypothesis II

For the second hypothesis, regression was used to quantify the extent to which reactive BP change and resting BP and PP predicted BP load. The logarithmic transformation was first applied to the BP load. The transformed outcome was then related to the independent variables of reactive BP change for normal, health, and total talking; resting BP; PP; and the average activity score from the 24-hour actigraph data, Hollingshead's Four Factor Index, and BMI. The 24-hour systolic BP and diastolic BP loads were used as the dependent variables.

The Hollingshead's Four Factor Index (p = .25), average activity score (p = .94), and BMI (? = ?0) were not significant predictors of BP load. Resting systolic BP was the only significant predictor of systolic BP load in a regression solution using each of the reactivity change scores. The significance levels of the resting systolic BP in each of the three regression solutions are /J = .0445 during normal talking, p = .0375 during health talking, and p = .0456 during total talking. No predictors were significant for diastolic BP load.

DISCUSSION

Present study findings may not have found evidence for the predictive value of reactivity change scores because of methodological issues, such as the choice of protocol or patient population, or because of physiological characteristics particular to older adults who are hypertensive. Another possible reason the changed scores in the current study were not statistically significant predictors of ambulatory BP could be explained by a Type 2 error. In other words, the hypotheses may have been wrongly rejected when they are actually true due to the small sample size.

A weakness of the study was the verbal report of height and weight of the patients. The use of measured height and weight would have been more reliable, although the reported BMI was a significant (p = .0001) independent variable in the univariate analysis and was used in the final analysis.

CLINICAL SIGNIFICANCE OF FINDINGS

Implications for the clinician are based on study results that validate resting BP as an indicator of the effectiveness of BP management. Given the ability of the resting BP to predict dynamic ambulatory measurements, the clinician should have confidence in the credibility of the resting BP as an assessment tool in BP management of older adults who are medicated and hypertensive, and have cardiovascular disease.

In a clinical setting, there may be a tendency for a clinician to underestimate the importance of a high initial resting BP, attributing it to patient stress or nervousness about the clinic visit. However, the study findings suggest if the initial resting BP, taken according to AHA guidelines, in this population is hypertensive, the clinician should be alerted to the possibility that the patient may have a high mean 24-hour BP and a high BP load. Blood pressures taken later in the clinic visit may be within normal limits and may not be predictive of BP management over 24 hours.

If the clinician is concerned the resting BP is falsely high or falsely low, the clinician may recommend the patient record the BP in the home environment at different times of the day. If these pressures are inconsistent with the clinic pressures, or if they are consistently high, then use of ambulatory monitoring may be considered. Ambulatory monitoring is particularly important in older patients with hypertension and cardiac disease whom the clinician suspects of having an increased BP load that may lead to left ventricular hypertrophy and an increased risk for mobility and mortality.

The results of this study can only be generalized to the population of older adults in cardiac rehabilitation who are medicated and hypertensive. These results may differ with samples of varying ethnic, gender, and economic status distributions. Future work should consider ethnic and gender comparisons and comparisons based on types and doses of antihypertensives used.

SUMMARY

The static measurement of resting BP in older adults with hypertension and cardiovascular disease provides two indices - resting systolic BP and PP - that predict ambulatory BP. In addition, resting systolic BP predicts BP load. Others have found a strong correlation between the resting clinic BP and cardiovascular morbidity (Franklin & Weber, 1994), and between resting clinic BP and the dynamic BP measurement of ambulatory BP. Thus, the results of this study provide further affirmation of the ability of resting BP to be predictive of dynamic BP, specifically for systolic BP.

Blood pressure management is important, but difficult, in this population. The dynamic BP measurement of ambulatory BP is an effective measurement method in older adults who are medicated because it is sensitive to sympathetic responses to the environment that remain elevated even with medication.

There was a trend in health talking BP reactivity to predict ambulatory BP. Perhaps, with a larger sample, or with a more stress-invoking question, the prediction would have been significant. Future studies are necessary to confirm the ability of resting BP to predict ambulatory BP in older adults who are medicated and hypertensive. Clinicians are faced with managing BP in this population daily and need more efficient measurement methods.

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TABLE 1

DESCRIPTIVE STATISTICS (N = 45)

TABLE 2

BLOOD PRESSURE REACTIVITY PROTOCOL

TABLE 3

DESCRIPTIVES OF MEAN BLOOD PRESSURE VARIABLES

10.3928/0098-9134-20020901-04

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