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From: Clinical Hypertension and Vascular Diseases: Hypertension in the Elderly Edited by: L. M. Prisant © Humana Press Inc., Totowa, NJ
8 Blood Pressure Measurement in Older Patients With
Hypertension
Jose Ramiro Arias-Vera, MD and William B. White, MD
CONTENTS
INTRODUCTION
OFFICE BLOOD PRESSURE
OUT-OF-OFFICE BLOOD PRESSURE MEASUREMENTS
CONCLUSION
REFERENCES
INTRODUCTION
Accurate measurement of blood pressure (BP) in older patients is vitally important for prognosis and intervention; however, obtaining reliable measurement data in this population is not always an easy task.
The office BP in older patients is often difficult to measure for a variety of reasons. For example, in older patients accurate BP measurement is challenging because alterations in cardiovascular physiology with the aging process produce an increase in BP variability. Furthermore, cer- tain structural changes in the blood vessel can add to the imprecision of many types of BP determination.
The objective of this chapter is to detail some of the specific age- related factors that play an important role in BP measurement and to review the benefits and pitfalls of self-BP (home) and ambulatory BP monitoring (ABPM) in the elderly.
OFFICE BLOOD PRESSURE
Most large outcome trials in hypertension utilized data obtained with the BP measured under standardized conditions at office visits and using the auscultatory method and a mercury column sphygmomanometer.
Thus, many physicians feel strongly that to apply these studies of prog- nosis and interventions, similar standard conditions and methods of BP determination should be used in clinical practice. However, there are inherent inaccuracies of office BP measurements that cause misdiag- noses and lead toward treatment that may not always be appropriate.
Defective equipment, poor measurement technique, and observer bias all may contribute as sources of error in measurement.
In an effort to minimize the potential error for BP measurement in practice, a number of guidelines have been published over the years that have focused on standardizing the technique. One of the most widely accepted of the guidelines has been by the American Heart Association (AHA) in 1993 (1). However, many studies showed that the majority of physicians and ancillary medical personnel in fact do not measure BP correctly as recommended by these guidelines. The potential medical, economic, and even legal implications of incorrect BP measurement are substantial. The AHA guidelines in the elderly are not different from those for other age groups. Thus, next we focus on certain age-specific conditions that need special attention when measuring BP in the elderly at the office. These include the issues of the auscultatory gap, orthostatic hypotension, pseudohypertension, and white-coat hypertension (WCH).
The Auscultatory Gap
A lengthy disappearance of the Korotkoff sounds between the sys- tolic blood pressure (SBP) and diastolic blood pressure (DBP) is referred to as the auscultatory gap. The auscultatory gap has a diagnostic signifi- cance because, if it is not recognized, it becomes a source of error in BP measurement; in addition, some data suggest it may be a marker of cardiovascular morbidity (2).
When the auscultatory gap is analyzed by wideband external pulse recording added to clinical auscultation, three types of gaps are identified (3): G1, G2, and G3. G1 and G2 are related to the intermittent variation in BP produced by the respiratory cycle. G1 is the intermittent disappearance of the Korotkoff sounds when the cuff pressure is just below the SBP and is produced by the phasic decrease in SBP during inspiration. G2 is the intermittent disappearance of the Korotkoff sounds when the cuff pres- sure is just above DBP produced by the phasic increase in BP during expiration.
G3 is the classically described auscultatory gap for which the disap- pearance of audible sounds between SBP and DBP is independent of respiratory variations. Missing the auscultatory gap will produce an underestimation of SBP and occasionally an overestimation of the DBP.
To avoid the incorrect assessment of the SBP level, estimation of SBP by palpation must be performed before auscultation. To avoid the overesti- mation of the DBP, auscultation should be continued for at least 10 mmHg after the first disappearance of the Korotkoff sounds.
The physiological etiology of the auscultatory gap is not fully under- stood, but it appears to be related to the physical properties of the arterial wall (3). There is a study that suggested that the G3 auscultatory gap may be associated with increased arterial stiffness and carotid atherosclerosis independent of age or BP level (2). Although this study did not find age to be an independent predictor of the gap, increased arterial stiffness is more common in the elderly. Increased arterial stiffness and atheroscle- rosis are independent risk factors for cardiovascular morbidity; thus, the presence of a G3 gap might be a surrogate marker for these conditions and may have an indirect correlation with increased cardiovascular morbidity.
Orthostatic Blood Pressure Changes
The maintenance of BP on standing is the result of complex physi- ological mechanisms that require intact function of the autonomic and cardiovascular systems. The BP response to postural changes in healthy individuals is characterized by a transient initial decrease in pressure during the first 15 seconds after standing followed by progressive increases in BP over 30 seconds that ultimately reach a value that is higher than the initial supine pressure (4). Orthostatic hypotension is typically defined as a fall of 20 mmHg or more in SBP or 10 mmHg or more in DBP after 3 minutes of standing (5). However, this definition has limited clinical significance because many patients can experience symp- toms of cerebral hypoperfusion with smaller decreases in the SBP, when they might be at risk for falls and syncope. Furthermore, there may be fairly marked intraindividual variability in the absolute change in ortho- static pressure at different times of the day (6,7) and on different days of the week (8).
Orthostatic hypotension becomes more common with increasing age (9–11). With aging, there are decreases in baroreflex responsiveness and reductions in the cardiovascular response to sympathetic stimuli as well.
However, these alterations in physiology do not fully explain the level and frequency of orthostatic hypotension that occurs in older people.
Many pathological conditions common in the elderly affect the auto- nomic system and produce more severe orthostatic hypotension, such as Parkinson’s disease, multiple system atrophy, or peripheral neuropa- thies. In fact, the orthostasis may occur before overt neurological symp- toms develop.
Therefore, evaluation of postural BP changes should form a part of the initial evaluation of elderly patients, and a significant drop in BP after 1 or more minutes of standing should be considered abnormal. Even if the orthostatic reduction in BP is initially asymptomatic, it is important to identify those individuals with varying degrees of postural hypotension because they are susceptible to significant BP falls induced by changes in clinical status or in response to vasoactive medications (12–14).
A particularly challenging group of patients are those who develop both hypotension on standing and supine hypertension. In fact, there is a direct correlation between the level of the supine BP and the degree of BP decrease on standing (8,15). Thus, in these hypertensive patients, carefully lowering the supine or seated BP may decrease the degree of orthostatic hypotension (7). The group of patients who have significant autonomic failure caused by conditions such as Parkinson’s disease and multiple system atrophy not only has supine hypertension and standing hypotension, but also can manifest severe abnormalities in BP regula- tion and may have a highly variable circadian BP (16,17). Beyond the more obvious clinical consequences of the hypotensive episodes, there are even data suggesting that orthostatic hypotension in the elderly may be a predictor of all-cause mortality (18,19).
Pseudohypertension
A significant overestimation of BP when measured noninvasively by the cuff as compared to directly measured (intra-arterial) BP has been termed pseudohypertension. Pseudohypertension is generally thought to be secondary to increased arterial wall stiffness; thus, the external pressure needed to occlude the artery is increased independent of inter- nal arterial pressure. In extreme cases, when the artery is highly calci- fied, the vessel may become noncompressible by an external cuff. Most investigators have defined pseudohypertension using an absolute cuff pressure of no less than 10 mmHg systolic and/or diastolic pressure above the directly measured pressure. However, given the lack of evi- dence of the clinical significance of directly measured BP, any value used to define pseudohypertension is relatively arbitrary.
The prevalence of pseudohypertension in the elderly is highly vari- able among different studies, ranging between as low as 1.7% and as high as 70% (20). Despite the methodological differences among these
studies, the major factor accounting for the different results has been the selection of individuals studied. Thus, in the group of elderly subjects in whom pseudohypertension was suspected, the incidence of confirmed pseudohypertension was the highest. On the other hand, on groups of randomly selected older individuals, pseudohypertension was relatively rare. Pseudohypertension is also more common in patients with acceler- ated atherosclerosis, such as those with end-stage renal failure (21).
It is often quite difficult to identify those patients with pseudo-hyper- tension. The condition should be suspected clinically in older hyperten- sive patients who lack a correlation between hypertension-related end target organ damage and the level of BP or when a patient with elevated arm BP experiences signs and symptoms of hypotension induced by antihypertensive medications.
The Osler’s sign has been recommended as a means to screen poten- tial patients for pseudohypertension (1). This sign is basically a finding associated with large arterial sclerosis and is positive when either the brachial or radial artery is still palpable after the BP cuff has been inflated above systolic pressure. Although an initial study conducted in selected patients with suspected pseudohypertension found signifi- cant correlation between a positive Osler’s sign and pseudohypertension (22), other studies in randomly selected individuals showed that this correlation is usually not significant (23,24). Thus, for general screen- ing, the Osler’s sign lacks reliability and has poor predictive value for pseudohypertension.
White-Coat Effect and White-Coat Hypertension
With the increased use of out-of-office BP measurements in the eld- erly, it has become evident that a large proportion of patients have an office BP that is higher than the measured BP value outside the medical environment. The prevalence of WCH is approximately 15–30% (25,26).
This condition should be suspected clinically when the office BP is high and when there is a lack of hypertension-related end target organ damage or when patients develop side effects from antihypertensive therapy typically associated with excessive reduction in BP.
WHITE-COAT EFFECT
The phenomenon of transient BP elevations when the individual is in a medical environment is called the white-coat effect. The exact preva- lence of individuals who develop the white-coat effect is not known, but it seems to increase with increasing age (27). The white-coat effect is a qualitative definition independent of absolute values, and it may be present as assessed by office readings in both normotensive and hy-
pertensive individuals. Use of home self-measured BP (SMBP) is an acceptable means to start the evaluation for a white-coat effect but as described below should be confirmed with 24-hour ambulatory BP recordings.
REVERSE WHITE-COAT EFFECT
The phenomenon in which the office BP is lower than the ambulatory BP is called reverse white-coat effect or, more recently, masked hyper- tension (28). Although far less studied than WCH, Wing et al. (29) reported that 21% of older patients studied had lower office than ambu- latory systolic pressures.
WHITE-COAT HYPERTENSION
WCH is defined when an untreated patient has a persistent office BP greater than 140/90 mmHg with an average daytime ambulatory BP below 135/85 mmHg (30). Most recent studies suggest that WCH is more common in the elderly individual than in middle-aged patients.
ABPM in conjunction with carefully measured office BPs is the only means to accurately diagnose a patient as having WCH. Self- or home BP measurements might suggest this condition but are not considered definitive.
OUT-OF-OFFICE BLOOD PRESSURE MEASUREMENTS Monitoring of BP outside the medical care environment has become an important part of clinical hypertension assessment and management.
There are two main forms of out-of-office BP monitoring: (a) self- or home monitoring, usually performed by the patient with a portable automatic or semiautomatic device or aneroid manometer plus stetho- scope and (b) ABPM, which uses automatic devices for repeated deter- minations during an extended time period, typically 24 hours. Both techniques have been shown to substantially enhance the clinician’s understanding of BP behavior and aid in diagnosis and therapeutic decision making.
Self-Measured Blood Pressure
The self-measurement of BP at home is a useful tool and adds to office BP in the evaluation and management of the hypertensive patient. How- ever, knowledge in this area is yet evolving. At this time, there is no absolute consensus about distribution of values of home BP in the gen- eral population, comparison of SMBP and office BP, standardization of devices and technique for SMBP, and the diagnostic or prognostic value of out-of-office BPs. Therefore, decisions for management of the hyper-
tensive patient should not be done based solely on out-of-office BP determinations. In this section, we describe this method and the current evidence about its value and indications focused in the elderly.
DEVICES FOR SELF-MEASURED BLOOD PRESSURE
Several types of BP monitors are available for use at home, including aneroid manometers, semiautomatic electronic sphygmomanometers, and mercury column sphygmomanometers. Aneroid manometers with a stethoscope are relatively simple to use and generally are the most eco- nomical type of self-monitoring units available. However, all the con- cerns about technique and biased readings with auscultatory BP measurement are even greater when patients perform the readings. For these reasons, they are usually not recommended. They are even less suitable in older patients lacking manual dexterity or when hearing loss is an issue.
Automatic electronic devices are the most convenient and during the past few years have clearly become the devices of choice for home or SMBP. Most electronic devices are of the oscillometric type and can be applied to the brachial or radial artery. Finger devices use the plethysmo- graphic technique and are the least accurate, so are not recommended for self-measurements. A number of the oscillometric brachial or radial devices have demonstrated accuracy under standard measuring condi- tions. However, wrist devices become inaccurate when the wrist is not maintained at heart level or is in extreme flexion or extension. Given this potential error in measuring technique, they are better used only when a brachial device is not a suitable option, such as in very obese patients.
Therefore, automatic brachial oscillometric devices are the first choice for self-measured BP.
A number of these devices are commercially available; however, only a few have been independently validated. The responsibility in certifying that the device used is accurate currently falls on the physician in charge.
The Association for the Advancement of Medical Instrumentation and the British Hypertension Society have rigorous protocols for validation (31,32). One special consideration in older patients is the fact that many oscillometric devices are less accurate in the elderly, probably because of increased arterial stiffness. Therefore, devices for use in the elderly need to have demonstrated accuracy in this age group. Added to this initial validation, a clinical comparison against a mercury column sphygmoma- nometer should be performed on a regular basis by the physician. It is also important to certify that the patient uses a cuff size correct for his or her arm circumference. The recommended bladder width should be 40% of the arm circumference, as recommended by the AHA (Table 1).
TECHNIQUE AND MEASUREMENTS
There is no consensus about the number and time of self-BP measure- ments. Some experts recommend that, for the initial evaluation of a patient, BP should be taken three consecutive times in the morning and three in the evening for 3 days a week for 2 weeks (33) and to have measurements performed both during the work period and during off- work days. Patients are usually fairly accurate when transcribing their own pressures, but underreporting or missed reporting of the readings is not that uncommon. Devices with memory capability that store multiple readings for future evaluation overcome this problem. Some devices are also able to transmit data telephonically to a receiving central unit, but they are not commonly used because of cost issues.
NORMAL VALUES FOR SELF-BLOOD PRESSURE
What represents normality for home BP is still a matter of debate.
There is consensus, however, about the fact that home BP should be lower than office BP in normotensive and hypertensive subjects. The American Hypertension Society recommends the value of 135/85 mmHg as the upper limit of normal for home BP (34). This is in agreement with studies showing that this value is roughly equivalent to an office BP of 140/90 mmHg (35).
INDICATIONS FOR SELF-MONITORING OF THE BLOOD PRESSURE
Although the theoretical advantages of self-monitoring are obvious, there is not yet sufficient prospective data to make a definitive conclu- sion about SMBP and end target organ damage, prediction of cardiovas- cular risk, or association with clinical outcomes. The available data suggest, however, that self-monitored BP does correlate better with echocardiographically determined left ventricular mass than clinic pres- sures in patients with mild hypertension (36,37), and that it is a better predictor of cardiovascular risk than office BP in older patients (38).
Table 1
Acceptable Bladder Dimensions (cm) for Arms of Different Size in Adults Arm circumference Cuff Bladder width Bladder length range at midpoint
Small adult 10 24 22–26
Adult 13 30 27–34
Large adult 16 38 35–44
Adult thigh 20 42 45–52
Adapted from the American Heart Association (1).
The self-monitored BP has the potential for reducing the bias and error in assessing the “true” pressure in a patient (which may be quite large if a small number of readings in the doctor’s office are used) (Table 2). In some studies, the self-monitored pressure has been shown to be similar to the attenuated BP seen with repeated measurements over time (i.e., weeks and months) in the clinic (39,40). Moreover, SMBP seems to correlate with mean daytime pressures as measured by ABPM better than office BP. Once antihypertensive therapy has been initiated, self-monitoring of the BP is an excellent way to evaluate the effective- ness of the therapy and avoid multiple doctor or nurse visits. Further- more, the relationship between time of dosing of antihypertensive therapy and BP levels may be easier to assess with self-monitoring patients. As a final attribute, adherence to therapy and BP control have been shown to improve when patients (even previously noncompliant ones) self-monitor their BP.
One important limitation of SMBP is that readings are usually taken under rested and relaxed conditions, so they might not accurately reflect BP in other situations. This is apparent when home readings are normal, yet ABPM demonstrates high values. Another limitation is that BP can- not be measured during sleep and, as discussed regarding relationship with disease, nocturnal BP alterations seem to be independently related to cardiovascular and cerebrovascular outcomes.
Ambulatory Blood Pressure Monitoring
The use of ABPM with devices able to record readings for 24 hours has had significant value in the evaluation of the hypertensive patient. It is an accurate and unbiased method of measuring BP while the subject is engaged in his or her regular daily activities. It also gives information about BP while the subject is sleeping, a factor of significant importance in cardiovascular morbidity that can only be measured by ABPM.
Before discussing the clinical utility of ambulatory BP recordings, one must develop a frame of reference for the values derived from the ambulatory BP recordings. Usually, physicians set the recorders to
Table 2
Usefulness of Self- or Home Blood Pressure Monitoring
• Distinguishes sustained hypertension from white-coat effect suggesting white-coat hypertension
• Assesses response to antihypertensive therapy
• Improves patient adherence to treatment
• Potentially reduces management costs
measure 50–100 BPs in 24 hours. There is a reproducible diurnal/noc- turnal pattern to BP during a 24-hour period of measurement in about 80% of patients. Typically, the pressure is highest while awake (espe- cially during work) and lowest during sleep. The data are expressed as 24-hour mean BP and often as the values during wakefulness and sleep.
BP during sleep is quite low compared to the office or clinic pressure, and BP during wakefulness is similar to the values obtained in the office.
These differences must be kept in mind when trying to interpret ambu- latory BP recordings. Most consensus groups have used a 24-hour BP greater than 135/85 mmHg as clearly abnormal based on several new outcome studies comparing ambulatory vs clinic BP in patients with hypertension.
RELATIONSHIP BETWEEN THE AMBULATORY BLOOD PRESSURE
AND HYPERTENSIVE DISEASE
One of the most important findings regarding the ambulatory BP has been its relationship to hypertension-related target organ disease. The majority of cross-sectional studies published to date have shown the ambulatory BP is superior to office BP in predicting target organ involve- ment. The most striking evidence has come from assessment of the relations among office BP, ambulatory BP, and indexes of left ventricular hyper- trophy (41–44). Large studies have demonstrated that ABPM is a better predictor of cardiovascular morbidity than conventional office BP (45,46). More recent data have also demonstrated that ambulatory BP is superior to office pressure in predicting hypertensive cerebrovascular disease (47). Most of these studies demonstrated that a loss of nocturnal decline in BP (so-called nondippers) conveys excessive risk for stroke and myocardial infarction.
Vascular dementia is also of major importance in the elderly. Although less clear, nocturnal hypertension or hypotension seem to play a role in the development of lacunar infarcts and deep white matter lesions. Most studies have shown that a nondipping status correlates with lacunar infarcts and white matter lesions (48–53), whereas others suggested that extreme dipping (>20% decline in nocturnal BP) might also be impli- cated in the development of lacunar infarcts (54). A nondipping pattern was an independent predictor for lacunar infarcts, diffuse white matter lesions, and vascular dementia (55).
One other area of interest in ABPM is the analysis of BP variability by conventional intermittent or by beat-to-beat BP measurements. Stud- ies suggested that increased BP variability is an independent risk factor for cardiovascular morbidity (56,57). Older patients and those with severe hypertension might be among those with excessive BP variability.
CLINICAL USEFULNESS OF AMBULATORY BLOOD PRESSURE
Several subsets of hypertensive diagnoses have been elucidated as a result of ABPM (Table 3). Clinical problems seen more often by prac- ticing physicians that are appropriate for ABPM include the assessment of possible WCH, which can be only diagnosed with ABPM; borderline hypertension (with and without evidence for target organ damage); and refractory hypertension in patients on complex antihypertensive regi- mens. ABPM is the only available method for diagnosis of nocturnal hypertension. Less often, ABPM can be used in the evaluation of patients with hypotensive symptoms while on antihypertensive drugs or caused by autonomic dysfunction and in those with suspected episodic hyperten- sion. Patients might benefit clinically when the ambulatory BP is known in addition to the measurements made in the medical care environment.
WCH and Borderline Hypertension. As described in this chapter, WCH can only be diagnosed by ABPM when the office BP is persis- tently over 140/90 and the average daytime BP is less than 135/85 mmHg.
This condition is suspected when office readings are high (usually, but not necessarily, in the high-normal range) and there is lack of evidence of hypertension-related end target organ damage. In these patients, home self-measured BP readings should be tried first. If SMBP is normal, ABPM is needed to confirm WCH; however, if it is high, WCH is ruled out. As discussed here, the subgroup of patients with WCH seems to have a lower cardiovascular risk than those with persistent hypertension.
However, given that their risk compared to normotensives is less clear, these patients should be closely followed. Furthermore, any patient with WCH can later develop persistent hypertension.
Reverse White-Coat Effect. Patients in any range of BP by the office readings can be found to have higher values by ABPM. This condition is also known as reverse white-coat effect. A recent study in older indi-
Table 3
Clinical Diagnoses or Problems for Which Noninvasive Ambulatory Blood Pressure Monitoring May Be Useful
• Office or white-coat hypertension
• Borderline hypertension with or without target organ involvement
• Evaluation of patients refractory to antihypertensive therapy
• Episodic hypertension
• Hypotensive symptoms associated with antihypertensive medications
• Autonomic dysfunction/nocturnal hypertension Adapted from ref. 58.
viduals with hypertension reported an incidence of 21% of reverse white- coat effect. Thus, it is likely that many patients with normal or high- normal readings at the office could be found to have hypertension by ABPM or what could be called white coat normotension. This phenom- enon highlights the importance of the clinical evaluation for assessing hypertension-related end target organ damage and, if present, consider- ing use of ABPM to diagnose hypertension when other methods show normality.
Refractory Hypertension. There is evidence that, in both middle- aged and older patients with hypertension, changes in ambulatory BP are better correlated than office BP to regression of left ventricular hyper- trophy. Therefore, ABPM is a good method to evaluate the patient with refractory hypertension and to assess therapy. ABPM might also iden- tify those with pseudorefractory hypertension caused by the white-coat effect vs those with real refractory hypertension. Moreover, in those patients with genuine refractory hypertension, ABPM can help to tailor therapy by identifying the specific time or times during the 24-hour period in which BP is not controlled.
Hypotension. As described in a separate section, orthostatic hypoten- sion is more common in the elderly. Typically, evaluation of positional BP changes in the office is sufficient to make this diagnosis. However, it has also been shown that orthostatic hypotension is poorly reproduc- ible when checked at different office visits or times of the day. Moreover, symptomatic hypotension may be induced by medications during their peak effect and not necessarily be discovered during an office visit.
Patients with autonomic dysfunction of any etiology might have severe orthostatic hypotension associated with significant supine hypertension.
Therefore, ABPM is useful for further evaluation of all these scenarios.
Nocturnal Hypertension. As discussed in the section on the relation- ship of ambulatory blood pressure and hypertensive disease, nocturnal hypertension and extreme nocturnal hypotension seem to be related to lacunar infarcts, ischemia of the periventricular white matter and dementia (48–55). Nocturnal hypertension is also an independent risk factor for cardiovascular morbidity. ABPM is the only method that has the capa- bility to evaluate BP during sleep.
CONCLUSION
Blood pressure determination is one of the most important parts in the clinical evaluation of an older patient. Therefore, the physician must make every effort to measure the BP accurately. Given that clinic or office BP is a highly variable parameter in the elderly, clinicians are
slowly but progressively moving away from decision making based solely on isolated readings at the office. The combined evaluation of office and self-measurements as well as use of 24-hour readings in selected cases often prove invaluable in the management of older patients with hyper- tension. As more information is accumulated about the diagnostic util- ity, prognostic significance, and added benefits in disease modification and management with the use of out-of-office BP measurements, the indications for SMBP and ABPM will be better defined. The elderly, for whom hypertension is so common and hypertension-related complica- tions are so frequently manifested, will be the population that will ben- efit the most from better assessment and management of BP-related pathology.
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