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J Am Coll Cardiol, 2002; 40:133-141 © 2002 by the American College of Cardiology Foundation |
* Department of Cardiology, Jichi Medical School, Tochigi, Japan
Manuscript received December 10, 2001; revised manuscript received March 28, 2002, accepted April 8, 2002.
* Reprint requests and correspondence: Dr. Kazuomi Kario, Department of Cardiology, Jichi Medical School, 3311-1, Yakushiji, Minamikawachi, Kawachi, Tochigi, 329-0498, Japan.
kkario{at}jichi.ac.jp
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Abstract |
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BACKGROUND: Although orthostatic hypotension (OHYPO), often found in elderly hypertensive patients, has been recognized as a risk factor for syncope and cardiovascular disease, both the clinical significance and the mechanism of orthostatic hypertension (OHT) remain unclear.
METHODS: We performed a head-up tilting test and brain magnetic resonance imaging (MRI) in 241 elderly subjects with sustained hypertension as indicated by ambulatory BP monitoring. We classified the patients into an OHT group with orthostatic increase of systolic blood pressure (SBP) of 
20 mm Hg (n = 26), an OHYPO group with orthostatic SBP decrease of 20 mm Hg (n = 23), and a normal group with neither of these two patterns (n = 192).
RESULTS: Silent cerebral infarcts were more common in the OHT (3.4/person, p < 0.0001) and OHYPO groups (2.7/person, p = 0.04) than in the normal group (1.4/person). Morning SBP was higher in the OHT group than in the normal group (159 vs. 149 mm Hg, p = 0.007), while there were no significant differences of these ambulatory BPs between the two groups during other periods. The OHT (21 mm Hg, p < 0.0001) and OHYPO (20 mm Hg, p = 0.01) groups had higher BP variability (standard deviation of awake SBP) than the normal group (17 mm Hg). The associations between orthostatic BP change and silent cerebrovascular disease remained significant after controlling for confounders, including ambulatory BP. The orthostatic BP increase was selectively abolished by alpha-adrenergic blocking, indicating that alpha-adrenergic activity is the predominant pathophysiologic mechanism of OHT.
CONCLUSIONS: Silent cerebrovascular disease is advanced in elderly hypertensives having OHT. Elderly hypertensives with OHT or OHYPO may have an elevated risk of developing hypertensive cerebrovascular disease.
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We performed a head-up tilting test (HUT), ambulatory blood pressure monitoring (ABPM) and brain magnetic resonance imaging (MRI), which is the most sensitive method of detecting silent cerebrovascular disease, in 241 asymptomatic elderly hypertensives.
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Methods |
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60 years) who satisfied the following criteria: 1) essential hypertension with average clinic BP (measured within one week before ABPM by standard cuff methods after resting for at least 5 min while seated) on 2 occasions at separate visits >140 mm Hg for systolic blood pressure (SBP) and/or 90 mm Hg for diastolic blood pressure (DBP); and 2) average 24-h SBP 130 mm Hg or DBP 80 mm Hg (10). Thus, patients with white-coat hypertension were excluded (10); previous research showed that the prevalence of silent cerebral infarct (SCI) and risk of stroke in white-coat hypertensives are comparable to those in normotensives (11–13). These patients were enrolled from the three participating clinics between April 1996 and August 2000, and 188 patients in the present study were included in our previous study (13,14). No patient had received any antihypertensive medication for at least 14 days before the study. After physical and laboratory examinations, we excluded patients with renal failure (serum creatinine level >130 mmol/l), hepatic damage present illness, or a past history of coronary artery disease (CAD) stroke, congestive heart failure, arrhythmia or other serious medical conditions. Patients with symptomatic OHYPO with SBP decrease >30 mm Hg 1 min after active standing, and those with possible diabetes mellitus (fasting glucose >5.5 mmol/l and/or hemoglobin A1c >6.0%), were also excluded. This study was approved by the Research Ethics Committee, Department of Cardiology, Jichi Medical School, and informed consent was obtained from each subject.
The body mass index was calculated as weight (kg)/height (m)2. Electrocardiographically verified left ventricular hypertrophy (ECG-LVH) was defined by abnormally high voltages of QRS complexes (RV5 + SV1 3.5 mV) associated either with flat T waves (<10% of R) or with ST-segment depression and biphasic T waves.
HUT and definition of OHT and OHYPO
After BP and pulse rate (PR) were measured with an interval of 1 min at baseline and after the subjects had been in a supine position for at least 10 min, they were positioned upright on a tilt table at an angle of 70° for 15 min. Three patients who developed presyncope during HUT were excluded from this study, and the remaining 241 patients were studied further.
Orthostatic BP and PR changes were calculated as: the average during 6 to 10 min during tilting minus the average in the supine position during the 1 to 5 min just before the tilting (9). We classified the patients into an OHT group with orthostatic SBP increase 20 mm Hg (n = 26), an OHYPO group with orthostatic SBP decrease 20 mm Hg (n = 23) and an orthostatic normotension group (ONT) with neither of these two patterns (n = 192).
ABPM
After HUT, ABPM was carried out on a weekday with an automatic ABPM device employing the oscillometric method (ABPM-6307s, NipponColin, Komaki, Japan; TM-2421, TM-2425, A&D, Tokyo, Japan); this device recorded BP and PR every 30 min for 24 h. Based on each patient’s diary, sleep BP was defined as the average BP from the time when the patient went to bed until the time he or she got out of bed, and awake BP as the average of BPs during the remainder of the day. The standard deviation of awake BPs of each patient was calculated. Morning BP was defined as the average BP during 2 h (4 to 5 points) after the time of awakening.
Brain MRI
Brain MRI was performed using a superconducting magnet with a main strength of 1.5 T (Toshiba MRT200FXII, Toshiba; SIGNA Horizon Ver. 5.8, General Electric, Vision, Siemens) within three months before or after ABPM. The T1- and T2-weighted images were obtained in the transverse plane with 7.8- to 8.0-mm-thick sections. The MRI images of the subjects were randomly stored and interpreted blind to the subjects’ names and characteristics, as reported previously (13,14), and they were evaluated for subcortical infarcts and deep white matter (DWM) lesions. An SCI was defined as a low-signal-intensity area (3 to 15 mm) on T1-weighted images that was also visible as a hyperintense lesion on T2-weighted images (11–14). Multiple SCIs were defined as 3 infarcts/person. Advanced DWM lesion was defined as detection of hyperintense multiple punctate lesions or such lesions at the early confluent stage or those that had reached confluency in the DWM area on T2-weighted images.
Neurohumoral factors
Blood collection was performed after 10 min in the supine position just before the tilting, and after 15-min of tilting in 87 consecutive patients enrolled between June 1, 1996, and July 1998. All of these patients were included in the entire study population (n = 241) (Table 1). Blood samples were immediately centrifuged at 3,000 rpm for 15 min, and plasma was decanted and stored at –80°C until analysis. Catecholamines were measured with high-pressure liquid chromatography (Hitachi, Tokyo, Japan). Plasma renin activity was determined using a radioimmunoassay for angiotensin-I (PRA-SRL; SRL, Tokyo, Japan). Vasopressin was determined using a competitive radioimmunoassay (Mitsubishi Kagaku, Tokyo, Japan). All these assays were performed at the Special Reference Laboratory (Tokyo, Japan), and the intra-/intercoefficient of variation was 0.81% 2.2% for the norepinephrine assay, 0.85%/2.1% for the epinephrine assay, 6.8%/6.6% for the renin activity assay and 1.7%/3.9% for the vasopressin assay.
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Statistical analysis
One-way analysis of variance was performed to evaluate differences among groups, Tukey’s honestly significant difference test was used for comparison of the mean values for pairs of groups, and the chi-square test was used to detect among-group differences in prevalence rates. Unpaired t tests and paired t tests were used for comparison of the mean values for two different groups. Changes of BP or PR from the baseline values were analyzed using paired t tests for each group. Adjusted odds ratio (OR) and 95% confidence intervals were calculated using logistic regression analysis. Differences with p < 0.05 (two-tailed) were considered statistically significant.
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Results |
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No significant differences existed in the levels of clinic BPs or ambulatory BPs, except for sleep DBP, among the groups (Table 2). Morning SBP was significantly higher (p = 0.007) and morning DBP tended to be higher (p = 0.09) in the OHT than in the ONT group. The sleep/awake BP ratio was significantly lower in the OHT than in the OHYPO group. Concerning abnormal diurnal BP variation patterns, the extreme-dipping pattern of nocturnal BP (sleep/awake SBP ratio <0.8) was more common in the OHT than in the ONT group (35% vs. 13%, p = 0.004), whereas the nocturnal BP rising pattern (sleep/awake SBP ratio >1.0) was more common in the OHYPO than in the ONT group (26% vs. 9.4%, p = 0.016). The levels and SDs of both awake SBP and DBP were higher in the OHT than in the ONT group. The SD of awake SBP was also higher in OHYPO than in ONT patients.
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20 mm Hg in the first HUT, 10 (77%) had an orthostatic SBP increase of 10 mm Hg, and 5 (38%) had a 20 mm Hg increase, in the second HUT.
Effect of alpha-adrenergic blocking
When we defined the OHT on the basis of the average orthostatic SBP increase of the first and second HUTs, 10 patients were classified into the OHT and 45 patients into the ONT group. Figure 2 shows the effect of alpha-adrenergic blocking on orthostatic BP change in each group. In the ONT group, alpha-blocking reduced baseline and orthostatic BPs. In the OHT group, alpha-blocking reduced only orthostatic BP, while baseline BP was not significantly affected. Orthostatic SBP tended to be more markedly reduced in the OHT than in the ONT group (–23 vs. –14 mm Hg, p = 0.09). The orthostatic BP increase was more markedly attenuated in the OHT than in the ONT group (p < 0.01).
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Discussion |
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Our main findings were that OHT, as well as OHYPO, is found fairly frequently in elderly Japanese patients with sustained hypertension, and that such patients with OHT have markedly advanced silent cerebrovascular disease. This study provides new evidence indicating that a U-curve relationship exists between orthostatic BP change and hypertensive cerebrovascular disease in the elderly.
Orthostatic BP dysregulation and cerebrovascular disease.
The number of SCIs and the prevalence of all silent cerebrovascular diseases (SCI, multiple SCIs and advanced DWM lesion) were significantly higher in the OHT than in the ONT group. Multiple SCIs were more common in the OHYPO than in the ONT group. These associations found in our elderly patients with sustained hypertension were previously also found in community-dwelling Japanese elderly subjects 75 years old (8), for whom the mean SCI per person was 3.6 in 10 OHYPO subjects (orthostatic SBP decrease 20 mm Hg), and 3.5 in 10 subjects with OHT (orthostatic SBP increase 20 mm Hg). These mean numbers of SCIs in both groups were significantly higher than the 2.1 in 20 ONT subjects with orthostatic BP increase of –20 to +20 mm Hg (both p < 0.05). In that study (8), posture-dependent BP change was assessed after active standing for 2 min. In the present study, HUT was performed to assess orthostatic BP dysregulation more precisely. Because the definitions of OHT and OHYPO were arbitrary, we empirically grouped the study patients into quintiles of orthostatic SBP increase and found a U-shaped relation between the orthostatic SBP change and silent cerebrovascular disease after controlling for other confounding factors, including ambulatory BP levels. This association was especially marked for multiple SCIs.
There have been no reports showing an association between OHT and cardiovascular events. A recent large population-based prospective study, the Atherosclerosis Risk In Communities study, disclosed that OHYPO is an independent risk factor for both stroke (relative risk [RR] = 2.0) (3) and CAD (RR = 3.5) (4). However, that study population consisted of middle-aged subjects, and the association between OHT and cardiovascular events was not examined.
Another prospective study on elderly men >70 years old showed that OHYPO was a risk for total mortality with an RR of 1.64 (2). In that study, a U-curve relationship was not found, but those investigators did not study the cardiovascular events separately. Silent cerebral infarct, which is now classified as a cerebrovascular disorder, type III, by the National Institute of Neurological Disorders and Stroke, has been proposed to be a predisposing condition for subsequent overt stroke. In fact, SCI is a potent predictor of future stroke, with an RR of about 5, in elderly hypertensives (13), and with an RR of about 10 in all adults (19). Thus, OHT may be a risk factor for future clinical stroke in elderly hypertensives.
Mechanism of orthostatic BP dysregulation in silent cerebrovascular disease
The mechanism of the association between orthostatic BP dysregulation (OHT and OHYPO) and silent cerebrovascular disease remains unclear. In addition, whether orthostatic BP dysregulation is a result or cause of silent cerebrovascular disease is not known. The fact that the OHT subjects had a significantly higher frequency of ECG-LVH in addition to being older (two significant cerebrovascular risk factors) may be the reason why they also had advanced silent cerebrovascular disease. In addition, somewhat fewer OHT subjects had previously been on antihypertensive medication, which might have altered baroreceptor response. However, even after controlling for these factors, the association between orthostatic BP dysregulation and silent cerebrovascular disease remained significant.
Autonomic nervous activity may be affected by cerebral infarction (20). Thus, one explanation for the association is that patients with more long-standing hypertension or more severe hypertension suffer greater degrees of silent cerebrovascular disease, leading to autonomic nervous dysfunction and orthostatic BP dysregulation. However, no significant differences existed among the OHT and the other two groups in the hypertension duration, previous antihypertensive therapy or ambulatory BP level. In further support of autonomic dysregulation in patients with OHT, OHYPO and cerebrovascular disease is the observation in Table 2 that BP variability was greater in these groups.
Increased morning BP might have contributed to the increase in the risk for silent cerebrovascular disease in the OHT group. Morning BP increase is reported to be associated with cardiac hypertrophy in hypertensive patients (21), and this may trigger cardiovascular events (22). Theoretically, orthostatic BP increase due to upright position after awakening could partly contribute to ambulatory morning BP. In fact, in our study, morning BP level was significantly higher in the OHT than in the ONT group.
Another possibility is that, particularly in elderly hypertensives with reduced cerebrovascular reserve capacity, frequent episodes of increased BP variability during daily activity might advance silent cerebrovascular disease. In addition, previous studies using brain MRI disclosed that elderly hypertensives with postprandial hypotension (23) and extreme-dipping of nocturnal BP (14) have more advanced hypertensive cerebrovascular disease. In elderly hypertensives, these relative hypotensive conditions (OHT and OHYPO, postprandial hypotension and extreme-dipping of nocturnal BP) increase the ambulatory BP variability, leading to silent and clinically overt cerebrovascular disease (24). In the present study, extreme-dipping status of nocturnal BP was more common in the OHT group, whereas the nocturnal BP rising pattern was more common in the OHYPO group. In addition, ambulatory BP variability (standard deviation of awake SBP) was increased in both the OHT and OHYPO groups compared with the ONT group. A recent prospective study (25) showed that increased postural BP variability is significantly associated with stroke prognosis in elderly nursing home residents. Thus, a hemodynamic mechanism might partly account for the association between orthostatic BP dysregulation and silent cerebrovascular disease in elderly hypertensives.
A recent population-based prospective study demonstrated that men with exaggerated stress-induced SBP response (>20 mm Hg) had 87% greater risk of ischemic stroke than less reactive men (26). Thus, excessive sympathetic reactivity to stress may be etiologically important for silent and clinical hypertensive cerebrovascular disease.
Racial difference
Silent OHYPO in elderly hypertensives (9.5%) is unexpectedly less common among Japanese than in Western populations, where OHYPO is reported to occur in up to 20% to 30% of elderly hypertensives (1). Defined as an orthostatic SBP increase of 20 mm Hg, OHT (11%) is found more frequently than OHYPO among elderly Japanese hypertensives. This orthostatic BP change might reflect a racial difference in the cardiovascular system response between Japanese and Westerners. This speculation may be supported by the finding in a comparative study (27) that, in elderly Japanese individuals, falling occurs at about one-fourth of the incidence in the U.S. This difference might be partly due to the Japanese lifestyle, in which customary squatting behavior would preserve the muscle strength and facilitate venous return from the lower extremities serving to prevent orthostatic BP decrease. All of the elderly subjects we studied engaged in this traditional Japanese form of squatting.
Mechanism of OHT
The mechanism of OHT remains unclear, although some pathogenic processes have been reported (6). Plasma norepinephrine and vasopressin levels during tilting were significantly higher and the orthostatic norepinephrine increase tended to be higher in the OHT than in the ONT group. In addition, morning BP, which was more closely associated with alpha-adrenergic activity than ambulatory BP during other periods (15,28), was increased in the OHT group. The orthostatic BP increase in the OHT group was diminished by alpha-adrenergic blockade. The orthostatic PR profile was comparable among the three groups. These findings suggest that orthostatic activation of sympathetic activation, particularly for alpha-adrenergic activity, might play some role in the pathogenesis of OHT.
The fact that patients with OHT had a higher frequency of ECG-LVH, as well as greater elevation in norepinephrine during tilting, suggests they may have congestive heart failure. A further study using echocardiograms will be necessary to confirm the presence of LVH or quantity the degree of systolic or diastolic ventricular dysfunction in the OHT patients.
Definition and reproducibility of OHT
As various factors affect orthostatic BP change, the reproducibility of OHYPO is relatively poor (29). The reproducibility of OHT when defined using the cutoff value of 20 mm Hg for orthostatic SBP increase was relatively poor in this study. In addition, the effect of "regression to the mean" may partly explain the observed orthostatic BP change, because the OHT group had the lowest supine BP, and the OHYPO group had the highest.
To minimize the effect of "regression to the mean" in defining OHT and OHYPO, we used the HUT (which measures BP levels every min) instead of the routine active standing test (sitting BP, and BPs 1 min and 3 min after standing). If increased BP variability is the problem with these patients, there will be days when they have supine hypertension and OHYPO and other days when they will have the reverse. Thus, ideally, the classification of OHT and OHYPO groups would have been based on three or more different postural BP measures. However, a significant positive correlation existed between orthostatic BP change in the first HUT and that in a second HUT performed within the following three to five weeks in this study, and no patients with OHT as indicated by the first HUT were classified into the OHYPO group at the second HUT. Thus, one HUT test seems to detect some individual characteristics of orthostatic BP regulation. Conversely, the repeated assessment of routine sitting and standing BP may be more practical for defining the OHT and OHYPO conditions. Further studies focusing on methods and reproducibility will be necessary to establish an adequate definition of OHT.
Study limitations
As this study was cross-sectional, a prospective study will be necessary in the future to strictly address the causality between orthostatic BP dysregulation and silent cerebrovascular disease. There is the possibility that when hypertension causes subclinical cerebrovascular disease in some specific brain area, BP variability increases owing to autonomic nervous system dysfunction. In addition, there was no placebo control arm for our alpha-adrenergic blocking study. Thus, to strengthen our conclusion that alpha-adrenergic hyperactivity is the predominant cause of OHT, a discontinuation study of alpha-adrenergic blockade to confirm the development of OHT again, or a plabebo-controlled study, will be necessary.
Conclusions
Given that elderly hypertensive patients with OHT or OHYPO often have advanced silent cerebrovascular disease, they may be at elevated risk of overt clinical cerebrovascular events. Elderly hypertensive patients should be followed with respect to orthostatic BP changes.
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Footnotes |
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