Home monitoring of blood pressure: usefulness as a predictor of persistent hypertension

Task Force II: blood pressure measurement and cardiovascular outcome

OBJECTIVE

To reach a consensus on the prognostic significance of new techniques of automated blood pressure measurement.

METHODS

A Task Force on the prognostic significance of ambulatory blood pressure monitoring wrote this review in preparation for the Eighth International Consensus Conference (28-31 October 2001, Sendai, Japan). This synopsis was amended to account for opinions aired at the conference and to reflect the common ground reached in the discussions.

POINTS OF CONSENSUS

(1) Prospective studies in treated and untreated hypertensive patients and in the general population have demonstrated that, even after adjusting for established risk factors, the incidence of cardiovascular events is correlated with blood pressure on conventional as well as ambulatory measurement. Ambulatory monitoring, however, significantly refines the prediction already provided by conventional blood pressure measurement. (2) White-coat hypertension is usually defined as an elevated clinic blood pressure in the presence of a normal daytime ambulatory blood pressure. Event-based studies in hypertensive patients have convincingly demonstrated that the risk of cardiovascular disease is less in patients with white-coat hypertension than in those with higher ambulatory blood pressure levels even after controlling for concomitant risk factors. Based on prognostic evidence, white-coat hypertension can now be defined as a conventional blood pressure that is persistently equal to or greater than 140/90 mmHg with an average daytime ambulatory blood pressure of below 135/85 mmHg. The issue of whether or not white-coat hypertension predisposes to sustained hypertension needs further research. (3) There is a growing body of evidence showing that a decreased nocturnal fall in blood pressure (<10% of the daytime level) is associated with a worse prognosis, irrespective of whether night-time dipping is studied as a continuous or a class variable. (4) Intermittent techniques of ambulatory blood pressure monitoring are limited in terms of quantifying short-term blood pressure variability. Proven cardiovascular risk factors such as old age, a higher than usual blood pressure and diabetes mellitus are often associated with greater short-term blood pressure variability. After adjusting for these risk factors, some - but not all - studies have nevertheless reported an independent and positive relationship between cardiovascular outcome and measures of variability of daytime and night-time blood pressure, for example standard deviation. (5) Reference values for ambulatory blood pressure measurement in children are currently based on statistical parameters of blood pressure distribution. In children and adolescents, functional rather than distribution-based definitions of ambulatory hypertension have yet to be developed. (6) Several studies of gestational hypertension have shown that, compared with office measurement, ambulatory blood pressure monitoring is a better predictor of maternal and fetal complications. Pregnancy is a special indication for ambulatory monitoring so that the white-coat effect can be measured and pregnant women are not given antihypertensive drugs unnecessarily. (7) Ambulatory pulse pressure and the QKD interval are measurements obtained by ambulatory monitoring that to some extent reflect the functional characteristics of the large arteries. The QKD interval is correlated with left ventricular mass, and ambulatory pulse pressure is a strong predictor of cardiovascular outcome. (8) Under standardized conditions, the self-measurement of blood pressure is equally as effective as ambulatory blood pressure monitoring in identifying the white-coat effect, but further studies are required to elucidate fully the prognostic accuracy of self-measured blood pressure in comparison with conventional and ambulatory blood pressure measurement.

CONCLUSIONS

Ambulatory blood pressure measurement refines the prognostic information provided by conventional blood pressure readings obtained in the clinic or the doctor's office. Longitudinal studies of patients with white-coat hypertension should clarify the transient, persistent or progressive nature of this condition, particularly in paediatric patients, in whom white-coat hypertension may be a harbinger of sustained hypertension and target-organ damage in adulthood. Finally, the applicability, cost-effectiveness and long-term prognostic accuracy of the self-measurement of blood pressure should be evaluated in relation to conventional blood pressure measurement and ambulatory monitoring.

Modern approaches to blood pressure measurement

BACKGROUND

Blood pressure (BP) is usually measured by conventional sphygmomanometry. Although apparently simple, this procedure is fraught with many potential sources of error. This review focuses on two alternative techniques of BP measurement: ambulatory monitoring and self measurement.

REVIEW

BP values obtained by ambulatory monitoring or self measurement are characterised by high reproducibility, are not subject to digit preference or observer bias, and minimise the transient rise of the blood pressure in response to the surroundings of the clinic or the presence of the observer, the so called white coat effect. For ambulatory monitoring, the upper limits of systolic/diastolic normotension in adults include 130/80 mm Hg for the 24 hour BP and 135/85 and 120/70 mm Hg for the daytime BP and night time BP, respectively. For the the self measured BP these thresholds include 135/85 mm Hg. Automated BP measurement is most useful to identify patients with white coat hypertension. Whether or not white coat hypertension predisposes to sustained hypertension remains debated. However, outcome is better correlated with the ambulatory BP than with the conventional BP. In patients with white coat hypertension, antihypertensive drugs lower the BP in the clinic, but not the ambulatory BP, and also do not improve prognosis. Ambulatory BP monitoring is also better than conventional BP measurement in assessing the effects of treatment. Ambulatory BP monitoring is necessary to diagnose nocturnal hypertension and is especially indicated in patients with borderline hypertension, elderly patients, pregnant women, patients with treatment resistant hypertension, and also in patients with symptoms suggestive of hypotension.

CONCLUSIONS

The newer techniques of BP measurement are now well established in clinical research, for diagnosis in clinical practice, and will increasingly make their appearance in occupational and environmental medicine.

Comparison of patient and staff assessment of MS patients' health status

This study compared change scores obtained on patient self-reported symptoms (MS-RS) with the neurological examination of the Kurtzke Functional Systems (FS) and change scores obtained on patient self-reported activities of daily living (ADL-MS) with the neurologist-determined Expanded Disability Status Scale (EDSS) that were obtained from two separate times separated by approximately seven months for 100 patients with multiple sclerosis. Percent agreement based on < or = 1 unit difference between patient and neurologists' change scores (Time 2-Time 1) ranged between 73% and 86% for MS-RS and FS measures and was 72% for ADL-MS and EDSS. Together, the ADL and MS-RS patient self-report scales provide health status information from the patient's perspective that can be useful in guiding the physical examination, in making comparisons from visit to visit and/or between visits, in assessing patients' quality of life, and in increasing patient satisfaction with medical care.

The sensitivity of human blood platelets to the aggregating agent ADP during different dietary sodium intakes in healthy men

We have investigated the effect of varying sodium intake on the renin-angiotensin system, ADP-induced platelet aggregation in vitro, and blood 5-HT concentrations in 9 male volunteers. Systolic blood pressure was slightly reduced during a low sodium diet, whereas the diastolic pressure remained unchanged. Plasma renin activity and aldosterone concentration both fell significantly when sodium intake was increased; plasma angiotensin II concentration also fell, but not significantly. There was a significant fall in haematocrit after an increased sodium intake, but there was no change in the whole-blood platelet count after correcting for this. There were no significant changes in either total (i.e. PRP) or platelet 5-HT concentrations. The extent of platelet aggregation induced by 5 and 20 mumol.l-1 of ADP increased significantly when dietary sodium intake was increased. When compared with low or normal sodium intakes, lower concentrations of ADP were required to produce 50% of maximum aggregation after a high sodium intake. The 5-HT2 receptor antagonist ketanserin (1 mumol.l-1 in vitro) reduced the extent of aggregation induced by 5 mumol.l-1 ADP after the volunteers had taken a high sodium diet, whereas the angiotensin II receptor antagonist saralasin (1 nmol.l-1) increased the rate of aggregation after the low sodium diet. Thus, during a high sodium intake, human platelets become more sensitive to the aggregating agent ADP. It is possible that this effect is mediated via platelet 5-HT2 receptors, since ketanserin abolished the increase in salt-induced aggregation seen with 5 mumol.l-1 ADP.

Holistic health patterning in multiple sclerosis

Multidimensional health patterning of three groups of persons with multiple sclerosis (MS) was examined. Changing patterns over a 5-year period for each group also were examined. Serial self-assessments of the subjects' prevalence of MS-related symptoms (motor, brainstem, sensory, elimination, mental-emotional) and level of ADL functioning (fine and gross motor activities, sensory/communication, socializing/recreation, intimacy) were obtained by mail. The number of subjects grouped by years since diagnosis was: 69 (0-5), 49 (greater than 5-10), and 93 (greater than 10). Study findings indicated significantly higher levels of functioning in areas of fine and gross motor activities and intimacy among the more recently diagnosed group but no difference among the groups for sensory/communication, recreation/socializing, and symptoms. Significant increases in motor and brainstem symptoms and decline in fine and gross motor activities and intimacy occurred over the 5-year period particularly for the 0 to 5 year postdiagnosis group. Knowledge of symptom and ADL patterning is essential for nurses and other health care providers in anticipating the concerns and needed services of persons with MS and their families.

No difference between home and clinic blood pressure measurements in pregnancy: a computerized telemetric study

Many decisions in pregnancy are based on one or two casual blood pressure estimations made in the antenatal clinic. No previous study has challenged the validity of this practice or attempted to discover whether there are significant differences between the blood pressures of pregnant women when they are measured in the clinic and when they are measured in their home environment. We measured the blood pressures of 35 healthy pregnant women both at the antenatal clinic and in their own homes. All the women were at between 28 and 32 weeks gestation. At both locations, ten consecutive blood pressure and pulse measurements were made at one minute intervals using a Dinamap 1846P automated blood pressure monitor. The readings taken in the clinic were supervised, whilst at home the patients used our blood pressure telemetry system without direct supervision, the results being transmitted automatically to the hospital computer via the public telephone network. The Dinamap results were analysed in detail. Each ten minute recording session was summarised in terms of the first, last, highest, lowest and mean of the systolic, diastolic and mean arterial blood pressure, and pulse measurements in that session. Also, two measures of the variability within a ten measurement series were considered, the average change in pressure or pulse from one reading to the next, and the difference between the highest and lowest readings of pressure and pulse in the series. All descriptors of the clinic and the home measurements were compared using the paired Student's t-test. Clinic and home blood pressure measurements were not significantly different from each other in any respect.(ABSTRACT TRUNCATED AT 250 WORDS)

A cross-sectional survey of home blood pressure in a rural community in northern Japan

A cross-sectional survey was performed on home blood pressure recordings (home BP) in a rural community in northern Japan. In total, 1190 participants (495 men and 695 women which consist 61.5% of the greater than or equal to 15 year-old regional population, n = 1933) were asked to measure home BP every morning for a month, using a semiautomatic BP measuring device. The actual measurements were done 16.8 +/- 10.2 times (mean +/- SD) for men and 19.0 +/- 9.4 times for women. Home systolic (SBP) and diastolic BP (DBP) was elevated gradually with age in both sexes, although DBP tended to fall after reaching 70 years old in men. SBP and DBP thus measured were significantly lower than those of casual BP of ordinary Japanese people reported by the Ministry of Health and Welfare, Japan, by 11.4 +/- 4.3 mmHg SBP (mean +/- SD) and 5.9 +/- 1.6 mmHg DBP in men, and 12.7 +/- 5.1 mmHg SBP and 8.1 +/- 2.5 mmHg DBP in women. When WHO criteria were applied to the home BP, 2.8% of men and 0.6% of women were considered to be definitely hypertensive, and 7.9% of men and 6.4% of women as of borderline cases, indicating the underestimation of hypertensive population by means of home BP. Based on these data, we demonstrated the values equal to 1SD or 2SDs above the mean in each age group to tentatively determine biological normalcy. It is necessary to define the relationship between home BP and target organ disease or hypertensive complications. A long-term prospective study is also necessary to define the relationship between home BP and long-term morbidity or mortality.

Effect of ambulatory blood pressure monitoring on the diagnosis and cost of treatment for mild hypertension

Detection of mild hypertension by a small number of casual blood pressures may be inaccurate for the determination of average blood pressure. Nonetheless, casual pressures remain the basis for the diagnosis and treatment of hypertensive patients. We compared casual and noninvasive ambulatory blood pressure monitoring in a consecutive series of 60 subjects evaluated for possible mild hypertension on the basis of casual pressures. Ambulatory blood pressure monitoring was performed on days of usual activity. Correlations between casual systolic and average ambulatory systolic pressures or casual diastolic and average ambulatory diastolic pressures were not significant. Nearly half of the subjects had average ambulatory systolic pressures less than 130 mm Hg. Sixty percent had average ambulatory diastolic pressures less than 85 mm Hg. Nearly 40% had both systolic and diastolic pressures less than those limits. A preliminary analysis of the effects of these results on the short-term cost of antihypertensive treatment was made, assuming that treatment could be withheld from those with average ambulatory pressures less than 130/85 mm Hg. This approach suggests that ambulatory blood pressure monitoring need not increase overall cost, if the results of this evaluation are used in the decision to treat.

Lithium carbonate--a competitive aldosterone antagonist?

Plasma renin activity (PRA), aldosterone (aldo) levels, electrolyte levels, and blood pressures were measured in 16 patients with affective disorders taking lithium prophylactically, and in 16 age and sex-matched control subjects. PRA and aldo levels were significantly elevated in the lithium-treated group. There was no difference between the groups in plasma electrolytes or erect and supine blood pressures, arguing against secondary aldosteronism. In the lithium-treated group, there was a significant positive correlation between both PRA and plasma aldo vs serum lithium. We postulate that lithium inhibits the action of aldosterone on the distal tubule in the kidney. Activation of the renin angiotensin system maintains normal blood pressure and plasma electrolytes.

Changing relation between home and clinic blood-pressure measurements: do home measurements predict clinic hypertension?

Blood-pressure screening in a family health centre identified 114 patients (53 male, 61 female) with diastolic pressures of 95 mm Hg and greater after three readings in the seated position (mean 163 [SEM 2]/104 mm Hg). All were instructed in the use of the 'Copal UA 231/251' electronic sphygmomanometer and produced a series of readings taken at home over 3 days. They were recalled after 2 weeks and 4 weeks for repeat clinic measurements of blood pressure. Blood pressure fell on successive clinic visits; at the final visit only 59 patients (31 male, 28 female) had diastolic pressures of 95 mm Hg or greater. Average day-time home blood-pressure measurements (155/94 mm Hg) were significantly lower than the screening blood-pressure measurements but were not significantly different from those at the third clinic visit (154/97 mm Hg). Home blood-pressure measurements were successful in predicting outcome at the third clinic visit in 90 (79%) patients; home-monitored pressures suggested normotension when the final clinic visit diastolic blood pressure was still above 95 mm Hg in only 16 (14%) patients. Only 2 of these had a final clinic diastolic pressure above 105 mm Hg. Home monitoring represents a practicable and acceptable alternative to repeated clinic measurements in the initial assessment of hypertensive patients.