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(Hypertension. 1999;34:261-266.)
© 1999 American Heart Association, Inc.
Scientific Contributions |
From the Research and Development Center of the Social Insurance Institution, Turku, Finland.
| Abstract |
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Key Words: blood pressure blood pressure monitoring, ambulatory blood pressure monitoring ventricular function albuminuria
| Introduction |
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Self-measured BP has usually been higher than daytime ambulatory BP.1 2 3 4 5 6 7 To the best of our knowledge, it is not known whether ambulatory BP is superior to self-measured BP as an indicator of left ventricular hypertrophy and microalbuminuria.
The purpose of our study was to compare multiple, carefully controlled clinic and self-measured home BP measurements with ambulatory BP monitoring in the clinical evaluation of untreated hypertension. More precisely, we wanted to examine and compare levels and relations of ambulatory, clinic, and self-measured home BPs as well as their relationships to albuminuria and echocardiographic measures of the left ventricle.
| Methods |
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200 000 inhabitants) in
southwestern Finland were requested to refer newly diagnosed,
moderately to severely hypertensive but pharmacologically untreated men
and women, 35 to 54 years old, to the study. The inclusion criteria
were a systolic or a diastolic BP
consistently between 180 and 220 mm Hg or between 100 and
120 mm Hg, respectively, as measured within the primary
healthcare system. Patients with coronary artery disease,
cerebrovascular disease, insulin-treated diabetes mellitus, or
hemodynamically significant valvular disease
and pregnant women were excluded from the study. The exclusion was
based on medical history, physical examination, routine biochemical
tests, exercise ECG, and echocardiography. Two
hundred thirty-nine of 252 subjects fulfilled the inclusion criteria.
Ambulatory BP monitoring was successfully completed for 233 subjects.
The study was conducted in compliance with the Second Declaration of
Helsinki and was approved by the ethical committee of the Social
Insurance Institution of Finland. All subjects gave their informed
consent.
Measurements
Recruitment BP was defined as the mean of the last 2
measurements made by the primary healthcare staff. Clinic BP was
measured by a trained nurse. It was recorded between 8
AM and 10 AM with the patient in the sitting
position with a mercury sphygmomanometer. A cuff with a
bladder width of 15 cm was used. Patients were requested to refrain
from heavy exercise in the morning and to avoid cola drinks, coffee,
tea, and smoking for at least 1 hour before the measurement. BP was
measured after the patient had rested for 15 minutes. The last 5
minutes of rest were spent in the measurement room with the cuff
around the right upper arm. Cuff inflation pressure was then determined
by palpating the disappearance and appearance of the radial pulse. BP
was recorded twice, with approximately a 2-minute interval.
Duplicate measurements were done in 4 separate sessions within 3 weeks.
Clinic BP was determined as the mean of the 4 duplicate BP
measures.
Home BP was self-measured with a semiautomatic oscillometric device
(Omron HEM 705C). The device meets the criteria for accuracy according
to the revised protocol of the British Hypertension Society and the
revised standards of the Association for the Advancement of Medical
Instrumentation.13 A cuff with a bladder width of 13 cm
was used for subjects with an arm circumference of
35 cm, and a cuff
with a bladder width of 15 cm was used for subjects with an arm
circumference >35 cm. Patients received written instructions and
individual guidance on how to measure BP correctly. Preparations for
self-measured home BP were the same as for clinic BP. Seated BP was
measured twice, approximately at a 2-minute interval every morning
between 6 AM and 9 AM and every evening between
6 PM and 9 PM on 7 consecutive days. Home BP
was determined as the mean of 14 duplicate measures.
Ambulatory BP was recorded with an auscultatory device (Suntech,
Accutracker II) according to the guidelines of the Berlin Consensus
Document.14 A cuff with the same bladder width as that
used in home measurements was used. Correct position of the microphone
was controlled when the recorder was fitted by use of
3
auscultatory readings with a mercury column sphygmomanometer connected
to the recorder's BP cuff. Ambulatory BP was recorded during
daytime (6 AM to 11 PM) at 15-minute intervals
and during nighttime (11 PM to 6 AM) at
30-minute intervals. Twenty-fourhour daytime, nighttime, awake, and
asleep BPs were calculated from hourly means. Only full hours of
wakefulness and sleep were included in the calculation of true awake
and true asleep BPs. BP data were edited automatically. Readings with a
quality failure code (patient ending the sample by pressing the stop
key, ECG connections giving erratic heartbeats or missing them
completely, Korotkoff sounds that were too weak or not detected enough,
loose cuff, or air leak) were rejected. Readings edited according to
quality failure test codes were rejected if systolic BP was out
of the range of 70 to 250 mm Hg, diastolic BP was out
of the range of 40 to 150 mm Hg or pulse pressure (mm Hg) was
not >0.43xdiastolic BP-18. A maximum of 2 hours missing
of the 24 hourly means was allowed. Three patients missed 2 hours, and
6 patients missed 1 hour. The missing hours were compensated by
corresponding mean nighttime or daytime BP values for calculations of
24-hour BPs.
Two-dimensionally controlled M-mode echocardiographic
examinations were successfully performed in 232 patients with the use
of an Aloca SST-860 color Doppler ultrasonoscope and a 3.5-MHz
phased-array transducer. All echocardiographic studies
were performed by the same experienced physician (H.K.), who also
analyzed the tracings blinded to the BP readings of individual
patients. Measurements were performed according to the recommendations
of the American Society of Echocardiography
(ASE).15 The leading edge to leading edge convention was
used. Left ventricular echograms were measured at or
immediately below the tips of mitral leaflets and averaged over
3
heart cycles. ASE cube left ventricular mass (g) was
calculated as 1.05x[(interventricular septal thickness in
diastole+left ventricular internal dimension in
diastole+posterior wall thickness in
diastole)3-left
ventricular internal dimension in
diastole3]. Corrected left
ventricular mass (g) was calculated with the equation
developed by Devereux and coworkers16 : 0.80x(ASE cube
left ventricular mass)+0.6.
Twenty-fourhour urine was collected for albumin measurements. Albumin was determined by nephelometry (Orion Diagnostica 667560), with a measurement range of 0.5 to 16 mg/dL. The day-to-day variation in albumin measurements was 6.2% at the level of 3.4 mg/dL of albumin, and the intra-assay variations were 5.7% at the level of 4.9 mg/dL of albumin and 3.9% at the level of 9.4 mg/dL of albumin.
Statistical Analyses
Statistical values are given as mean±SD. Before statistical
analyses, the skewed distribution of albuminuria
data was corrected logarithmically. Differences between 2 BP
variables were tested by paired t test.
Repeated-measures ANOVA was used for comparisons of >2 BP
variables. If significant, the pairwise comparisons were made with
application of the rule for multiple comparisons recommended by
Bonferroni. Bland-Altman plots17 were used to show
individual variations in differences of self-measured home and clinic
BPs and of clinic and daytime ambulatory BPs on different BP levels.
Associations between clinic BPs, self-measured home BPs, ambulatory
BPs, albuminuria, and echocardiographic
measures of the left ventricle were tested by calculating bivariate
Pearson's product moment correlation coefficients. To determine
independent BP correlates of left ventricular mass index,
stepwise multivariate regression analyses with
age, gender (1man; 2 women), and clinic, self-measured home, and
ambulatory daytime, nighttime, and 24-hour BPs were made.
| Results |
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Comparisons Within Clinic, Self-Measured Home, and Ambulatory
BPs
The BP variation between the 4 clinic measurement sessions (Figure 1) was small but statistically
significant (P<0.001, ANOVA). When compared with the first
clinic session, mean diastolic BP of the second session was
1.6±6.6 mm Hg higher (P<0.01; 5th to 95th
percentiles, -9 to +14 mm Hg), mean diastolic BP of
the fourth session was 1.7±7.6 mm Hg lower (P<0.01;
5th to 95th percentiles, -11 to +15 mm Hg), and mean
systolic BP of the fourth session was 3.2±11.5 mm Hg
lower (P<0.001; 5th to 95th percentiles, -16 to +22
mm Hg).
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Throughout clinic sessions, the first systolic BP readings were higher than the second (Figure 1). The mean differences between all first and second BP readings (first readings minus second readings) were 0.9±2.7 mm Hg (P<0.001; 5th to 95th percentiles, -3 to +6 mm Hg) for systolic BP and 0.1±1.8 mm Hg (P=NS; 5th to 95th percentiles, -2.5 to +3.0 mm Hg) for diastolic BP.
Self-measured home BPs and heart rates are shown in Table 2. When compared with the morning BP, home evening systolic BP was 3.7±6.6 mm Hg higher (P<0.001; 5th to 95th percentiles, -7.6 to +15.5 mm Hg) and home evening diastolic BP was 1.0±4.6 mm Hg higher (P<0.01; 5th to 95th percentiles, -7.1 to +8.5 mm Hg). The mean differences between all first and second readings of the 14 home sessions (first readings minus second readings) were 2.5±2.6 mm Hg (P<0.001; 5th to 95th percentiles, -1.7 to +6.4 mm Hg) for systolic BP and 1.3±1.6 mm Hg (P<0.001; 5th to 95th percentiles, -1.1 to +3.9 mm Hg) for diastolic BP.
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Ambulatory awake BP was 1.3±1.5/0.9±1.0 mm Hg higher (P<0.001 for systolic and diastolic BPs; 5th to 95th percentiles, -0.3 to +3.7/-0.2 to +2.8 mm Hg) than ambulatory daytime BP, and ambulatory asleep BP was 1.4±3.0/1.0±2.2 mm Hg lower (P<0.001 for systolic and diastolic BPs; 5th to 95th percentiles, -1.4 to +7.6/-1.1 to +5.9 mm Hg) than ambulatory nighttime BP.
Comparisons Between Clinic, Self-Measured Home, and Ambulatory
BPs
The overall differences between clinic, home, and ambulatory
daytime BP values were highly significant (P<0.001 for
systolic and diastolic BP, ANOVA). Self-measured
home BP was 5.6±8.8/1.7±6.5 mm Hg lower (P<0.001
for systolic and diastolic BP) than clinic BP
(Table 2, Figure 2). When compared
with clinic BP, ambulatory daytime and awake systolic BPs were
3.8±9.9 and 5.1±9.9 mm Hg higher, respectively
(P<0.001), and ambulatory daytime and awake
diastolic BPs were 2.7±6.8 and 1.7±6.9 mm Hg lower,
respectively (P<0.001) (Table 2, Figure 2).
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The differences between self-measured home and clinic BPs and between ambulatory and clinic BPs were normally distributed, with 95% to 98% of the individual differences lying within the range of mean difference ±2 SDs (Figure 2).
Clinic BP correlated significantly (P<0.001) with systolic/diastolic ambulatory daytime (r=0.73/0.59), nighttime (r=0.65/0.55), 24-hour (r=0.73/0.62), and self-measured home (r=0.77/0.67) BPs. Self-measured home BP correlated significantly (P<0.001) with ambulatory daytime (r=0.78/0.70), nighttime (r=0.68/0.64), and 24-hour (r=0.78/0.73) BPs.
Relationships of BPs to the Left Ventricle and Albuminuria
The correlations of clinic and self-measured home BPs to left
ventricular mass index and 24-hour urinary albumin
increased with increasing number of measurement sessions (data not
shown) and reached with 4 measurement sessions the correlations
observed for ambulatory BP (Table 3). Left ventricular
mass index correlated slightly more strongly with self-measured home
morning than evening systolic/diastolic BPs
(r=0.46/0.43, P<0.001 and
r=0.41/0.37, P<0.001 for home morning and
evening BPs averaged over the first 4 duplicate morning and evening
measures, respectively).
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In stepwise multivariate regression analyses, the variation of left ventricular mass index was significantly explained by gender and self-measured home systolic BP in models that originally included age, gender, and clinic, self-measured home, and ambulatory daytime, nighttime, and 24-hour systolic and diastolic BPs; by gender and self-measured home diastolic BP in models with diastolic BPs; and by gender and self-measured mean arterial pressure in models in which systolic and diastolic BPs were substituted with mean arterial pressures (Table 4). The findings were essentially the same in models in which self-measured home BPs averaged over all morning and evening duplicate measures of 7 consecutive days were substituted with home morning BPs averaged over the duplicate morning measures of the first 4 days. For example, gender and self-measured home morning systolic BP explained 36% (P<0.0001) of the cross-sectional variation in left ventricular mass index in models originally including age, gender, and clinic, self-measured home morning, and ambulatory daytime, nighttime, and 24-hour systolic and diastolic BPs.
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| Discussion |
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Another important finding was that differences between clinic and ambulatory BP values and between clinic and self-measured home BP values were smaller than usually reported.1 2 3 4 5 6 7 12 Ambulatory daytime systolic BP was even slightly higher than clinic systolic BP. Our data are consistent with those of Pearce and colleagues,19 who made population-derived comparisons between ambulatory and carefully controlled multiple clinic BPs. The correlations between clinic and ambulatory BPs were relatively high and in agreement with studies based on a large number of patients20 21 22 or on multiple clinic BP measurements.19 In contrast to earlier studies,5 23 BP decreased only slightly with increasing number of clinic measurement sessions. Within measurement sessions, BP differences between the first and second readings were smaller than previously reported.23
Various factors may explain why clinic BP appeared lower and its variation smaller than expected. First, a large cuff with a bladder width of 15 cm was used in the clinic BP measurements. Compared with self-measured home and ambulatory BP, clinic BP would have been, on average, 3/2 mm Hg higher if it had been measured with cuffs with the same bladder widths as used in home measurements and ambulatory monitoring.24 Second, the clinic BP was measured 3 times per session. The first measurement to determine the cuff inflation pressure may have had a habituating effect before the 2 ordinary readings. Third, the clinic BP was measured with careful preliminary preparations and standardized measurement techniques. Fourth, an alerting reaction may be associated with measurement by a physician.10 11 In our study, the clinic BP was measured by a trained nurse.
Our study also suggests that middle-aged hypertensive men and women who
represent a normal socioeconomic distribution of the urban
population are highly compliant and trainable to measure BP reliably.
The correlations between self-measured and clinic and between
self-measured and ambulatory BPs were of the same size as seen between
clinic and ambulatory BPs. Self-measured home systolic BP was
10 mm Hg lower than ambulatory daytime systolic and
6 mm Hg lower than clinic systolic BP. The differences
between clinic, self-measured, and ambulatory daytime
diastolic BP values were minor. We found that self-measured
home morning BP was, on average, 3.7/1.0 mm Hg lower than
self-measured evening BP. However, compared with home evening BP, home
morning BP was a slightly better indicator of left
ventricular hypertrophy.
In agreement with previous findings, awake BP values were slightly higher and asleep BP values were slightly lower than corresponding arbitrary daytime and nighttime BP values.25 The correlations of daytime and nighttime BPs with characteristics of left ventricular hypertrophy and with albuminuria were as high as those observed for true awake and asleep BPs. Our findings indicate that normal and reference values for true awake and asleep BPs and for daytime and nighttime BPs differ slightly. Both methods are equally reliable in the determination of the severity of hypertension.
To conclude, nonphysician-measured clinic and self-measured home BPs, averaged over 4 carefully controlled duplicate measures, indicate albuminuria and left ventricular hypertrophy of untreated middle-aged hypertensives equally as well as ambulatory BP. Differences between clinic, home, and ambulatory BP values are quite small and mainly reflect differences in measurement techniques and activities during measurements. Reference values for carefully controlled clinic, self-measured home, and ambulatory BPs are needed.
| Acknowledgments |
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| Footnotes |
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Received March 31, 1999; first decision April 19, 1999; accepted April 27, 1999.
| References |
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