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(Hypertension. 1997;30:1531-1537.)
© 1997 American Heart Association, Inc.
Articles |
Diagnosing Gestational Hypertension and Preeclampsia With the 24-Hour Mean of Blood Pressure
From the Bioengineering & Chronobiology Laboratories, ETSI Telecomunicación, University of Vigo, Campus Universitario, Vigo, 36200 Spain.
Correspondence and reprint requests to Prof Ramón C. Hermida, PhD, Bioengineering and Chronobiology Labs, ETSI Telecomunicación, Campus Universitario, VIGO (Pontevedra) 36200, SPAIN. E-mail rhermida{at}tsc.uvigo.es
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Abstract |
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Abstract The use of ambulatory blood pressure monitoring has provided a method of blood pressure assessment that may compensate for some of the limitations of isolated measurements. Here we aim to examine prospectively the effectiveness of the commonly used 24-hour mean as a potential screening test for the identification of gestational hypertension and preeclampsia. We analyzed 503 blood pressure series from 71 healthy pregnant women and 256 series from 42 women who developed gestational hypertension or preeclampsia. Forty-eight-hour blood pressure monitoring was done once every 4 weeks after the first obstetric consultation. Sensitivity and specificity of the 24-hour mean of blood pressure were computed for each trimester of pregnancy by comparing distributions of values obtained for healthy and complicated pregnancies, without assuming an a priori threshold for diagnosing gestational hypertension on the basis of mean blood pressure. Sensitivity ranges from 31.8% for diastolic blood pressure in the second trimester to 84.1% for systolic blood pressure in the third trimester. However, specificity is as low as 6.9% for diastolic blood pressure in the first trimester. The positive predictive value does not reach 55% for any variable in any trimester. The higher relative risk was consistently obtained for systolic blood pressure (4.9 in the third trimester). Despite the highly statistically significant differences in blood pressure found between healthy and complicated pregnancies in all trimesters, the daily mean of blood pressure does not provide a proper and stable individualized test for diagnosing hypertensive complications in pregnancy. Other indexes obtained from the blood pressure series have been shown, however, to identify early in pregnancy those women who subsequently will develop gestational hypertension or preeclampsia, rendering ambulatory blood pressure monitoring a useful, but still costly, technique in pregnancy.
Key Words: blood pressure • hypertension, gestational • pregnancy • normotension • preeclampsia • blood pressure monitoring, ambulatory
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Introduction |
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Blood pressure measurement is one of the most frequently used screening tests in pregnancy.1–5 Conventional BP values, however, have several shortcomings; they provide a measurement that represents only a fraction of the 24-hour BP profile, usually under circumstances that may have a pressor effect, and the technique is fraught with potential errors.6,7 Common sources of measurement error associated with casual BP values include instrument defects and examiner technique.8 In addition, maternal posture can significantly affect BP in pregnant women.7 Therefore, casual BP readings are neither diagnostic of nor a good predictor for preeclampsia.2,9–11 The development of automatic instrumentation for indirect noninvasive ABPM makes it possible to follow the time course of BP variation around the clock in large groups of subjects.12,13 The use of these monitors has provided a method of BP assessment that may compensate for some of the limitations of office and even self-measurements.14–16
In chronic hypertensive patients, the correlation between the BP level and the current target organ damage and the eventual cardiovascular risk and long-term prognosis is closer for ambulatory measurements than for clinic measurements.17–19 The use of a reliable and accurate automated ABPM device is the logical approach to overcoming many of the problems associated with conventional BP measurement.14,20 ABPM has the added advantage that, in addition to the immediate derivation of absolute BP values, it also gives the extra dimension of facilitating analysis of the circadian variation of BP in pregnancy.9,11
Once the advantages of ABPM over casual sampling can be established, the question remains of what to do with the data thus obtained. Kyle et al16 have investigated the effectiveness of second trimester 24-hour ABPM as a screening test for preeclampsia. They reported that the awake SBP and the MAP were significantly higher at 18 and 28 weeks of gestation in those women who subsequently developed preeclampsia. Despite the differences in BP between the groups, the best predictive measurement with regard to BP was MAP at 28 weeks of gestation, providing a sensitivity of 65%, specificity of 81%, and a positive predictive value of 31% for the prediction of preeclampsia. Daytime or nighttime values of BP did not provide a better diagnosis. Brown et al21 reported a positive predictive value of 63% when a cutoff value of 70 mm Hg nocturnal DBP after 26 weeks' gestation was used for predicting preeclampsia.
As in the general nonpregnancy practice, the most common approach is still to rely on the arithmetic mean of all values determined by ABPM. In a retrospective study of 745 BP 48-hour profiles sampled by ABPM on 189 clinically healthy pregnant women and 100 women with a diagnosis of gestational hypertension or preeclampsia, we have shown11 that the circadian pattern of SBP, MAP, and DBP was significantly higher in complicated pregnancies as compared with healthy ones as early as the first trimester of pregnancy. However, the use of the 24-hour mean of BP provided a very poor screening test for an individualized early diagnosis of gestational hypertension or preeclampsia.11
In an attempt to corroborate and extend conclusions from this preliminary retrospective study, here we report results from an ongoing prospective study of BP variability during pregnancy. In particular, we aim to examine prospectively the effectiveness of the commonly used 24-hour mean of ABPM, as compared with other indexes also obtained from the BP series, as a potential screening test for the early identification of gestational hypertension and preeclampsia in pregnant women that were systematically monitored from the first obstetric visit to the hospital until delivery.
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Methods |
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Subjects
We studied 113 Caucasian pregnant women (71 with uncomplicated pregnancies, 28 who developed gestational hypertension, and 14 who developed preeclampsia, here defined as gestational hypertension and proteinuria, above 300 mg/24 h in urine, with or without edema). All women received obstetric care at the Obstetric Physiopathology Unit, Hospital General Clínico Universitario de Galicia, Santiago de Compostela, Spain. Reasons for receiving medical care at this Unit include, among others, family or personal history of either gestational hypertension; preeclampsia; chronic hypertension; or cardiovascular, endocrine, bleeding, or metabolic disease; and a personal history of previous spontaneous abortion, multiple pregnancy, obesity, and aged or youthful nulliparous pregnancy (<18 or >35 years). The incidence of gestational hypertension and preeclampsia in this Unit is about three times that of the general obstetric population in our setting. Inclusion criteria were absence of any condition requiring the use of antihypertensive medication, age (18 to 40 years), and gestational age (<16 weeks at the time of inclusion). Exclusion criteria were, among others, multiple pregnancy, chronic hypertension, chronic liver disease, any disease requiring the use of anti-inflammatory medication, diabetes or any other endocrine disease such as hyperthyroidism, and being unable to tolerate the use of an ambulatory BP monitor. Subjects providing fewer than four BP profiles were eliminated from the study. The Ethical Committee of Clinical Research from the Medical School approved the study. All volunteers signed consent forms before entering the study.
BP Assessment
The SBP, MAP, and DBP of each subject were automatically
monitored every 30 minutes during the day (9 AM to 11
PM) and hourly during the night for 48 hours with an
ABPM-630 Colin device at the time of recruitment, and then every 4
weeks until delivery. BP series were eliminated from analysis
when they showed an irregular schedule during the days of
sampling, an odd sampling with spans of more than 3 hours without BP
measurement, or a night resting span shorter than 6 hours or more than
12 hours. The total number of BP series provided by the women under
investigation fulfilling all mentioned requirements set a priori
was 759 (503 from healthy pregnant women and 256 from women with a
diagnosis of gestational hypertension or preeclampsia). All women were
living during sampling on their usual diurnal waking (
8
AM to 12 midnight for most subjects), nocturnal resting
routine, following everyday life conditions with minimal restrictions:
they were told to follow a similar schedule during the days of sampling
and to avoid the use of medication for the duration of the trial. The
clinical evaluation of the monitor according to the standards published
by the Association for Advancement of Medical
Instrumentation22 has been previously
established.23 The BP cuff was worn on the nondominant arm.
ABPM was performed in addition to the woman's routine antenatal care,
and no person was hospitalized during monitoring. Cuff size was
determined by upper arm circumference at the time of each visit. ABPM
always started between 10 AM and 1 PM. During
monitoring, all subjects maintained a diary regarding information about
their activity cycles, dietary consumption, physical activity,
emotional state, and other external or internal stimuli possibly
affecting BP.
Obstetric Care
All issues related to ABPM (including handling and preparation
of the monitors, individualized explanation about their use to each
patient, and processing of the data provided by any given pregnant
woman after monitoring) were always handled by the same member of the
research group in one room of the Unit. Conventional obstetric
examinations of the pregnant women, usually done on the same day just
before starting ABPM, were carried out by other members of the
department in different rooms of the Unit. Diagnosis of gestational
hypertension (conventional BP values above 140/90 mm Hg for
SBP/DBP without clinical record of hypertension prior to pregnancy)
or preeclampsia (as defined above) was made using information from the
conventional obstetric examinations and routine analyses of
urine. Information obtained from ABPM was withheld from the patient and
the obstetrician taking conventional care of the patient.
Statistical Methods
Original oscillometric data were first edited according to
commonly used criterion for the removal of outliers and measurement
errors.24,25 The remaining data were analyzed by
the use of Chronolab,26 a software package for biologic
signal processing by linear and nonlinear least-squares estimation
that, among others, includes the single and population-mean
cosinor methods,27,28 as well as the fit of
multiple components.27 Each BP series was analyzed
by the least-squares fit of a multiple component cosine curve with
periods of 24 and 12 hours to determine the rhythm-adjusted mean or
MESOR (midline estimating statistic of rhythm) and the amplitudes of
both components. This model has been shown to describe sufficiently
well the circadian pattern of BP variability,29–31 despite
the fact that other ultradian rhythms can be demonstrated as
statistically significant in some but not all individuals studied by
48-hour ABPM. Since the data were obtained at an unequidistant sampling
rate covering two cycles (48 hours), the MESOR provides a better
estimation of the true 24-hour mean than the average of all BP values
(usually overestimating the true mean due to the denser sampling during
activity).
Sensitivity and specificity of the 24-hour mean of BP were computed for each trimester of pregnancy by comparing distributions of values for mean BP obtained for healthy and complicated pregnancies, without assuming an a priori threshold for diagnosis of gestational hypertension based on the 24-hour mean BP. Sensitivity is defined as the probability that the clinical test is positive given that the person has the disease (that is, the proportion of persons with the disease identified as such by the clinical test). Specificity is defined as the probability that the clinical test is negative given that the person does not have the disease (that is, the proportion of healthy subjects identified as such by the clinical test). Additionally, we also computed the positive and negative predictive values (proportion of subjects with a positive test that really has the disease and proportion of subjects with a negative test that is really healthy, respectively), as well as the relative risk, defined as the proportion of subjects with a positive test that really has the disease divided by the proportion of subjects with a negative test that really have the disease. A good clinical test should have values for sensitivity, specificity, and positive and negative predictive values close to 100%, while the relative risk is markedly larger than 1. If the relative risk is, for instance, 10, then persons with a positive test are 10 times as likely to have the disease than persons with a negative test.32
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Results |
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Figs 1
and 2 represent the frequency
histograms with the distributions of the 24-hour mean of SBP and DBP,
respectively, computed from all 48-hour series sampled in each
trimester of pregnancy. The comparison of histograms between healthy
(top) and complicated pregnancies (bottom) does not show a clear
separation between these populations for any given trimester. Even in
the third trimester, complicated pregnancies can be characterized by a
24-hour mean value of as low as 106 mm Hg for SBP (Fig 1, bottom
left) or 58 mm Hg for DBP (Fig 2, bottom left). Moreover, 125 of
130 BP profiles sampled in the third trimester from women with
complicated pregnancies have a 24-hour mean value lower than 135
mm Hg for SBP (Fig 1, bottom left). Only one of those 130 BP series
has a 24-hour mean above 85 mm Hg for DBP (Fig 2, bottom
left).
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Since no reference value for the 24-hour mean has yet been provided to
be used as an upper limit for diagnosis of gestational hypertension or
preeclampsia on the basis of the results of ABPM, sensitivity and
specificity derived from the histograms of Figs 1
and 2 were evaluated
directly by comparing the distributions obtained for each of the two
populations. The values thus computed are given in Table 1 (which also includes results for the
MAP). For all the cardiovascular parameters
included in Table 1, sensitivity corresponds to the largest possible
value found for an assumed maximum specificity of 100%.
Correspondingly, the values of specificity provided in the table are
computed assuming a possible sensitivity of 100%. A similar approach
was also used to compute positive and negative predictive values.
Results from this table indicate an increase in sensitivity with
respect to the values obtained compared with values sampled during
office hours.9 This higher sensitivity is a reflection of
the population differences in circadian MESOR documented previously
even for the first trimester of pregnancy.9 Specificity is,
however, much lower than that computed on the basis of casual
measurements. Sensitivity ranges from 31.8% for DBP in the second
trimester to 84.1% for SBP in the third trimester. Specificity is as
low as 6.9% for DBP in the first trimester. This
cardiovascular variable shows the poorest results,
with sensitivity and specificity as low as 56% and 23%, respectively,
in the third trimester of pregnancy. The positive predictive value does
not reach 55% for any variable in any trimester, too low for a
proper individualized diagnosis of gestational hypertension or
preeclampsia. The relative risk increases with gestational age. The
best results were consistently obtained for SBP, with a
relative risk close to 5 in the third trimester and corresponding
values for sensitivity and specificity of 84% and 65%,
respectively.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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The values of sensitivity and specificity provided in Table 1
need
to be considered carefully. If one uses a high constant value for
diagnosis of gestational hypertension based on the 24-hour mean
(135/85 mm Hg for SBP/DBP has been recently established for
diagnosing hypertension33), sensitivity will be very low or
even zero (as for the first and second trimesters, when no one single
BP series actually exceeded that threshold, as shown in Figs 1 and 2).
Specificity, on the contrary, will be very high, reflecting the fact
that the criterion will identify practically all subjects as
normotensive. This situation is graphically displayed in Fig 3, which represents sensitivity
and specificity computed for each trimester of pregnancy as a function
of the 24-hour mean of SBP (top) and DBP (bottom) as possible threshold
for diagnosis.
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Results from Fig 3 indicate that as we decrease the threshold value the
sensitivity will increase. Specificity, on the contrary, will decrease
rapidly, since, as indicated in Figs 1 and 2, there is a considerable
amount of overlap between the distributions on the 24-hour mean
obtained for normotensive and hypertensive pregnant women in all
trimesters of gestation. The values shown in Table 1 somehow
represent an average result indicating how much sensitivity can
be improved and how much specificity will be lost by increasing
sensitivity. Fig 3 shows that the slopes for increasing sensitivity and
decreasing specificity while lowering the threshold value of mean BP
are quite similar and very pronounced. This indicates that a small
change in the optimal threshold would result in an important loss in
either sensitivity or specificity. The results shown in Fig 3
characterize an unstable and thus poor diagnostic test.
It is important to note, however, that the combination of sensitivity
and specificity reaches the highest possible value for a 24-hour mean
SBP of 108 mm Hg in the first and second trimesters of pregnancy
and of 112 mm Hg in the third trimester of pregnancy. The
"best" threshold for DBP is at 64, 63, and 66 mm Hg for each
trimester of pregnancy. These values are markedly below those currently
used for defining hypertension with regard to ABPM,33 and
also below for the threshold value of nocturnal DBP provided in early
studies.21 For these threshold values, sensitivity and
specificity are both above 85% for the 24-hour mean of SBP in the
first and second trimesters and above 90% for the third trimester. The
relative risk increases up to 11 in the first and second trimesters and
up to 25 in the last trimester of pregnancy, when the differences in
mean BP between healthy and complicated pregnancies are much more
pronounced.9 These values could be considered acceptable
for a diagnostic test, but Fig 3 indicates that those
values could not be reproducible inasmuch as a little change in the
threshold would result in a pronounced reduction in sensitivity or
specificity, and in relative risk. In any event, results indicate that
elevations in BP greater than the threshold provided above markedly
increase the risk of subsequent gestational hypertension. Results for
the optimal threshold of the 24-hour mean DBP given above are much
poorer, with sensitivity of 67%, 68%, and 82%, specificity of 84%,
87%, and 85% and a relative risk of 4, 5, and 7 for each of the three
trimesters, respectively.
Results from Table 1 indicate that the highly statistically significant
differences that can be found in the 24-hour mean between healthy and
complicated pregnancies in all three trimesters of
gestation9,11 apply to the population, but do not provide a
proper individualized diagnostic test for gestational
hypertension or preeclampsia when we rely for diagnosis on just the
average of all BP values sampled by ambulatory monitoring. Daytime or
nighttime values of BP did not provide a better diagnosis in our study.
The sensitivity obtained from the 24-hour mean is, however, much higher
than the corresponding values obtained from casual sampling for the
same subjects.9
Another approach for diagnosing hypertension on the basis of ABPM
relies on the BP load,34,35 defined as the proportion of BP
values exceeding a given threshold (usually 140/90 for SBP/DBP during
activity and 120/80 during resting hours36). To validate
this approach to data sampled in pregnancy, we computed the BP load (as
the percentage of BP values exceeding 140/110/90 mm Hg for
SBP/MAP/DBP during daytime or 120/95/80 mm Hg during nighttime)
for all available 759 BP series monitored in pregnant women. Since the
conventional assessment of hypertension relies on absolute casual
values exceeding 140 or 90 mm Hg for SBP or DBP, respectively,
results based on the computation of BP load will be expressed as a
function of the maximum load, defined as the maximum of three values of
BP load, those computed for SBP, MAP, and DBP, respectively, for any
given subject. We also computed the mean load as the average of the
values obtained for the three cardiovascular
variables. As for the 24-hour mean, we did not establish a
priori any given value of BP load for diagnosis of gestational
hypertension. Instead, sensitivity and specificity were computed by
direct comparison of the distributions of values obtained for the
groups of normotensive and hypertensive pregnant women in each
trimester of pregnancy. Results from Table 2 indicate that sensitivity and
specificity are mostly equivalent whether one relies for diagnosis on
the maximum load or on the mean load. For the composite of all three
trimesters, sensitivity was 62%, with a positive predictive value of
54%. Specificity was 74%, with a lower value of 65% in the third
trimester of pregnancy. These results are comparable to those obtained
for the 24-hour mean (Table 1), in keeping with similar conclusions
found earlier in the diagnosis of mild to moderate hypertension based
on the same two parameters obtained from
ABPM.37
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In conclusion, ABPM has clear advantages over conventional casual
sampling with respect to the diagnosis of gestational hypertension or
preeclampsia. Both sensitivity and relative risk are markedly higher
for the 24-hour than for casual values.9 Relying on the
average of all values sampled by ABPM (or on the circadian MESOR as a
better approach when using nonequidistant sampling) provides a test
that seems to be unstable and therefore questionable for individualized
diagnosis. Results in Figs 1 through 3 indicate that a 24-hour mean
greater than 110/65 mm Hg for SBP/DBP increases the relative risk
of subsequent gestational hypertension or preeclampsia. Differences in
mean BP between healthy and complicated pregnancies are highly
statistically significant as early as in the first trimester of
gestation,9 with BP values well within the accepted range
of normotension, even for the women with a later diagnosis of
preeclampsia. Compared with the common approach of relying on the
24-hour mean of ABPM, the combined approach of establishing tolerance
intervals for the circadian variability of BP as a function of
gestational age, and then computing the so-called "hyperbaric
index" (area of BP excess above the upper limit of the tolerance
interval) by comparing any patient's BP profile with those intervals
(tolerance-hyperbaric test37), has been shown to provide a
high sensitivity and positive predictive value for the early detection
of pregnant women who subsequently will develop gestational
hypertension or preeclampsia, with an associated relative risk of 25 in
the first trimester of gestation and increasing up to 230 in the third
trimester.15 Limitations of this approach stem from the
fact that instrumentation for automatic monitoring, although advanced,
is not perfect, is still quite expensive, and is not well tolerated
during pregnancy, especially when the sampling rate is high. Despite
these limitations, sequential measurements of BP early in pregnancy are
good predictors of subsequent gestational hypertension or preeclampsia.
The tolerance-hyperbaric test avoids most of the limitations described
here for the 24-hour mean BP when used for the individualized diagnosis
of hypertensive complications in pregnancy, rendering ABPM a useful
technique in pregnancy.
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Selected Abbreviations and Acronyms |
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Acknowledgments |
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This research was supported in part by grants from Dirección General de Investigación Científica y Técnica, DGICYT, Ministerio de Educación y Ciencia (PB92-1111 & PB93-0372); Consellería de Educación e Ordenación Universitaria, Xunta de Galicia (XUGA-32202B97, 32205B95 & 32201B95); and Vicerrectorado de Investigación, Universidad de Vigo. The authors appreciate the helpful comments and suggestions from the reviewers.
Received May 28, 1997; first decision June 25, 1997; accepted June 25, 1997.
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References |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
1. Moutquin JM, Rainville C, Giroux L, Raynauld P, Amyot G, Bilodeau R, Pelland N. A prospective study of blood pressure in pregnancy: prediction of preeclampsia. Am J Obstet Gynecol. 1985;151:191–196.[Medline] [Order article via Infotrieve]
2. O'Brien WF. Predicting pre-eclampsia. Obstet Gynecol. 1990;75:445–452.[Medline] [Order article via Infotrieve]
3. Page EW, Christianson R. The impact of mean arterial pressure in the middle trimester upon the outcome of pregnancy. Am J Obstet Gynecol. 1976;125:740–746.[Medline] [Order article via Infotrieve]
4. Reiss RE, O'Shaughnessy RW, Quilligan TJ, Zuspan FP. Retrospective comparison of blood pressure course during preeclamptic and matched control pregnancies. Am J Obstet Gynecol. 1987;156:894–898.[Medline] [Order article via Infotrieve]
5. Villar MA, Sibai BM. Clinical significance of elevated mean arterial blood pressure in second trimester and threshold increase in systolic or diastolic blood pressure during the third trimester. Am J Obstet Gynecol. 1989;160:419–423.[Medline] [Order article via Infotrieve]
6. Halberg E, Delmore P, Finch M, Cornélissen G, Halberg F. Chronobiologic assessment of deviant human blood pressure: an invitation for improvements. In: Hayes DK, Pauly JE, Reiter RJ, eds. Chronobiology: Its Role in Clinical Medicine, General Biology, and Agriculture, Part A. New York, NY: Wiley-Liss; 1990:305–318.
7. Sibai BM. Pitfalls in diagnosis and management of preeclampsia. Am J Obstet Gynecol. 1988;159:1–5.[Medline] [Order article via Infotrieve]
8. National High Blood Pressure Education Program Working Group. Report on high blood pressure in pregnancy. Am J Obstet Gynecol. 1990;163:1691–1712.[Medline] [Order article via Infotrieve]
9.
Ayala DE, Hermida RC, Mojón A, Fernández
JR, Iglesias M. Circadian blood pressure variability in healthy and
complicated pregnancies. Hypertension. 1997;30:603–610.
10. DeVoe SF, O'Shaughnessy RW. Clinical manifestations and diagnosis of pregnancy-induced hypertension. Clin Obstet Gynecol. 1984;27:836–853.[Medline] [Order article via Infotrieve]
11. Hermida RC, Ayala DE, Mojón A, Iglesias M. High sensitivity test for the early diagnosis of gestational hypertension and preeclampsia, II: circadian blood pressure variability in healthy and hypertensive pregnant women. J Perinat Med. 1997;25:153–167.[Medline] [Order article via Infotrieve]
12. Cornélissen G, Haus E, Halberg F. Chronobiologic blood pressure assessment from womb to tomb. In: Touitou Y, Haus E, eds. Biologic Rhythms in Clinical and Laboratory Medicine. Berlin, Germany: Springer-Verlag; 1992:428–452.
13. Staessen J, Bulpitt CJ, O'Brien E, Cox J, Fagard R, Stanton A, Thijs L, Van Hulle S, Vyncke G, Amery A. The diurnal blood pressure profile: a population study. Am J Hypertens. 1992;5:386–392.[Medline] [Order article via Infotrieve]
14. Halligan A, Shennan A, Thurston H, de Swiet M, Taylor D. Ambulatory blood pressure measurement in pregnancy: the current state of the art. Hypertens Preg. 1995;14:1–16.
15. Hermida RC, Ayala DE, Mojón A, Fernández JR, Silva I, Ucieda R, Iglesias M. High sensitivity test for the early diagnosis of gestational hypertension and preeclampsia. IV. Early detection of gestational hypertension and preeclampsia by the computation of a hyperbaric index. J Perinat Med. 1997;25:254–273.[Medline] [Order article via Infotrieve]
16. Kyle PM, Clark SJ, Buckley D, Kissane J, Coats AJS, De Swiet M, Redman CWG. Second trimester ambulatory blood pressure in nulliparous pregnancy: a useful screening test for pre-eclampsia? Br J Obstet Gynaecol. 1993;100:914–919.[Medline] [Order article via Infotrieve]
17. Parati G, Pomidossi G, Albini F, Malaspina D, Mancia G. Relationship of 24 hour blood pressure mean and variability to severity of target organ damage in hypertension. J Hypertens. 1987;52:93–98.
18. Perloff D, Sokolow M, Cowan R, Juster RP. Diagnostic value of ambulatory blood pressure measurements: further analyses. J Hypertens. 1989;7(suppl 3):S3–S10.
19.
Sokolow M, Werdegar D, Kain HK, Hinman AT. Relationship
between level of blood pressure measured casually and by portable
recorders and severity of complications in essential hypertension.
Circulation. 1966;34:279–298.
20. Greer IA. Ambulatory blood pressure in pregnancy: measurements and machines. Br J Obstet Gynaecol. 1993;100:887–889.[Medline] [Order article via Infotrieve]
21. Brown MA, Robinson A, Martin A, Buddle ML, Cario G, Hargood J, Whitworth LA. Can ambulatory blood pressure monitoring (ABPM) predict the development of preeclampsia? Proceedings of the 10th World Congress of the International Society for the Study of Hypertension in Pregnancy; August 4–8, 1996; Seattle, Wash. Abstract 139.
22. Association for the Advancement of Medical Instrumentation. American National Standard for Electronic or Automated Sphygmomanometers. Washington, DC: AAMI; 1987.
23. White WB, Lund-Johansen P, McCabe EJ. Clinical evaluation of the Colin ABPM 630 at rest and during exercise: an ambulatory blood pressure monitor with gas-powered cuff inflation. J Hypertens. 1989;7:477–483.[Medline] [Order article via Infotrieve]
24. Cornélissen G. Instrumentation and data analysis methods needed for blood pressure monitoring in chronobiology. In: Scheving LE, Halberg F, Ehret CF, eds. Chronobiotechnology and Chronobiological Engineering. NATO ASI series; series E: Applied Sciences, no 120. Dordrecht, Netherlands: Martinus Nijhoff; 1987:241–261.
25. Staessen J, Fagard R, Lijnen P, Thijs L, Vaa Hoof R, Amery A. Ambulatory blood pressure monitoring in clinical trials. J Hypertens. 1991;9(suppl 1):S13–S19.
26. Mojón A, Fernández JR, Hermida RC. Chronolab: an interactive software package for chronobiologic time series analysis written for the Macintosh computer. Chronobiol Internat. 1992;9:403–412.[Medline] [Order article via Infotrieve]
27. Bingham C, Arbogast B, Cornélissen G, Lee JK, Halberg F. Inferential statistical methods for estimating and comparing cosinor parameters. Chronobiologia. 1982;9:397–439.[Medline] [Order article via Infotrieve]
28. Nelson W, Tong YL, Lee JK, Halberg F. Methods for cosinor rhythmometry. Chronobiologia. 1979;6:305–323.[Medline] [Order article via Infotrieve]
29. Hermida RC, Ayala DE, Fernández JR, Mojón A. Time-specified reference limits for ambulatorily monitored blood pressure in clinical health. Biomed Instrum Technol. 1993;27:235–243.[Medline] [Order article via Infotrieve]
30. Hermida RC, Fernández JR. Computation of time-specified tolerance intervals for ambulatorily monitored blood pressure. Biomed Instrum Technol. 1996;30:257–266.[Medline] [Order article via Infotrieve]
31. Lemmer B. Cardiovascular chronobiology and chronopharmacology. In: Touitou Y, Haus E, eds. Biologic Rhythms in Clinical and Laboratory Medicine. Berlin, Germany: Springer-Verlag; 1992:418–427.
32. Rosner B. Fundamentals of Biostatistics. 2nd ed. Boston, Mass: Duxbury Press; 1986:51–56.
33. O'Brien E, Staessen J. Normotension and hypertension as defined by 24-hour ambulatory blood pressure monitoring. Blood Pressure. 1995;4:266–282.[Medline] [Order article via Infotrieve]
34. Zachariah PK, Sheps SG, Ilstrup DM. Blood pressure load: a better determinant of hypertension. Mayo Clin Proc. 1988;63:1085–1091.[Medline] [Order article via Infotrieve]
35.
Zachariah PK, Sheps SG, Bailey KR, Wiltgen CM, Moore
AG. Age-related characteristics of ambulatory blood pressure load and
mean blood pressure in normotensive subjects. JAMA. 1991;265:1414–1417.
36. White WB. Blood pressure load and target organ effects in patients with essential hypertension. J Hypertens. 1991;9(suppl 8):S39–S41.
37. Hermida RC, Mojón A, Fernández JR, Ayala DE. Computer-based medical system for the computation of blood pressure excess in the diagnosis of hypertension. Biomed Instrum Technol. 1996;30:267–283.[Medline] [Order article via Infotrieve]
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R. C. Hermida and D. E. Ayala Prognostic Value of Office and Ambulatory Blood Pressure Measurements in Pregnancy Hypertension, September 1, 2002; 40(3): 298 - 303. [Abstract] [Full Text] [PDF]
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R. C. Hermida and D. E. Ayala Evaluation of the Blood Pressure Load in the Diagnosis of Hypertension in Pregnancy Hypertension, September 1, 2001; 38(3): 723 - 729. [Abstract] [Full Text] [PDF]
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R. C. Hermida, D. E. Ayala, and M. Iglesias Predictable Blood Pressure Variability in Healthy and Complicated Pregnancies Hypertension, September 1, 2001; 38(3): 736 - 741. [Abstract] [Full Text] [PDF]
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R. C. Hermida, D. E. Ayala, A. Mojon, and J. R. Fernandez Time-Qualified Reference Values for Ambulatory Blood Pressure Monitoring in Pregnancy Hypertension, September 1, 2001; 38(3): 746 - 752. [Abstract] [Full Text] [PDF]
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 J. A Staessen, E. T O'Brien, L. Thijs, and R. H Fagard Modern approaches to blood pressure measurement Occup. Environ. Med., August 1, 2000; 57(8): 510 - 520. [Abstract] [Full Text]
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R. C. Hermida, D. E. Ayala, A. Mojon, J. R. Fernandez, I. Alonso, I. Silva, R. Ucieda, and M. Iglesias Blood Pressure Patterns in Normal Pregnancy, Gestational Hypertension, and Preeclampsia Hypertension, August 1, 2000; 36(2): 149 - 158. [Abstract] [Full Text] [PDF]
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R. C. Hermida, J. R. Fernandez, A. Mojon, and D. E. Ayala Reproducibility of the Hyperbaric Index as a Measure of Blood Pressure Excess Hypertension, January 1, 2000; 35(1): 118 - 125. [Abstract] [Full Text] [PDF]
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 G. Bellomo, P. L. Narducci, F. Rondoni, G. Pastorelli, G. Stangoni, G. Angeli, and P. Verdecchia Prognostic Value of 24-Hour Blood Pressure in Pregnancy JAMA, October 20, 1999; 282(15): 1447 - 1452. [Abstract] [Full Text] [PDF]
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