(Hypertension. 1999;34:472-477.)
© 1999 American Heart Association, Inc.
Scientific Contributions |
From the Department of Medicine, Brigham and Women's Hospital (T.J.M., F.M.S., P.R.C.), Boston, Mass; Merck and Company (T.J.M.), Westwood, Mass; Welch Center for Prevention, Epidemiology, and Clinical Research, Johns Hopkins University (L.J.A.), Baltimore, Md; Duke University Medical Center, Duke Hypertension Center (L.P.S.), Durham, NC; Department of Nutrition, Harvard School of Public Health (F.M.S.), Boston, Mass; Kaiser Permanente Center for Health Research (T.M.V., W.M.V.), Portland, Ore; Division of Epidemiology and Clinical Applications, National Heart, Lung, and Blood Institute (D.G.S.-M.), Bethesda, Md; Department of Epidemiology (L.C.-E.), University of North Carolina at Chapel Hill; Pennington Biomedical Research Center (D.W.H.), Baton Rouge, La; and Kaiser-Permanente Center for Health Research (T.M.V.), Honolulu, Hawaii.
Correspondence to Thomas J. Moore, MD, Suite 365, 690 Canton St, Westwood, MA 02090. E-mail thomas_moore{at}merck.com
| Abstract |
|---|
|
|
|---|
Key Words: blood pressure monitoring, ambulatory nutrition diet blood pressure
| Introduction |
|---|
|
|
|---|
ABPM is often used in testing antihypertensive drugs. Compared with standard BP measurements, it simplifies the determination of the time of a drug's peak and trough effects,8 shows minimal placebo effect,8 9 and offers less within-subject test-retest variability than casual office readings.9 10
There is less experience with ABP in trials of nonpharmacological therapy. The Dietary Approaches to Stop Hypertension (DASH) Trial11 provided an opportunity to measure ABPM in a large, randomized, controlled, nonpharmacological trial in 362 subjects. Our goals were to determine the effect of the DASH diets on diurnal BP and to determine whether participants would accept and comply with ABPM methodology in a clinical trial setting.
| Methods |
|---|
|
|
|---|
Participants
We enrolled 459 DASH participants in 5 separate cohorts over a
2-year period. We measured ABP in cohorts 2 through 5, which included
362 subjects. Unless otherwise noted, results reported in this study
are from the 354 persons who had a satisfactory run-in ABPM. We
excluded the 8 persons who failed to produce a satisfactory run-in
recording. We reasoned that, if ABP was the primary outcome
variable in a trial, those unsuccessful in obtaining a run-in
recording would not have been randomized into the trial.
Participants were healthy, community-dwelling adults (aged
22 years),
not on antihypertensive medication, who had an average systolic
BP <160 mm Hg and diastolic BP 80 to 95 mm Hg
(mean of 6 random-zero [RZ] sphygmomanometer measurements across 3
screening visits). Major exclusion criteria have been previously
reported.11 We emphasized recruitment of minorities to
ensure that two thirds of DASH participants were from a minority
background and 90% of minority participants were blacks.
BP Measurements
ABPM recordings were obtained at the end of run-in and
intervention periods with the use of the Space Labs 90207
device. The devices were programmed to take readings
automatically every 30 minutes and to repeat a reading if
systolic BP (SBP), diastolic BP (DBP), or heart
rate fell outside predefined acceptable ranges (SBP, 70 to 240
mm Hg; DBP, 40 to 150 mm Hg; heart rate, 20 to 150 bpm). After
wearing the monitors for
24 hours, participants returned to the
clinic, and the monitors' data were downloaded. ABPM was considered to
be satisfactory if there were
14 acceptable readings between 6
AM and midnight (based on a previous report that indicated
that 14 daytime readings provide measurement replication comparable to
that seen with 28 to 52 measurements per monitoring
period13 ). If there were <14 acceptable readings,
participants were asked to wear the device for another 24-hour period.
For analysis, the ABPM data were cleaned, eg, null values were
removed, and data were trimmed and edited so that we included
24
hours of readings.
For comparison, random-zero sphygmomanometer BP (RZ-BP) measurements were obtained with the use of a standardized protocol at all 4 clinical sites. Trained, certified staff measured BP in participants who had been quietly seated for 5 minutes with Hawksley RZ mercury manometers and appropriate-size cuffs. The BP on any given day was defined as the average of 2 measurements taken 30 seconds apart. RZ-BPs were measured at each of 3 screening visits and on 4 separate days during the last 2 weeks of a 3-week run-in period: baseline RZ-BP was the average of pressures from these 7 visits. RZ-BP was again measured on 5 separate days during the final 2 weeks of feeding of the intervention diets. The mean BP from these 5 visits represented the end-of-intervention RZ-BP.
Diets
All participants ate the control diet (typical of what many
Americans eat) during the 3-week run-in period. They were then
randomized to receive 1 of 3 intervention diets for 8 weeks. One third
of participants continued the same control diet. One third consumed a
diet rich in fruits and vegetables but otherwise similar to the control
diet. The final third consumed a combination diet that emphasized
fruits, vegetables, and low-fat dairy products; included whole
grains, poultry, fish, and nuts; and was reduced in fats, red meat,
sweets, and sugar-containing beverages. Body weight was kept constant
by adjusting calories as needed. Alcoholic beverages were limited to
2/d. The sodium content was similar in all 3 diets:
3 g/d.
Detailed information on the diets and the feeding procedures has been
previously published.11 12
Outcomes
The primary outcome for DASH was the change in
RZ-BP.11 Change in ABP from the run-in to end of
intervention period was a prespecified secondary outcome. For each ABPM
tracing, mean 24-hour BP, mean daytime BP, and mean night BP were
calculated for SBP and DBP. We defined "daytime" as 7
AM to 11 PM and "night" as 11
PM to 7 AM because these times most closely
approximated our participants' average times of awakening and falling
asleep on the day they wore the ABP monitor. (Eighty-eight
percent of participants awakened between 5 and 9 AM; 87%
retired between 10 PM and 1 AM). For the 9
participants who had satisfactory ABPM at run-in but not at end of
intervention, we used the run-in values as their
end-of-intervention measurement.
For analyses of the BP response to diets during daytime versus
night, we used both the actual BP levels and the qualitative
classification of participants as dippers/nondippers. We defined a
"dipper" as a participant whose average SBP during the night fell
10% compared with his/her average day SBP. Nondippers fell
<10%.
Change in RZ-BP was defined as the difference between end of run-in and end of intervention. For persons without follow-up RZ-BP measurements in the last 2 weeks of intervention feeding, end-of-intervention BP was the average of the last 2 weekly measurements taken earlier in the intervention period.
Analytical Approaches
Data are presented as mean±95% CIs unless otherwise
noted. For primary analyses, between-diet differences in BP
change were tested by 2-way ANOVA, adjusted for clinical center. A
between-diet difference was considered statistically significant at
P<0.05 (2-tailed). For assessing differences in the effects
of the diets on 24-hour SBP and DBP in subgroups (eg, men versus women,
minority versus nonminority), we used diet-by-race and diet-by-gender
interaction terms and multiple regression models. For comparison of the
BP effect of the diets measured by RZ-BP versus APBM, the responses to
the control diet were greater for RZ-BP than ABPM, and therefore we
adjusted the BP change with the fruit/vegetable and combination diets
for the control diet change. We then calculated the RZ-BP change minus
the ABPM change. We computed the variance of this statistic, accounted
for the correlated nature of the data, and used a z score to
test for statistical significance. This procedure is equivalent to
testing for interaction in a 2-way design that involves treatment
status and measurement technique, with the subject as a random blocking
factor.
To determine whether any of the 3 diets caused a change in dipper/nondipper status, we categorized each participant as dipper or nondipper at the end of run-in and then again at end of intervention. Then, within each diet assignment, we tested whether diet significantly changed dipper status (either from dipper to nondipper or vice versa) with McNemar's test. We examined change in dipper status in all participants combined and in black and hypertensive subgroups.
| Results |
|---|
|
|
|---|
Table 1 provides baseline demographic
characteristics and BP for the 354 participants who provided
satisfactory run-in ABPM. We defined hypertension as
140 mm Hg
SBP and/or
90 mm Hg DBP on the basis of the average of RZ-BP
readings taken on 7 separate days (screening visits and run-in period).
Twenty-nine percent of the participants were hypertensive at the
beginning of the trial. At run-in, 24-hour ABP and RZ-BP were
similar.
|
After 8 weeks of intervention feeding, the control diet group showed no significant change in either RZ-BP or 24-hour ABP (Figure 1). The combination diet significantly reduced BP measured by both methodologies, while the fruit/vegetable diet had an intermediate effect (Figure 1).
|
In the control diet group, there was a slightly greater fall in RZ-BP than in ABP. After adjustment for differences in this control diet effect, there were no significant differences in the BP effect detected by the 2 BP measurement methods for either the fruit/vegetable or combination diet (Table 2).
|
ABPM demonstrated that the combination diet exerted its BP-lowering effect throughout the day and night (Figure 2). With the combination diet, both SBP and DBP fell significantly during 24 hours, daytime, and night in all participants combined (Table 3). Pressure fell in prespecified subgroups as well, although the changes did not always achieve statistical significance, perhaps as a result of small subgroup size. Formal tests of interactions between diet and subgroup status indicated no statistically significant differences between the BP effect in men versus women, minorities versus nonminorities, or younger versus older participants, although the greater ABP response to the combination diet in minorities versus nonminorities approached statistical significance (eg, 24-hour SBP, P=0.08). Hypertensive subjects had a significantly greater SBP and DBP fall than normotensives during day, night, and 24-hour recordings (P<0.05 for interaction). In contrast, the fruit/vegetable diet provided less overall BP lowering than the combination diet, and the changes were nonsignificant in several time periods/subgroups (data not shown).
|
|
Finally, we examined the effect of the diets on dipper/nondipper status. The percentages of nondippers at end of run-in and end of intervention were as follows: for the control diet, 44% and 43% (P=0.87); for the fruit/vegetable diet, 55% and 50% (P=0.33); and for the combination diet, 42% and 35% (P=0.29). Thus, none of the diets significantly changed dipper/nondipper status in all participants combined. Dipper status also did not change significantly in black or hypertensive subgroups (data not shown).
| Discussion |
|---|
|
|
|---|
The DASH combination diet lowered ABP through both day and night. The net-of-control declines in day versus night SBP (-4.4 versus -4.5 mm Hg) and DBP (-2.7 versus -2.7) with the combination diet were nearly identical (Table 3). Review of the hourly pressures (Figure 2) confirms a consistent reduction through the day and night. We defined nondippers as those with <10% decline in nocturnal SBP. Overall, 47% of our participants were nondippers. We saw no change in the dipper status with any of our diets. Previous studies of lifestyle changes have not consistently shown round-the-clock BP lowering. For example, Moore et al14 reported that sodium restriction lowered pressure more during the night than day in 15 hypertensives, and Straznicky et al15 found that a low fat diet reduced SBP during the day but not night. Exercise training also lowered BP more during the day than night in several trials.16 17 18 Potassium supplementation in 3 daily doses did lower ABP throughout the day and night.19 Thus, some nonpharmacological measures may exert their BP effect over limited times of the day or night. The DASH combination diet produced a sustained, round-the-clock BP effect.
The magnitudes of the BP responses measured by RZ-BP and ABP were very similar, as were the qualitative responses to the 3 diets (combination diet effect>fruits/vegetables>control). The similarity in the results captured by these 2 very different measurement methods provides additional corroboration that the DASH combination diet significantly lowered BP. Previous studies of nonpharmacological treatments have often shown either different BP effect sizes by standard methods versus ABP20 21 or significant responses with one measurement but not the other.15 22 Two studies of salt restriction did show significant correlation between the changes in resting versus ambulatory pressure,14 23 but both of these studies determined resting pressure by averaging 20 to 60 separate BP measurements. Most other studies used fewer measurements and thus may not have captured as representative an estimate of BP. In DASH, our feeding-study design afforded us daily contact with participants, which allowed frequent BP measurements. We estimated resting pressure from RZ-BP taken on 7 different days for baseline and 5 different days for posttreatment level. The robustness of these estimates may explain the concordance of effect size in our RZ-BP versus ABP measurements.
Will research participants accept ABP methodology and use it correctly? Of the 362 participants who were asked to wear the ABP monitors, only 1 refused. For both run-in and end-of-intervention measurements, 2% to 3% of participants were unsuccessful on their first attempt but successful on a second try. Overall, if ABP had been the primary outcome variable in our trial, 98% of eligible participants would have provided acceptable run-in recordings and thus could have been randomized into the trial. Of these, 97% provided acceptable end-of-intervention recordings. In addition, participant compliance was excellent: on average, usable recordings yielded >90% of total expected BP readings during both day and night. We should note that participants with body mass index >35 kg/m2 were not eligible for DASH. ABPM may be less successful in extremely obese participants because of the difficulty in placing the ABP cuff.
In some circumstances, RZ sphygmomanometry may offer advantages over ABPM. For example, when frequent measurements on different days are needed (eg, documenting the time course of a response), repeated ABPM may be impractical. Also, when high rates of follow-up are difficult to achieve, as in long-term studies, some participants may agree to conventional BP measurements but not ABPM. Finally, in studies in which frequent clinic visits will be required for other reasons (such as in feeding studies like DASH), the additional "participant-burden" cost of RZ-BP measurements may be minimal.
In conclusion, our ABPM results show that the DASH combination diet lowered BP through the day and night. ABP responses to the DASH combination diet were similar in magnitude to those measured by RZ-BP. ABPM was well accepted by our study participants, who showed excellent compliance with the technique. On the basis of these findings, we believe that ABPM is a suitable methodology for measuring BP outcomes in trials of dietary antihypertensive therapy.
| Acknowledgments |
|---|
| Footnotes |
|---|
| Appendix 1 |
|---|
|
|
|---|
Received September 30, 1998; first decision November 2, 1998; accepted April 29, 1999.
| References |
|---|
|
|
|---|
2.
Imai Y, Abe K, Sasaki S, Minami N, Nihei M, Munakata
M, Murakami O, Matsue K, Sekino H, Miura Y. Altered circadian blood
pressure rhythm in patients with Cushing's syndrome.
Hypertension. 1988;12:1119.
3. Caruana MP, Lahiri A, Cashman PM, Altman DG, Raftery EB. Effects of chronic congestive heart failure secondary to coronary artery disease on the circadian rhythm of blood pressure and heart rate. Am J Cardiol. 1988;62:755759.[Medline] [Order article via Infotrieve]
4. Fogari R, Zoppi A, Malamani GD, Lazzari P, Destro M, Corradi L. Ambulatory blood pressure monitoring in normotensive and hypertensive type 2 diabetics: prevalence of impaired diurnal blood pressure patterns. Am J Hypertens. 1993;6:17.[Medline] [Order article via Infotrieve]
5.
Verdecchia P, Schillaci G, Guerrieri M, Gatteschi C,
Benemio G, Boldrini F, Porcellati C. Circadian blood pressure changes
and left ventricular hypertrophy in essential
hypertension. Circulation. 1990;81:528536.
6.
Shimada K, Kawamoto A, Matsubayashi K, Ozawa T. Silent
cerebrovascular disease in the elderly: correlation with ambulatory
pressure. Hypertension. 1990;16:692699.
7.
Appel LJ, Stason WB. Ambulatory blood pressure
monitoring and blood pressure self-measurement in the diagnosis and
management of hypertension. Ann Intern Med.. 1993;118:867882.
8. Bieniaszewski L, Staessen JA, Thijs L, Fagard R. Ambulatory blood pressure monitoring in clinical trials. Ann N Y Acad Sci. 1996;783:295303.[Medline] [Order article via Infotrieve]
9. Staessen JA, Thijs L, Mancia G, Parati G, O'Brien ET, on behalf of the Syst-Eur Investigators. Clinical trials with ambulatory blood pressure monitoring: fewer patients needed? Lancet. 1994;344:15521556.[Medline] [Order article via Infotrieve]
10. Staessen JA, Fagard R, Thijs L, Amery A, and the participants in the Fourth International Consensus Conference on 24-Hour Ambulatory Blood Pressure Monitoring. A consensus view on the technique of ambulatory blood pressure monitoring. Hypertension. 1995;26(pt 1):912918.
11.
Appel LJ, Moore TJ, Obarzanek E, Vollmer WM, Svetkey
LP, Sacks FM, Bray GA, Vogt TM, Cutler JA, Windhauser MM, Lin P,
Karanja N, Simons-Morton D, McCullough M, Swain J, Steele P, Evans MA,
Miller ER, Harsha DW. Clinical trial of the effects of dietary patterns
on blood pressure. N Engl J Med. 1997;336:11171124.
12. Sacks FM, Obarzanek E, Windhauser MM, Svetkey LP, Vollmer WM, McCullough M, Karanja N, Lin P, Steele P, Proschan MA, Appel LA, Bray GA, Vogt TM, Moore TJ. Rationale and design of the Dietary Approaches to Stop Hypertension Trial (DASH): a multicenter controlled-feeding study of dietary patterns to lower blood pressure. Ann Epidemiol. 1995;5:108118.[Medline] [Order article via Infotrieve]
13. Dickson D, Hasford J. 24-Hour blood pressure measurement in antihypertensive drug trials: data requirements and methods of analysis. Stat Med. 1992;11:21472158.[Medline] [Order article via Infotrieve]
14. Moore TJ, Malarick C, Olmedo A, Klein RC. Salt restriction lowers resting blood pressure but not 24-h ambulatory blood pressure. Am J Hypertens. 1991;4:410415.[Medline] [Order article via Infotrieve]
15. Straznicky NE, Louis WJ, McGrade P, Howes LG. The effects of dietary lipid modification on blood pressure, cardiovascular reactivity and sympathetic activity in man. J Hypertens. 1993;11:427437.[Medline] [Order article via Infotrieve]
16. Somers VK, Conway J, Johnston J, Sleight P. Effects of endurance training on baroreflex sensitivity and blood pressure in borderline hypertension. Lancet. 1991;227:13631368.
17. Marceau M, Kouame N, Lacourelere Y, Clerous J. Effects of different training intensities on 24-hour blood pressure in hypertensive subjects. Circulation. 1993;88:28022811.
18. Cox KL, Puddey IB, Morton AR, Burke V, Beilin LJ, McAleer M. Exercise and weight control in sedentary overweight men: effects on clinic and ambulatory blood pressure. J Hypertens. 1996;14:779790.[Medline] [Order article via Infotrieve]
19. Fotherby MD, Potter JF. Potassium supplementation reduces clinic and ambulatory blood pressure in elderly hypertensive patients. J Hypertens. 1992;10:14031408.[Medline] [Order article via Infotrieve]
20. Fortmann SP, Haskell WL, Wood PD, and the Stanford Weight Control Project Team. Effects of weight loss on clinic and ambulatory blood pressure in normotensive men. Am J Cardiol. 1988;62:8993.[Medline] [Order article via Infotrieve]
21.
Blumenthal JA, Siegel WC, Appelbaum M. Failure of
exercise to reduce blood pressure in patients with mild hypertension.
JAMA. 1991;266:20982104.
22. Superko HR, Myll J, DiRicco C, Williams PT, Bortz WM, Wood PD. Effects of cessation of caffeinated-coffee consumption on ambulatory and resting blood pressure in men. Am J Cardiol. 1994;73:780784.[Medline] [Order article via Infotrieve]
23. Schorr U, Turan S, Distler A, Sharma AM. Relationship between ambulatory and resting blood pressure responses to dietary salt restriction in normotensive men. J Hypertens. 1997;15:845849.[Medline] [Order article via Infotrieve]
This article has been cited by other articles:
![]() |
M. L. Jehn, D. J. Brotman, and L. J. Appel Racial Differences in Diurnal Blood Pressure and Heart Rate Patterns: Results From the Dietary Approaches to Stop Hypertension (DASH) Trial Arch Intern Med, May 12, 2008; 168(9): 996 - 1002. [Abstract] [Full Text] [PDF] |
||||
![]() |
L. R Harriss, D. R English, J. Powles, G. G Giles, A. M Tonkin, A. M Hodge, L. Brazionis, and K. O'Dea Dietary patterns and cardiovascular mortality in the Melbourne Collaborative Cohort Study Am. J. Clinical Nutrition, July 1, 2007; 86(1): 221 - 229. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. M Hodgson, V. Burke, L. J Beilin, and I. B Puddey Partial substitution of carbohydrate intake with protein intake from lean red meat lowers blood pressure in hypertensive persons. Am. J. Clinical Nutrition, April 1, 2006; 83(4): 780 - 787. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. J. Kim, Y.-H. Ahn, C. Chon, P. Bowen, and S. Khan Health Disparities in Lifestyle Choices Among Hypertensive Korean Americans, Non-Hispanic Whites, and Blacks Biol Res Nurs, July 1, 2005; 7(1): 67 - 74. [Abstract] [PDF] |
||||
![]() |
L. Zhao, J. Stamler, L. L. Yan, B. Zhou, Y. Wu, K. Liu, M. L. Daviglus, B. H. Dennis, P. Elliott, H. Ueshima, et al. Blood Pressure Differences Between Northern and Southern Chinese: Role of Dietary Factors: The International Study on Macronutrients and Blood Pressure Hypertension, June 1, 2004; 43(6): 1332 - 1337. [Abstract] [Full Text] [PDF] |
||||
![]() |
I. Hajjar and T. Kotchen Regional Variations of Blood Pressure in the United States Are Associated with Regional Variations in Dietary Intakes: The NHANES-III Data J. Nutr., January 1, 2003; 133(1): 211 - 214. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. Naruszewicz, M.-L. Johansson, D. Zapolska-Downar, and H. Bukowska Effect of Lactobacillus plantarum 299v on cardiovascular disease risk factors in smokers Am. J. Clinical Nutrition, December 1, 2002; 76(6): 1249 - 1255. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. L. Neuhouser, D. L. Miller, A. R. Kristal, M. J. Barnett, and L. J. Cheskin Diet and Exercise Habits of Patients with Diabetes, Dyslipidemia, Cardiovascular Disease or Hypertension J. Am. Coll. Nutr., October 1, 2002; 21(5): 394 - 401. [Abstract] [Full Text] [PDF] |
||||
![]() |
K. Bjorklund, L. Lind, B. Vessby, B. Andren, and H. Lithell Different Metabolic Predictors of White-Coat and Sustained Hypertension Over a 20-Year Follow-Up Period: A Population-Based Study of Elderly Men Circulation, July 2, 2002; 106(1): 63 - 68. [Abstract] [Full Text] [PDF] |
||||
![]() |
L. K. Massey Dairy Food Consumption, Blood Pressure and Stroke J. Nutr., July 1, 2001; 131(7): 1875 - 1878. [Abstract] [Full Text] [PDF] |
||||
![]() |
D. A. Freedman and D. B. Petitti Salt and Blood Pressure: Conventional Wisdom Reconsidered Eval Rev, June 1, 2001; 25(3): 267 - 287. [Abstract] [PDF] |
||||
![]() |
M. G. Warner Complementary and Alternative Therapies for Hypertension Complementary Health Practice Review, October 1, 2000; 6(1): 11 - 19. [PDF] |
||||
![]() |
P. R. Conlin, T. J. Moore, S. L. Swartz, E. Barr, L. Gazdick, C. Fletcher, P. DeLucca, and L. Demopoulos Effect of Indomethacin on Blood Pressure Lowering by Captopril and Losartan in Hypertensive Patients Hypertension, September 1, 2000; 36(3): 461 - 465. [Abstract] [Full Text] [PDF] |
||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Hypertension Home | Subscriptions | Archives | Feedback | Authors | Help | AHA Journals Home | Search Copyright © 1999 American Heart Association, Inc. All rights reserved. Unauthorized use prohibited. |