Journal of Human Hypertension (1999) 13, 361 366 1999 Stockton Press. All rights reserved 0950-9240/99 $12.00 http://www.stockton-press.co.uk/jhh ORIGINAL ARTICLE The magnitude and duration of ambulatory blood pressure reduction following acute exercise JP Wallace, PG Bogle, BA King, JB Krasnoff and CA Jastremski Clinical Exercise Physiology Laboratory, Department of Kinesiology, Indiana University, Bloomington, IN, USA The purpose of this study was to observe the magnitude and duration of the ambulatory blood pressure (BP) reduction following exercise and to identify the peak intervals of BP reduction throughout the 24-h diurnal period. Subjects were 25 normo- (N 116.7/ 78.2 10.0/7.2 mm Hg) and 21 hypertensive (H 140.8/96.9 13.9/9.6 mm Hg) adults. Twenty-four hour ambulatory blood pressures (SBP systolic and DBP diastolic) were recorded following exercise (E 50 min 50% VO 2 max) and during a non-exercise control day (C). The 24-h pressures were compared between the E and C days for (1) duration and magnitude of the BP reduction following exercise, and for (2) the time of day for the diurnal patterns to exhibit reductions in BP. No BP differences were found for N between E and C days. Significant reductions in BP were found for 24-h average SBP ( 6.8 mm Hg) and DBP ( 4.1 mm Hg), daytime (06.00 22.00 hrs) SBP ( 6.9 mm Hg) and DBP ( 3.3 mm Hg), and sleep (22.00 06.00) SBP ( 5.1 mm Hg) and DBP ( 4.4 mm Hg) for H subjects only. H also demonstrated an 11 h reduction in SBP ( 8.3 2.2 mm Hg) and 4 h reduction in DBP ( 6.0 1.7 mm Hg) following exercise. For the diurnal variation, the peak interval of reduction in SBP ( 7.0 2.6 mm Hg) was for 11 h; from 11.00 21.00 hrs. For DBP, a significant reduction ( 5.7 0.7 mm Hg) was found for 5 h; from 11.00 15.00 h. Thus, exercise reduces both systolic and diastolic BP for a significant length of time postexercise as well as reduces pressures during the time of day that typically exhibits higher diurnal pressures. Keywords: hypertension; post-exercise hypotension; diurnal rhythm Introduction Ambulatory blood pressure (BP) monitoring can provide useful information regarding the character of the BP throughout a normal day. In addition to sampling the real-life setting, the advantages of the ambulatory BP technology include improved reliability and sensitivity 1 and increased accuracy 2,3 when compared to the casual and clinical methods. Even though the use of 24-h ambulatory BP monitoring has been recommended in the study of BP and exercise, 4 it s use in exercise has been limited. 5 15 Ambulatory monitoring has been used to observe the response to acute exercise 8,9,11,13 15 as well as to physical conditioning. 5 7,9,10,12 The findings from the studies that observed the BP following exercise have been inconsistent. Reported findings range from a reduction in systolic pressure, 8,13,15 mean pressure, 15 or diastolic pressures 13,15 to no change. 9,14 In addition to these inconsistent findings, unanswered questions remain for the study of ambulatory BP following exercise. That is, what is the Correspondence: Janet P Wallace, PhD, FACSM, Associate Professor, Director of Adult Fitness, Clinical Exercise Physiology Lab, Indiana University, Bloomington IN 47405, USA Received 25 August 1998; revised 14 October 1998; accepted 7 December 1998 magnitude and duration of the BP reduction following exercise and what are the time periods of a 24-h day exhibiting peak BP reductions following exercise? The purpose of this study was to observe the magnitude and duration of the ambulatory BP reduction following exercise and to identify the peak time intervals of BP reduction throughout the 24-h diurnal period. Materials and methods The design of this study was to compare the 24-h ambulatory BPs of normotensive and hypertensive adults on a non-exercise control day to a 24-h period following exercise on a different day. Procedures included (1) BP screening, (2) maximal graded exercise test, and (3) the measurement of 24-h BPs on a non-exercise control day and after a 50-min submaximal exercise bout of 50% intensity. The order of the control and exercise days were randomised; except the submaximal exercise day did not precede the maximal exercise day. All procedures were previously approved by the Committee for the Protection of Human Subjects.
362 Ambulatory blood pressure following exercise Subjects Subjects were 25 normotensive and 21 hypertensive middle-aged adults. Hypertensive subjects were defined by the following: (1) having had a previous diagnosis of hypertension by a primary physician and were currently exhibiting elevated pressures by (a) having a mean systolic BP (SBP) 140 and/or a mean diastolic BP 90 taken (Hawksley Random Zero Sphygmomanometer) from at least two readings on 2 days, 3 days apart 16 ; or (b) exhibiting a mean daytime ambulatory BP of 135/85 mm Hg. 17 Subject exclusion included (1) significant cardiovascular disease, (2) hypertensive medications or other medications that may affect BP, (3) significant dysrhythmia, (4) brachial artery bruits, and (5) cardiac or renal transplant patients. Clearance by the subject s primary physician was required for each subject prior to participation in the study. After the screening procedures, an informed consent was explained to the subject and signed prior to continuance in the study. Blood pressure screening For all subjects, three BPs were taken on two separate days, 3 days apart (a total of six measurements) with a random zero sphygmomanometer. All BPs were taken in the seated position. On the first day, BPs were taken in both arms. The arm with the highest BP was used for the screening on the second day as well as for the average of six screening pressures. This screening was also used to separate subjects into the normotensive (SBP 140 mm Hg and DBP 90 mm Hg) and hypertensive (SBP 140 mm Hg and/or DBP 90 mm Hg) groups based on the definitions of the World Health Organisation. 16 Graded exercise test The graded exercise test was performed on a motor driven treadmill and began at speeds between 2.5 and 4.0 mph at 0% grade. The grade was increased 1.0% every minute until a maximal voluntary effort was achieved. Expired gases were measured breathby-breath on Sensor Medics 2900 Metabolic Cart. Maximal performance was confirmed by respiratory exchange ratio above 1.1. Exercise stimulus The exercise stimulus was similar to established protocols used in previous studies 18,19 a 50-min intermittent walk (5 10 min walk with 3 min rest periods) on a motor driven treadmill at 50% of VO 2 max. Oxygen uptake was measured during the 4th to 6th minutes to confirm the exercise intensity. For each bout, the work rate was adjusted if it was not within ±10% of the target oxygen uptake. Following the adjustment, another gas collection was made, after steady state was achieved, to confirm the intensity. Heart rate (via ECG) was measured every minute during the exercise session; BP (via auscultation) was measured every 2 to 5 min. Twenty-four hour blood pressure monitoring The order of presentation of the non-exercise control day and exercise day was randomised for the subjects. Both the control and exercise BP measurements began at the same time of day (mean ± s.d. = 10.02 ± 1.05 hrs). The time span between the termination of exercise and the beginning of the monitoring period was 20 to 30 min. This time period represented the time it took for the subject to take a shower and the time it took to place the monitor on the subject. The time span between control and exercise sessions was a minimum of 2 days and maximum of 7 days. The Accutracker II was used for all ambulatory measurements. The sampling interval averaged every 15 min ± 5 min for day hours (06.00 hours to 22.00 hours) and every 45 ± 5 minutes for night hours (22.00 hours to 06.00 hours). One repeat measurement was taken if the first measurement was unsuccessful during the daytime hours and two repeat measurements were taken during the nighttime hours if the first measurement was unsuccessful. The inflation of the cuff for each measurement was 30 mm Hg greater than the previous reading. The cuff deflation rate was set at 3 mm Hg per second. Subjects were asked to document (1) time of sleeping, (2) time at work, and (3) time at leisure activities. Subjects were instructed (1) not to exercise, (2) not to take a shower, and (3) to relax and straighten out the arm during the recording interval for the waking hours of the entire 24-h period. Individual BP measurements were reviewed for missing and erroneous readings. Readings were purged if (1) data were missing, (2) SBP was lower than diastolic pressure or if systolic pressure was 240 mm Hg or 50 mm Hg, or (3) diastolic pressure was 140 mm Hg or 40 mm Hg, in accordance with Staessen et al. 20 System tagged data was purged if (1) systolic pressures deviated ± 50 mm Hg or (2) diastolic pressures deviated ± 20 mm Hg from the surrounding values. Twenty-four hour data were analysed as (1) average 24 h, (2) average hourly pressures for recovery for 24 h following exercise, and (3) average hourly pressures for the 24-h clock for (a) SBP and for (b) DBP. The pressures used in these averages were the actual values recorded. No values were weighted for time. Statistical methods Descriptive statistics were used to describe the characteristics of the subjects. A one-way (group) ANOVA with repeated measures was used to analyse the ambulatory data for 24-h, day and sleep intervals. A two-way ANOVA (hypertensive state exercise condition) with repeated measures (24 h) was used to compare the 24-h BP data. If significant effects for BP state were found, a Student s paired t-test was used to compare the control vs exercise data for each hour of the day for (1) the 24 hours following exercise and (2) for the 24 hours of the clock. Data are presented in means and standard errors unless stated otherwise. Statistical significance was set at P 0.05 level.
Results Subjects A total of 46 subjects were recruited for the study; 25 normotensive and 21 borderline hypertensive adults. Characteristics of the subjects are summarised in Table 1. All variables were similar between the groups except for BPs, height, weight, and the distribution of the sex of the subjects. The normotensive group consisted of 32% men and 68% women, whereas the hypertensive group consisted of 66% men and 33% women. Every hypertensive subject exhibited elevated BPs in the screening or in the 24-h ambulatory control session. For the BP screening, 42% of the subjects had both systolic and diastolic pressures elevated, 48% had only diastolic elevated, 5% had systolic elevated, and 5% had neither elevated. For the 24-h ambulatory measurements, 67% had both systolic and diastolic elevated, 10% had neither elevated, and 24% had systolic elevated. The screening pressures (140.8/ 96.9 ± 13.9/7.2 mm Hg) did not differ from the preexercise pressures (140.2/96.3 ± 13.9/10.3 mm Hg) for the hypertensive group. As a group, the subjects achieved the target 50% VO 2 max for the submaximal exercise bout as verified by the collection of expired gases; 49.4 ± 14.0% for normotensive and 49.8 ± 9.1% for hypertensive groups. 24 hour ambulatory blood pressure monitoring The average number of BPs taken over the 24-h period was 90.1 ± 12.07 and the percentage of pressures used in the data analysis was 84.8 ± 1.3 for the control session and 84.3 ± 0.4 for the exercise session. The ambulatory BPs found in this study were similar to those reported for normotensive and hypertensive adults. 13,21 The day and sleep times corresponded to the selected 06.00 to 22.00 h by ±30 min. Ambulatory blood pressure following exercise Figure 1 summarised the 24-h pressures by the traditional averaged pressure intervals: 24 h, day (06.00 22.00 h), and sleep (06.00 22.00 h) intervals. No significant differences were found between control and exercise days for normotensive subjects. For hypertensive subjects, significant differences were found between exercise and control pressures, both systolic and diastolic, for the 24-h day and sleep periods. A significant difference for repeated measures was found for the two-way ANOVA of the 24-h data (F = 5.22, P 0.05). Figure 2 illustrates the BPs for each hour throughout the 24-h period following the completion of exercise and Figure 3 illustrates the BPs for each hour throughout a 24-h clock, representing the effects on diurnal patterns. No BP differences were found for normotensives between exercise and control days. However, hypertensives demonstrated a significant 11 h reduction in systolic pressure ( = 8.3 ± 2.2 mm Hg) and 4 h reduction in diastolic pressure ( = 6.0 ± 1.7 mm Hg) following exercise. Throughout the 24-h clock, the peak interval of reduction in systolic pressure ( = 7.0 ± 2.6 mm Hg) was for 11 h during the afternoon and evening hours (11.00 21.00 h). For diastolic pressures, a significant reduction ( = 5.7 ± 0.7 mm Hg) was found for 5 h during the afternoon hours (11.00 15.00 h). Thus, exercise reduces both systolic and diastolic BPs for a significant length of time postexercise and reduces 363 Table 1 Demographic information of subjects Variable Normotensive Hypertensive n 25 21 Sex 8 17 14 8 Age (yrs) 49.9 ± 11.0 # 48.4 ± 11.7 Height (cm) 168.3 ± 7.3 172.6 ± 10.7* Weight (kg) 75.4 ± 18.4 85.3 ± 18.5* Systolic blood pressure a 116.7 ± 10.0 140.8 ± 13.9* (mm Hg) Diastolic blood pressure a 78.2 ± 7.2 96.9 ± 9.6* (mm Hg) Mean arterial pressure a 91.0 ± 7.3 111.6 ± 10.3* (mm Hg) 24-h systolic pressure b 117.8 ± 8.7 141.7 ± 10.6* 24-h diastolic pressure b 71.9 ± 6.3 89.0 ± 8.6* 24-h mean pressure b 87.2 ± 7.1 106.6 ± 9.3* Percent body fat (%) 25.9 ± 8.0 26.1 ± 5.4 VO 2 max 31.0 ± 8.2 30.0 ± 6.7 (ml/min 1 kg 1 ) # Mean ± standard deviation. a Average of six screening blood pressures. b 24-h ambulatory pressures for the control period. *Significant group difference at P 0.05. Figure 1 A comparison between control and exercise ambulatory blood pressures, averaged over 24 h, daytime (06.00 to 22.00 h), and sleep (22.00 06.00 h) periods for normotensive and hypertensive adults. Data are reported in means and standard errors.
Ambulatory blood pressure following exercise 364 Figure 2 Blood pressures throughout the 24-h period following exercise vs the control day for hypertensive adults. The 24-h period is divided into (1) day of exercise (Day 1), (2) sleep, and (3) day after exercise (Day 2). Data are reported as means and standard errors. The duration of significant differences between exercise and control days is indicated by the bold horizontal arrow. pressures during the critical times of normal elevations. Discussion The purpose of this study was to observe the magnitude and duration of the ambulatory BP reduction following exercise and to identify the peak intervals of BP reduction throughout the 24-h diurnal period. Twenty-four hour ambulatory BPs were compared between a randomised non-exercise control day and a separate day following exercise for normotensive and hypertensive adults. As expected, significant reductions in systolic both and diastolic BPs were found following exercise for hypertensive subjects, but not for normotensive subjects. Significant reductions in 24-h, daytime, and sleep averages were found for both systolic and diastolic pressures. On an hourly basis, systolic pressures were reduced for hypertensive subjects for 11 h following exercise and diastolic pressures for 4 h. Similarly, significant reductions in both systolic and diastolic BPs were found throughout the time of day that typically exhibits higher diurnal pressures. Subjects The subjects in this study were comparable to those found in most studies that have examined exercise treatment in hypertension. 4 There was a sex difference between groups. Proportionally, the hypertensive group had twice as many men than the normotensive group. The differences found in height and weight can be attributed to the sex differences. This sex difference is inconsequential because there is no sex difference in BP changes with exercise. 4 Ambulatory blood pressures following exercise Several investigators have observed the 24-h ambulatory BP response to exercise, 8,9,11,13 15 but only three have reported reductions in systolic, 8,13,15 mean, 15 or diastolic pressures. 8,15 The inconsistencies in these studies may be attributed to study design, ambulatory techniques, or small numbers of subjects. The design of three of the six studies focused on comparing BP responses of children of different races, 11 monitoring a case study, 8 or utilising home BP monitoring instead of ambulatory monitoring 14 and may not be appropriate for a comparative discussion. Even though the other three studies 9,13,15 may appear to be of similar design to this study, the findings remain contradictory. Similar to this study, Pescatello and colleagues 13 found reductions in absolute BPs following exercise whereas Ruekert and colleagues 9 and Brownley and colleagues 15 did not. Design differences of these may be found in (1) the analysis of the post-exercise data and (2) the treatment of the control period. In the studies led by Ruekert 9 and Brownley, 15 ambulatory BPs were compared to a 20 to 30-min
Ambulatory blood pressure following exercise 365 Figure 3 Diurnal blood pressures throughout a 24-h clock for the exercise vs the control day for hypertensive adults. Data are reported as means and standard errors. The duration of significant differences between exercise and control days is indicated by the bold horizontal arrow. baseline period prior to the exercise treatment rather than to a control period similar to the time period for the exercise treatment. Whereas, this study and the study led by Pescatello 13 compared ambulatory pressures between the control and exercise treatment days at the same time of day. Using a comparison of post-exercise BPs to pre-exercise BPs may be questionable for measurements taken over a 24-h period. Significant differences could be detectable just because of the periodicity of diurnal variation in BP itself. For example, if the period of pre-exercise pressures were taken at a time of day when pressures usually peak or nadir, most subsequent nonexercise pressures could be significantly different. Whereas, comparing the BP from post-exercise time periods to the corresponding time periods taken on the non-exercise day should control for the influence of periodicity of diurnal variation and is considered to be a more valid approach. The control period also varied among studies. Both this study and the study reported by Pescatello and colleagues 13 measured ambulatory pressures on a separate control day without exercise whereas Ruekert and colleagues 9 did not. Brownley and colleagues incorporated a control day in their design, however, the control period included 20 min of rest prior to the measurement of ambulatory pressures. The use of 20 min of rest can be considered to be an intervention, in itself, which has the potential to lower BP. A comparison between a second intervention strategy (ie, the control rest period) may not be appropriate when the purpose of the study is to observe the influence of exercise only. The average number of hypertensive subjects used in the previous studies was 5.0 ± 4.6 (range = 1 12 subjects). 8,9,11,13 15 This study utilised 21 hypertensive subjects which is four times the average number of subjects used in the previous studies. The power of the results of this study ranges from 0.740 to 0.984. Thus, this study enhances the previous studies by the utilisation of a greater number of subjects and by the comparison of the BPs between a control day to the exercise day. This study adds more information to that obtained from Pescatello and colleagues. 13 Her group found the BP reduction for 12 h, but only measured ambulatory BP for 13 h. In addition, this study measured ambulatory BP for 24 h and found that the duration of the postexercise reduction lasted for only 11 h. Blood pressure reductions were found in this study, not only for a period of time following exercise, but at critical times for BP elevations during the 24-h diurnal patterns. Ambulatory blood pressures throughout the 24 h diurnal period Although the postexercise BP response has been the focus of several studies, 8,9,11,13 15 no one has
366 Ambulatory blood pressure following exercise observed the influence of exercise on the diurnal BP patterns throughout the day. The diurnal variation in BP is well established. 22 Pressures are usually lowest during the night (22.00 to 06.00 h) and highest during the day with daily peaks after waking (06.00 h) and at the end of the working hours (17.00 h). 22 Persistently higher pressures are found throughout the daytime work hours (08.00 to 17.00 h). 22 Interestingly, a rapid increase in morning BPs has been related to the morning incidence of coronary events. 22 The primary time of day for exercise for the subjects in this study was morning (ending time = 10.02 ± 1.05 h). These findings suggest that the duration of the BP reduction following morning exercise extends through the period of the day that typically exhibits the highest BPs. Thus, the clinical significance of morning exercise may be a reduction in BP at critical afternoon and evening periods. Evening exercise will probably not affect the afternoon pressure elevations because the duration of the reduction may not extend through the entire 24-h period to reach the afternoon of the next day. On the other hand, evening exercise may reduce the morning rise in BP that has been associated with cardiac events. Nevertheless, the observation of the effects of exercise on the diurnal variation of BP may be useful to determine the most effective time of day for exercise which may be consequential in the control of hypertensive disease and its outcome. Unanswered questions include (1) what time of day for exercise may be the most effective in lowering overall BP; (2) what time of day for exercise may be the most effective in lowering daytime BPs; (3) what time of day for exercise may be the most effective in lowering the morning peak in BP; and (4) is it a reduction in the morning peak in BP more effective in controlling the disease outcome than an overall reduction in BP? Acknowledgements Funded by Indiana Affiliate of the American Heart Association (IN-94-070-GIA) and the Indiana University Adult Fitness Program. References 1 Mann S et al. Ambulant blood pressure: reproducibility and the assessment of interventions. Clin Sci 1980; 59: 497 500. 2 James G et al. The reproducibility of average ambulatory, home, and clinic pressure. Hypertension 1988; 11: 545 549. 3 Pickering T. Clinical applications of ambulatory blood pressure monitoring: The white coat syndrome. Clin Investig Med 1991; 14: 212 217. 4 American College of Sports Medicine. Position Stand: physical activity, physical fitness, and hypertension. Med Sci Sports and Exercise 1993; 25: i x. 5 Gilders R, Voner C, Dudley G. Endurance training and blood pressure in normotensive and hypertensive adults. Med Sci Sports and Exercise 1989; 21: 629 636. 6 Van Hoof R et al. Effects of endurance training on blood pressure at rest, during exercise and during 24 hours in sedentary men. Am J Cardiol 1989; 63: 945 949. 7 Seals D, Reiling M. Effect of regular exercise on 24 hour arterial pressure in older hypertensive humans. Hypertension 1991; 18: 583 592. 8 Southard D, Hart L. Case Report: The influence on blood pressure during daily activities of a single session of aerobic exercise. Behavioral Med 1991; 135 142. 9 Ruekert P, Slane P, Lillis D, Hanson P. Hemodynamic patterns and duration of post-dynamic exercise hypotension in hypertensive humans. Med Sci Sports and Exercise 1996; 28: 24 32. 10 Blumenthal J, Siegel W, Applebaum M. Failure of exercise to reduce blood pressure in patients with mild hypertension. JAMA 1991; 266: 2098 2104. 11 Harshfield G et al. Aerobic fitness and the diurnal rhythm of blood pressure in adolescents. Hypertension 1990; 11: 810 814. 12 Marceau M, Kouame N, Lacourciere Y, Clerous J. Effects of different training intensities on 24 hour blood pressure in hypertensive subjects. Circulation 1993; 88: 2803 2811. 13 Pescatello L, Fargo A, Leach C, Scherzer H. Short-term effect of dynamic exercise on arterial blood pressure. Circulation 1991; 83: 1557 1561. 14 Somers V et al. Postexercise hypotension is not sustained in normal and hypertensive humans. Hypertension 1991; 18: 211 215. 15 Brownley K, West S, Hinderliter A, Light K. Acute aerobic exercise reduces ambulatory blood pressure in borderline hypertensive men and women. Am J Hypertens 1996; 9: 200 206. 16 WHO Expert Committee. Arterial Hypertension. Geneva: Geneva, 1978. 17 The Scientific Committee. The Scientific Committee Consensus document on non-invasive ambulatory blood pressure monitoring. J Hypertens 1990; 8 (Suppl 6): 135 140. 18 Bennett T, Wilcox R, MacDonald I. Post-exercise reduction of blood pressure in hypertensive men is not due to acute impairment of baroreflex function. Clin Sci 1984; 76: 97 103. 19 Wilcox R, Benett T, Brown A, MacDonald I. Is exercise good for high blood pressure? Br Med J 1982; 285: 767 769. 20 Stassen J et al. Ambulatory blood pressure monitoring in clinical trials. J Hypertens 1991; 9 (Suppl 1): S13 S19. 21 Cox J, O Malley K, Atkins N, O Brien E. A comparison of the twenty-four hour blood pressure profiles in normotensive and hypertensive subjects. Hypertension 1991; 9 (Suppl 1): S3 S6. 22 The National High Blood Pressure Education Program Coordinating Committee. National high blood pressure education program working group report on ambulatory blood pressure monitoring. Arch Intern Med 1990; 150: 2270 2280.