Twenty-four hour, ambulatory blood pressure responses ... - Nature

Journal of Human Hypertension (2000) 14, 547–553  2000 Macmillan Publishers Ltd All rights reserved 0950-9240/00 $15.00 www.nature.com/jhh

ORIGINAL ARTICLE

Twenty-four hour, ambulatory blood pressure responses following acute exercise: impact of exercise intensity TJ Quinn

University of New Hampshire Department of Kinesiology, Durham, NH 03824, USA

Objectives: Mild to moderate acute, endurance exercise has generally been shown to reduce blood pressure (BP) in hypertensive (HT) individuals. Whether a slightly more strenuous bout of exercise can elicit a greater and more prolonged BP reduction is unknown. Therefore, the purpose of this study was to examine the effects of two, 30-min exercise bouts, conducted at 50% and 75% of maximal oxygen uptake (VO2max), on the quantity and quality of BP reduction over a 24-h period. Methods: Sixteen, Stage 1 and 2 non-medicated, HT (8 men/8 women) subjects were matched with normotensive (NT) men and women (n ! 16). All subjects were evaluated for VO2max with a symptom-limited treadmill test and then completed a 30-min exercise bout at 50% and 75% of VO2max as well as a control (no exercise) session in random fashion on separate days. Twentyfour hour ambulatory BPs were measured after both the exercise and control settings. Data was assessed at 1, 3, 6, 12, and 24 h post-exercise and control session. Results: A repeated-measures ANOVA showed non-sig-

nificant differences between HT men and women and that both exercise intensities, relative to the control session, significantly (P ! 0.05) reduced systolic (S) and diastolic (D) BPs. NT subjects showed non-significant reductions following both intensities. The reductions in the HT men and women averaged 4 and 9 mm Hg (SBP)/5 and 7 mm Hg (DBP) for 50% and 75%, respectively. On average, the HT subjects (men and women combined) maintained significant SBP reductions for 13 h after the 75% bout compared to 4 h after the 50% intensity. Likewise, DBP was reduced for an average of 11 h following the 75% bout compared to 4 h after the 50% intensity. Conclusions: These results suggest that an exercise bout conducted between 50–75% VO2max significantly decreases SBP and DBP in HT subjects and that a greater and longer-lasting absolute reduction is evident following a 75% of maximum bout of exercise. Journal of H um an H ypertension (2000) 14, 547–553

Keywords: treadm ill exercise; hum ans; m en; wom en

Introduction Twenty-five percent of the United States adult population is hypertensive (HT)1 and those individuals with blood pressure (BP) values exceeding 160/95 mm Hg have a 150–300% higher annual incidence rate for coronary artery disease (CAD), congestive heart failure (CHF), intermittent claudication, and stroke as compared to normotensive (NT) subjects.2 It is clear that aggressive pharmacological therapies in individuals with marked elevations (Stage 3 and 4) in arterial BP have resulted in dramatic reductions in myocardial infarction (MI) and stroke.3,4 Less clear, though (due, primarily, from inadequately powered studies), is the benefit of this pharmacological therapy, especially in certain female ethnic groups5 with mild to moderate hypertensive disease due to the possible deleterious side effects of these medications on other risk factors Correspondence: Timothy J Quinn, PhD, University of New Hampshire, Department of Kinesiology, Field House – #35, Durham, NH 03824, USA. E-mail: tjq!christa.unh.edu Received 8 February 2000; revised 23 March 2000; accepted 6 June 2000

known to impact CAD.3,6 This has led physicians and allied health care professionals to examine alternative therapies in an effort to reduce arterial BP in these populations. The Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure7 recommends increased physical activity as one alternative therapy and research involving exercise training in HT populations suggests that the majority (75%) of subjects involved in these studies8–12 exhibit significant reductions in arterial BP. Previous research involving acute exercise in HT populations suggested that exercise intensity had little impact on either the quantity or quality (length of time) of any BP reduction.13,14 However, most of this research has involved only short-term (1–12 h) post-exercise BP evaluations and very few data are available using ambulatory BP measurements. In the only acute exercise/ambulatory BP study, Brownley et al15 reported a significant reduction in systolic BP (SBP) for up to 5 h post-exercise following 20 mins of cycle ergometry conducted at 60–70% of age-predicted maximal heart rate. Marceau et al,13 in a training study, have suggested that the reduction following exercise is intensity-dependent. They found that

Blood pressure reduction following exercise TJ Quinn

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higher intensity exercise produced greater benefits especially during the evening and sleeping hours as compared to lower intensity exercise. Thus, if previous investigators monitored BP following exercise only during the waking hours, they would logically conclude no difference attributable to exercise intensity. In addition, in those studies that have studied exercise intensity, only mild to moderate activity has been researched. Pescatello et al14 studied six HT men for 24-h following exercise conducted at 40% and 70% of maximal oxygen uptake (VO2max) on separate days. No intensity effect was observed but there was an average systolic (S) and diastolic (D) BP reduction of 5 and 8 mm Hg, respectively over the 24-h period. Further, Marceau et al13 studied previously sedentary, HT men (n " 8) and one woman in an effort to evaluate training programmes conducted at 50 and 70% of VO2max. They found a 5-mm Hg reduction, regardless of training intensity, in both SBP and DBP measurements over 24 h. Finally, Rueckert et al16 found SBP and DBP to be significantly reduced for 2 h post-treadmill exercise conducted at one moderate (70% VO2max) intensity. However, these reductions returned to baseline during the ambulatory period. In the only study to assess a strenuous exercise bout, Somers et al17 reported an 8 mm Hg reduction in both SBP and DBP in 12 HT subjects following graded cycle ergometry to maximal voluntary capacity. Blood pressure returned to pre-exercise values after 1 h. Four13–15,17 of these studies used cycle ergometry as the exercise modality. It is important to study weight-dependent activity, such as walking, conducted at different exercise intensities, and to track the BP response for 24 h. This may allow allied health-care professionals to prescribe these types of activities routinely. Therefore, the major purpose of the present study was to determine the impact of acute, weight-dependent exercise, conducted at different intensities, on BP-lowering quantity and quality in HT men and women. Secondly, since there are only limited data on HT women regarding acute exercise and BP reductions, it is important to determine if gender differences exist during this post-exercise period.

Materials and methods Subjects Sixteen men (n " 8) and women (n " 8) with documented Stage 1 and 2 HT were recruited and subsequently qualified to participate. None of the subjects were on medication known to treat high BP. An additional 16, NT, men and women subjects were matched with the HT subjects according to age, body composition, and functional capacity. None of the subjects were regular (ie, three times per week) exercisers. Table 1 shows subject characteristics. Procedures Prospective HT subjects reported to the Exercise Physiology Laboratory on three separate occasions Journal of Human Hypertension

to document either Stage 1 or 2 BP elevations. An informed consent, approved by the Institutional Review Board, was read and signed prior to any measurements. Blood pressure was evaluated by the same, trained investigator via auscultation using the appropriate sized cuff and a mercury sphygmomanometer following AHA guidelines and procedures documented by Hagberg et al.18 Pressures were recorded in both arms and BP was measured three times per visit. Subsequently, during the study, only the arm which had the highest BP recordings was measured. Once the study criteria (ie, Stage 1 or 2 BP elevation) had been met, HT subjects were required to obtain health history records as well as permission from their personal physician. They then reported to the laboratory four additional times. The first session was to assess body composition via skinfold measures and to perform a maximal oxygen uptake (VO2max) test on the treadmill. Skinfold sites included the tricep, subscapula, suprailiac, abdominal, and thigh. Percent body fat was determined using the equations developed by Jackson, Pollock and Ward.19,20 A Modified Astrand protocol21 was used for the VO2max test and BP, heart rate, 12-lead ECG rhythm, and expired respiratory gases were monitored and measured. This protocol allows the subject to self-select his/her walking or running speed and then the grade is increased by 2.5% every 2 min. The participants inspired room air through a Parkinson-Cowan dry gas meter for volume determination and expired gases were analysed with Ametek oxygen and carbon dioxide analysers. The dry gas meter and the analysers were calibrated prior to each test. A computerised gas analysis system which gives printouts every 30 sec for ventilation (VE), VO2, VCO2 and respiratory exchange ratio was used. Subjects were excluded from the study if the treadmill test was stopped for reasons other than fatigue or if 2 mm or more of STsegment depression occurred on the ECG. Once these tests had been completed, NT subjects were recruited in an effort to match on age, gender, body composition, and functional capacity. The same tests (except the pre-exercise BP screenings) were performed on the NT subjects. All subjects then reported to the laboratory three additional times, at the same time of day (08.00) to perform two, 30-min exercise bouts conducted at 50% and 75% of maximum as well as a sitting control session in random fashion on separate days with at least 3 days separating trials. The 75% trial was selected to provide a relatively high degree of physiological stress. Recently, it has been shown that training of HT subjects can occur and be maintained in the 75–85% of maximum range.22 Therefore, this intensity had practical implications. The subjects were asked to avoid caffeine for the initial 24-h study and to record all food and significant activity during the time-period. Since this study involved a repeated-measures design, it was important to replicate diet for each additional trial. Diets were analysed for total calories (kcals), percentages of kcals from carbohydrate, fat, and protein, and sodium intake. Prior to and after each exercise session total body mass was obtained. Subjects


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Table 1 Normotensive (NT) and hypertensive (HT) subject characteristics (mean ± s.d.) NT

Age (yrs) Ht (cm)a Wt (kg)a % Fat VO2max (ml/kg/min) SBP (mm Hg) DBP (mm Hg) a

HT

Men

Women

Men

Women

39.7 (4.2) 176.5 (10.4) 79.1 (5.2) 20.3 (3.2) 41.4 (5.3) 124 (6) 81 (4)

38.3 (3.3) 163.8 (7.5) 63.2 (4.0) 24.6 (6.0) 36.5 (7.4) 118 (8) 72 (8)

41.3 (8.9) 178.3 (9.6) 86.4 (7.1) 21.2 (4.5) 40.1 (4.9) 153 (12) 92 (6)

43.6 (7.4) 160.0 (6.2) 66.8 (6.9) 26.0 (8.2) 36.3 (6.2) 152 (11) 93 (4)

Men were significantly taller and heavier than the women.

were instructed to drink water in an amount equivalent to any weight lost. Following each of these sessions, subjects sat quietly for 30 mins and BP was taken by auscultation every 10 mins. The subjects were fitted with the ambulatory BP system (Suntech Accutracker II, Suntech Medical Instruments, Inc, USA) during the recovery period. The ambulatory system had been calibrated against a mercury sphygmomanometer according to the manufacturer’s instructions prior to each session. Subjects were instructed on how the device worked and, when activated, to hold their arm as still as possible. The ambulatory unit was programmed to take measurements every 15 min during the waking hours and once an hour during sleep. Each subject came back to the laboratory the following morning and the data were downloaded to the computer for evaluation. During the control session, subjects sat quietly for 30 min and then wore the ambulatory unit for the next 24-h period. Statistical analyses Differences between variables were analysed using an ANOVA with repeated-measures design followed by a Tukey post hoc test, if necessary. Dependent variables included heart rate (HR), SBP, and DBP. Descriptive variables were analysed with a Student’s t-test. Significance was determined at the P ! 0.05 level.

Results Diet/total body mass Diet was not significantly different across the three trials. However, men consumed significantly (P ! 0.05) more kcals than women (2325 ± 418 vs 1985 ± 379 kcals, respectively) and HT subjects tended to consume more than NT participants (2490 ± 910 vs 2205 ± 875 kcals, respectively) although this was not statistically significant. There were no differences relative to sodium intake and caffeine ingestion was controlled in the study. The 75% exercise bout yielded slightly greater losses in total body mass (range " 0.8–1.1 kg) as compared to the 50% bout (range " 0.2–0.6 kg) but this was not statistically significant. Subjects drank water equivalent to their weight loss prior to leaving the laboratory.

Exercise tests None of the subjects (HT or NT) exhibited any untoward signs or symptoms during the maximal test or the two exercise intensity tests. Further, all of the subjects were able to complete both 30-min exercise bouts with no overt symptoms of distress. Exercise SBP/DBP for all HT subjects averaged 164 ± 12 mm Hg/94 ± 5 mm Hg for the 50% bout and 189 ± 17 mm Hg/96 ± 6 mm Hg for the 75% bout. Ambulatory systolic and diastolic blood pressures Hypertensive men and women were not significantly different (except that HT women maintained significant SBP reductions through the 12-h measurement point after the 75% bout) and responded similarly during the post-exercise BP measurement periods. Regardless, since there are few data regarding HT women in the literature, the figures are broken down by gender to show specific responses. In HT men, the 75% exercise intensity significantly reduced SBP for 10.5 h while the 50% bout reduced SBP for an average of 5.8 h (Figure 1). The DBP in HT men was reduced for an average of 11.9 h following the 75% bout as compared to 5.5 h after the 50% bout (Figure 2). The HT women responded in a similar fashion in that subjects significantly reduced SBP for 15.4 h after the 75% bout (Figure 1) while the 50% bout resulted in a significant lowering which lasted, on average, 2.7 h (Figure 2). The DBP in HT women was reduced for an average of 9.8 h following the 75% bout as compared to 2.9 h after the 50% bout. The quantity (length of reduction) of SBP and DBP reduction in both the HT men and women was significantly reduced following the 75% workbout as compared to the 50% exercise bout (P ! 0.05). In general, when HT men and women are pooled together, the 75% session yielded larger (up to 10 mm Hg, SBP; 9 mm Hg, DBP, P ! 0.05) and longer-lasting (up to 12 h, P ! 0.05) reductions. Heart rate Figure 3 shows HR responses of HT men and women (combined). Exercise HRs during the 75% of VO2max bout averaged 88% of HRmax while the 50% of VO2max bout was conducted at 69% of Journal of Human Hypertension


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Figure 1 Twenty-four hour SBP response of hypertensive men and women following the exercise sessions as compared to the control session (closed symbols = men; open symbols = women). Values are means ± s.d. *Both the 50 and 75% VO2max exercise intensities are significantly lower than the control value at the same timepoint, P ! 0.05. #The 75% VO2 max exercise intensity is significantly lower than the control at the same timepoint, P ! 0.05.

HRmax. The 24-h recovery HRs during the 75% of VO2max bout were significantly lower at each time point as compared to both the control and 50% of VO2max workbout.

Discussion The major results of this study suggest that: (1) a 75% of VO2max workload appears to offer a more sustained and substantial reduction in both SBP and DBP as compared to a 50% workbout in HT men and women; (2) Stage 1 and 2 HT men and women respond in a similar fashion relative to BP reduction following exercise; and (3) exercise up to 75% of maximal oxygen uptake appears safe and is well-tolerated in Stage 1 and 2 HT men and women. This is the first acute, 24-h ambulatory BP study that has Journal of Human Hypertension

Figure 2 Twenty-four hour DBP response of hypertensive men and women following the exercise sessions as compared to the control session (closed symbols = men; open symbols = women). Values are means ± s.d. *Both the 50 and 75% VO2 max exercise intensities are significantly lower than the control value at the same timepoint, P ! 0.05. #The 75% VO2max exercise intensity is significantly lower than the control at the same timepoint, P ! 0.05.

compared men and women, suggesting no gender difference. Investigators who have used long-term, exercise training18,23,24 in the control of elevated BP generally report no substantial difference between HT men and women. This acute, exercise study appears to corroborate those findings. Ambulatory BP The fact that higher intensity exercise had a more profound effect on BP reduction in both HT men and women is unique and tends to conflict with some early research involving either acute BP14 responses or exercise training.18,24,25 Most adaptations to exercise training are directly proportional to the intensity of the activity.21 The present study does support


Figure 3 Average heart rate responses of HT men and women according to exercise intensity. Values are means ± s.d. *Fifty percent workbout is significantly lower than the control at the same time point, P ! 0.05. **The 75% workbout is significantly lower than the control at the same timepoint, P ! 0.05. Pre, preexercise; Exercise, average exercise heartrate; 0, 1, 3, 6, 12, 24, hours post-exercise.

this concept. However, Pescatello et al14 showed that 30 mins of cycling exercise conducted at 40% of VO2max produced the same BP-lowering effect as a 70% of VO2max workbout. This study involved only six HT males, some of whom were on BP-lowering medications prior to the study, and only nonweight bearing activity. Likewise, Hagberg et al18 found SBP equally lowered by exercise conducted for three, 15-min sessions at either 50 or 70% of VO2max in older HT patients. Brownley et al15 studied only one exercise intensity and found SBP to be significantly lower for 5 h post-exercise as compared to a non-exercise day. Exercise intensity, in the aforementioned activity and BP studies,14,15,18 was controlled in the range of 40% to 70% of VO2max. Exercise, in this range would be categorised as ‘light to moderate’ activity. The present study established a slightly higher intensity (75% VO2max) than previous research to determine if a slight increase in physiological stress could elicit a more profound BP-lowering effect. These data suggest that a slightly higher exercise intensity does elicit a greater effect on BP than that observed in previous studies. Marceau et al13 may have documented why these lower intensities provided the same positive effect on BP as the higher intensity exercise. They showed, in nine HT subjects, that training at 50% and 70% of VO2max resulted in significant reductions in BP but that the degree of reduction varied throughout the day depending on intensity. It appears that the 50% workload elicited its positive BP-reduction primarily during the waking hours while the 75% bout exhibited its maximal effect during the evening and sleeping hours. Therefore, in studies that only measured post-exercise BP during the waking hours it would be expected that the lower intensity exercise would produce similar effects as the higher intensity workout. It is worth clarifying again that the work by Marceau and colleagues was a training study while the present study involves acute exercise. Regardless, the present acute study supports this finding. It can be seen from Figures 1 and 2,

that SBP and DBP are lower following the 75% as compared to the 50% bout. The mechanism of this increased post-exercise BP reduction with higher intensity exercise is poorly understood. Rueckert et al16 in an acute exercise study reported BP reductions lasting up to 2 h. They found that the ‘post-exercise hypotension’ followed a biphasic pattern: the initial drop (first 30 mins) was due to a decrease in total and regional vascular resistance followed by a drop in cardiac output (CO). While CO was not measured in this study, it is possible that CO was depressed for a longer period following the 75% bout due to the significantly reduced HR response as compared to the 50% bout (Figure 3). Chronic exercise training studies suggest other mechanisms thought to be involved including increases in peripheral blood flow,26 vasodilatory metabolities,27 a reduction in alpha-adrenergic responsiveness,28 a heightened arterial baro-receptor sensitivity,29 and a decreased resting sympathetic nerve discharge following exercise.30 These other mechanisms may play an important role in BP reduction following low intensity exercise. The question of whether the hypotensive effect reported in training studies is a true result of training or is a transient effect of a previous exercise bout must be considered. Somers et al17 have suggested that the hypotensive effect is indeed a result of training since most acute studies reported only short-term BP reductions. However, the present study results coupled with findings by Pescatello et al14 and Brownley et al15 suggest that the duration of the hypotensive effect is substantially longer than 1–2 h. Perhaps it is possible that the longer the post-exercise hypotensive effect, the more likely the accumulation of these acute exercise effects become more important when considering explanations for BP lowering induced by chronic exercise. While it is clear that motivated subjects can be endurance trained at 75–85% of maximum, it is unlikely that the vast majority of the population would choose to do so on their own volition due to the initial discomfort and, perhaps, an increased potential for injury. Interestingly, however, the subjects in this study did not perceive either exercise intensity to be overly stressful. Regardless and of more practical concern, the accumulation of exercise effects may be of particular importance, especially in a HT population. Recently, the Centers for Disease Control and Prevention and the American College of Sports Medicine31 recommended a public health statement stating that ‘every US adult should accumulate 30 min or more of moderate intensity physical activity on most, and preferably all, days of the week’. If HT patients could perform higher intensity work for short periods of time but do this several times per day then the BP reductions would be very applicable to the general HT population. If acute BP reductions could be accumulated then activity conducted at 75% of maximum may be a clinically significant recommendation that allied health care professionals could share with their patients. Clearly, more work in this area is warranted.

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Most of the ambulatory BP studies have shown short-term (1–2 h) reductions in SBP and DBP.16,17 However, the data from the present study agree with those of Pescatello et al14 who showed BP reductions lasting 12.7 h and Brownley et al.15 Again, Marceau et al13 have shown that exercise intensity impacts BP reductions in different ways. That is, higher intensity exercise decreases BP during evening and sleeping hours whereas, lower intensity exercise reduced BP exclusively during the waking period. The data from the present study support this but also suggest that the higher intensity exercise elicited the effect throughout both the waking and sleeping periods. One might speculate that perhaps, over time, the training programme used by Marceau et al13 provided a dampening effect of what was observed during the waking hours of this present acute response study.

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Conclusions The results of this study suggest that exercise conducted at either 50% or 75% of maximum aerobic capacity elicits significant reductions in both SBP and DBP in HT men and women. However, a bout conducted at 75% of VO2max does appear to yield a larger and longer-lasting BP reduction as compared to the 50% intensity. These data suggest that exercise is a valuable tool for short-term control of BP in HT adults. Further work should be performed to determine if shorter durations of exercise, conducted more than once daily result in BP reductions and whether these reductions can be maintained longer than 10–12 h post-activity. If significant reductions can be attained then it may be possible for health care professions to reduce medication amounts for HT individuals.

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Acknowledgements Special thanks are extended to Dr Robert Kertzer and Dr Robert W Kenefick who provided their time as well as critical comments during the preparation of this manuscript. Also, many thanks to the volunteer subjects for their time and patience.

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29 Bennett T, Wilcox RG, MacDonald IA. Post-exercise reduction of blood pressure in hypertensive men is not due to acute impairment of baroreflex function. Clin Sci 1984; 67: 97–103. 30 Floras JS et al. Postexercise hypotension and sympathoinhibition in borderline hypertensive men. Hypertension 1989; 14: 28–35. 31 Pate RR et al. Physical activity and public health: a recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine. JAMA 1995; 273: 402– 407.

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