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 Table of Contents  
ORIGINAL ARTICLE
Year : 2013  |  Volume : 10  |  Issue : 1  |  Page : 17-24

Effect of interval training program on rate-pressure product in the management of hypertension in black African male subjects: A randomized controlled trial


1 Department of Biomedical Technology, School of Health Technology, Federal University of Technology, Owerri, Nigeria
2 Department of Medical Rehabilitation, Faculty of Health Sciences and Technology, University of Nigeria, Enugu Campus, Enugu, Nigeria
3 Department of Medical Rehabilitation, College of Medicine, University of Nigeria, Enugu Campus, Enugu, Nigeria
4 Department of Radiology, Federal Medical Center, Owerri, Nigeria
5 Department of Physiotherapy, University of Nigeria Teaching Hospital, Ituku Ozalla, Enugu, Nigeria

Date of Web Publication29-Aug-2013

Correspondence Address:
Sikiru Lamina
Department of Biomedical, School of Health Technology, Federal University of Technology, Owerri
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0331-8540.117236

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  Abstract 

Background: Rate-pressure product is a determinant of cardiovascular risk in patient with hypertension and one of the major predictors of myocardial oxygen consumption. Aim: The primary purpose of the present study was to investigate the effect of interval training program on rate-pressure product in subjects with hypertension. Materials and Methods: Two hundred and forty-five male patients of essential hypertension with mild to moderate systolic blood pressure between 140 and 179 mmHg and diastolic blood pressure between 90 and 109 mmHg were age-matched and grouped into interval group ( n = 140) and control group ( n = 105). The interval (work:rest ratio of 1:1) group was involved in an 8-week interval training program of between 45 and 60 min at intensities of 60-79% of the maximum heart rate, while the control group remained sedentary during this period. Blood pressure, maximum volume of oxygen consumed (VO 2 max), and rate-pressure product were assessed. Results: Findings of the study revealed significant effect of exercise training program on rate-pressure product and VO 2 max. The correlation of rate-pressure product with systolic blood pressure was much stronger (87% variance) at P < 0.05. Conclusion: It was concluded that moderate intensity interval training program is an effective means of lowering myocardial oxygen consumption and an adjunct non-pharmacological management of essential hypertension.

Keywords: Hypertension, interval exercise, rate-pressure product


How to cite this article:
Lamina S, Okoye GC, Ezema CI, Anele TI, Ezugwu AU. Effect of interval training program on rate-pressure product in the management of hypertension in black African male subjects: A randomized controlled trial. Niger J Basic Clin Sci 2013;10:17-24

How to cite this URL:
Lamina S, Okoye GC, Ezema CI, Anele TI, Ezugwu AU. Effect of interval training program on rate-pressure product in the management of hypertension in black African male subjects: A randomized controlled trial. Niger J Basic Clin Sci [serial online] 2013 [cited 2020 Aug 13];10:17-24. Available from: http://www.njbcs.net/text.asp?2013/10/1/17/117236


  Introduction Top


Hypertension and its complications are largely responsible for morbidity and mortality of all age groups. [1],[2] Inability to supply oxygen to the myocardium when demanded appears to be related to several cardiovascular events, including transient myocardial ischemia, acute myocardial infarction, and sudden death. Myocardial oxygen consumption (MVO 2 ) is correlated with the rate-pressure product (RPP) [heart rate (HR) × systolic blood pressure (SBP)], and this hemodynamic parameter has been shown to follow a circadian pattern similar to that observed with cardiovascular events. [3]

In essential hypertension, there is an increased sympathetic activity, which increases further risk of cardiaovascular morbidity and mortality. [4] RPP is a major determinant of cardiac oxygen consumption and is a noninvasive method of assessing MVO 2 . [4],[5] Therefore, in cardiac patients, it is necessary to achieve not only decrease in blood pressure (BP), but also decrease in HR and oxygen consumption of the heart in essential hypertension. [5]

Direct measurement of MVO 2 is difficult in routine clinical practice, but it can be easily calculated by indirect methods like Stroke work, Pick's Principle, the tension time index, and RPP. [6] RPP is the product of HR and SBP (RPP = SBP × HR/1000). [7],[8] It is an easily measurable index, which correlates well with MVO 2 and defines the response of the coronary circulation to myocardial metabolic demands. It is a good index of MVO 2 in patients with ischemic heart disease. [9]

The internal myocardial work performed is represented by RPP and external myocardial work performed is generally expressed as stages of exercise. [10] HR and RPP are easily measured hemodynamic variables, and are good predictors of MVO 2 during exercise, including the other variables (interbeat duration, end systolic pressure, end diastolic pressure, systolic diameters, the degree of ventricular hypertrophy, etc.) reflecting the contractile state of the heart and ventricular volume, which may further improve the predictability. [11] There are very few reports on the effect of exercise on RPP in the management of hypertension, particularly in black African subjects. However, genetics and environment have been implicated in the cause and other factors in hypertension. [12],[13],[14] Also, it has been reported that interval exercise training burns more calories and is a more effective way to condition the heart than the other forms of exercise. [15] Hence, this study was designed to evaluate the effect of interval exercise on BP and RPP in black African subjects with hypertension.


  Materials and Methods Top


Ethical approval for the study was granted by the Ethical Committee of Kano State Hospitals Management Board and the Faculty of Health Sciences, College of Medicine, University of Nigeria, Enugu Campus. Subjects were fully informed about the experimental procedures, risks, and protocol, after which they gave their informed consent in accordance with the design and pattern of the American College of Sports Medicine (ACSM) guidelines regarding the use of human subjects, as recommended by the human subject protocol. [16]

Research design

In the present study, age-matched, randomized, double-blind independent groups design was used to determine the influence of the interval training program on RPP. Subjects' ages were arranged in ascending order (from 50 to 70 years) and then assigned to interval and control groups in an alternating pattern (age-matched). One week washout period was established, and pretest was administered to all subjects on the last day of the washout period. Following washout and pretest, all subjects were placed on methyldopa; the interval group involved in interval training programs for 8 weeks, while the control group remained sedentary during the period. At the end of the training and sedentary period, another 1 week washout period was established and posttest was administered to all subjects on the last day of the washout period.

Subjects

Population for the study consisted of male essential hypertensive subjects attending the hypertensive clinic of Murtala Muhammed Specialist Hospital (MMSH), Kano, Nigeria. The study was carried out between 24 October 2007 and 24 February 2009. Sample size was determined using the sample size calculator by Creative Research System Survey Software (Petaluma, CA, USA).

Inclusion criteria

Only those who volunteered to participate in the study were recruited. Subjects of age range between 50 and 70 years with chronic mild to moderate and stable (> 1 year duration) hypertension (SBP between 140 and 179 mmHg and DBP between 90 and 109 mmHg) were selected. Subjects who had stopped taking antihypertensive drugs or who were on a single antihypertensive medication were recruited for the study. All subjects were sedentary and had no history of psychiatry or psychological disorders or abnormalities.

Exclusion criteria

Obese or underweight [body mass index (BMI) between 20 and 30 kg/m 2 ] patients, smokers, alcoholics, diabetics, and patients with other cardiac, renal, respiratory diseases were excluded. Those involved in vigorous physical activities and who were above averagely physically fit (VO 2 max > 27 and > 33 ml/kg/min for over 60 and 50 years of age, respectively) were also excluded.

A total of 323 chronic and stable, essential mild to moderate male patients with hypertension satisfy the necessary study criteria. Subjects were age-matched and randomly grouped into interval (162) and control (161) groups. They were fully informed about the experimental procedures, risks, and protocol.

Pretest procedure

Washout period


All subjects on antihypertensive drugs were asked to stop all forms of medication and as replacement were given placebo tablets (consisted of mainly lactose and inert substance) in a single-blind method. [17],[18] All subjects including those not on any antihypertensive medications were placed on placebo tablets for 1 week; this is known as "washout period." The purpose of the washout period was to get rid of the effects of previously taken antihypertensive drugs/medications. During the washout period, all subjects were instructed to avoid any strenuous physical activities and report to the hypertensive clinic for daily BP monitoring and general observation. The pretest procedure was conducted at the last day of the washout period in the Department of Physiotherapy of MMSH between 8:00 a.m. and 10:00 a.m.

Physiological measurement

Subjects' resting BP (SBP and DBP) and HR were monitored from the right arm as described by Walker, et al.[19] using an automated digital electronic BP monitor (Omron digital BP monitor, Model 11 EM 403c; Omron, Tokyo, Japan). The equipment was used to take the BP and HR at rest, during exercise, and after exercise test. This procedure was repeated and the averages of the two readings were recorded. These measurements were monitored between 8:00 a.m. and 10:00 a.m. on each test day. RPP was obtained using the formula recommended by De Meersman et al. [7]

Stress test

The Young Men Christian Association (YMCA) submaximal cycle ergometry test protocol was used to assess subjects' aerobic power as described by ACSM [20] and Golding, et al. [21] The bicycle ergometer seat height was adjusted and the subjects' knee slightly flexed when the pedal was in the down position. Exercise test started with a 2-3 min warm-up at zero resistance in order to acquaint the subjects with the cycle ergometer. According to Brook et al. [22] and Pollock and Wilmore, [23] a middle-aged, less fit, cardiac patient generally begins at 100 or 150-300 kg/m/min (from 17 W or 25 W to 50 W, respectively) with power increments of 5-25 W/. The YMCA protocol uses two to four 3-min stages of continuous exercise; two HR-power output data points (steady-state HR) of between 110 and 150 beats/min are needed. The two steady-state HRs were plotted against the respective workload on the YMCA graph sheet. A straight line was drawn through the two points and extended to the subject's predicted maximum HR (220 − age). The point at which the diagonal line intersects the horizontal predicted HRmax line represents the maximal working capacity for the subject. A perpendicular line was drawn from this point to the baseline where the maximal physical workload capacity was read in kg/m/min, which was used to predict the subject's VO 2 max. This procedure was done for both pre- and posttest stress test. At the end of the test was a recovery period of 2-3 min (cool-down) at zero resistance pedaling.

Test procedure

The test procedure was conducted in the Department of Physiotherapy of MMSH, Kano, between 8:00 a.m. and 10:00 a.m.

Training program

Following stress test and prior to the exercise training, all subjects in the interval and control groups were re-assessed by the physician and were prescribed with aldomet (methyldopa) as necessary. During the training and sedentary period (8 weeks), all subjects in the interval and control groups were placed on methyldopa according to their pre-recruitment doses and responses at 250 mg and 500 mg daily. Methyldopa was preferred because it does not alter normal hemodynamic responses to exercise. [24] It is a well-tolerated and mostly prescribed antihypertensive drug in Nigeria, [25] particularly northern Nigeria where the study was conducted, and it is also useful in the treatment of mild to moderately severe hypertension. [26] Subjects maintained these prescriptions with regular medical consultation and observation throughout the period of this study.

The interval group (group 1)

After a 10-min warm-up (pedaling at zero resistance), subjects in the interval group exercised on a bicycle ergometer at a moderate intensity of between 60% and 79% of their HRmax reserve [27],[28],[29] that was estimated, as stated below, using the expression 220 − age of the subject, as recommended by ACSM. [27] The starting workload was 100 kg (17 W) which was increased at a pedal speed of 50 rpm to obtain 60% of their HRmax, which was increased in the first 2 weeks and leveled up at 79% of their HRmax and this value was maintained throughout the remaining part of the training period at a work: Rest duration of 1:1 of 6 min each. [27] During the 6-min rest interval period, subjects pedaled at zero intensity. The initial exercise session was increased from 45 min in the first 2 weeks of training and leveled up at 60 min throughout the remaining part of the training. Following the exercise, another 10 min cool-down was established by pedaling at zero resistance. Exercise session of three times per week was maintained throughout the 8 weeks period of training.

The control group (group 3)

Subjects in the control group were instructed not to undertake any organized or structured physical activity apart from the activity of daily living during the 8 weeks period of study.

Posttest procedure

Washout period


At the end of the 8 weeks training and sedentary period, all subjects remained sedentary (no exercise) and were asked to stop methyldopa. Subjects were instead prescribed with placebo tablets in a single-blinded method for 1 week in order to get rid of the effect of the methyldopa taken during the training period.

Post-training physiological (SBP and DBP) assessment and stress test were conducted as earlier described in the pretest procedures using standardized protocols, techniques, and methods by the same investigators.

All pre- and posttest measurements were recorded on a data sheet. Two hundred and forty-five subjects (140 from interval group and 105 from control group) completed the 8-week training program. Seventy-eight subjects (22 from interval group and 56 from control group) had dropped out because of non-compliance, unfavorable responses to methyldopa and exercise training, or had incomplete data; therefore, the data of 245 subjects were used in the statistical analysis [Figure 1].
Figure 1: Study design flowchart

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Statistical analysis

Following data collection, the measured and derived variables were statistically analyzed. The descriptive statistics (Means and standard deviations) of the subjects' physical characteristics, estimated VO 2 max, and other cardiovascular parameters were determined. Independent t-test was conducted to assess the treatment outcome. Pearson product moment correlation was also computed for the variables (changes in RPP, BP, and changes in VO 2 max) of interest. In the t-test and correlation tests, the difference between subjects' post-training and pre-training measurements (changed score) were used as dependent measures. All statistical analyses were performed using the statistical package for the social sciences, Windows Version 16.0 (Chicago IL, USA). The probability level for all the above tests was set at 0.05 to indicate significance.


  Results Top


The subjects' age ranged between 50 and 70 years. Mean ± SD values for age, height, weight, and BMI, respectively, were as follows: Interval group: 58.40 ± 6.91 years, 167.78 ± 7.81 cm, 70.18 ± 11.37 kg, 24.96 ± 3.88 kg/m 2 ; control group: 58.27 ± 6.24 years, 167.89 ± 5.31 cm, 68.47 ± 17.07 kg, 24.16 ± 4.91 kg/m 2 . There was no significant difference in age between the groups (t = 0.156, P = 0.876).

Subject's pre-treatment versus post-treatment mean ± SD values for SBP (mmHg), DBP (mmHg), RPP, and VO 2 max (ml/kg/min) for the exercise group (166.05 ± 14.10, 96.80 ± 3.38, 13.83 ± 2.35, and 23.67 ± 9.15 vs. 150.35 ± 16.67, 94.08 ± 5.31, 11.34 ± 1.63, and 37.46 ± 7.42, respectively) and control group (160.87 ± 13.23, 97.17 ± 1.43, 13.93 ± 4.05, and 21.23 ± 5.76 vs. 163.47 ± 14.88, 96.10 ± 2.67, 12.43 ± 3.67, and 22.82 ± 7.44, respectively) are given in [Table 1].
Table 1: Groups pre- and post - test mean (X)±SD (N=245)


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Student's t-test Results indicated a significant reduction in the exercise group over control group in the following parameters: SBP (t = 13.148, P = 0.000), DBP (t = −6.560, P = 0.000), RPP (t = −4.193, P = 0.000), and VO 2 max (t = 11.959, P = 0.000) at P < 0.05 [Table 2].
Table 2: Groups changed scores mean (X)±SD and t-test values (N=245)


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Results showed significant positive correlation between baseline RPP and SBP (r = 0.550) and RPP and HR (r = 0.791). [Figure 2] shows the correlation of RPP with HR was much stronger (87.3% variance).
Figure 2: Correlation between baseline RPP, and SBP and HR (N = 245)

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Results also showed significant negative correlation between exercise changes in RPP and changes in VO 2 max (r = −0.553) at P < 0.05 [Figure 3].
Figure 3: Correlation between training changes in VO2max and RPP (n =140)

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  Discussion Top


Findings of the present study indicated significant reduction in SBP, DBP, and HR and significant increase in VO 2 max as a result of interval exercise training. Several previous studies [30],[31],[32] have reported similar findings. The present study also demonstrated a significant reduction in exercise group RPP compared to control group values. Our study also revealed a significant correlation between baseline SBP, DBP, and RPP.

A similar study was conducted by Zivkovic, et al.[33] in 2001 and they obtained similar Results. They evaluated the effect of rehabilitation on RPP in patients with survival myocardial infarction and mild arterial hypertension. A sample of 25 patients, with average BP 150/94 mmHg and who survived acute myocardial infarction 6 months before rehabilitation were enrolled in the study. Submaximal cycle exercise testing was performed before and after a 3-week rehabilitation program (walking, bicycle training, and aerobic exercise). RPP and exercise testing time were obtained before and after rehabilitation. They reported s significant decrease in RPP at rest and during submaximal exercise testing. They also reported an improvement of exercise capacity expressed by prolonged exercise time.

Eshani et al.[34] investigated whether prolonged, intense exercise training can improve the left ventricular function in patients with coronary artery disease. They studied 25 patients (age: Mean ± SE = 52 ± 2 years). Subjects in the exercise group completed a 12-month program of endurance exercise training. The training program consisted of endurance exercise of progressively increasing intensity, frequency, and duration. During the last 3 months, the patients were running an average of 18 miles/week or doing an equivalent amount of exercise on a cycle ergometer. The control group consisted of 14 subjects with comparable maximal exercise capacities and ejection fractions, but they did not exercise. During maximal exercise, SBP and RPP were higher after training.

May and Nagle [35] conducted a study to evaluate the effects of two factors, progression of coronary artery disease and physical training of individuals with coronary artery disease, on RPP. Subjects were grouped into experimental (E, n = 71) and two control (C-1, n = 26; C-2, n = 24) groups. Subjects in groups E and C-1 had initial tests confirming coronary artery disease, and subjects in group C-2 had initial tests within normal limits. Subjects in group E received treatment consisting of regular aerobic exercise with controlled intensity, frequency, and duration. Subjects in groups C-1 and C-2 received no regular exercise for a period of 10-12 months. Changes in estimated maximal aerobic capacity (VO 2 max), maximal RPP, and submaximal RPP from initial to final tests were analyzed for all the groups. The authors reported no significant changes in estimated VO 2 max or RPP in the control groups, which indicated no effect of progression of the disease or testing procedure familiarity. The estimated VO 2 max for group E increased significantly (P < 0.01); the RPP increased significantly (P < 0.01) in maximal exercise and decreased significantly (P < 0.01) in submaximal exercise. The authors concluded that the physiological changes both in the exercising skeletal muscle and the myocardium play a role in the symptomatic improvement and increased maximal work capacities in individuals with coronary artery disease after regular aerobic exercise.

There seems to be conscientious agreement that exercise has beneficial effect on RPP. However, the present study differs from others in the type of exercise and exercise parameters or the population investigated and the subjects' condition.

Clinical implications

SBP, DBP, and RPP were all strongly associated with increased risk factors for hypertension and cardiovascular risk in hypertension. [36],[37] There seems to be a consensus that regular physical activity can effectively and significantly control the BP (SBP and DBP). [27],[38],[39] Though RPP is mathematically derived from both SBP and HR, [40],[41] however, it has been reported that RPP is a good index of MVO 2 . In spite of this fact, regular physical activity has been proved as an effective adjunct intervention with respect to BP reduction. MVO 2 is an important factor that could affect exercise tolerance, functional capacity, physical work capacity, quality of life, survival, and mortality rate for cardiovascular disease and all causes of diseases in hypertension. [42],[43],[44],[45],[46],[47]

Limitations of the study

The present study demonstrated a beneficial role of interval exercise training in the down-regulation of RPP in middle-aged and elderly male black African subjects with essential hypertension. However, the study suffers from some limitations including non-inclusion of data from female and young subjects with hypertension and failure to bilaterally assess the BP from both arms. These limitations, however, warrant attention in future studies.


  Conclusion Top


Our study demonstrated a rational basis for the adjunct role of long-term moderate-intensity interval exercise training in the down-regulation of BP and RPP, in middle-aged and elderly male subjects with chronic essential hypertension. Therefore, exercise specialists and other therapists should feel confident in the use of this form of therapy as non-pharmacological adjunct management and on improving physical work capacity of subjects with hypertension.

 
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    Figures

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