Impact Of Isotonic Hand Grip Exercise On Blood Pressure And Sympathetic Response
Physical exercise is one of the essential elements for controlling BP. Physical exercise controls BP through multiple long-term mechanisms which include decrease in sympathetic nerve traffic, potentiation of baroreceptor reflex, reduced arterial stiffness, increase total systemic arterial compliance, increase release of endothelium-derived nitric oxide and increase insulin sensitivity. Recent evidence also suggest that acute dynamic exercise result in transient changes in physiological variables that lead to reduction in BP for 12 to 16 hours following the exercise act. However, the compliance of people towards exercise has not been very encouraging for healthcare professionals due to a number of reasons like time, space and economic constraints. It is therefore necessary to provide an exercise therapy which is feasible for people. Isotonic handgrip exercise is a simple, cheap and feasible form of physical exercise which can be performed at the person’s convenience at any time or place using simple equipment like handgrip dynamometer. Before we prescribe IHG exercise to population it is essential to determine whether IHG exercise actually tends to lower blood pressure to an extent that is at least equivalent to the common form of exercises like brisk walking which is prescribed and known to have beneficial effect in reducing BP.
Cardiovascular reactivity hypotheses have been closely associated with BP reactivity and individual differences in such reactivity are prospectively related to hypertension and coronary artery indices. The cold pressor test (CPT), which measures the response of BP to the stimulus of external cold, has long been a standard test for characterization of sympathetic function and has been documented to predict the subsequent risk of hypertension in normotensive persons. However, scant literature is available which indicates the short term or long-term effects of IHG exercise on BP and cardiovascular reactivity neither in normotensives nor in prehypertensives.
The current study is therefore designed to study and compare the short-term effects of IHG exercise on BP and cold pressor response with the short-term effects of BW in Prehypertensives.
Methods
This repeated measures study design included 60 volunteers (30 males and 30 females) in the age group of 18-25, diagnosed with prehypertension; those in the 120–139/80–89 mmHg BP. Untrained participants of all socioeconomic class and falling under the normal Body Mass Index (BMI) range, with prehypertension were included in the study. Participants were excluded from the study if they were smokers or present with any chronic illness or chronic usage of medical drugs. Pregnant females were also excluded. A written informed consent was obtained from all participants prior to their participation in the study. The Human Research Ethics committee (HREC) of Pramukh Swami Medical College, Karamsad approved this study.
Protocol
During a pre testing session, the maximal voluntary contraction (MVC) of hand grip strength was performed. 30% MVC was set and was used as an appropriate magnitude of contraction during intervention. The study protocol required participants to be present for three consecutive days. The participants were asked to avoid the intake of any stimulant (drugs, coffee etc) for a period of at least 30 min before the measurement. The participants were also asked to empty the bladder before the measurement and relax quietly in sitting position for a period of at least 5 minutes prior to measurement of BP.
Procedure for BP and Pulse Rate (PR) Measurements
Systolic, Diastolic BP (SBP, DBP) and PR were measured in the left arm in sitting position with arm and back support, uncrossed legs and feet on the floor using the Omron HEM 711 DLX Automatic BP instrument (Accuracy, BP: ±4 mm Hg, Pulse: ±5, validated by Association for the Advancement of Medical Instrumentation, AAMI and European Society of Hypertension). BP was recorded at intervals of 1 minute till the difference between two consecutive BP readings is less than 5 mm Hg. The average of the two consecutive readings was used for statistical analysis. Pulse pressure (PP) was calculated as SBP – DBP and Mean Arterial Pressure (MAP) was calculated from the average values of SBP and DBP using the formula, MAP = DBP + 1/3(PP) respectively.
Procedure of CPT
For the CPT, the right hand of the participant was immersed above the wrist for 1 minute in a custom made thermocole box filled with ice water at 10° C, during which time the BP and PR were measured in the opposite arm at 60 seconds and recorded. Three measures of cold pressor reactivity were calculated: the maximum changes in SBP, DBP and PR from the control values during the cold stimulus.
Experimental Procedure
On day two, pre exercise baseline SBP, DBP and PR of the participants were recorded on arrival. This was followed by CPT procedure. Participants were asked to perform IHG exercise of the dominant hand at 30% of MVC for a period of 20 minutes at a cadence of 2 seconds of contraction / 3 seconds of release. (Rate of contraction: 12/ min). After completion of 20 minutes of IHG exercise, BP and PR were measured and recorded as post exercise measurements. CPT responses were recorded following 20 minutes of exercise. The same sequence of procedures was followed after 60 minutes of exercise and the measurements recorded as post exercise 60 minutes. The procedure explained above was same on Day 1 and Day 3, except that day 1 involved no exercise and day 3 had the participants perform BW on a treadmill for a duration of 20 minutes at an intensity of 60% Heart Rate Reserve (HRR). Heart rate (HR) and BP were monitored at intervals of every 5 minutes and exercise was stopped if the heart rate rose above 85% Maximum HR or BP above 180/ 110 mmHg. The time for recording BP and PR after the exercise on day 2 and day 3 coincided with the time for recording the BP and PR on day 1 so as to reduce the possibilities of circadian variation.
Since gender differences were observed in BP response to isotonic handgrip exercise among prehypertensives, the collected data were analyzed separately for male and female participants.
Statistical Analysis
A repeated measure ANOVA (General Linear Model) with a LSD post hoc analysis to determine specific differences was used to analyze the data. SPSS v 20. 0 was used and an alpha level of less than 5% (p ≤ 0. 05) was considered statistically significant. All data are presented as means ± SD.
Recent studies have proven that small reductions of BP in prehypertensive or hypertensive population could have significant health benefits. Studies suggest that a 2mm Hg drop in DBP would lead to a 17% decrease in Hypertension, 6% reduction in Coronary Heart Disease and 15% reduction in Stroke related events. The results of the present study revealed that 20 minutes of IHG exercise reduces BP in prehypertensive young male and females. Immediately after 20 minutes of IHG exercise, mean reduction in PR, SBP, DBP, MAP and PP were observed both in female and male participants whereas there was an increase in mean of all the above parameters after BW. The mean reductions of PR, SBP and PP of females were higher in IHG exercise as compared to BW. However, mean DBP (-2. 83±4. 20) and MAP (-3. 14±3. 16) of BW were higher than IHG exercise. Similarly, the mean reductions of PR, SBP, MAP and PP of males were higher in IHG exercise as compared to BW except for reductions in DBP which was higher in BW.
Earlier studies reported variations in reductions of SBP and DBP to various forms of exercise. Quinn TJ observed 4 mm Hg and 5 mm Hg reductions in SBP and DBP to treadmill walking for 30 minutes at 75% VO2 max, whereas Wallace et al observed 8 mm Hg and 6 mm Hg in SBP and DBP respectively, after treadmill exercise of 5 sessions of 10 minutes at 50% VO2 max. Pescatello et al, Lehmkuhl et al, Hara et al, Rueckert et al, in their studies found no significant changes in BP after various intensities of treadmill walking and running.
Differences in reductions of BP and PR of this present study from past studies can be attributed to the different duration and intensities of the exercise, as the present study had focused on the benefits of only 20 minutes of exercising, which was the least of all the above-mentioned studies. Various studies in the past have postulated numerous potential mechanisms responsible for the reduction in BP following handgrip exercises, most of these studies focusing on isometric handgrip exercises. Some of the factors include oxidative stress, improved endothelium-dependent vasodilatation, and modulation of Autonomic Nervous system. Despite the fact that the present study recommending IHG exercise to reduce BP in prehypertensives, the exact mechanisms responsible for BP reductions following IHG exercise remains elusive.
CPT response immediately after IHG exercise and BW showed a rise in DBP in both female and male participants, however this increase was quite larger on BW day. At 60 minutes post exercise, DBP response to CPT returned close to baseline resting values on IHG as compared to BW day, where the DBP stayed higher than baseline values. Once stimulated by a stressor, the sympathetic system sets off a rise in heart rate and blood pressure, but usually these effects return to normal levels within a very short period of time (5 minutes) after the withdrawal of the stressor. Diastolic blood pressure is the index of peripheral resistance. Higher diastolic pressure even after the withdrawal of the cold stimulus indicated that once constricted through sympathetic stimulation, vessels took longer to return to their normal original diameters. Persons with higher cardiovascular reactivity to a stressor show slower rate of recovery after the withdrawal of the stressor responsible for sympathetic stimulation, indicating that the autonomic control system is not competent enough to lower heart rate and blood pressure to the baseline quickly.
Limitations of the Study
This study had some limitations: First, our inclusion criteria were purposely restrictive so as to limit the strong confounding effects of age, BMI, and training, but they also limit the generalization of our findings to the population studied. Secondly, being a repeated measures study design, the practice effects on participants on three consecutive days were not controlled. Finally, it focused only on the acute effect of IHG exercise on BP and PR parameters, hence further studies should advance the findings of this research by taking into consideration, the long-term training effects of IHG exercise.
Conclusion
One of the common barriers to exercise among patient and normal population is time. The present study protocol requires very little adjustments in day to day routine and at the same time is effective to yield a better reduction in resting SBP and PP in comparison to treadmill walking. This might increase the adherence of prehypertensives to exercise as the IHG exercise can be considered as participation in leisure time. The clinical benefits of IHG exercise found out from this study, which is least explored till date, can be considered as a novel therapy in transcending time and cost and might be provided as an alternative method for prehypertensive population to control BP by improving exercise adherence.
