|Year : 2013 | Volume
| Issue : 1 | Page : 29-32
Study of sympathetic nerve activity in young Indian obese individuals
B Kalpana1, Jnaneshwar Shenoy2, J Shiva Kumar3, Shankar Bhat1, Aswini Dutt1
1 Department of Physiology, Yenepoya Medical College, Mangalore, Karnataka, India
2 Department of Physiology, Father Muller's Medical College, Mangalore, Karnataka, India
3 Department of Physiology, Karnataka Institute of Medical Sciences, Hubli, Karnataka, India
|Date of Web Publication||21-Jun-2013|
Department of Physiology, Yenepoya Medical College, Yenepoya University, Mangalore-575 018, Karnataka
Source of Support: None, Conflict of Interest: None
Background: Obesity is the culmination of a chronic imbalance between energy intake and energy expenditure. This energy balance can be potentially affected by the activity of autonomic nervous system (ANS). Altered sympathetic nerve function may be of importance in obesity. Objective: The present study is an attempt to pinpoint the defect (if any) in the activity of sympathetic limb of the ANS in obesity, by subjecting to isometric exercise stress. Materials and Methods: A total of 81 females belonging to the age group of 18-22 years were recruited for the study. The participants were divided into two groups as normal weight and obese based on WHO guidelines for Asia Pacific region. After recording the resting blood pressure, they were subjected to isometric exercise by Handgrip dynamometer. Blood pressure was recorded again, and the difference was noted down. All recorded parameters were compared between two groups using unpaired t test. The relationship between body mass index (BMI) and rise in diastolic pressure was quantified by Pearson's correlation test. A P value less than 0.05 was considered as significant. Results: In obese, the diastolic pressure was significantly higher at rest, but showed reduced rise during handgrip test in comparison with normal weight individuals. Also, the rise in diastolic pressure exhibited a negative relation with BMI. Conclusion: The result is suggestive of impaired autonomic function at rest and reduced sympathetic activity in the group of obese when subjected to stress. This could make them more prone for future development of hypertension or other cardiovascular disorders.
Keywords: Body mass index, isometric exercise, obesity
|How to cite this article:|
Kalpana B, Shenoy J, Kumar J S, Bhat S, Dutt A. Study of sympathetic nerve activity in young Indian obese individuals. Arch Med Health Sci 2013;1:29-32
|How to cite this URL:|
Kalpana B, Shenoy J, Kumar J S, Bhat S, Dutt A. Study of sympathetic nerve activity in young Indian obese individuals. Arch Med Health Sci [serial online] 2013 [cited 2020 Jan 24];1:29-32. Available from: http://www.amhsjournal.org/text.asp?2013/1/1/29/113557
| Introduction|| |
The scourge of obesity affects a wide range of people across diverse ethnic groups, age ranges, and socio-economic status.  It is the culmination of a chronic imbalance between energy intake and energy expenditure. The energy balance is to a reasonably large extent affected by the status of autonomic nervous system (ANS) activity in the individual. It has been proposed that there may be a reduced reactivity in established obesity, which contributes to maintenance of the obese state. 
Obesity can be quantified by using various anthropometric measurements and derivations. Body mass index (BMI) is one such important indicator of obesity. It has been observed that Asians are more prone to obesity-related disorders when compared with BMI-matched individuals from other ethnicities. ,, So, the present study was conducted based on the Asian guidelines for obesity.
Alterations in sympathetic activity can lead to obesity. Depression of sympathetic activity could result in deficient thermogenesis, positive energy balance, and consequent weight gain. On the other hand, sympathetic over activity could predispose to the development of obesity-related hypertension.  Studies done in western population have shown that signals derived from adipose tissue have been found to alter the CNS responses, and thereby influences the activation of sympathetic nervous system, and these responses are affected by both adiposity levels as well as by gender, with younger women demonstrating lower sympathetic activity,  and fewer studies have been done in India.
As per the Asian guidelines of obesity (2009), this work was carried out. This study is an attempt to detect whether such changes are also prevalent in young Indian obese females and also to pinpoint the exact defect (if any) in the sympathetic arm of the ANS in obesity, by using the hand grip dynamometer as an investigative tool.
| Materials and Methods|| |
The present study was conducted at Yenepoya medical College Mangalore, after obtaining the requisite approval from institutional ethics committee. A total of 81 females in the age group of 18-22 years, leading a sedentary lifestyle, were recruited for the study from the student population. Individuals with the habit of alcohol/tobacco consumption, respiratory or cardiovascular disorders and on medications that could alter the autonomic nervous activity were excluded. Written informed consent was taken from each participant after describing in full detail the procedure and purpose of the study.
Standing height was measured up till last 0.1 cms without foot wear, with the subjects back to a wall and with both heels placed together and touching the base of the wall. Weight was recorded without foot wear and with empty pockets. BMI was calculated using Quetlet's formula. Participants were divided into two groups based on BMI (as per WHO Asian Guidelines). Those with BMI between 18.5 - 22.9 kg/m 2 were considered as controls group and those with a BMI of more than 25 kg/m 2 as obese group.
All the recordings were done in physiology laboratory between 10 am to 12 noon. Subjects were asked to take a rest for 15 minutes, and then the resting blood pressure (BP) was recorded in sitting position. Isometric hand grip exercise test (HGT) procedure was explained and demonstrated to each individual before they were subjected to it. Subjects with their dominant hand were asked to exercise Maximum Voluntary Contraction by gripping the handgrip dynamometer, as hard as possible, for few seconds. The maximum force exerted was noted down. After giving rest for 5 minutes, the subjects were asked to perform isometric handgrip exercise at 30% of their maximal voluntary contraction with their dominant hand up to 2 minutes in sitting posture. During the test, subjects were instructed to breathe normally. Blood pressure was recorded at the end of 2 minutes. The rise of diastolic blood pressure (DBP) at the end of the procedure was calculated as follows: Maximum BP during the test-baseline BP.
The rise of diastolic blood pressure at the end of the procedure was calculated. A rise of diastolic blood pressure of 16 mm Hg or more was taken as normal, 11 to 15 mm Hg as borderline, and 10 mm Hg or less considered as an abnormal response. 
The blood pressure parameters recorded in both groups, at rest, during the Hand Grip test, and the delta values obtained were compared by using students unpaired 't' test. The rise in diastolic blood pressure during HGT was also correlated with BMI using Pearson's correlation test over the entire range of BMI coming under the study purview. Analysis was done by SPSS version 17, and a probability (P) value less than 0.05 was considered as statistically significant.
| Results|| |
The 81 young females who were recruited for this study were categorized into two groups based on their BMI as normal weight and obese. The SBP and DBP values in both the groups were compared at rest and during the HGT [Figure 1]. The resting values of SBP and DBP were on the higher side in obese individuals, but statistical significance was elicited only for SBP. However, there was no significant difference in the values of SBP and DBP between the groups when recorded during the HGT.
The delta values of DBP (rise in DBP from baseline values) observed during the isometric test showed a statistically highly significant result in normal weight subjects compared to obese subjects [Table 1].
When the rise in DBP in response to HGT was correlated with BMI over the ranges in this study population, there was a significant negative correlation exhibited [Table 2].
| Discussion|| |
The handgrip test demonstrates reactivity to stress put by isometric exercise. The present study was an attempt to evaluate autonomic functions in obese when subjected to these kinds of stresses.
Stimulation of sympathetic system results in an increase in arterial pressure. This may be either due to an increase in heart rate and force of contraction, leading to an increase in cardiac output and blood pressure or by vasoconstriction and resultant increase in total peripheral resistance and blood pressure, or both. The first effect is due to increased activity in cardiac sympathetic fibers, whereas the second is due to increased activity in peripheral vasoconstrictor fibers. 
The present study showed significantly higher mean values of resting SBP in obese. Similar results were also observed by other studies conducted on different age groups and in both genders across the world. Guizar JM et al, and Tonhajzerova I et al, found a significantly higher resting SBP and DBP in Mexican adolescent boys and Slovakian adolescents, respectively. Esposito et al, also noticed an increase in SBP and DBP recorded in night time and over 24 hour period in Italian women in the age range of 24-40 years. However, the obese subjects in these studies had a BMI of more than 30 kg/m 2 , but in the present study, the BMI cut off points at the lower end for obesity were 25 kg/m 2 . Hence, the results of the present study were comparable to the observations of Akhter S et al, wherein a higher resting SBP and DBP were observed in Bangladeshi adults (18-40 years). Rajalakshmi et al, also observed similar results in age group similar to the present study but it covered both the genders. Unlike these studies, however, we did not notice a significantly higher basal DBP, but the numerically higher values noticed in the present study showed a borderline significance (P = 0.054), which suggests that our results are also in concordance with these studies and is suggestive of an impaired autonomic function at rest.
The cause for higher basal BP values in obese individuals is that the increased adipose tissue in obesity demands additional blood flow, which, in turn, increases the cardiac output. Moreover, sympathetic activation also contributes for this situation.  The rise in DBP during Handgrip test was significantly less in obese when compared to that observed in normal individuals. Similar results were observed by Bedi M et al, and Nageswari et al.  in preadolescent age group and by Srinath CG et al., and Akhter S et al,  in adults. The isometric exercise performed using the Handgrip dynamometer results in a heart rate-dependent increase in cardiac output and blood pressure with little if any change in the total peripheral resistance.
The observed reduced DBP response in obese group is more likely to be due to a reduced increase in peripheral vascular response to maneuvers activating sympathetic system.  The present study noticed a borderline response to HGT in obese, which is suggestive of a reduced sympathetic activity in obese individuals when subjected to stress; this may entail an increased susceptibility to develop cardiovascular disorders. Moreover, this study also noticed a significant negative correlation in rise in DBP with BMI, which also points to a lower sympathetic nerve function in obesity. This reduced sympathetic activity could further contribute to deficient thermogenesis, positive energy balance, and weight gain in humans.  This decreased sympathetic activity may be the result of a defect in sympathetic nerve activation or alternatively in peripheral adrenoreceptors behavior. 
| Conclusion|| |
The results of our study suggest that an impaired autonomic function in obese subjects (i.e. decreased sympathetic activity during HGT) is detectable in obese females at a very early age. This could make them more prone for risk of development of hypertension or other cardiovascular disorders in later stages of their life. Since autonomic function tests are simple, non-invasive, and reliable, they can be used as a mode of screening for cardiovascular risk factors, which helps in early intervention, in order to prevent the associated morbidity and mortality in obese individuals.
Limitations of our study were all the subjects were females; smaller sample size, measurement of blood glucose or oral glucose tolerance test and metabolic syndrome components were not evaluated, and the study is limited to a single sympathetic test. Further studies will be undertaken to validate this finding with these limitations in mind and also by using other tests for studying ANS like heart rate variability (HRV) and cardiovascular responses to mental/physical stressors.
| Acknowledgement|| |
Teaching and Non-Teaching staff, Department of Physiology, Yenepoya Medical College, Mangalore for their support and encouragement for this work.
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[Table 1], [Table 2]