|Year : 2014 | Volume
| Issue : 1 | Page : 37-41
Assessment of relationship between measures of obesity and arterial stiffness in young healthy adults
Suganthi Vajiravelu1, Anu Sengottaiyan2, Sivagami Gurusamy1, Shankar Radhakrishnan3
1 Department of Physiology, Vinayaka Missions Kirupananda Variyar Medical College, Tamil Nadu, India
2 Department of Physiology, Annapoorna Medical College, Salem, Tamil Nadu, India
3 Department of Community Medicine, Vinayaka Missions Kirupananda Variyar Medical College, Tamil Nadu, India
|Date of Web Publication||7-Apr-2014|
Department of Physiology, Vinayaka Missions Kirupananda Variyar Medical College, Salem 636 308, Tamil Nadu
Background: Obesity increases the risk of cardiovascular diseases. Overweight and obese individuals have significantly stiffer arteries than normal weight individuals, which might lead on to various cardiovascular complications. Aim: This study was undertaken to assess the effect of body fat on arterial stiffness in young adults. Arterial stiffness was analyzed by stiffness index (SI) and reflection index (RI) derived from digital volume pulse (DVP) waveform. Settings and Design: A cross-sectional study was conducted among healthy adults in the age group of 17-25 years from private medical, nursing, and dental colleges in Tamil Nadu. Materials and Methods: Ninety-seven young healthy adults of both sexes in the age group of 17-25 years were included in the study. Anthropometric measures like height, total body weight, body mass index (BMI), and waist circumference (WC) were measured. SI and RI derived from the finger photoplethysmographic DVP waveform. Statistical Analysis: Associations between SI and RI, and BMI and WC were assessed with Pearson correlation coefficient. Results: There was a strong correlation between SI/RI and BMI and WC in males and females (r > 0.9). Conclusion: Obesity is associated with arterial stiffness in the young Indian population the association between SI/RI and BMI, the age at which it appears, and the prevalence of obesity among the young adults warn us about the increase in incidence of cardiovascular diseases.
Keywords: Body mass index, digital volume pulse, reflection index, stiffness index, waist circumference
|How to cite this article:|
Vajiravelu S, Sengottaiyan A, Gurusamy S, Radhakrishnan S. Assessment of relationship between measures of obesity and arterial stiffness in young healthy adults. Trop J Med Res 2014;17:37-41
|How to cite this URL:|
Vajiravelu S, Sengottaiyan A, Gurusamy S, Radhakrishnan S. Assessment of relationship between measures of obesity and arterial stiffness in young healthy adults. Trop J Med Res [serial online] 2014 [cited 2019 Jun 25];17:37-41. Available from: http://www.tjmrjournal.org/text.asp?2014/17/1/37/130181
| Introduction|| |
Obesity is becoming an epidemic worldwide. Increase in body weight has been found to be an important predictor for stroke, cardiovascular morbidity, and mortality in middle-aged and elderly people. The increasing prevalence of obesity among younger age groups has raised the concern about the long-term implications of obesity on the cardiovascular system in young adults and children. 
Obesity, along with its associated risk factors like dyslipidemia, hypertension, and inflammation, affects the cardiovascular system. Obesity may also have a direct adverse effect on blood vessels resulting in arterial stiffness, and thereby leading to premature vascular aging.  Excess weight appears to have effects on the vascular structure in individuals as young as 20-25 years. Overweight and obese individuals have significantly stiffer arteries than normal weight individuals. Rachel et al., have shown the relationship between the effect of total body fat and visceral fat in younger and older adults.  Many studies have shown that abdominal fat rather than total body fat is an important predictor of arterial stiffening in older adults. ,
Stiffness in aorta and other large arteries like carotid and femoral has been studied with the measurement of pulse wave velocity (PWV) in these vessels. Studies have shown that the peripheral pulse wave patterns, like the Digital Volume Pulse (DVP) waveform recorded in the finger, resemble the aortic pulse wave form, and therefore, contour analysis of the DVP provides a simple, reproducible, non-invasive measure of large and peripheral artery stiffness. 
The degree to which the total body fat or the abdominal fat affects arterial stiffness in young adults of the Indian population is still not known. So, this study was undertaken to assess the relationship between the measures of obesity like total body fat [body mass index (BMI)] and waist circumference (WC; abdominal fat) with stiffness index (SI) and reflective index (RI), measures of arterial stiffness calculated from DVP recorded with a finger photoplethysmograph in young adults.
| Materials and Methods|| |
Ninety-seven participants of both genders in the age group between 17 and 25 years were recruited from private medical, dental, and nursing colleges in Tamil Nadu. The group consisted of both obese and non-obese subjects. All the subjects were free of any diseases and were not taking medications for any illness. Exclusion criteria included participants with hypertension, diabetes mellitus, or any other long-term illness. This study was approved by the institutional ethical committee. Written informed consent was obtained from all the participants.
Measurements of body weight and WC were taken with a standard weighing scale and measuring tape, respectively. BMI was calculated by dividing the participant's weight in kilograms by the square of his/her height in meters (height measured with a stadiometer). Obesity was defined as a BMI >30, as defined by the World Health Organization (WHO).
Arterial blood pressure was recorded using a manual sphygmomanometer.
Recording of DVP
DVP was recorded with finger photoplethysmograph using infrared light at a wavelength of 940 nm, placed on the right index finger of the subjects. The signal from the instrument was digitalized by a digital converter with a frequency of 100 Hz and the converter was connected to the computer. DVP recording was done with the help of Virtual Oscilloscope software.
DVP wave contains two peaks, systolic and diastolic peaks. Early systolic peak is formed by pulse wave transmitted from the left ventricle to the finger directly. Diastolic peak is due to the pulse wave reflected back to the vessel from the small arteries of lower body. This reflection path length is proportional to the subject's height (h). The time delay between systolic peak and diastolic peak is called pulse transit time (PTT or ∆T). Stiffer arteries have a shorter PTT which was measured with Image tool software. The pulse trace system analyzes the average DVP waveform and gives the absolute values of SI based on the entered subject's height.  SI is calculated with the formula: SI = subject's height (h)/PTT. RI is calculated with the formula: RI = magnitude of diastolic peak (b)/magnitude of systolic peak (a) ×100.
SPSS software version 16, IBM, London, was used for statistical analysis. Mean and standard deviation were calculated for all the parametric variables. Associations between SI and RI and anthropometric measures like BMI and WC were assessed with Pearson correlation coefficient.
| Results|| |
[Table 1] gives the mean and standard deviation of the comparable parameters, BMI and WC, and the markers of arterial stiffness, SI and RI, of the study population.
|Table 1: Mean and standard deviations of the parametric variables in the study group |
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[Table 2] shows that SI and RI increase with BMI and that BMI has a strong correlation with SI and RI (r > 0.9). This shows that arterial stiffness increases definitely with increase in total body fat, even in younger individuals. To illustrate the effect of body fat on SI, the whole group was divided into various categories of BMI classification as given by WHO and it was noted that as the BMI increased, there was a linear increase in SI and RI, which was found to be statistically significant (P < 0.001). The strong association between BMI, and SI and RI was consistent.
[Table 3] gives the correlation between WC, and SI and RI in both sexes. WC, an indicator of abdominal obesity, has also been found to increase the arterial stiffness in young adults (r > 0.8). By applying unpaired Student's t-test, we found a statistically significant difference in SI and RI in both males and females in the two groups of individuals based on WC (P < 0.001). There was not much difference in the correlation between WC, and SI and RI between males and females.
|Table 3: Correlation of stiffness index and reflection index with waist circumference |
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The results given above indicate that in the young adults included in the study, increase in both total body fat and abdominal fat has a strong impact on the arterial stiffness.
| Discussion|| |
Our study indicates that measures of body fat, both total body fat (BMI), and abdominal fat (WC) strongly increase the arterial stiffness even in young adults of the Indian population. We had selected people in the age group of 17-25 years without any other illnesses to prevent the influence of other risk factors for arterial stiffening.
We used the technique of recording DVP by finger photoplethysmography which can be used to measure central and peripheral arterial stiffness. Millaseu et al., have shown that DVP waveform resembles the carotid waveform and SI calculated from the DVP wave in the finger has significant correlation with PWV recorded in large arteries.  This technique is inexpensive and easy to use. It has reliability and, therefore, has been used in this study. In this study, SI and RI calculated from DVP give us an idea about the stiffness in central and peripheral arteries in the study group.
It was observed in this study that with the increase in BMI and WC, the SI and RI also increased irrespective of the younger age. Many studies have shown the effect of body weight, abdominal fat, BMI, etc., on large arterial stiffening in older adults.  This is the first Indian study to show the effect of obesity on arterial stiffening in young healthy adults. The strength of association of measures of obesity like BMI and WC with arterial stiffness in our study indicates that the excess weight begins to affect the vascular system at a very early stage of life. Therefore, body fat has both long-term (as in older adults) and short-term effects on vascular aging.
Dangardt et al., have done a 5-year follow-up study in adolescents and have shown that childhood obesity aggravates the effect of obesity on arterial stiffening in adolescents. So, obesity starts to affect the vascular tissues at a very young age.  Toto Moukou et al., reported that among the young hypertensives, there was a definite increase in arterial stiffness in obese hypertensives when compared to lean hypertensives. These studies predict that be it young or old, with or without associated risk factors, obesity per se can induce arterial stiffness. 
Some studies have shown that abdominal fat poses higher risk for early arterial stiffening and some others have shown that BMI is a better predictor for the risk. , But in our study, which included the Indian population, it was found that any measure of obesity, be it BMI (indicator of global fat) or WC (indicator of abdominal fat), was strongly correlated with the SI. So, in the Indian population, any form of obesity can lead to early vascular aging leading to cardiovascular complications.
There are various mechanisms by which body fat can contribute to arterial stiffening. Obesity, especially visceral obesity, is usually associated with insulin resistance. Insulin resistance may exert its vascular effects through hyperinsulinemia or the effects of hyperglycemia.  Hyperinsulinemia may exert its effects through stimulation of vascular smooth muscle growth. Insulin also has a nitric oxide mediated potent vasodilator effect which is lost in insulin resistance.  Any of these factors may be responsible for large artery stiffness in obesity.  High leptin level in obesity is also considered to be responsible for aortic stiffness. Leptin induces vascular smooth muscle proliferation, increases sympathetic nerve activity, and increases the release of pro-inflammatory cytokine which induces inflammation. Therefore, high leptin levels may be a reason for the cardiovascular complications due to obesity.  Obesity also contributes to arterial stiffness through low-grade inflammation. 
Orr et al., conducted a 2-year follow-up study in which diet-induced weight gain was assessed in young adults wherein a positive correlation was found between weight gain and arterial stiffness. They related this effect of short-term weight gain on arterial stiffness to decreased insulin sensitivity, dyslipidemia, renin-angiotensin system, and increased sympathetic activity and, thereby, increased vascular tone. So, even a moderate weight gain in short duration leads to arterial stiffness. 
Increase in the rate of arterial stiffness with increase in body weight that is seen in young adults has raised much concern about the complications associated with arterial stiffness such as development of hypertension and the risk of stroke and coronary artery diseases at an earlier age. This study has shown an increase in stiffness with increase in BMI and WC in the age group of 17-25 years. This could be considered to be an acute effect of excess body fat on arterial stiffness. Studies have shown all the above complications caused in older people as a chronic effect of excess body fat leading to arterial stiffness. 
The other concern about the data in this study is how much of the effect of excess body fat on arterial stiffness can be reversed. Laura et al., observed the effect of weight loss on arterial de-stiffening and the magnitude of de-stiffening was related to the magnitude of weight loss. The weight loss program was for 12 weeks and a 5-10% weight loss was able to reduce large artery stiffness. They attributed the de-stiffening effect to changes in elastic content and collagen matrix in the vessel wall, and changes in local, humoral, and neural modulation of tone of the vessels. 
| Conclusion|| |
In the Indian population, both global obesity and abdominal obesity promote arterial stiffness. At a young age where weight gain and weight loss can be a frequent happening, obesity is considered to be a modifiable risk factor for arterial stiffness to a certain level. Aerobic exercise also has been found decrease to the arterial stiffness in individuals. , So, regular exercise and diet restriction leading to weight loss can reduce the rate of arterial stiffness and also cause de-stiffening of arteries.
| Acknowledgments|| |
We wish to acknowledge the guidance and support extended by our Head of the Department, Prof. Dr. Milind V. Bhutkar, for this study and also thank him for giving his valuable advice in completing the manuscript. We thank Dr. K. N. Maruthy, Professor, Narayana Medical College for developing the instrument and for his guidance in conducting this study.
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[Table 1], [Table 2], [Table 3]