Correlation between abdominal fat and myocardial blood flow in sedentary and non sedentary male workers at rest

Background: Sedentary life has emerged as a risk factor for various negative health. Abdominal obesity plays a major role in the pathogenesis of several metabolic and cardiovascular medical problems. The myocardial blood flow can be easily measured by knowing hemodynamic predictors the heart rate and systolic blood pressure which correlate better with the myocardial oxygen consumption. Method: In this cross sectional study 70 sedentary and 70 non-sedentary (30-40 years) age matched male workers were selected. Their waist circumference, waist hip ratio, heart rate and systolic blood pressure were measured at rest. The rate pressure product was calculated to assess the myocardial blood flow.  Results: The waist circumference and waist hip ratio and the systolic blood pressure were significantly (P< 0.05) lower in non-sedentary group compared to sedentary group. The heart rate and rate pressure product both showed very highly significant (P< 0.0001) reduction in non-sedentary group compared to sedentary group. Conclusion: This study shows that the sedentary workers’ myocardial oxygen consumption is much high at rest and they are more prone to ischemia due to stress and exercise.

IJBAR (2014) 05 (02) www.ssjournals.com 2.1 Waist circumference (WC) measurement was done with minimal, adequate clothing (light cloths) with feet 25-30 cm apart and weight equally balanced with a tailor's measuring tape in a plane perpendicular to the long body axis at the level of umbilicus without compression of the skin with nearest to 0.1 cm (WC>/=90 cm) was defined as abdominal obesity using WHO Asia Pacific prospective guidelines 2.2 Hip circumference (HC) measurement was done with minimal, adequate clothing (light cloths) across the greater trochanter with legs and feet together by a measuring tape without compressing the skin fold.

2.3
Waist-hip ratio is the ratio of WC and HC was calculated and is the measure of central pattern of fat distribution. (>0.9for male and >0.8 for females).

Heart rate measurement:
Heart rate was measured when subject was relaxed, in supine position, by finding the radial artery pulsation and counting the pulse rate for one minute. 2.5 Blood pressure measurement: Blood Pressure was recorded in the supine position in the right arm to the nearest 2mm Hg using the mercury sphygmomanometer. Two readings were taken 5 minutes apart and the mean of two was taken as the blood pressure. For those whose BP>140/90mmHg, three BP recordings were recorded with a gap of 1 day in between. The average of second and third was considered as the final blood pressure. 2.6 Rate Pressure Product: Is calculated using the following formula. Rate Pressure Product (RPP) = Heart Rate (beats per minute) X Systolic Blood Pressure (mmHg).

Statistical analysis:
Statistical analysis was done by using Student's unpaired't' test. P value was taken as significant at 5 percent confidence level (p < 0.05).

Result
In the present study the waist circumference and waist hip ratio was significantly (P< 0.05) lower in non-sedentary group compared to sedentary group. The systolic blood pressure also showed a statistically significant (P< 0.05) reduction in the non-sedentary group. The heart rate and rate pressure product both showed very highly significant (P< 0.0001) reduction in non-sedentary group compared to sedentary group.

Discussion
Physical inactivity is commonly associated with cardiovascular diseases 14,15 . Obesity is a well-known risk factor for coronary heart diseases. From the recent studies it is clear that the central obesity is a high risk factor for developing cardiovascular diseases 16 .
The resting coronary blood flow in human is about 225 ml /min. which is about 4 to 5 percent of the total cardiac output. The cardiac output (CO) under severe exercise may increase six fold to nine fold. While, the coronary blood flow increases three fold to fourfold during severe exercise to supply the extra nutrients needed to the heart, which is not as much as the increase in work load. Therefore the O2 supply to the myocardium could not meet its energy requirement. Increased myocardial demands during exercise or other stress must be met by equivalent increased the coronary blood flow. Myocardial ischemia results from imbalance between O2 supply to the myocardium and its O2 requirement 17 .The heart rate, the frequency of cardiac contraction is a very important determinant of oxygen consumption of the whole heart as there is a linear relation between increases in heart rate and increases in cardiac O2 requirement. Another important determinant of myocardial oxygen consumption is the peak systolic blood pressure (SBP) or the peak systolic tension developed by the left ventricle 18 . Under normal conditions, the product of systolic blood pressure by the heart rate has been found to adequately reflect changes in myocardial oxygen consumption. In this study, the sedentary workers had a significantly high RPP compared to non sedentary workers at rest. This shows that the sedentary workers' myocardial oxygen consumption is much high at rest and they are more prone to ischemia due to stress and exercise. Research with heart disease patients has shown a physiologic correlation between the RPP, the onset of angina pectoris, and the electrocardiographic abnormalities during exercise 18,19 . RPP provides an objective yardstick to evaluate the effect of cardiac performance in various clinical, surgical, or exercise intervention.

Conclusion
This study establishes the ill effects of sedentary life style on the myocardial blood flow. The decreased flow is evident as early as age 30-40 years. This shows the importance of exercise in adult's life. Our findings provide a possible mechanistic explanation for the consistent observation that central obesity is a strong risk factor for cardiovascular impairment. Public health efforts are urgently neededto promote an active life style and provide weight control methods that can be successful and sustained over a lifetime to prevent the development of reduced myocardial blood flow and ischemia in young adults in future.