The Physiology Of Thermogenesis In Different People

Purpose:Only recently has it been realized that nonshivering thermogenesis in adult humans can increase energy expenditure to regulate body temperature,which may be a effecitve way to prevent and reduce obesity.But surprising we don' t know much about the physiology of nonshivering thermogenesis.This study was designed to focuse on the precise determination of thermophysiology in different individuals,and to form the basis for further studies such as environmental and pharmacological interventions.Methods:First study:Thirteen subjects were recruited,and were exposed in different temperatures ranging from 16.0 to 31.0?.Self-report(a visual analoge score metric programmed into an iPAD App),changes of heart rate and heart rate variability,and surface electromyograpgy were measured.Second study:seventeen young men(13 lean,4 obese)were recruited,and were exposed in different temperatures ranging from 16.0 to 31.0?.Energy expenditure,respiratory quotient(RQ),mean skin temperature,core temperature,heart rate,heart rate variability and blood pressure were measured,and brown adipose tissue was quantified by PET/CT.Results:First study:1)sEMG in Pectoralis Major,Rectus Femoris and Trapezius is related to temperature ranged 26-31?(p<0.05).Heart rate variability is related to temperature ranged 16-31?(p<0.05).Heart rate decreased linearly as a function of chamber temperature,and exhibed a“flex”point in most subjects at the point of shivering(p<0.05).sEMG of Trapezius,and low-frequency component of heart rate variability were the most sensible parameters to independently predict shivering.2)The shivering threthold temperature in lean healthy people was 19.4-23.1?.Second study:1)The relationship between energy expenditure and environment temperature in lean healthy people was a“U”shape curve as hypothesized.The energy expenditure of nonshivering thermogenesis in lean subjects was about 16.7%rest energy expenditure.However,there was no clearly noticeable NST temperature range in obese subjects.2)There is a relationship between skin-core temperature and fat(%)(p<0.05).3)Obese individuals started to shivering at similar temperatures as the lean group.4)Both lean and obese people have BAT,but the volume and activity of BAT in obese people are lower than those in lean people.5)Blood pressure doesn' t change when temperature changes.Conclusions:1)sEMG,“flex”heart rate and heart rate variability are objective measurements to detect shivering threshold.sEMG of Trapezius,and low-frequency component of heart rate variability are the most sensible parameters to independently predict shivering.2)The relationship between energy expenditure and environment temperature in lean healthy people was a "U" shape curve as hypothesized.The energy expenditure of nonshivering thermogenesis in lean subjects was about 16.7%rest energy expenditure.There was no clearly noticeable NST temperature range in obese subjects,which may be related to the lower volume and activity of BAT in obese people.3)Despite of higher insulations,obese individuals in our study started to shivering at similar temperatures as the lean group,suggestion that either the NST mechanism was reduced and/or shivering was a sensory response more than a mechanism purely depending on the drop in core body temperature.4)Blood pressure is not related to the changes in chamber temperature,suggested that mild cold won' t injury humans blood pressure,Subjects reported they can tolerate the mild cold for a long time,which suggested that research on mild cold is feasible.