Study On The Optimal Option Of The Range Of Pressure Used In Ischemia-reactive Hyperemia Model Of Calf Skeletal Muscle

Objective:The purpose of this study was to optimize the ischemia and reactive hyperemia model made by tourniquet compression.By applying three different pressure values to tourniquet,the ischemia-reactive hyperemia model of calf skeletal muscle was established respectively under the corresponding pressure value,and the characteristics of BOLD time signal curve were observed in order to find the range of pressure applied on the tourniquet with high repeatability of the model and the influencing factors of skeletal muscle BOLD signal were further controlled.Methods:The ischemia and reactive hyperemia model of calf skeletal muscle was implemented by tourniquet compression.Ten healthy volunteers aged from 20 to 35 years old were scanned by BOLD functional MRI of calf skeletal muscle.The right upper brachial artery systolic blood pressure of each volunteers was measured before scanning,and the tourniquet pressure was set to brachial artery systolic pressure plus 30mm Hg(P30 model),70mm Hg(P70model)and 90mm Hg(P90 model)respectively,corresponding to three different models.Each volunteer was scanned by BOLD-MRI under the three different pressure models.The scanning process is divided into two parts:one is 3D-T1WI anatomical image scanning,the other is BOLD functional image scanning,including resting period(152s),ischemic period(352s)and reactive hyperemia period(360s).The collected data were post-processed to form the BOLD time signal curve under each pressure value model,and the curve parameters of gastrocnemius,soleus,tibialis anterior,tibialis posterior and fibula muscle were measured and analyzed statistically,including:the minimum ischemic value(MIV),variation of value during ischemia(S_Δ),the hyperemia peak value(PHV),the time to peak(TTP)and the end value(EV).Result:1.Characteristics of BOLD time signal curve during ischemia period:in the P30 model,the BOLD time signal curve of all muscles showed a consistent downward trend during ischemia period.However,in the P70model,the ischemia period of the curves showed different trend characteristics,of which 92%showed downward trend,2%showed no trend,and 6%showed upward trend.Even if the curve appeared as a downward trend,the degree of decline was not consistent.Some of the curves decreased slightly during the whole ischemia period,and the BOLD signal value at the end of ischemia period was closer to the baseline level.In the P90 model,the signal during ischemia period also showed different trend characteristics,among which 78%showed varying degrees of downward trend,22%showed upward trend,all the trends of the curves during ischemic period were analyzed by the Cox-Stuart trend test with statistically significance,P<0.05.2.Characteristics of BOLD time signal curve during reactive hyperemia period:the BOLD signal of all muscles increased rapidly during reactive hyperemia period,decreased after reaching the peak value,and gradually stabilized at the baseline level.Moreover,a characteristic of the curves was found that in the model with higher pressure,the peak value of BOLD signal in reactive hyperemia period was higher.Statistical analysis showed that the PHV of all curves in P90 model were significantly higher than that in the P30model,the PHV of tibialis posterior and fibula in P90 model was higher than that in P70 model,and in gastrocnemius,the PHV in P70 model was higher than that in P30 model(P<0.05).3.The comparison of BOLD time signal curve parameters among the three models:the S_Δof gastrocnemius,soleus and fibula in P90 model was significantly lower than that in P30 model and P70 model,and the MIV of corresponding muscles in P90 model was significantly higher than that in P30model and P70 model.The PHV of all muscles in P90 model was significantly higher than that in P30 model,the PHV of tibialis posterior and fibula in P90model was significantly higher than that in P70 model,and the PHV of gastrocnemius in P70 model was significantly higher than that in P30 model;the TTP value of tibialis posterior in P90 model was significantly higher than that in P30 model and P70 model(P<0.05).There was no significant difference in EV among the three models(P>0.05).4.Comparison of BOLD time signal curve parameters among the five muscles:in P30 model,the TTP and EV had no significant difference among the five groups of muscles(P>0.05),but there were differences in S_Δ,MIV and PHV.In P70 model,there were no significant differences in PHV and EV among the five groups of muscles(P>0.05),but there were differences in S_Δ,MIV and TTP.In P90 model,there were no significant differences in S_Δ,TTP and EV among the five groups of muscles(P>0.05),but there were differences between MIV and PHV.Conclusion:When the pressure applied on the tourniquet is set to the upper brachial artery systolic blood pressure plus 30mm Hg,the BOLD time signal curve of calf skeletal muscle shows a consistent downward trend during ischemia period.After tourniquet deflation,the BOLD signal increases rapidly,reaches the peak,then falls back,and finally stabilizes at the baseline level.The P30 model has high stability and repeatability,which is suitable for the study of the changes of calf skeletal muscle perfusion by BOLD-MRI,it can reflect the vascular reserve capacity more accurately.However when the tourniquet pressure was set to the P70 model and P90 model formed by brachial artery systolic blood pressure plus 70mm Hg and 90mm Hg respectively,the BOLD time signal curve during ischemia period showed different trends,including upward trend,no trend and downward trend in different degrees.And the different trends of ischemic period might have a significant impact on the parameters of time signal curve during ischemia period and reactive hyperemia period.Obviously,the stability and repeatability of P70 model and P90 model are poor,so they are not suitable for BOLD-MRI to study the changes of perfusion state of calf skeletal muscle.