Introduction: Cardiovascular diseases(CVDs)remain the number one cause of death worldwide,which brought a great burden on individual,national and global economics.As a major indicator of cardiovascular morbidity and mortality,blood pressure(BP),especially nighttime BP and BP variablitiy needs to be monitored for the control of CVDs.However,designed with an inflatable cuff,most of the state-of-the-art BP meters cannot achieve ambulatory BP monitoring.On the other hand,an alternative cuffless BP measurement technique based on pulse transit time(PTT)has attracted rising interest recently.The current PTT-based BP estimation model was built on Moens-Korteweg equation,which assumes the artery to be a passive,thin-wall and homogeneous tube.However,arterial wall in reality exhibits a specific layered structure and consists of elastin,collagen fibres and smooth muscles.In fact,the PTT-BP relationship was found by many studies to be easily deteriorated by vasoconstriction/dilation,which reflects the vascular smooth muscle activation level,i.e.,VSM tone.Therefore,the objective of this study is to build a novel PTT-BP model based on arterial wall structure and constitutes,and to investigate the influence of VSM tone on the PTT-BP relationship theoretically by simulation study.