Different Arterial Occlusion Protocols on the Radial Strain of Arterial Wall M. Rafati 1 , M. Mokhtari-Dizaji 2 , H. Saberi 3 1 Tarbiat Modares University/Medical Physics Department, PhD student, Tehran, Iran 2 Tarbiat Modares University/Medical Physics Department, Associate Professor, PhD, Tehran, Iran 2 Tehran Medical Sciences University/Radiology Department, associate Professor, MD, Tehran, Iran Abstract— The purpose of the present study is to compare arterial vasodilation in response to two different occlusion cuff positions and different protocols under a reactive hy- peraemic stimulus. For comparing two different occluding cuff positions and extracting optimal reactive hyperaemia protocol, ten healthy young adults were studied. The relative strain and hemodynamic changes of the left brachial artery were calculated with motion estimation from the sequential ultrasonic images and power Doppler sonogram. The results of the two different occlusion cuff positions with left proxi- mal upper arm and distal forearm occlusions showed that the brachial artery vasodilation are significantly greater under the upper arm occlusion than in those with forearm occlusion. The results of optimal reactive hyperaemia proto- cols showed that optimum occlusion pressures, occlusion time, time after releasing cuff for recording ultrasonic im- ages and estimating relative strain are 150mmHg, 5min, 45- 60s with higher vasodilation and blood flow changes. It is concluded that the magnitude of relative strain and blood velocity would be related to not only to the choice of the location of cuff inflation, the magnitude of occlusion pres- sure and time but also to the time interval after the release of the occlusive cuff. Keywords— Ultrasound, Biomechanical behavior, Bra- chial artery, Reactive hyperaemia I. INTRODUCTION The vascular endothelium includes a single layer of cells covering the arterial internal surfaces that causes growth, vasoregulation and vasoprotection in arteries [1]. Researchers showed that endothelium function is changed by age and sex, smoking, high cholesterol, heart failure, special coronary artery, diabeties and …[2-4]. Blood flow exerts a force on the arterial endothellial surface known as haemodynamic shear stress. This mechanical stimulus causes the release of nitric oxide (NO) from the endothe- lium, which is a vasodilator [5]. Blood flow stimulus factor is produced by two methods: active and reactive hyperaemia. Active hyperaemia occurs in response to an increase in metabolic activity (exercise), whereas reactive hyperaemia occurs following an external occlusion of the artery. In both conditions, hyperaemia generates an in- crease in shear stress induced vasodilation. Reactive hy- peraemia induced brachial artery vasodilation, also re- ferred to as flow mediated dilation is used extensively in research to assess changes in endothelial function in a variety of clinical populations and age groups [1, 2, 5]. Thus the purpose of the present study is to compare rela- tive strain in response to different protocols under a reac- tive hyperaemic stimulus. Then the effect of different protocols of flow reactive stimulation on the hemody- namic changes of the brachial artery is evaluated and optimal protocol with relative strain maximum and veloc- ity changes maximum is proposed. II. MATERIALS AND METHODS A. Theory For estimating the arterial radial strain, spontaneous arte- rial diameter changes ) (t d were measured. The maxi- mum diameter changes was calculated based on the maximum systolic diameter, ) (t d s , and the minimum diastolic diameter, ) (t d d . Considering the relative changes of arterial diameter, radial strain ) (t r was defined as [6]: d r d t d t ) ( ) ( Where, d d is the end diastolic diameter. In the present study, to assess brachial artery vasodilation caused under a reactive hyperaemic stimulus, relative strain was de- fined as the ability of vessel's endothelium to produce nitric oxide: ) (Re ) (Re ) ( . Re st st Stress strain lative r r r ) (Stress r , and ) (Re st r are radial strains in a reactive hy- peraemia and without it, respectively. B. Study Population For comparing external occlusion of the left brachial and the left radial arteries on the biomechanical effect of the left brachial artery and reach occlusion site with higher relative strain and so optimal reactive hyperaemia protocol, relative strain and blood velocity of left brachial O. Dössel and . ( Eds.): WC 2009,I FMBE Proceedings 25/IV, pp. www.springerlink.com W C. Schlegel 1490–1493, 2009.