The effect of reactive artery hyperaemia on the radial strain of the brachial artery: Definition of optimum cuff position

*Instruction: Measurement of brachial artery diameter variation by ultrasound methods has commonly been used to test the endothelial function. It is known that the artery diameter is increased by flow stimulation. Therefore in the present study, the effect of external obstruction, as flow stimulation, on the radial strain of the brachial artery was assessed. Also the biomechanical behavior of the artery due to the changes in obstruction cuff position was evaluated. Methods: Firstly, for evaluating the effect of flow stimulation on healthy men's brachial artery, 200 mmHg pressure and 5 minutes of obstruction was applied. Then, without flow stimulation, it was evaluated by ultrasonic method. In order to evaluate the optimum cuff position with maximum biomechanical variation of the brachial artery, arteries of two regions including the proximal brachial (upper arm) and middle forearm of 10 healthy men were obstructed by 200 mmHg of stress. By acquiring artery diameter variation and estimation of radial strain, multiple frames of the B-mode ultrasonic images were saved on personal computer and maximum artery diameter in the systolic phase, artery diameter in the end of the diastolic phase and the shape of offline were measured. According to relative diameter variations, radial strain percentages were estimated. The effects of external obstruction and the position of this obstruction on the radial strain of the brachial artery were analyzed by t-test. Results: In the first stage, the results of ultrasonic evaluation of the left brachial artery showed that the radial strain induced by stress (200 mmHg) was significantly increased 3.5 times compared to the normal condition without stress. Evaluation of the obstruction's location and its effect on the relative brachial artery diameter showed that with the application of 200 mmHg obstruction in 1/3 of the superior arm and the middle forearm, the radial strain of the artery were 10.44 ± 2.63 % and 4.97 ± 3.61 %, respectively. The statistical analysis of the brachial artery radial strain showed a significant difference between the two obstruction's locations and 33% increase of the obstructed brachial artery's diameter variation in 1/3 of the superior arm. Conclusion: The brachial artery's radial strain is increased by the external obstruction of the artery. This increase seems to be larger in the upper arm region of the artery compared to the middle forearm region.