A computer model of the effect of venous-arterial-venous extracorporeal membrane oxygenation venous return of oxygenated blood on right atrial recirculation and tricuspid valve blood oxygen saturation.

OBJECTIVE: Venous-arterial venous extracorporeal membrane oxygenation (V-AV ECMO), as a new clinical application of ECMO, showed great clinical application potential in the treatment of patients with combined cardiopulmonary failure. Given the complicated cannulation strategy of V-AV ECMO, its influence on the hemodynamics of the human circulatory system remained unclear. METHODS: In this paper, a fluid-structure interaction was used to study the effect of V-AV ECMO oxygenated blood shunt ratio on right atrial recirculation and tricuspid valve (TV) blood oxygen saturation. In this study, the right atrium, superior vena cava supplying cannulae and inferior vena cava draining cannulae model of a specific patient was constructed. Seven cases with shunt ratio of 12.50%, 18.75%, 25.00%, 31.25%, 37.50%, 43.75% and 50.00% were designed. RESULTS: The streamline diagram and velocity contour of oxygenated blood, recirculation fraction (RF), correlation of three variables (shunt ratio, RF, and oxygen saturation), and the oxygen saturation of blood at the TV were extracted for the study. Study results showed that, first, as the shunt ratio increased, the RF of the seven cases was 14.64%, 29.87%, 33.85%, 40.12%, 40.40%, 40.02%, and 38.09%. Second, with the increase of the shunt ratio, oxygen saturation of blood at the TV in seven cases was 82.1%, 82.5%, 83.3%, 83.3%, 84.0%, 84.6%, and 85.3%. CONCLUSIONS: In this study, the shunt ratio had a strong correlation with the RF and oxygen saturation of blood at the TV. As the shunt ratio increased, the RF initially increased and then stabilized. However, oxygen saturation of blood at the TV would increase with the increase of the shunt ratio, but the degree of increase was small. This research provided useful information for surgeons and operators using V-AV ECMO.

Hemodynamic mechanism of pulsatile tinnitus caused by venous diverticulum treated with coil embolization.

BACKGROUND AND OBJECTIVE: Coil embolization has become a new treatment method for pulsatile tinnitus (PT) caused by sigmoid sinus diverticulum (SSD). Although this therapy has achieved good results in clinical reports, the hemodynamic mechanism of coils in the treatment of PT in SSD remained unclear. METHODS: Finite element method (FEM) and computational fluid dynamics (CFD) were combined to explore the hemodynamic mechanism of coil embolization in SSD treatment. Three personalized geometric models of sigmoid sinus were established according to the CTA data of patients. Coil model were established by FEM, and the hemodynamic differences of SSD before and after coiling were compared by transient CFD method. RESULTS: Velocity streamlines disappeared in the SSD after coiling. At the peak time (t1 = 0.22 s), the SSD-average velocity decreased in every patient. The average value of the decreased in three patients was 0.154 ± 0.028 m/s (mean ± SD). Wall average pressure (Pavg) also showed a decline in every patient. Average of decrements of three patients was 17.69 ± 4.91 Pa (mean ± SD). Average WSS (WSSavg) was also reduced in every patient. The average value of WSS drop was 9.74 ± 3.02 Pa (mean ± SD). After coiling, the proportion of low-velocity region in the sigmoid sinus cortical plate dehiscence (SSCPD) area increased. Average of increments was 22.1 ± 5.36% (mean ± SD). CONCLUSIONS: A reduction in SSD-average velocity, wall pressure, and WSS were the short-term hemodynamic mechanism of coil embolization for PT. Coil embolization increased the proportion of low-velocity region in the SSCPD area, thereby creating a hemodynamic environment that easily produced thrombus and protects blood vessels from the impact of blood flow. This phenomenon was the long-term effect of coil embolization.

Biomechanical effects of the novel series LVAD on the aortic valve.

BACKGROUND AND OBJECTIVE: The series type of LVAD (i.e., BJUT-II VAD) is a novel left ventricular assist device, whose effects on the aortic valve remain unclear. METHODS: The biomechanical effects of BJUT-II VAD on the aortic valve were investigated by using a fluid-structure interaction method. The geometric model of BJUT-II VAD was virtually implanted into the ascending aorta to generate the realistic flow pattern for the aortic valve (i.e., support). In addition, the biomechanical states of the aortic valve without BJUT-II VAD support was computed as control (i.e., control case). RESULTS: Results demonstrated that the biomechanical effects of BJUT-II VAD were quite different from that resulting from traditional "bypass LVAD." Compared with those in the control case, BJUT-II VAD support could significantly reduce the stress load of the leaflet (maximum stress, 0.5 MPa in the control case vs. 0.12 MPa in the support case). Similarly, the rapid valve opening time (100 ms in the control case vs. 175 ms in the support case) and rapid valve closing time (50 ms in the control case vs. 150 ms in the support case) in the support case were obviously longer than those in the control case. Moreover, BJUT-II VAD support reduced retrograde blood flow during the diastolic phase and significantly changed the distribution of WSS of the leaflets. CONCLUSIONS: In summary, while unloading the left ventricle, BJUT-II VAD could provide beneficial biomechanical states for the aortic leaflets, thereby reducing the risk of aortic valve disease.