RESUMO
Swimmers generate vortices around their bodies during underwater undulatory swimming (UUS). Alteration of UUS movement would induce changes in vortex structure and fluid force. This study investigated whether a skilled swimmer's movement generated an effective vortex and fluid force for increasing the UUS velocity. A three-dimensional digital model and kinematic data yielded during UUS with maximum effort were collected for one skilled and one unskilled swimmer. The skilled swimmer's UUS kinematics were input into the skilled swimmer's model (SK-SM) and unskilled swimmer's model (SK-USM), followed by the kinematics of the unskilled swimmer (USK-USM and USK-SM, respectively). The vortex area, circulation, and peak drag force were determined using computational fluid dynamics. A larger vortex with greater circulation at the ventral side of the trunk and a greater circulation vortex behind the swimmer were observed in SK-USM compared to USK-USM. USK-SM generated a smaller vortex on the ventral side of the trunk and behind the swimmer, with a weaker circulation behind the swimmer compared to SK-SM. The peak drag force was larger for SK-USM than for USK-USM. Our results indicate that an effective vortex for propulsion was generated when a skilled swimmer's UUS kinematics was input in the other swimmer's model.
RESUMO
BACKGROUND: Intra-ventricular blood flow dynamics is considered as an important component of left ventricular (LV) function assessment. The purpose of this study was to evaluate the LV diastolic function in chronic kidney disease (CKD) with different degrees of LV diastolic dysfunction (LVDD) by using flow energetic parameters. METHODS: In this study, a total of 96 cases were recruited, including 58 CKD patients and 38 healthy controls. CKD patients were divided into 2 groups according to LVDD severity, named as DD1 and DD2. Vector flow-mapping (VFM) analysis was executed to calculate left ventricle average energy loss (EL) during early filling phase (E-EL_ave), atrial filling phase (A-EL_ave), diastole phase (D-EL_ave), and ejection phase (S-EL_ave). Moreover, the average vortex circulation during early filling phase (E-cir_ave) and atrial filling phase (A-cir_ave) was also assessed in the apical three-chamber view. The rate of average EL during early filling and atrial filling was expressed as E/A-EL. RESULT: Compared to the control group, A-EL_ave, S-EL_ave, and A-cir_ave in the DD1 group were higher (P < 0.05), and all parameters were obviously higher in the DD2 group (P < 0.05). In the control group and the DD2 subgroup, the E-EL_ave value was significantly higher than A-EL_ave value, which was opposite to the DD1 group. As diastolic dysfunction worsened, E-EL_ave and D-EL_ave risen gradually (P < 0.05), and A-EL_ave and S-EL_ave were slightly elevated with no significance. There were significant correlations between LV diastolic function and flow energetic parameters. Stepwise multiple regression analysis revealed that various LV function parameters could be regarded as independent predictors of average diastolic EL (all P < 0.01). CONCLUSIONS: For CKD patient with LVDD and LVEF > 50%, effective LV filling and systolic ejection with optimized energy consumption have been impaired. As a new flow-derived index, EL can quantitatively evaluate LV diastolic function in terms of blood fluid dynamics in CKD with various LVDD.