Stent effects on hemodynamics of cerebral aneurysm by non-uniform lattice Boltzmann method / 医用生物力学

Objective To investigate the effects of triangle stents with different rotation angles on hemodynamics of cerebral aneurysms. Methods A non-uniform lattice Boltzmann method (LBM) was adopted to make local refinement on grids near the stent, and a scheme for the curved boundary conditions was used to numerically simulate the stented cerebral aneurysms. The stream plots of flows in the aneurysms, the velocity profiles at the aneurysm orifice and the velocity reduction were obtained and analyzed to evaluate the effects of stents with different rotation angles on treating cerebral aneurysms. Results With respect to velocity reduction, the best treatment effect was achieved in the triangle stent with rotation angle of 180°, while the triangle stent without any rotation caused the smallest velocity reduction. In addition，the dynamic differences were not obvious in triangle stents with different rotation angles at small porosities. Conclusions The non-uniform LBM combined with curved boundary conditions can be used to study hemodynamic characteristics of the cerebral aneurysm accurately, which provides reference for the design of such stent and also offers some guidance for intervention therapy in clinic.

Numerical study on multiscale simulation for hemodynamics of systemic-pulmonary shunt procedure based on lattice Boltzmann method / 医用生物力学

Objective Based on time-coupled multiscale coupling algorithm, to simulate the hemodynamics after systemic-pulmonary shunt procedure on single ventricular patient so as to obtain the local three-dimensional (3D) fluid field and global hemodynamic information before and after surgery. MethodsFirstly, the 0D-3D coupled multiscale hemodynamic model of systemic-pulmonary shunt procedure was established based on the lumped parameter model (0D) before surgery and the shunt model (3D), then the 0D-3D interface coupling condition and the time coupling algorithm were discussed. Secondly, the multiscale simulation of 3D CFD (computational fluid dynamics) model coupled with 0D lumped parameter model was realized based on lattice Boltzmann method. Finally, the multiscale simulation results were compared with patient’s 0D simulation results to study the hemodynamic changes before and after surgery. Results The global hemodynamic change and local 3D flow pattern were obtained by this multiscale simulation. The pulmonary blood flow distribution ratio was increased from 32.21% to 57.8%. Conclusions The systemic-pulmonary shunt procedure can effectively increase the blood supply of pulmonary circulation by implanting the shunt between the systematic circulation and pulmonary circulation. The geometrical multiscale method can effectively simulate both the coarse global and detailed local cardiovascular hemodynamic changes, which is of great significance in pre-operation planning of cardiovascular surgery.

The Changes of Body Compositions and Associated Factors in CAPD Patients During First One Year / 대한신장학회잡지

PURPOSE: CAPD is an important treatment modality along with hemodialysis and kidney transplantation in end stage renal disease. Malnutrition is very common and associated with increased morbidity and mortality in CAPD patients. The cause of malnutrion in CAPD patients might be multifactorial. This prospective study was carried out to investigate nutritional changes for 1 year after initiation of peritoneal dialysis by measurement body composition, especially lean body mass (LBM) using bioelectrical impedance analysis (BIA) and dual energy X-ray absorptiometry (DEXA) and to evaluate the factors associated with malnutrition in CAPD patients. METHODS: Among new CAPD patients from May, 2001 to Dec, 2002 in our hospital, 25 patients were enrolled. Body weight, LBM, LBM percen t (%LBM), fat mass, fat mass percent (%fat mass), ECF volume and ECF/TBW were compared between 1st month and 12th month after initiation of PD. The biochemical parameters, Urea kinetic modeling, Peritoneal equilibration test, the amounts of glucose absorption through the dialysate, the amounts of protein and albumin loss through the dialysate were measured at the same time point with measurement of the body composition. RESULTS: There were significantly decreased LBM (46.3+/-9.1 kg to 44.7+/-9.0 kg in BIA, 45.7+/-9.3 kg to 42.1+/-7.9 kg in DEXA, p< 0.05, respectively) but significantly increased fat mass (16.3+/-6.2 kg to 20.2+/-7.9 kg in BIA, 15.7+/-6.6 kg to 20.1+/-7.4 kg in DEXA, p<0.01, respectively) during first one year. Mean weekly Kt/V were significantly correlated with the changes of LBM (r=-0.64 in BIA, r=-0.81 in DEXA, p<0.01, respectively). With the multiple regression test, 1st month weekly Kt/V in BIA and DEXA were significant predictors of the changes of LBM for 1 year (beta-coefficients: -0.573 in BIA, -0.773 in DEXA, p<0.01, respectively). CONCLUSION: Adequate dialysis, especially 1st month adequacy, is very important for maintaining good nutritional status for one year after initiation of peritoneal dialysis.

Adequate Dosage for Midazolam Premedication in Koreans / 대한마취과학회지

BACKGROUND: Midazolam is often used as an anxiolytic premedication before surgery. Although the sedative, anxiolytic, and amnestic properties of midazolam may be desirable before the induction of general anesthesia, respiratory function is impaired frequently by larger doses of midazolam. Therefore, we evaluated the adequate doses of midazolam premedication on anxiolytic and sedation without its serious side effects. METHODS: Eighty ASA I or II adult patients scheduled for elective minor surgery were randomly allocated to four groups according to premedication doses of midazolam. They were group 1: midazolam 0.05 mg/kg IM for lean body mass (LBM); group 2: midazolam 0.075 mg/kg IM for LBM; group 3: midazolam 0.1 mg/kg IM for LBM.; group 4: midazolam 0.125 mg/kg IM for LBM. Blood pressure, heart rate, bispectral index (BIS), oxygen saturation (SpO2), anxiety visual analogue scale (VAS), and observer's assessment of alertness and sedation (OAA/S) scores were measured before and at 30 minutes after midazolam premedication. The frequency of apnea, defined as a cessation of spontaneous respiration for more than 10 seconds, was recorded. Induction time and dose requirements in propofol-induced general anesthesia were recorded at the loss of opening their eyes on verbal command and eyelid reflex after starting the propofol infusion. Following intubation, blood pressure and heart rate were measured. RESULTS: The bispectral index and anxiety VAS was significantly decreaced in group 3 and group 4. However, oxygen saturation were significantly lower in group 4 compared with group 3. CONCLUSIONS: We concluded that group 3 (midazolam 0.1 mg/kg IM for LBM) is the proper premedication dosage for anxiolytic and sedation in Koreans without respiratory side effects.

The Effect of Declining Small Solute Clearance on Protein Intake and Nutritional Status in Progressive Renal Failure / 대한신장학회잡지

BACKGROUNDS: Malnutrition is common in patients with chronic renal failure(CRF) and various signs of malnutrition are strong predictors of increased morbidity and mortality. Monitoring of protein intake and nutritional status is therefore important in the clinical management of CRF patients. Few studies have demonstrated direct correlations among renal function, protein intake, and nutritional status in a prospective study although clinical experiences suggest such relationship. The aim of this study was to prospectively evaluate correlations between renal function, protein intake, and nutritional status during progressive renal failure. METHODS: A total of 431 studies on renal function, protein intake, and nutritional status was carried out in 282 patients with normal renal function and varying degrees of renal failure before beginning dialysis. Renal functional indices included weekly Kt/Vurea, total weekly creatinine clearance(Ccr, L/week/1.73m2), creatinine clearance(Ccr, mL/min/1.73m2), urea clearance(Curea, mL/min) and residual renal function(RRF, mL/min). Protein intake was assessed from the protein equivalent of total nitrogen appearance normalized by standard weight(nPNA, g/kg/day) by DOQI formula[nPNA(D)], Bergstr m formula 1[nPNA(B1)] and Bergstr m formula 2[nPNA(B2)]. Nutritional indices were fat free edema free body mass(FFEFBM, kg) by creatinine kinetics, %lean body mass(LBM, %) and serum albumin(g/dL). We evaluated correlations between renal function, protein intake and nutritional status by linear regression analysis. In a separate analysis, 237 studies from 94 patients with follow-up studies were analyzed for correlations among renal function, protein intake, and nutritional status. RESULTS: There was a highly significant correlation among weekly Kt/Vurea, weekly creatinine clearance, and residual renal function, among nPNA(D), nPNA (B1), nPNA(B2), and between FFEFBM and %LBM. Significant correlation was also observed between weekly Kt/Vurea and nPNA, between weekly Kt/ Vurea and FFEFBM, between weekly Kt/Vurea and %LBM, between nPNA and FFEFBM, and between nPNA and %LBM. The results were the same in patients with follow-up studies. CONCLUSION: These results clearly demonstrate that renal urea and creatinine clearance is closely correlated with protein intake and nutritional status in predialysis patients. With declining small solute clearances, protein intake decreased and nutritional status became worse. Starting dialysis before malnutrition becomes apparent may improve patient morbidity and mortality after dialysis.

Segmental Bioelectrical Impedance Analysis(SBIA) for Determining Body Composition / 대한지역사회영양학회지

A new bioelectrical impedance method has been developed and evaluated. The electrodes; were made of stainless steel and electrical interfaces were created by an upright subject gripping hand electrodes and stepping onto foot electrodes. Eight tactile electrodes were in contact with surfaces of both hands and feet; thumb, palm and fingers, front sole, and rear sole. Automatic on-off switches were used to change current pathways and to measure voltage differences for target segments. Segmental body resistances and whole body resistance(RWHOLE)were measured in 60 healthy subjects. Segmental resistances of right arm(RRA), left arm(RLA), trunk(RT), right leg(RRL) and left leg(RLL)were310.0+/-61.6 omega, 316.9+/-64.6 omega, 25.1+/-3.4 omega, 236.8+/-31.2 omega and 237.6+/-30.4 omega, respectively. Individual segmental impedance indexes(Ht2/RRA, Ht2/RT, and Ht2 /RLA) were closely related to lean body mass(LBM)as measured by densitometry ranged from r=0.925 to 0.960. Ht2/(RRA+RT+RLA) predicted LBM slightly better(r=0.969) than the traditional index, Ht2/RWHOLE(r=0.964), supporting the accuracy of the segmental measurement. A multiple regression equation utilizing Ht2/RRA, Ht2/RT and Ht2/RRL predicted LBM with r=0.971. Ht2/RRA term of the regression contributed to more than 40% of the LBM prediction, indicating that lean mass of arm represented whole body LBM more closely than other body segments. The new bioimpedance method was characterized by upright posture, eight tactile electrodes, segmental measurements and utilization of electronic switches in comparison with the traditional method. The measurement with this new method was extremely reproducible, quick and easy to use.

Bioelectrical Impedance Analysis (BIA) of the Estimation of Total Body Water and Lean Body Mass in Patients with Renal Failure / 대한신장학회잡지

Bioelectrical impedance analysis (BIA) was used to determine total body water (TBW) and lean body mass (LBM) in patients with renal failure. The body's electrical resistance (R) was measured by the voltage to current ratio, injecting an 800microA alternating current with a frequency of 50KHZ and detecting a voltage drop between the wrist and the ankle. Impedance index (Height2/Resistance) compared favorably with TBW measured by deuterium (D2O) dilution method as the reference, giving the correlation coefficient (r) of 0.966 and standard error estimation (SEE) of 2.71 liter. The index was compared with LBM determined by dual-energy x-ray absorptiometry (DEXA) as the reference, giving r of 0.970 and SEE of 3.00kg. The r of 0.985 and SEE of 2.15kg were found between the reference method. BIA appeared to have a somewhat lower accuracy than those of the reference method. However, it is a useful clinical tool for estimating body composition, because it is easy, rapid and non-invasive. The existing BIA method is based on an extremely simple conductor model of the body. The accuracy may be improved further, based on a more realistic model for the body.