Browsing by Author "Urzua, Jorge"

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    Decreased Nitric Oxide Products in the Urine of Patients Undergoing Cardiac Surgery
    (W B SAUNDERS CO-ELSEVIER INC, 2009) Lema, Guillermo; Urzua, Jorge; Jalil, Roberto; Canessa, Roberto; Vogel, Andrea; Moran, Sergio; Fajuri, Alejandro; Carvajal, Claudia; Aeschlimann, Nicolas; Jaque, Maria P.
    Objective: Renal vasoconstriction has been blamed as a cause of perioperative renal dysfunction after cardiac surgery. Endothelial function is a critical determinant of vascular tonus, including vasoconstriction. The objective of this study was to establish whether the release of the endothelial vasodilator nitric oxide (NO) or NO products is altered in patients undergoing surgery with cardiopulmonary bypass in 3 different clinical conditions.
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    Renal function and cardiopulmonary bypass in pediatric cardiac surgical patients
    (2006) Lema, Guillermo; Vogel, Andrea; Canessa, Roberto; Jalil, Roberto; Carvajal, Claudia; Becker, Pedro; Jaque, Maria Paz; Fajardo, Christian; Urzua, Jorge
    We studied prospectively the perioperative changes of renal function in nine children undergoing cardiac surgery with cardiopulmonary bypass (CPB). Glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were measured with inulin and I-131-hippuran clearances before CPB, during hypo and normothermic CPB, following sternal closure and 1 h postoperatively. Urinary alpha glutathione S-transferase (alpha GS-T) was measured pre- and postoperatively as a marker for tubular cellular damage. Plasma and urine creatinine and electrolytes were measured. Free water, osmolal and creatinine clearances, as well as fractional excretion of sodium (FeNa) and potassium transtubular gradient (TTKG) were calculated. GFR was normal before and after surgery. ERPF was low before and after surgery; it increased significantly immediately after CPB. Filtration fraction (FF) was abnormally elevated before and after surgery; however, a significant decrease during normothermic CPB and sternal closure was found. Alpha GS-T presented a moderate, but nonsignificant increase postoperatively. FeNa also increased in this period, but not significantly. Creatinine, osmolal, free water clearances, as well as TTKG, were normal in all patients pre- and postoperatively. We conclude that there is no evidence of clinically significant deterioration of renal function in children undergoing repair of cardiac lesions under CPB. Minor increases of alpha GS-T in urine postoperatively did not confirm cellular tubular damage. There was no tubular dysfunction at that time.
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    The valuation of multidimensional American real options using the LSM simulation method
    (PERGAMON-ELSEVIER SCIENCE LTD, 2008) Cortazar, Gonzalo; Gravet, Miguel; Urzua, Jorge
    In this paper we show how a multidimensional American real option may be solved using the LSM simulation method originally proposed by Longstaff and Schwartz [2001, The Review of the Financial Studies 14(1): 113-147] for valuing a financial option and how this method can be used in a complex setting. We extend a well-known natural resource real option model, initially solved using finite difference methods, to include a more realistic three-factor stochastic process for commodity prices, more in line with current research. Numerical results show that the procedure may be successfully used for multidimensional models, expanding the applicability of the real options approach.