Reliability Considerations on Redundant Systems with Repair

It is well-known that a method of increasing system reliability is the addition of redundancy and/or repair. In this paper, the reliability models of complex systems with redundancy and/or repair are formulated by birth-death processes and semi-Markov processes. The authors show how the system modification yields the increase in mean time to system failure. They show how the system with repair yields the increase in mean time to system failure compared with the similar system without repair. Finally, they also show that the system reliability depends upon the repair time distributions and that many calculations of the system reliability suggest the significant properties

Evaluation of the Appropriate Root Pressure for Maintaining Heartbeat during an Aortic Cross-clamp for Primary Repair of the Aortic Arch in Premature Infants with Associated Cardiac Anomalies

We developed a new cardiopulmonary bypass (CPB) method to minimize myocardial damage during aortic arch reconstruction. In this method, coronary flow and heartbeat were stabilized by maintaining the aortic root pressure with an adjusted preload of the ventricle during aortic cross-clamping. This study was performed to determine the appropriate root pressure to maintain the heartbeat without causing deterioration of ventricular function. Study 1. Under partial CPB, the ascending aorta was cross-clamped in 6 pigs (group 1). Experimental data at various systolic aortic root pressures was analysed to determine the appropriate root pressure. Study 2. In group 2 (control, n＝6), the aorta was not clamped, while in group 3 (n＝6), the aorta was cross-clamped for 60 min and the systolic aortic root pressure was maintained at the pressure determined in study 1. Study 1. The diastolic coronary flow was stabilized at values comparable to that before initiation of CPB (6.6±1.4ml/beat) when the systolic aortic root pressure was above 80mmHg. Intracardiac pressure and the myocardial oxygen consumption (MvO2) seemed to be acceptable when the systolic aortic root pressure was below 100mmHg. Therefore, 90mmHg was selected for study 2. Study 2. Perioperative cardiac function did not differ between the groups. We concluded that 90mmHg was the systolic aortic root pressure appropriate for this method

Efficacy of MCI-186, a free-radical scavenger and antioxidant, for resuscitation of nonbeating donor hearts

ObjectiveOxygen-derived free radicals are responsible in part for reperfusion injury in globally ischemic myocardium. In this study, the efficacy for resuscitation of nonbeating donor hearts of MCI-186, a free-radical scavenger and antioxidant, was investigated in a pig transplantation model.MethodsCardiac arrest was induced by asphyxiation. After 30 minutes of global ischemia, the hearts were excised and immediately reperfused from the aortic root with normoxemic blood cardioplegia (Po2 100 mm Hg) for 20 minutes, followed by perfusion with hyperoxemic blood (Po2 300 mm Hg). MCI-186 (3 mg/kg) was administered into the aortic root for the first 30 minutes of reperfusion in the treated group (n = 6), and untreated hearts were used as a control group (n = 6). Transplantation was performed with the heart beating.ResultsPosttransplantation recovery of cardiac output, end-systolic pressure–volume ratio, and first derivative of pressure of the left ventricle in the treated group were significantly better than those in the control group. The coronary sinus–aortic root difference in malondialdehyde levels remained low throughout reperfusion in the treated group but abruptly increased after initiation of oxygenated blood perfusion in the control group. The MCI-186–treated hearts showed low degree of edema and well-preserved ultrastructure with normal-appearing organelles, whereas the untreated hearts had marked swelling of mitochondria and scant glycogen granules.ConclusionMCI-186 exerts a cardioprotective action at least partly by inhibition of lipid peroxidation. Antioxidant therapy at the initial reperfusion is essential to successful resuscitation of nonbeating hearts by continuous myocardial perfusion

Stochastic system reliability modeling

xii, 285 p. : ill. ; 23 cm

Stochastic system reliability modeling

xii, 285 p. : ill. ; 23 cm