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This study tested the hypothesis that the developing heart is susceptible to oxygen-mediated damage after reintroduction of molecular oxygen and that this "unintended" reoxygenation injury causes lipid peroxidation and functional depression that may contribute to perioperative cardiac dysfunction. Among 49 Duroc-Yorkshire piglets (2 to 3 weeks old, 3 to 5 kg) 15 control studies were done without hypoxemia to test the effects of the surgical preparation (n = 10) and 60 minutes of cardiopulmonary bypass (n = 5). Twenty-nine piglets underwent up to 2 hours of ventilator hypoxemia (with inspired oxygen fraction reduced to 6% to 7%) to lower arterial oxygen tension to approximately 25 mm Hg. Five piglets did not undergo reoxygenation to determine alterations caused by hypoxemia alone. Twenty-four others received reoxygenation by either raising ventilator inspired oxygen fraction to 1.0 (n = 12) or instituting cardiopulmonary bypass at oxygen tension 400 mm Hg (n = 12). Ventilator hypoxemia produced sufficient hemodynamic compromise and metabolic acidosis that 18 piglets required premature reoxygenation (78 +/- 12 minutes). To avoid the influence of acidosis and hemodynamic deterioration during ventilator hypoxemia, five others underwent 30 minutes of hypoxemia during cardiopulmonary bypass (circuit primed with blood at oxygen tension 25 mm Hg) and 30 minutes of reoxygenation (oxygen tension 400 mm Hg) during cardiopulmonary bypass. Biochemical markers of oxidant damage included measurement of coronary sinus and myocardial conjugated dienes to determine lipid peroxidation and antioxidant reserve capacity assessed by incubating myocardial tissue in the oxidant t-butylhydroperoxide. Functional recovery was determined by inscribing pressure volume loops to determine end-systolic elastance and Starling curves by volume infusion. No biochemical or functional changes occurred in control piglets. Hypoxemia without reoxygenation did not change plasma levels of conjugated dienes, but lowered antioxidant reserve capacity 24%. Reoxygenation by ventilator caused refractory ventricular arrhythmias in two piglets (17% mortality), raised levels of conjugated dienes 45%, and reduced antioxidant reserve capacity 40% with recovery of 39% of mechanical function in the survivors. Comparable biochemical and functional changes occurred in piglets undergoing ventilator hypoxemia and/or cardiopulmonary bypass hypoxemia and reoxygenation on cardiopulmonary bypass. We conclude that hypoxemia increases vulnerability to reoxygenation damage by reducing antioxidant reserve capacity and that reoxygenation by either ventilator or cardiopulmonary bypass produces oxidant damage with resultant functional depression that is not a result of cardiopulmonary bypass. These findings suggest that initiation of cardiopulmonary bypass in cyanotic immature subjects causes an unintended reoxygenation injury, which may increase vulnerability to subsequent ischemia during surgical repair.

IntroductionCardiopulmonary bypass (CPB) is used increasingly to correct cyanotic heart defects during early infancy, but myocardial dysfunction is often seen after surgical repair. This study evaluates whether starting CPB at a conventional, hyperoxic P02 causes an "unintentional" reoxygenation (ReO2) injury. We subjected Repair ofheart defects causing cyanosis is performed on cardiopulmonary bypass (CPB)I in early infancy with increasing frequency. Postoperative cardiac dysfunction is the major cause of morbidity and mortality despite successful surgical correction and is more common in infants than in adult cardiac patients (29). The conventional method ofstarting CPB in hypoxemic infants is to raise P02 to > 400 mmHg by mixing their blood with fluid in the extracorporeal circuit pre-circulated at hyperoxic levels. We have speculated that such abrupt reoxygenation causes an "unintended reoxygenation injury" (2) and adds to subsequent intraoperative oxidative stress due to surgical ischemia that provides a bloodless field, and limits the effectiveness of a cardioplegic strategy shown previously to reduce reperfusion damage (3, 4). Our hypothesis is based on experimental evidence that cyanosis reduces endogenous myocardial antioxidants and reoxygenation enhances free radical generation (5). In support of this hypothesis, clinical reports show myocardial lipid peroxidation in pre-ischemic biopsies from cyanotic children (6), cardioplegic protection is less adequate in cyanotic versus normoxic patients despite shorter ischemic intervals (7) and myocardial dysfunction in cyanotic infants placed on extracorporeal membrane oxygenation (ECMO) despite absence of surgical ischemia (8,9). Studies indicate reactive oxygen species mediate reperfusion/reoxygenation injury (10) via the classic Haber-Weiss (Fenton) pathway ( 1). An alternate mechanism of oxidant injury was proposed recently by Beckman et al.(4), whereby superoxide anion (O -) and nitric oxide (NO) interact to form cytotoxic 02 species ( 12). We showed recently cyanotic infantile hearts reoxygenated on CPB have a burst ofNO which was associated with oxidant damage and myocardial dysfunction which could be ameliorated by either adding a NO synthase (NOS) inhibitor or antioxidants to the priming solution ofthe CPB circuit (2). Unfortunately, NOS inhibition with a L-arginine analog produced severe systemic vasoconstriction and resulted in pancreatic damage despite its cardioprotective effect and the antioxidants added to the CPB prime are not available clinically.Alternative strategies do, however, exist during conventional cardiac operations that can reduce NO and 0-production. For example, generation of 0-and NO is P02 dependent (13,14), and controlling the rate of reintroduction of molecular oxygen when CPB is started and cardioplegic solution is administered may avoid the burst of NO and 0-that follows

Structural examination of human heart specimens at the microscopic level is a prerequisite for understanding congenital heart diseases. It is desirable not to destroy or alter the properties of such specimens because of their scarcity. However, many of the currently available imaging techniques either destroy the specimen through sectioning or alter the chemical and mechanical properties of the specimen through staining and contrast agent injection. As a result, subsequent studies may not be possible. X-ray phase-contrast tomography is an imaging modality for biological soft tissues that does not destroy or alter the properties of the specimen. The feasibility of X-ray phase-contrast tomography for the structural examination of heart specimens was tested using infantile and fetal heart specimens without congenital diseases. X-ray phase-contrast tomography was carried out at the SPring-8 synchrotron radiation facility using the Talbot grating interferometer at the bending magnet beamline BL20B2 to visualize the structure of five non-pretreated whole heart specimens obtained by autopsy. High-resolution, three-dimensional images were obtained for all specimens. The images clearly showed the myocardial structure, coronary vessels, and conduction bundle. X-ray phase-contrast tomography allows high-resolution, three-dimensional imaging of human heart specimens. Intact imaging using X-ray phase-contrast tomography can contribute to further structural investigation of heart specimens with congenital heart diseases.Electronic supplementary materialThe online version of this article (doi:10.1007/s00246-016-1527-z) contains supplementary material, which is available to authorized users.

The activity of aortic glutathione peroxidase, a selenium-dependent enzyme, significantly decreased in rats 4 and 8 months after the injection of streptozotocin (STZ). Catalase activity was shown to occur at low levels in rat aorta and was not influenced by the diabetic state. Superoxide dismutase activity was less than detectable. The activity of selenium-dependent glutathione peroxidase in kidney, but not in lung and liver, increased in diabetic rats. Catalase and superoxide dismutase activities in the kidney were not altered. The plasma lipid peroxide value increased in diabetic rats. The selenium content in plasma of diabetic rats increased markedly while the increase in plasma glutathione peroxidase activities was insignificant. The observed abnormalities in plasma of STZ rats were improved by insulin treatment. The defects in glutathione peroxidase in the diabetic rat aorta were restored by insulin treatment. These results may suggest that the capacity of the antioxidative defense system in the aorta decreased in the diabetic state, and this may help clarify the mechanism of the pathogenesis of endothelial dysfunction associated with diabetes.