Cardiac Tolerance to Ischemia in Neonatal Spontaneously Hypertensive Rats

Assessing abdominal aorta narrowing using computational fluid dynamics

This paper investigates the effect of developing arterial blockage at the abdominal aorta on the blood pressure waves at an externally accessible location suitable for invasive measurements such as the brachial and the femoral arteries. Arterial blockages are created surgically within the abdominal aorta of healthy Wistar rats to create narrowing resemblance conditions. Blood pressure is measured using a catheter inserted into the right femoral artery. Measurements are taken at the baseline healthy condition as well as at four different severities (20, 50, 80 and 100 %) of arterial blockage. In vivo and in vitro measurements of the lumen diameter and wall thickness are taken using magnetic resonance imaging and microscopic techniques, respectively. These data are used to validate a 3D computational fluid dynamics model which is developed to generalize the outcomes of this work and to determine the arterial stress and strain under the blockage conditions. This work indicates that an arterial blockage in excess of 20 % of the lumen diameter significantly influences the pressure wave and reduces the systolic blood pressure at the right femoral artery. High wall shear stresses and low circumferential strains are also generated at the blockage site.

Neonatal rat hearts cannot be protected by ischemic postconditioning

Although there are abundant data on ischemic postconditioning (IPoC) in the adult myocardium, this phenomenon has not yet been investigated in neonatal hearts. To examine possible protective effects of IPoC, rat hearts isolated on days 1, 4, 7 and 10 of postnatal life were perfused according to Langendorff. Developed force (DF) of contraction was measured by an isometric force transducer. Hearts were exposed to 40 or 60 min of global ischemia followed by reperfusion up to the maximum recovery of DF. IPoC was induced by three cycles of 10, 30 or 60 s periods of global ischemia/reperfusion. To further determine the extent of ischemic injury, lactate dehydrogenase (LDH) release was measured in the coronary effluent. Tolerance to ischemia did not change from day 1 to day 4 but decreased to days 7 and 10. None of the postconditioning protocols tested led to significant protection on the day 10. Prolonging the period of sustained ischemia to 60 min on day 10 did not lead to better protection. The 3x30 s protocol was then evaluated on days 1, 4 and 7 without any significant effects. There were no significant differences in LDH release between postconditioned and control groups. It can be concluded that neonatal hearts cannot be protected by ischemic postconditioning during first 10 days of postnatal life.