Cryopreservation of equine sperm: optimal cooling rates in the presence and absence of cryoprotective agents determined using differential scanning calorimetry.

Optimization of equine sperm cryopreservation protocols requires an understanding of the water permeability characteristics and volumetric shrinkage response during freezing. A cell-shape-independent differential scanning calorimeter (DSC) technique was used to measure the volumetric shrinkage during freezing of equine sperm suspensions at cooling rates of 5 degrees C/min and 20 degrees C/min in the presence and absence of cryoprotective agents (CPAs), i.e., in the Kenney extender and in the lactose-EDTA extender, respectively. The equine sperm was modeled as a cylinder of length 36.5 microm and a radius of 0.66 microm with an osmotically inactive cell volume (V(b)) of 0.6V(o), where V(o) is the isotonic cell volume. Sperm samples were collected using water-insoluble Vaseline in the artificial vagina and slow cooled at < or = 0.3 degrees C/min in an Equitainer-I from 37 degrees C to 4 degrees C. By fitting a model of water transport to the experimentally obtained DSC volumetric shrinkage data, the best-fit membrane permeability parameters (L(pg) and E(Lp)) were determined. The combined best-fit parameters of water transport (at both 5 degrees C/min and 20 degrees C/min) in Kenney extender (absence of CPAs) are L(pg) = 0.02 microm min(-1) atm(-1) and E(Lp) = 32.7 kcal/mol with a goodness-of-fit parameter R(2) = 0.96, and the best-fit parameters in the lactose-EDTA extender (the CPA medium) are L(pg)[cpa] = 0.008 microm min(-1) atm(-1) and E(Lp)[cpa] = 12.1 kcal/mol with R(2) = 0.97. These parameters suggest that the optimal cooling rate for equine sperm is approximately 29 degrees C/min and is approximately 60 degrees C/min in the Kenney extender and in the lactose-EDTA extender. These rates are predicted assuming no intracellular ice formation occurs and that the approximately 5% of initial osmotically active water volume trapped inside the cells at -30 degrees C will form innocuous ice on further cooling. Numerical simulations also showed that in the lactose-EDTA extender, equine sperm trap approximately 3.4% and approximately 7.1% of the intracellular water when cooled at 20 degrees C/min and 100 degrees C/min, respectively. As an independent test of this prediction, the percentage of viable equine sperm was obtained after freezing at 6 different cooling rates (2 degrees C/min, 20 degrees C/min, 50 degrees C/min, 70 degrees C/min, 130 degrees C/min, and 200 degrees C/min) to -80 degrees C in the CPA medium. Sperm viability was essentially constant between 20 degrees C/min and 130 degrees C/min.

Not all neonatal hearts are equally protected from ischemic damage during hypothermia.

Despite hypothermia, pediatric cardiac surgeons continue to experience difficulties in providing adequate myocardial protection in newborns. This study examines the effects of deep hypothermia on neonatal heart tolerance to ischemia by measuring metabolic responses and the time to onset of ischemic contracture, or "stone heart." After control right ventricular biopsy specimens were obtained, hearts of newborn pigs (n = 36) were excised and placed in temperature-regulated baths: 37.5 degrees +/- 0.5 degrees C (n = 9), 19.0 degrees +/- 0.5 degrees C (n = 14), and 12.0 degrees +/- 0.5 degrees C (n = 13). With a compliant balloon in the left ventricle to measure pressure, time to onset of ischemic contracture (greater than 2-mm Hg rise) was recorded, and sequential biopsies were done. Data indicated hypothermia significantly (p less than 0.001) prolonged time to onset of ischemic contracture from 29.5 +/- 1.7 minutes (mean +/- standard error of the mean) at normothermia to 150.0 +/- 6.4 minutes at 19 degrees C and to 283.8 +/- 46.4 minutes at 12 degrees C. Lactate buildup at 30 minutes of ischemia was significantly reduced by 70% with hypothermia. Decline in adenosine triphosphate level was significantly reduced by 50% (19 degrees C) and 75% (12 degrees C) with hypothermia. More importantly, a subgroup of hearts in each hypothermia group (n = 5 per group) was identified by 38% to 48% lower adenosine triphosphate stores before ischemia compared with the group means.(ABSTRACT TRUNCATED AT 250 WORDS)

Posterior wall disruption of the left ventricle after mitral valve replacement: management of bleeding and cardiac enlargement.

Two patients who underwent mitral valve replacement sustained posterior left ventricular disruption postoperatively and survived. Management consisted of repair from outside the heart without removal of the mitral prosthesis. This was achieved with a running Prolene suture in the atrioventricular junction in one patient and pledgeted sutures in the other who had transverse midventricular disruption. Biologic glue was crucial in controlling hemorrhage after the repair in both cases. The patient with transverse midventricular disruption required placement bilaterally of pectoralis muscle flaps to close the sternal wound because of swelling and dilatation of the heart.