Existence of global solutions in a model of electrical activity of the monodomain type for a ventricle

Introduction: A monodomain model of electrical activity for an isolated ventricle is formulated. This model is written as a reaction diffusion PDE coupled to an ODE, The Rogers-Mculloch model is used to represent the electrical activity through the cell membrane. Method: We give a definition of weak and strong solution of the variational Cauchy problem associated to the monodomain model. A sequence of approximate solutions of Faedo-Galerkin type is proposed.Results: It is shown that the sequence of approximate solutions converge to a weak solution according to the proposed definition. Finally, we have that this weak solution is also a strong solution. Conclusion: The monodomain model of electrical activity in an isolated ventricle that is proposed has a weak solution in an appropriate sense. In addition, this weak solution is also a strong solution.

Ischemic preconditioning: antiarrhythmic effects and electrophysiological mechanisms in isolated ventricle

The objective of this study was to identify cellular electrophysiological mechanisms by which ischemic preconditioning decreases arrhythmias in an isolated ventricular tissue model of ischemia and reperfusion. Electrical activity was recorded with microelectrodes from endocardium and epicardium of paced guinea pig right ventricular free walls. Control preparations were exposed for 15 min to Tyrode solution modified to simulate selected ischemic conditions and then were reperfused for 30 min with normal solution. Preconditioned tissues were exposed to a 2- or 5-min period of simulated ischemia before this same protocol. Neither preconditioning protocol affected incidence of ventricular tachycardia (VT) in ischemia; however, the 5-min protocol significantly decreased premature beats (PVB) and transmural conduction block. Preconditioning for 5 min, but not 2 min, significantly decreased reperfusion-induced VT and PVB. Ischemic preconditioning did not change effects of ischemia or reperfusion on action potential duration, effective refractory period, or endocardial conduction time. However, preconditioning markedly attenuated depression of transmural conduction by ischemia and early reperfusion and thereby prevented conduction delays necessary for transmural reentry.

Studies on the Regulation of Enzyme Binding During Anoxia in Isolated Tissues of Busycon Canaliculatum

The role of pH and protein kinase second messengers in triggering or potentiating anoxia-linked changes in enzyme binding to particulate matter were evaluated using in vitro incubations of isolated ventricle strips of Busycon canaliculatum (L.) (Prosobranchia, Melongenidae). Incubating whelks under anoxic conditions for 4h reduced the percentage of phosphofructokinase (PFK), aldolase, glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and pyruvate kinase (PK) activity associated with cellular particulate matter. Triose phosphate isomerase, phosphoglycerate kinase, phosphoglyceromutase and enolase showed no changes in enzyme binding when whelks were subjected to anoxic stress in vivo. Incubating isolated ventricle strips in vitro under anoxic conditions simulated the changes seen in vivo in whole, anoxic whelks with respect to the percentage of PFK and PK bound during anoxic stress; both whole-animal studies and isolated tissue studies showed reduced PFK and PK binding after 4 h of anoxic incubation. Tissue pH could be artificially changed by incubating isolated ventricle strips in sea water buffered to a desired pH. This permitted an investigation of the effect of intracellular pH on PFK and PK binding in situ. PFK and PK responded to altered intracellular pH with increased enzyme binding at lower intracellular pH values and decreased enzyme binding at higher intracellular pH values. These binding patterns were exactly the opposite of those observed during anoxia; during anoxia stress, both intracellular pH and the percentage of PFK and PK associated with particulate matter decreased. Addition of the second messenger compounds dibutyryl cyclic AMP, dibutyryl cyclic GMP or phorbol 12-myristate 13-acetate plus the calcium ionophore A23187 had no effect on the percentage of activity bound to subcellular structures measured under either normoxic or anoxic conditions. This study suggests that enzyme binding in vivo is not regulated by changes in intracellular pH or concentrations of protein kinase second messenger compounds during anoxia.

Isolated ventricles following intraventricular hemorrhage

✓ Panventricular enlargement often follows intraventricular hemorrhage in the premature neonate. During a recent 12-month period, the authors identified five infants who required shunting because of symptomatic post-hemorrhagic hydrocephalus, which was progressive despite serial lumbar punctures and the use of indwelling subcutaneous ventricular reservoirs. In the first 6 months following placement of the initial shunt, four of the infants required an additional shunt for isolated ventricles. Two children had isolation of the lateral ventricles and required bilateral shunts. Two other children had isolation of the fourth ventricle from the lateral ventricular system and required posterior fossa shunts. All of the children were treated successfully using multiple shunts. In all cases, progressive dilation of the isolated ventricle was unaccompanied by the usual clinical signs of shunt malfunction. It appears that isolated ventricular systems are common following post-hemorrhagic hydrocephalus and these children must be followed closely with ultrasound and computerized tomography scanning.

The Role of Venous Pressure in Regulation of Output from the Heart of the Octopus, Eledone Cirrhosa (Lam.)

1. The influence of perfusion pressure on stroke volume and heart rate was examined in the isolated ventricle. Input pressure, within the physiological range (10–20 cm of water), had a direct effect upon stroke volume and heart rate. Output back pressure had an inverse effect upon stroke volume and no effect upon heart rate. 2. Sites that could vary input pressure were investigated by selective denervation in the whole animal. The results indicated that the efferent branchial vessel and auricle may be involved, as well as the branchial hearts and lateral venae cavae. 3. It is proposed that the pressure of venous blood has a limited effect upon ventricular output in vivo.