No abstract

Cardiac oxygen availability and oxygen consumption were used in a theoretical study as indexes of myocardial energy supply and utilization, respectively. A detailed computer simulation of the closed-loop canine cardiovascular system was utilized to study the dependence of these indexes on timing of the intraaortic balloon pump. Oxygen availability exhibited higher sensitivity to balloon timing than oxygen utilization. While maximum augmentation of oxygen availability was 58 percent, oxygen consumption could be reduced by only 13 percent. Animal experiments were initiated to validate the theoretical results. The results of both the animal experiments and the computer simulation suggested that neither balloon timing which maximizes oxygen availability nor timing which minimizes oxygen consumption correlates with timing which minimizes aortic end diastolic pressure. Thus, end diastolic pressure, presently used as a determinant of proper timing in patients undergoing cardiac assistance, was found to be a poor index of ventricular energy consumption. A performance index comprised of clinically available variables, was formulated to reflect myocardial energy balance. In this performance index, mean diastolic pressure was used to represent energy availability and peak systolic pressure was used as an index of oxygen consumption. Their relationship to oxygen balance and their dependence on timing were studied using the computer simulation of the canine cardiovascular system and animal experiments. Theoretical and experimental results suggest that such an index is capable of representing O2 balance and can be used to control phasing of the device.

As previously reported,'q2 a polymer-ceramic composite designed for endosseous implant applications has been developed. The composites were prepared by the free-radical polymerization of an acrylic acid solution and a difunctional acrylate in the presence of 0.3 pm akunina powder. Mechanical testing indicated that the material had a compressive yield strength of 89-102 MPa (13-15 ksi) and an elastic modulus of 2055-2740 MPa (300-400 ksi). The average porosity of the composite was determined to be in the range of 50-55 ~0 1 % .A unique property of this material is its ability to gradually swell in aqueous media to a degree which can be precisely controlled via the extent of matrix cross-linking. The present material was designed to obtain an equilibrium swelling level of 15-25 vol % in Ringers solution a t 40OC. The advantages of such controlled swelling in an endosseous implant material are twofold. First, it allows for rapid adaptation of the prosthesis to the contour of the socket. Second, it induces a state of compressive stress around the implant site. It has been suggested that the presence of such a force field will result in the stimulation of bone f o r m a t i~n .~~ This paper reports the initial results obtained from a series of animal implantation experiments utilizing this swelling composite material. EXPERIMENTAL PROCEDURESix adult mongrel dogs were used in these experiments. Following standard aseptic procedures, four holes were made in each canine femoral shaft with a 3/16-in. (4.76 mm) Michelle 1aminect.omy trephine. Cylindrical implant specimens which had been machined to a diameter of 4.65-4.67 mm were placed in the right femur of each animal.Approximately 4 weeks later, additional specimens were inserted into the animal's left

Hyperparathyroidism with or without adenoma has occasionally been reported in association with lithium treatment, and in symptomatic patients depression, psychosis and an exacerbation of existing psychopathology may occur. Three lithium-treated patients with hyperparathyroidism are reported, in whom discontinuation of lithium in one and removal of parathyroid adenomata in two led to both a reduction in plasma calcium levels and an improvement in their psychopathology.