Reliability of left atrial pressure estimation from left ventricular filling measurement in a total artificial heart.

A physiological control of a total artificial heart (TAH) requires reliable information on left arterial pressure (LAP). When LAP is derived indirectly from intrinsic TAH parameters like end diastolic volume (EDV) and diastole duration (Td), the transfer function and associated uncertainties need to be well understood.We derived a computational equivalent to a hydraulic model consisting of the venous compliance, the heart valve and the pump chamber, and studied the filling phase in cases of different venous compliance. We calculated a family of curves of pump chamber volume as a function of time for different venous compliances and LAP. To visualize the LAP transfer function and uncertainties associated to EDV, Td measurement error and unknown venous compliance a family of similar curves in the vicinity of assumed measurement was found and visualised in the parameter space.Results were in a realistic absolute range and showed expected trends despite some simplifications in the simulation model. The venous compliance has no significant influence on LAP values extracted from EDV and Td, except at very low values. The uncertainty in the extracted LAP is particularly high for high EDV and short Td.A physiological regulation therefore does not have to be individually adapted to the patient's venous compliances, but has to deal with uncertainties in the input values like blood pressures extracted from intrinsic device parameters.

Leg strength and performance of large white tom turkeys fed various protein and energy levels.

Three floor-pen experiments were conducted to determine the effects of varying protein and energy levels on body weight, feed efficiency, mortality, bone breaking-strength, and bone ash, calcium, and phosphorus in large white male turkeys. Increasing metabolizable energy by 100 kcal/kg diet increased body weight and feed efficiency. Increasing dietary protein during starter or finisher periods by 15% resulted in increased body weights by as much as 12%. Modifying dietary protein and energy levels over these ranges did not affect bone strength of toms at market weight.

Effects of monensin and bambermycins on the performance of market turkeys.

The effects were examined of monensin and the bambermycins in feed on growing turkeys. The drugs were used alone and in combination. A total of 1,600 hen and tom turkeys were divided into 32 pens. Four treatments were used, including 45 or 90 g/ton (907 kg) monensin either to 10 wk of age or to market age with and without adding of 2 g/ton of bambermycins. Evaluation parameters, including body weight, feed efficiency, and mortality, were done at 6, 10, and 13 wk of age for hens and 6, 10, and 18 wk of age for toms. Adding bambermycins increased body weights of hens at 10 wk of age and toms at 6 and 10 wk of age. No differences among treatments were noted at market weight within any of the parameters studied. No differences among treatments were noted in efficiency or mortality by the conclusion of the trial.

The reversible displacement of the passive diastolic p-V curve in the isolated guinea pig left ventricle.

We studied viscoelastic behaviour of the isolated diastolic guinea pig left ventricle (LV), manifested in changes of the hysteresis loop of the pressure-volume (p-V) diagram, produced by acute volume loading. Specifically, we investigated how the width of the hysteresis depends on the way LV volume loading, and whether changes in the hysteresis width are reversible. Each of 11 LV was instrumented with a catheter for injection and withdrawal of saline, and a micromanometer (Millar, 2F) to measure LV pressure. LV were loaded by the computer controlled injection of saline in 6-8 sequential injection steps of 100 microl each with a pause of 5 s, followed by a similar withdrawal pattern. In protocol A (N = 5), a 100 microl higher maximal LV volume (LVVmax) was reached during injection than in the control run, and in protocol B (N = 6), the time spent at LVVmax was longer (20 vs. 5 s pause). In both protocols a reproducible displacement of the passive p-V curve during volume unloading was observed, reflected in the increase of the hysteresis width by 23+/-8% in protocol A, and 12+/-3% in protocol B. Reversible displacement of the passive diastolic p-V curve after large aperiodic volume change suggests participation of reversible phenomena, like extracellular fluid filtration, and may in part provide an answer to the phenomenon of preconditioning.

Relaxation of epicardial strains after volume changes in the isolated guinea pig left ventricle.

Cardiac muscle is a porous viscoelastic material, exhibiting stress relaxation and hysteresis after being passively stretched. We investigated whether these material properties are also manifested in relaxation of epicardial segment lengths of the passive diastolic left ventricle (LV). For this purpose LV pressure and biaxial epicardial strains were measured simultaneously in isolated guinea pig hearts, arrested in diastole and instrumented to manipulate LV volume. Our study confirmed the existence of epicardial strain relaxation in both axial and circumferential directions, though it was much less expressed than LV pressure relaxation. Since the volume calculated from the segment lengths also revealed relaxation phenomena, our findings suggest that epicardial strain relaxation was connected with exchange of fluid from the LV cavity into the tightened epicardial vessels and back and not with the transformation of the LV shape.

[Flexural strength tests of repaired amalgam specimen]. / Prüfung der Biegefestigkeit reparierter Amalgamprüfkörper.

Test results of four types of alloys: Flexural strength declined significantly with increasing age of the specimen, however, differently for the tested alloys. The increase in mercury content of the repair amalgam did not influence flexural strength. The combination of materials with each other demonstrated that none of the amalgams was particularly suitable as a repair amalgam.

Collagen stabilization induced by natural humic substances.

Humic substances are polyphenolic compounds. They have antiviral as well as desmutagenic effects and react with biopolymers such as collagen; thereby they have no toxic side effects by oral administration. In vitro incubation with humic substances raises the breaking point of the tail tendon of the rat by about 75%. The chemical resistance of the collagen fibres in tail tendon collagen is also increased by in vitro incubation with humic substances, at least insofar as the ultrastructurally and biophysically measurable destruction of the collagen fibres by 4 M guanidinium chloride is inhibited. As humic substances increase the mechanical and chemical resistance of collagen fibres and promote their "maturity", it seems likely that this effect of humic substances depends upon their interaction with the hydrogen bonding and covalent bonding of the collagen fibres. Such a conclusion is confirmed by the results of X-ray diffraction analysis.