Evaluation of changes in trabecular bone architecture and mechanical properties of minipig vertebrae by three-dimensional magnetic resonance microimaging and finite element modeling.

The study objective was to analyze the three-dimensional (3D) trabecular architecture and mechanical properties in vertebral specimens of young and mature Sinclair minipigs to assess the relative contribution of architecture to bone strength. We used 3D magnetic resonance microimaging (MRmicroI) and direct image analysis to evaluate a set of standard structural measurements and new architectural descriptors of trabecular bone in biopsy specimens from L2, L3, and L4 vertebrae (n = 16 in each group) from young (mean age, 1.2 years) and mature (mean age, 4.8 years) minipigs. The measurements included bone volume/tissue volume (BV/TV), marrow star volume (Ma.St.V), connectivity density (ConnD), and two new parameters, percent platelike trabeculae (% plate) and percent bone in the load direction (% boneLD). The % plate, calculated from surface curvature, allowed the delineation of plates from rods. The % boneLD quantified the percentage of bone oriented along the long axis of the vertebral body. We showed that 3D MRmicroI can detect the subtle changes in trabecular architecture between the two age groups. ConnD, star volume, % plate, % boneLD, and BV/TV were found to be more effective than the model-based, derived indices (trabecular thickness [Tb.Th], trabecular separation [Tb.Sp], and trabecular number [Tb.N]) in differentiating the structural changes. BV/TV, % plate, and % boneLD significantly increased (p < 0.05) in all three vertebral sites of the mature minipigs. The significant decrease in ConnD and star volume in the mature vertebra was consistent with the concurrent increase of platelike trabecular bone (p < 0.05). Overall, ConnD, star volume, % plate, and % boneLD provided a coherent picture of the architectural changes between the two age groups. Apparent modulus and maximum stress were determined experimentally on biopsy specimens from L2 vertebrae (n = 16). When apparent modulus was predicted using 3D MRmicroI data sets as input for finite element modeling (FEM), the results were similar to the experimentally determined apparent modulus (p = 0.12). Both methods were then used to compare the young and the mature animals; the experimental and predicted apparent modulus were significantly higher for the mature group (p = 0.003 and 0.012, respectively). The experimental maximum stress in the vertebra of the mature animals was twice as high as that for the young animals (p = 0.006). Bone quantity (BV/TV or bone mineral content [BMC]) alone could explain approximately 74-85% of the total variability in stress and modulus. The inclusion of either ConnD or % boneLD with BV/TV in a multiple regression analysis significantly improved the predictability of maximum stress, indicating that architecture makes additional contributions to compressive strength in normal minipig vertebra.

No-needle dialysis (NND): experience with the new carbon transcutaneous hemodialysis (HD) access device (CTAD).

A new carbon transcutaneous access device (CTAD) for hemodialysis id described the precludes the need for needle puncture. The device consists of a vitreous carbon access port attached to a PTFE graft. A disposable connector provides for movement of blood from the device into and out of the dialyzer. Twenty-one of the devices have been implanted in 18 patients. Overall 9 month patency rate is 64.3%, comparing favorably with conventional PTFE grafts. The incidence of infection (1 per .05 patient months) and thrombosis (28.6% at 9 months) similarly compare favorably with other forms of vascular access. The CTAD provides a unique opportunity by permitting hemodialysis without the pain or risk of needle punctures.

Cerebral CT findings in drug abuse: clinical and experimental observations.

Computed tomographic changes compatible with cerebral atrophy have been observed clinically and in experimental drug abuse animals. Most of the patients were thought to be polydrug users, but amphetamines and alcohol were two of the more commonly misused drugs. In the experimental animals, the effects of amphetamine, secobarbital, and marijuana were studied. Brain damage was present in the animals that received intravenous amphetamine.

Cerebral microvascular injury in experimental drug abuse.

An experimental drug abuse research project is reported, in which monkeys and rats were placed on various I.V. amphetamine (Desoxyn) and I.V. barbiturate (Seconal) regimes. The monkeys were studied by serial cerebral angiography. At the end of the study all animals were sacrificed for histological examination. I.V. methamphetamine produced relatively severe cerebral vascular injury and brain damage in most animals. At least part of the damage seemed to be the result of direct vascular injury, arterial and venous. The misuse of Seconal and Ritalin also appeared to be hazardous, but these studies are incomplete, and the degree of hazard has not been fully evaluated.