Craig R. Hassler

Quantification of bone stresses during remodeling

Abstract An experiment to quantitate the effect of compressive stress upon bone remodeling rate was devised. Remodeling herein is described as the renewal process of bone separate from initial formation. A finite element mathematical model of the rabbit calvarium was devised. Actual rabbit calvaria were stressed utilizing a load cell monitored lever type loading device. They were periodically stained with fluorescing bone seeking dyes. Upon necropsy, histologic sections were prepared and the growth rate at known locations in the stressed area was measured by planimetry. Observed bone formation was subdivided into lamellar and fibrous. Lamellar bone formation (remodeling) rate remained above control levels until stresses of approximately 360 psi were reached; above this level remodeling rate fell to or below control. Fibrous bone exhibited higher formation rates which decreased with increasing stress but remained above control. At stresses approaching 1000 psi the technique could not measure formation rates due to the confused fibrous bone formation.

Mathematical and experimental studies on the mechanics of plated transverse fractures

Abstract A combined experimental and mathematical stress analysis approach to study the mechanics of a plated transverse fracture is described. Experimental results were obtained by placing strain gages on an equine third metacarpal and a bone plate. Two mathematical models for the mechanics of a bone and bone plate are presented. One is based on simple beam bending theory. The other is based on a more refined finite element representation for the deformations. Comparisons of experimental data and predicted results from the simple model are given and discussed. These comparisons provide a degree of confidence in the ability of a theoretical model to represent the actual deformations. The comparisons also show limitations of the simple beam model and the need for a more refined model such as a finite element representation. The resulting stress protection of the bone due to the bone plate and the percentage of load transferred through the plate are presented for a uniform loading condition. The advantages of a combined experimental and theoretical mechanics study are pointed out.

Identification and evaluation of noninvasive blood pressure measuring techniques

Abstract The applicability of noninvasive blood pressure devices to the rhesus monkey and beagle dog during toxicological research protocols was investigated. An extensive literature survey of this subject was undertaken. Newer developments in this field and blood pressure measurement in the two species of interest were noted. A survey of all known manufacturers of noninvasive blood pressure measurement equipment was made. From this list sample devices were selected for animal studies. An acute study was performed on both dogs and monkeys to ascertain the accuracy of the selected devices. The Physiometrics USM-105 device was found to be the most accurate for measuring systolic and diastolic pressures in both dogs and monkeys. In chronic studies, monkeys and dogs were monitored for 3 weeks. The Physiometrics device was found to be the most satisfactory. The Arteriosonde 1010 and Infrasonde devices were found to be acceptable but not as accurate. In dogs, at least 50% of the animals could be trained within 1 week to tolerate blood pressure measurement and give reasonable readings; 75% could be trained in 2 weeks. In monkeys, approximately 60% of the animals would yield reasonable blood pressure readings, and the conditioning and training periods appeared much less critical.

EXPERIMENTAL STUDY OF PEDESTRIAN INJURY MINIMIZATION THROUGH VEHICLE DESIGN

The overall objective of this experimental investigation of pedestrian/vehicle impacts was to conduct representative impacts of unembalmed cadavers in order to (1) pioneer the establishment of impact tolerance levels for the pelvis and legs of a standing pedestrian and (2) explore the ability of a few selected geometry and compliance modifications to the impacting vehicle to increase the impact velocities that can be tolerated. A series of 15 experimental impacts were conducted which covered a speed range from 10 to 30 mph. Dynamic data obtained included high-speed films and time histories of (1) bumper and hood edge forces, (2) horizontal and vertical ground reaction forces, and (3) pelvic acceleration. Three of the key results are that (1) injuries to the lower body of an adult pedestrian are strongly dependent upon vehicle design, (2) the pedestrian leg injury mechanism is a complex dynamic event influenced significantly by both the bumper force and the ground friction force, and (3) a threshold tolerance value of pelvic acceleration appears to exist below which pelvic injuries do not occur. Language: en

Measurements of healing at an osteotomy in a rabbit calvarium: The influence of applied compressive stress on collagen synthesis and calcification☆

Abstract Experimental data which establish a correlation between applied compressive stress in a rabbit calvarium and calcium formation, collagen synthesis, and histologic interpretation are presented. Estimates of collagen synthesis and calcium formation are obtained from measuring 45Ca and 3H proline uptakes. Stress distributions are obtained using a finite element analysis and photoelastic techniques. For the cases presented here, maximum 45Ca and 3H proline uptakes, as well as maximal histologic healing indices, are found at stress levels in the 10–30 psi range.

An Orally Administered Microcapsule System for Treating Chronic Renal Failure Patients

Ingestible adsorbents for the removal of uremic metabolites are being investigated as adjunctive therapy in the treatment of chronic uremia. In particular, a microcapsule product containing urease and zirconium phosphate (UZP) has been investigated for removing urea. A dog model, simulating chronic uremia, was developed to investigate: (1) the concentration of various nitrogenous metabolites (urea, creatinine, and uric acid) in the GI tract, (2) flux rates of H2O and various nitrogenous metabolites in the GI tract, and (3) the efficacy of the microcapsule product. The results of these perfusion studies suggest that urea and creatinine can be removed from the GI tract via ingestible adsorbents. In addition, the model may be useful in investigating suspect uremic toxins, e.g., guanidinosuccinic acid (GSA). The reduction of blood urea nitrogen levels in the dog model when the animal was fed the microcapsule product was limited by the capacity of the zirconium phosphate to bind ammonium ion. Preliminary clinical studies with the microcapsule product indicate that it may be of potential adjunctive therapy in patients suffering from chronic renal failure.

Potential Delivery of Contraceptive Agents to the Female Reproductive Tract

Vaginal contraceptives have played a positive role in fertility planning for years. Prior to the introduction of intrauterine devices (IUDs) and oral contraceptives (OCs), jellies, creams, and suppositories were used, sometimes in conjunction with the diaphragm or condom, but usually they served as the sole barrier.1 The higher failure rates of the vaginal contraceptives in relation to other contraceptive devices (IUDs and OCs) were believed to be due primarily to the inconsistent use of the method rather than to failure of the method during use.

MMB4 DMS: cardiovascular and pulmonary effects on dogs and neurobehavioral effects on rats.

The objectives of these studies were to determine the cardiopulmonary effects of a single intramuscular administration of 1,1′-methylenebis[4-[(hydroxyimino)methyl]-pyridinium] dimethanesulfonate (MMB4 DMS) on dogs and on the central nervous system in rats. On days 1, 8, 15, and 22, male and female dogs received either vehicle (water for injection/0.5% benzyl alcohol/methane sulfonic acid) or MMB4 DMS (20, 50, or 100 mg/kg). Pulmonary function was evaluated for the first 5 hours after concurrent dosing with cardiovascular monitoring; then cardiovascular monitoring continued for 72 hours after dosing. Rats were dosed once by intramuscular injection with vehicle (water for injection/0.5% benzyl alcohol/methane sulfonic acid) or MMB4 DMS (60, 170, or 340 mg/kg). In dogs, 100 mg/kg MMB4 DMS resulted in increased blood pressure, slightly increased heart rate, slightly prolonged corrected QT, and moderately increased respiratory rate. There were no toxicological effects of MMB4 DMS on neurobehavioral function in rats administered up to 340 mg/kg MMB4 DMS.

Evaluation of a non-invasive telemetry method for determining blood pressure in dogs

POSTER NUMBER 164 DISCUSSION