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Biomedical subjects

N J Stewart

Publications and source records attributed to N J Stewart.

29 records · Page 2Linked to original sources
PubMed1992

A theoretical model of the knee and ACL: theory and experimental verification.

A three-dimensional mathematical model of the human knee joint was developed to examine the role of single ligaments, such as an anterior cruciate ligament (ACL) graft in ACL reconstruction, on joint motion and tissue forces. The model is linear and valid for small motions about an equilibrium position. The knee joint is modeled as two rigid bodies (the femur and the tibia) interconnected by deformable structures, including the ACL or ACL graft, the cartilage layer, and the remainder of the knee tissues (modeled as a single element). The model was demonstrated for the equilibrium condition of the knee in extension with an anterior tibial force, causing anterior drawer and hyperextension. The knee stiffness matrix for this condition was measured for a human right knee in vitro. Predicted model response was compared with experimental observations. Qualitative agreement was found between model and experiment, validating the model and its assumptions. The model was then used to predict the change in graft and cartilage forces and joint motion of the knee due to an increment of load in the normal joint both after ACL removal and with various altered states simulating ACL reconstructions. Results illustrate the interdependence between loads in the ACL graft, other knee structures, and contact force. Stiffer grafts and smaller maximum unloaded length of the ligament lead to higher graft and contact forces. Changes in cartilage stiffness alter load sharing between ACL graft and other joint tissues.

Anterior Cruciate Ligament↗
PubMed1991

Quantitation of the alternate movement rate in normal and diabetic subjects.

Functional abnormalities of alternate movement rate (AMR) of finger and foot tapping were quantitated in 162 patients with diabetic neuropathy and 30 control subjects using a simple electronic device. The quantitative AMR (QAMR) averaged 29.5 +/- 3.0 for finger tapping and 20.4 +/- 3.7 for foot tapping in controls, and 27.5 +/- 4.8 (P less than 0.05) and 17.0 +/- 5.6 (P less than 0.005) for finger and foot, respectively, in diabetic patients. Fifty-one patients had abnormal QAMR in the finger and 79 in the foot. The QAMR values correlated with the results of nerve conduction studies of patients. Testing for abnormalities of AMR is a useful addition to the testing of dysfunction secondary to diabetic neuropathy. It provides quantitation of a common, subject-initiated, functional task more accurately than possible by clinical observation.

Adult↗
PubMed1991

Effects of laminin on functional reinnervation of target organs by regenerating axons.

Reinnervation of sweat glands, skeletal muscle and skin was studied in the mouse paw after section of the sciatic nerve and repair by entubulation with collagen conduits, with and without a coating of laminin. After operation, sweat glands activated by pilocarpine reappeared at 32 days and increased in number to 67% of control counts. Muscle action potentials (during sciatic nerve stimulation) were recorded from the interosseus muscle at 39 days. The potential amplitudes increased to 30% of controls. The first withdrawal response from pin prick to the paw was observed at about 34 days, the response score increasing to 66% of control. There were no significant differences at any test interval between the control group and the group with laminin added.

Animals↗
PubMed1984

Comparative study of three methods of resuscitation: closed-chest, open-chest manual, and direct mechanical ventricular assistance.

Presented are the results of a comparison study of three forms of circulatory support during ventricular fibrillation: closed-chest compression (CCC), open-chest manual compression (OCMC), and direct mechanical ventricular assistance (DMVA). DMVA is a method of circulatory support using a bell-shaped device that is affixed to the heart by apical suction and that alternately compresses and expands the ventricles. CCC produced a cardiac index (CI) of 780 mL/min/m2 (19% of control) with a mean arterial pressure (MAP) of 26 mm Hg (23% of control). Both forms of direct cardiac compression produced higher values. OCMC at 60 compressions per minute (CPM) produced a CI of 2,069 mL/min/m2 (52% of control) with an MAP of 50 mm Hg (45% of control). DMVA at the same rate produced a CI of 2,780 mL/min/m2 (70% of control) with an MAP of 72 mm Hg (65% of control). The values for DMVA at 60 CPM were significantly higher than for OCMC at 60 CPM (P less than .005 for CI, and P less than .0005 for MAP). Changing from standard CCC to DMVA at 90 CPM produced the greatest hemodynamic improvements: MAP increased by 250%, and CI increased by 340%. With DMVA at 90 CPM, the systolic pressure, stroke index, and CI were not statistically different from control, prearrest values.

Animals↗
PubMedDate not supplied

Surgical treatment of aseptic olecranon bursitis.

Most cases of aseptic olecranon bursitis respond to conservative treatment, yet some will develop a chronic bursitis with sufficient symptoms to warrant surgery. Over a 10-year period 21 cases of aseptic olecranon bursitis were treated surgically at our institution. Surveillance was a minimum of 2 years and averaged 5.2 years. The procedure provided complete and long-term relief in only 40% (two of five) of patients with rheumatoid arthritis, whereas 94% (15 of 16) of the patients without rheumatoid arthritis did well (p = 0.028, Fisher's Exact test). No patients had deep infection or draining wounds. Properly performed surgical treatment of aseptic olecranon bursitis appears to offer long-lasting symptomatic relief to patients without rheumatoid arthritis.

Adolescent↗
PubMedDate not supplied

Development and psychometric evaluation of the Environment-Behavior Interaction Code (EBIC).

BACKGROUND: Although the behavioral changes with progressive dementia are seen to increasingly depend on the environmental context until late stage disease, measurement has not reflected this interaction in real time to allow examination of antecedents to disruptive behavior. OBJECTIVES: To develop and evaluate the psychometric properties of the Environment-Behavior Interaction Code (EBIC) for use in dementia care research with either sequential or nonsequential analyses of behavioral data. METHOD: Development of the computer-based (sequential event format) EBIC provided an observational coding system to classify all behavior and environmental context in real time, so that the probability of social environmental antecedents to resident disruptive behavior could be estimated. A checklist (interval format) EBIC, based on the same behavioral taxonomy, was developed for clinical outcome research. A total of 158 elderly residents of dementia care units were purposively selected from three large long-term care facilities for the psychometric study components. RESULTS: Psychometric results indicated significant (p < 0.01) known-groups validity for the disruptive behavior construct, which was defined as a composite of aversive, harmful, and high intensity neutral behavior. Interrater agreement for the event format of the EBIC was estimated by average kappa (0.65) and percentage agreement (78%). For the interval format, the mean interrater kappa was 0.80 with 96% agreement. Stability of the event format using a 2-week retest interval ranged from r= .50 (positive behavior) to r = 0.73 (negative behavior, defined as aversive + harmful). On replication with a new sample, stability was higher for positive (r = 0.92) and negative (r = 0.95) components, and for composite scores of nondisruptive (positive + low intensity neutral; r = 0.65) and disruptive (r= 0.85) behavior. CONCLUSION: This research provided support for the reliability and validity of both event and interval EBIC formats. Measurement using the EBIC taxonomy has applicability to dementia care research questions that call for either sequential analysis of social interactions or nonsequential analysis of behavioral outcomes in intervention studies.

Aged↗
PubMedDate not supplied

Effect of anterior cruciate ligament graft tensioning direction, magnitude, and flexion angle on knee biomechanics.

The objective of this study was to determine the biomechanical effect of graft tensioning during reconstruction of the anterior cruciate ligament. We evaluated the magnitude of the tensioning force (22 or 67 N), the flexion angle at which the tension was applied (extension or 30 degrees of flexion), and the direction of application of the tensioning force (proximal, distal, or distal with a posterior force simultaneously applied to the tibia) on 10 fresh cadaveric knees. The anterior cruciate ligament was reconstructed using a bone-patellar tendon-bone graft. The graft was then temporarily fixed during the application of each of 12 combinations of tensioning variables listed above. After each fixation, graft force and joint motion were measured during anterior tibial loads. Tensioning direction and the flexion angle significantly affected graft force and joint motion, while the magnitude of the graft tensioning did not. Graft forces were greater when the tensioning was applied at 30 degrees of flexion. Compared with distal tensioning with and without posterior tibial force, graft forces with proximal tensioning were greater in extension and lower in flexion. The position of the tibia relative to the femur was posterior and externally rotated, compared with normal, for all combinations of tensioning variables in both unloaded and anterior load states.

Anterior Cruciate Ligament↗