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Biomedical subjects

S I Reger

Publications and source records attributed to S I Reger.

At least 19 recordsLinked to original sources
PubMed2001

Validation test for climate control on air-loss supports.

OBJECTIVE: To develop a simple, reproducible validation test protocol for classification of air-loss support systems. DESIGN: Simultaneous experimental measurement of moisture loss and temperature reduction at the air-loss support surface-human body equivalent interface from a sweating human skin analogue. SETTING: A hospital department of physical medicine and rehabilitation. OTHER PARTICIPANTS: These 3 manufacturers contributed 14 support surfaces. INTERVENTIONS: Test support surfaces and a standard foam mattress were placed on a hospital bed. Water was circulated to a loading gauge, placed on a dry moisture reservoir, and connected to a water bath to keep the interface at 37 degrees +/- 0.5 degrees C. The loading gauge and support surface was adjusted 23cm below the water bath level and the air flow through the interface initiated. After the dry moisture reservoir came to temperature equilibrium for 30 minutes, it was replaced with a wet one that was saturated with 36g of saline. The temperature change and evaporation rate were recorded throughout a 90-minute test period. MAIN OUTCOME MEASURES: Temperature of support surface interface and evaporation rate. RESULTS: Clustered data from temperature reduction and standardized rate of moisture loss yielded 3 groups of support surfaces in categories of no air loss (control), low air loss (LAL), and high air loss. The mean values of the characteristic temperature reduction and rate of moisture loss differed significantly between the groups. By multiple comparisons with Bonferroni's adjustment, the group means differed significantly for average temperature reduction (p <.017) and for standardized rate of moisture loss (p =.0001). The measured temperature change at any instant of time reflected the effect of evaporation and the opposing effect of thermal conductivity. CONCLUSION: Measurements of support interface climate change allowed for selective grouping of LAL surfaces according to rate of moisture evaporation and the resulting temperature reduction. Neither temperature change nor evaporation rate alone was sufficient to determine the microclimate characteristics of the support surface. Combined, these characteristics can effectively describe the performance of any LAL support system and may be used to define standards of performance.

Air Conditioning↗
PubMed2000

Electrical stimulation for pressure sore prevention and wound healing.

This paper reviews applications of therapeutic electrical stimulation (ES) specific to wound healing and pressure sore prevention. The application of ES for wound healing has been found to increase the rate of healing by more than 50%. Furthermore, the total number of wounds healed is also increased. However, optimal delivery techniques for ES therapy have not been established to date. A study of stimulation current effects on wound healing in a pig model has shown that direct current (DC) stimulation is most effective in wound area reduction and alternating current (AC) stimulation for wound volume reduction at current densities of 127 microA/cm2 and 1,125 microA/cm2, respectively. Preliminary studies have been carried out at two research centers to assess the role of ES in pressure sore prevention. Surface stimulation studies have shown that ES can produce positive short-term changes in tissue health variables such as regional blood flow and pressure distribution. The use of an implanted stimulation system consisting of intramuscular electrodes with percutaneous leads has been found to produce additional long-term changes. Specifically, gluteal muscle thickness increased by 50% with regular long-term ES application concurrent with a 20% decrease in regional interface pressures and increased tissue oxygen levels. These findings indicate that an implantable ES system may have great potential for pressure sore prevention, particularly for individuals who lack sensation or who are physically unable to perform regular independent pressure relief.

Aged↗
PubMed1999

Experimental wound healing with electrical stimulation.

The effect of alternating current (AC) and direct current (DC) stimulation was studied on experimental pressure ulcer healing in a new monoplegic pig model. The study was conducted in 30 healthy young Hanford minipigs. The rate of wound healing, histology, vascularization, collagen formation, microbiology, perfusion, and the mechanical strength of the healed wounds were studied. Normal pigskin was compared to denervated control and denervated AC and DC stimulated healed skin. Hind limb denervation was by right unilateral extradural rhizotomies from the L2 to S1 nerve roots. Reproducible uniformly controlled Stage III or higher tissue ulcers were created. When compared to the control wounds, both the AC and DC stimulated wounds showed reduced healing time and increased perfusion in the early phases of healing. DC stimulation reduced the wound area more rapidly than AC, but AC stimulation reduced the wound volume more rapidly than DC. The electrical stimulation did not reduce the strength of the healing wounds below those of the nonstimulated controls. The applied current appears to orient new collagen formation even in the absence of neural influences.

Animals↗
PubMed1999

A low-cost, portable system for the assessment of the postural response of wheelchair users to perturbations.

Maintaining seated postural stability presents a serious challenge to wheelchair users in vehicles, even during normal driving conditions. The purpose of this research was to develop a system for the study of seated postural control in response to perturbations similar to those that might be experienced during vehicle turning and braking. A servo-controlled tilt platform was constructed to provide a low-cost, small, and easily transportable device for generating precise and repeatable perturbations. Tilt platform operation was examined for accuracy and reproducibility of a desired perturbation. Repeatability was high with a mean signal-to-noise ratio (SNR) of 45.4 for a given perturbation measured across 11 subjects. An initial comparison of stability results obtained on the tilt platform and in a vehicle showed a correspondence, although differences were apparent. The tilt platform has been used successfully to assess balance in spinal cord-injured subjects and to test wheelchair securement systems.

Acceleration↗
PubMed1995

Evaluation of a pressure sore model using monoplegic pigs.

This study evaluated a newly developed swine monoplegic pressure sore model by testing the uniformity of the initial wound size. The natural healing also was evaluated. Nine minipigs were used. The hindlimb was denervated by transecting the unilateral nerve roots L1 through S2. At 5 to 14 days, 800 mmHg of pressure was applied to the denervated skin over the trochanteric area with a 3-cm-diameter disk compressing the skin and subcutaneous tissue against the underlying bone for 48 hours. The wound was then debrided of devascularized tissue. Wound surface areas were calculated from photographs. Wound volumes were obtained by measuring the volume of saline needed to fill the wound defect. Full-thickness sores of uniform size developed in all pigs without mortality or complications. Wound surface area and volume increased initially, peaked, and then decreased in an exponential fashion. This model provides a new tool for direct comparison of pressure sore treatment modalities for short- and long-term studies.

Animals↗
PubMed1987

Enhanced stabilization of porous-coated metal implants with tricalcium phosphate granules.

Tricalcium phosphate (TCP) granules were tested as a possible alternative to bone graft as an interposition material to stabilize porous-coated metal implants in overreamed femoral intramedullary canals in dogs in vitro and in vivo. TCP granules provided as much stability as bone graft or a press fit in the in vitro testing. At six weeks in the in vivo system, the TCP stabilized specimens had an increased average resistance to tensile testing, but the increase was not significant. At six months, however, TCP-stabilized specimens exhibited a significant increase in resistance to pull-out force (p less than 0.05). Histologic examination revealed incorporation of the TCP granules in bone bridging from the endosteal cortex to the porous surfaces. TCP granules might be useful as a synthetic interposition material for stabilization of porous-coated metal components. TCP granules exhibited osteoconductive properties.

Animals↗
PubMed1985

The effect of core decompression on femoral head blood flow in steroid-induced avascular necrosis of the femoral head.

Previous reports from this and other laboratories have shown that the histological changes in the femoral head that are associated with steroid treatment are consistent with avascular necrosis of the femoral head. In this experiment, we studied the effect of core decompression on femoral head blood flow in steroid-treated rabbits using the microsphere technique. The results showed that there was a gradual decline of femoral head blood flow in animals that received weekly injections of methylprednisolone without core decompression. The femoral head blood flow in animals that underwent core decompression after six weeks of steroid treatment showed a gradual normalization within four weeks after core decompression.

Adrenal Cortex Hormones↗
PubMed1984

Safety of anterior cement fixation in the cervical spine: in vivo study of dog spine.

There is increased use of methylmethacrylate in the treatment of neoplastic lesions of the spine. The advantage of this treatment is immediate stabilization, thus avoiding prolonged immobilization. In vivo study using a dog model showed that anterior fixation with cement, with or without Gelfoam as insulation material, produced no spinal cord injury.

Animals↗
PubMed1984

Reconstruction of the cervical spine following anterior vertebral body resection: a mechanical analysis of a canine experimental model.

In some quadriplegic patients whose acute spinal injury consists of a vertebral body fracture with bony retropulsion anteriorly and ligamentous damage posteriorly, it is appropriate to perform a decompression of the injured spinal cord by excision of the fractured body. Reconstruction of such a spine to achieve immediate and ultimate stability can be quite difficult. This is a report of mechanical testing using a canine in vitro experimental model to simulate different general types of reconstruction systems applicable to the spine destabilized as above. The results explain some of the previously noted failures of the traditional anterior strut grafting procedures. In addition, one of the reconstruction systems tested (anterior and posterior tension bands compressing an anterior strut graft into place) appeared to have sufficient immediate stability to eliminate the need for a halo-vest in the postoperative period. If such a reconstruction system were to prove clinically applicable, it would be quite beneficial to the quadriplegic patient in his rehabilitation.

Animals↗
PubMed1984

The use of methylmethacrylate cement as an instantaneous fusion mass in posterior cervical fusions: a canine in vivo experimental model.

The authors previously predicted the failure of posterior cervical fusions utilizing methylmethacrylate cement as an instantaneous "fusion" mass, based on research using an in vitro canine experimental model. This report describes the results of in vivo canine studies on the same subject. Three groups of dogs had application of a posterior C4-C5 20-gauge cerclage wire and autologous iliac crest bone graft; application of a posterior C4-C5 20-gauge cerclage wire and methylmethacrylate cement; or application of a C4-C5 20-gauge cerclage wire only. This group represented the control group. The dogs were allowed to live for 3 months postoperatively, at which time they were killed and their spine fusions studied radiologically, mechanically, and histologically. Five of the bone fusions united solidly radiologically. Their flexion stability was statistically superior to the others. Histologic studies confirmed solid union of the fusion mass to the underlying bone. Four of the six methylmethacrylate fusions demonstrated cerclage wire fracture and methacrylate-bone separation by the second postoperative month. At the time the dogs were killed, their flexion stability was statistically inferior to the bone fusions and tended to be inferior to the controls as well. Histologically, fibrous tissue was noted to have grown between the methacrylate "fusion" mass and the underlying bone. This work provides a mechanical explanation for the well-known success of the traditional bony fusion. It further supports our original prediction regarding the failure of methylmethacrylate "fusions."

Animals↗
PubMed1984

Comparative strength of anterior spinal fixation with bone graft or polymethylmethacrylate. Experimental operations and observations on dogs.

In 23 dogs, polymethylmethacrylate (PMMA) was safely implanted in the region of the spinal cord. The dogs were treated by bone or cement fixation after anterior excision of a single cervical vertebral body. Fixation was compared at 0-18 weeks, with control values obtained from 11 dogs. Anterior cement fixation did not displace after 18 weeks. The anterior bone graft appeared to achieve adequate fixation strength around six weeks. The strength of the bone-graft fixation increased, while that of cement fixation decreased somewhat with time. At all time intervals, the ratio of energy absorption to structural failure was somewhat higher with bone graft than with PMMA.

Animals↗
PubMed1984

Enhancement of bone ingrowth by the use of bone matrix as a biologic cement.

In an effort to enhance bone growth into implants with porous coatings, a decalcified bone cement was used to secure fixation of the implants in canine femora. Rods with porous coatings were inserted bilaterally into the femoral medullary canals of nine dogs of varying sizes. A demineralized bone paste was used to enhance the fixation in one side, with the contralateral limb serving as a control. Pull-out testing and gross and roentgenographic examination of the specimens confirmed that the demineralized bone matrix enhanced fixation.

Animals↗
PubMed1983

Femoral head blood flow in long-term steroid therapy: study of rabbit model.

Using a rabbit model, previous studies showed steroid-induced hyperlipidemia with subsequent fatty embolization of the subchondral arteries and hypertrophy of the marrow fat cells, followed by elevation of femoral head pressure from the normal level of 25 cm to nearly 60 cm H2O after eight weeks of treatment. This has led us to believe that pressure changes lead to decreased blood flow in the femoral head. In our study of 22 New Zealand white adult rabbits, weighing an average of 4.0 kg, 14 received a weekly dose of 12.45 mg of methylprednisolone (Depo-Medrol), and eight served as control. Femoral head blood flow was established using the radioactive microsphere technique. Control and cortisone-treated rabbits had femoral head blood flow measured 6, 8 and 10 weeks after treatment. The average blood flow in the control femoral heads averaged 0.2039 +/- 0.076 ml/min/gm, with no difference in the left side and the right side. In the treated group, the average blood flow at ten weeks was 0.162 +/- 0.039 ml/min/gm on the right and 0.164 +/- 0.037 ml/min/gm on the left, which was significantly different. This is parallel to unpredictable clinical findings in human beings.

Animals↗
PubMed1983

Comparative strengths of various anterior cement fixations of the cervical spine.

In vivo study, using cadaveric dog cervical spine, was performed in which the middle segment of the vertebral body was removed producing anterior instability. Eleven various methods of stabilization utilizing polymethylmethacrylate and other fixation devices were employed, and their static strength in hyperextension was tested and compared. A portion of the same dog's cervical spine in each case was used as a control. The results indicate that all fixation methods failed to regain the normal structural strength in extension. Cement with wire or chain methods of fixation were superior to other methods in this study. Fixation rigidity approaching rigidity of the normal spine appeared to be a significant factor determining the strength of the reconstructed cervical spine. Combined anterior and posterior fixation did not provide further strength, although it did increase the rigidity of the fixation.

Animals↗
PubMed1981

Vacuum as a grasping force.

Three lifting systems for small objects were designed using vacuum as an artificial prehensile force. The first system for persons with C4-5 quadriplegia employed a vacuum pump, pneumatic tubing and a customized wrist-hand orthosis. For more severely disabled persons with C4 quadriplegia, the authors adapted this vacuum pick-up system by substituting a lightweight, tubular aluminum mouthstick in place of the orthosis as the primary grasping utensil. A 3rd variation, the suction mouthstick, lifted small objects and turned pages by using only the suction power generated by the person's own inspiratory force without additional mechanical amplification.

Hand↗
PubMed1981

Cortisone-induced intrafemoral head pressure change and its response to a drilling decompression method.

Intramedullary head pressure changes were studied in a group of cortisone-treated New Zealand white rabbits. In addition to femoral head pressure measurements, serum cholesterol levels were followed serially and pathologic specimens from cortisone-treated femoral heads were obtained. Surgical decompression by a drilling method was performed and pressures were remeasured at four weeks following decompression. Persistent increases in cholesterol levels and in intrafemoral head pressures were noted, particularly from six to eight weeks after initiation of steroid treatment. Cholesterol levels were elevated to four times control values and femoral head pressures averaged 2 1/2 times the control values (60 cm of water vs 24.6 +/- 5.5 cm of water). Surgical decompression by drilling effectively reduced the once elevated pressures to control values. A relationship between increased fat cell size, increased intramedullary pressure and decreased femoral head blood flow in steroid-treated rabbits is postulated. The applicability of these data to humans with steroid-induced ischemic necrosis of the femoral head has yet to be demonstrated.

Animals↗