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Biomedical subjects

L S Nichter

Publications and source records attributed to L S Nichter.

At least 19 recordsLinked to original sources
PubMed1995

The physiologic basis for nonconventional vascular perfusion.

It is traditionally thought that the exchange of oxygen occurs only at the capillary level, with both arterial inflow and venous outflow required. However, as early as 1970, studies have indicated that significant arteriolar and venular diffusion of O2 and CO2 occurs. The precapillary and postcapillary diffusion of oxygen and carbon dioxide and their potential regulation via the Bohr effect are key elements in understanding the success of nonconventional vascular perfusion (arterialized venous, total arterial, total venous), where the capillary circulation is bypassed. In retrograde "reverse-flow" island flaps, there is an anterograde blood flow through the capillary bed, with nonconventionally reversed flow within the arterial and venous systems, respectively. The reversal of venous flow is best explained as a combination of valvular insufficiency and the existence of vein-vein bypass channels via the venae comitantes.

Animals↗
PubMed1994

Evaluation of a temporary arteriovenous shunt to establish neovascularization in a musculocutaneous flap: an experimental study.

On the dorsum of adult Sprague-Dawley rats, 3 x 7 cm pedicle flaps were raised and a temporary arteriovenous shunt (AVS) from anastomosis of the tail artery and vein was placed beneath. Fourteen, 21 and 28 days later, the pedicle flaps were converted to island flaps leaving only the AVS attachment. The degree of subsequent flap viability was directly related to the amount of time before flap conversion. At 14, 21 and 28 day intervals, there was 33.4%, 73.5% and 98% flap viability, respectively. Long-term AVS patency was found not to be required for flap survival. Normal hair growth, quantity and quality, occurred in only the 28 day delay group. Microangiography and histologic examination revealed extensive neovascularization from both the AVS artery and vein extending into the muscle, subcutaneous tissue and skin layers of each island flap. In summary, neovascularization of a large random pattern musculocutaneous island flap is possible using a temporary arteriovenous shunt. Flap survival is directly related to the length of time between AVS placement and cutaneous pedicle division, although long-term AVS patency is not required for continued flap viability. Hair growth may directly reflect the degree of underlying neovascular maturation. This AVS neovascularization technique could be applied to create new donor sites for free tissue transfer.

Animals↗
PubMed1994

Debridement of bacterial and particulate-contaminated wounds.

Debridement of contaminated wounds is an essential component of uncomplicated wound healing. Efficient techniques should be capable of removing bacteria as well as foreign matter because of the well-known ability of foreign bodies to potentiate infection. We have compared the ability of current debridement techniques with the relatively new ultrasound debridement to clean wounds contaminated with bacteria and particulate matter. In part I, we prepared dorsal wounds on 15 Sprague-Dawley rats, and 20 mg of Montmorillonite clay soil fraction, a well-known infection-potentiating factor, was placed in each wound. Animals were randomly assigned to one of three treatment groups: ultrasound debridement, soaking, and irrigation. The amount of clay removed from each wound was measured. In part II, 48 Sprague-Dawley rats were given a standard wound and inoculated with a subinfective dose of Staphylococcus aureus bacteria and 10 mg of Montmorillonite clay particles. Each rat was randomly assigned to a debridement technique--soaking, scrubbing, high-pressure irrigation, and ultrasound--and was examined after 7 days for inflammatory responses. Results of part I demonstrated that ultrasound debridement and irrigation remove statistically equal amounts of clay (p < 0.05). In part II, we found that high-pressure irrigation and ultrasound debridement effectively treat contaminated wounds (gross infection, p < 0.05; wound induration, p < 0.0001; bacteria counts, p < 0.002). This study presents ultrasound debridement as effective treatment of contaminated wounds.

Animals↗
PubMed1994

Modulation of collagen synthesis by transforming growth factor-beta in keloid and hypertrophic scar fibroblasts.

Keloid and hypertrophic scars are fibrous growths characterized by overabundant collagen deposition. We examined the effect of transforming growth factor-beta (TGF-beta), a known stimulant for the production of connective tissue matrices, on the rate of collagen synthesis in keloid fibroblasts (KFs), hypertrophic scar fibroblasts (HSFs), and normal skin fibroblasts (NSFs). Fibroblasts were cultured in three-dimensional fibrin-gel matrices in the presence or absence of TGF-beta (5 ng/ml) or anti-TGF-beta neutralizing antibody (50 micrograms/ml). Secreted collagen levels, labeled with 3H-proline, were measured after 48 hours. KFs produced up to 12 times more collagen than NSFs, and up to 4 times more than HSFs. Although KFs increased their rate of collagen production by up to 2.7 times in response to TGF-beta, HSFs and NSFs did not (p = 0.065). Anti-TGF-beta antibody reduced the rate of collagen synthesis of KFs by 40% (p = 0.003), although it did not suppress collagen production in HSFs (p = 0.06) and NSFs (p = 0.75). We conclude that although KFs and HSFs are similar in that they both overproduce collagen, they are different in that only KFs display a marked sensitivity to TGF-beta, which is abundant during the proliferative phase of wound healing.

Antibodies↗
PubMed1994

Comparison of various delivery systems for demineralized bone matrix in a rat cranial defect model.

Demineralized bone matrix (DBM) has been successfully used as a substitute for bone grafting. Autogenous bone grafts may cause site morbidity and undergo significant resorption. DBM may overcome these problems, but it has no mechanical stability until bone formation has occurred. We tested various alloplastic implants (i.e., Surgicel, polydioxanone [PDS], porous polyethylene [Medpor], and Gelfoam) in combination with DBM and compared it with DBM alone in a 9 x 9 mm rat cranial defect model. Histological and biomechanical measurements were performed at postoperative month 2. Among the study groups, Gelfoam/DBM inhibited bone formation to varying degrees and was the only group that displayed an inflammatory response. Mechanical pushout tests using a servohydraulic testing frame were conducted. The Medpor/DBM implant displayed the strongest support at 2 months; maximum load was 95% of intact skull. Surgicel/DBM and DBM alone were comparable; maximum load was 66% of intact skull. Gelfoam/DBM and PDS/DBM displayed the weakest support (48% of intact skull). We conclude that, after 2 months of implantation, alloplastic/DBM composites provide osseous structural integration. Gelfoam/DBM is not an effective delivery system for DBM in our model.

Analysis of Variance↗
PubMed1992

Restoration of venous outflow by simultaneous creation of an arteriovenous shunt and pedicle flap using a rat model of foot replantation.

Replantation of amputated rat feet utilizing an efferent arteriovenous shunt constructed between the distal posterior tibial artery and the proximal posterior tibial vein, in the absence of all other venous drainage, provides an alternative pathway to the normal venous drainage in a replanted rat foot. However, this substitute venous drainage was insufficient to prevent progressive ischemia and necrosis of some or all of a replanted rat foot. When a cutaneous pedicle flap supplemented the arteriovenous shunt, venous drainage was much improved, tissue hypoxia and edema began to subside on the third day, severe tissue necrosis was prevented, and seven of eight feet replanted by this technique survived. These observations may be useful in replantation in humans when veins in the amputated part are too small to be used or so damaged that they cannot be repaired or reconstructed by a vein graft, but arteries can still provide a means of returning blood from the amputated part. Constructing an alternative pathway to the normal venous drainage pattern may allow severely damaged parts to survive after replantation.

Anastomosis, Surgical↗
PubMed1992

The biomechanical efficacy of an oscillating K-wire driver.

A new oscillating drill, designed for insertional ease and safety, was biomechanically tested using an MTS 812 servohydraulic material testing machine (Instrom). Holding strength and drilling force were compared against a traditional rotary drill using rabbit tibias to approximate the diameter and cortical thickness of human metacarpals. Three differently sized (0.028-, 0.045-, and 0.062-in. diameter) K-wires were evaluated for each drill. Mean peak axial load (drilling force) was significantly different for each wire driver type in each of the three sized K-wires (p < or = 0.01). The oscillating drill used an average of 3 N less force to penetrate either cortex. Mean peak pull-out force (holding strength) was higher for the oscillating drill, but the difference was not significant (p > or = 0.5). This study indicated that the oscillating drill required less force for insertion and had a similar holding strength as the rotary drill. In addition, our drill has been shown to be less damaging to surrounding soft tissues. This new type of drill is likely to be advantageous in the fields of hand, microsurgery, orthopedic, and plastic surgery, where bone fixation is often near vital neurovascular structures.

Animals↗
PubMed1992

Demineralized bone matrix polydioxanone composite as a substitute for bone graft: a comparative study in rats.

Demineralized bone matrix (DBM) has been successfully used as a substitute for bone grafting. Autogenous bone grafts (ABG) may cause donor site morbidity and undergo significant resorption. DBM may overcome these problems but is mechanically unstable when originally placed. We explored using a slowly resorbable template, polydioxanone (PDS), in combination with DBM and compared it to ABG in a rat 9 x 9 mm cranial defect model. After both 1 and 3 months, histologically and biochemically well-formed bone was present in ABG/PDS and DBM/PDS-treated defects, but not in control defects (PDS alone). Mechanical push-out tests using a servohydraulic testing frame were conducted. Maximum load before failure of DBM/PDS increased from 65% at 1 month to 100% of that of intact skull at 3 months. In contrast, ABG/PDS was 50% as strong as DBM/PDS and not significantly stronger than PDS alone. ABG/DBM did not significantly increase in strength from 1 to 3 months. We conclude that DBM/PDS is better than ABG/PDS in treating cranial defects in the rat model, and that an absorbable osteoinductive bone substitute with superior mechanical advantage is possible without the disadvantages of ABG.

Animals↗
PubMed1991

Leech therapy: when once is not enough.

Venous congestion is a constant threat in the survival of free flaps, pedicled flaps, tissue replantations and traumatized tissue. Leech therapy has proved effective in salvaging much of these compromised tissues. To be effective, leeches must be both readily available and hungry, requirements not always easily met. Our investigation seeks to establish a means to return sated leeches to their previous unfed, hungry state for reuse. Sated leeches were purged of their blood meals by placement in 3% hypertonic saline or by gentle finger pressure, then exposed to serotonin 0 microM (control), 10 microM, 30 microM or 90 microM for 20 min. Subsequent rebiting/refeeding was observed and analysed. Leeches bathed in serotonin rebit or reattached at nearly four times the rate of unexposed leeches; 30% vs 8% respectively. Biting, however, is not refeeding. Overall, 41 leeches were treated with serotonin with four (10%) refeeding. Those that refed consumed a significantly smaller blood meal than the initial feeding; 50% +/- 47% SD vs 348% +/- 143% SD of original body weight. None of the control group refed. As a method for routinely reusing leeches, serotonin bathing cannot be recommended. In the immediate postoperative period with the sudden emergence of venous congestion requiring leech therapy, but with an inadequate number available, this 20% [corrected] refeed rate after 10 microM serotonin exposure could potentially determine the success or failure of the flap/replantation until fresh leeches are made available.

Animals↗
PubMed1991

Expanding the limits of composite grafting: a case report of successful nose replantation assisted by hyperbaric oxygen therapy.

A successful nose replantation assisted by hyperbaric oxygen therapy is presented, with a brief discussion of the possible mechanisms and a brief literature review of the use of hyperbaric oxygen in tissue preservation and replantation. Although it is not certain that the hyperbaric oxygenation ensured the survival of the replanted nose in this 2-year-old girl, there was documented change in graft appearance during the initial hyperbaric oxygen treatment. A 1-month, 1-year, and 2-year follow-up is included.

Child, Preschool↗
PubMed1989

Efficacy of debridement and primary closure of contaminated wounds: a comparison of methods.

Proper management of highly contaminated traumatic wounds frequently requires delayed primary closure of healing by secondary intention to prevent subsequent infection. This animal study compares the efficacy of various wound debridement methodologies to prevent infection following primary closure of treated contaminated wounds. Forty-four Sprague-Dawley rats with uniform, paravertebral incisions were studied. Each wound was inoculated with a standard amount of Staphylococcus aureus bacteria and allowed to remain open for two hours. Each wound was treated before wound closure by one of four debridement methods: (1) surgical scrubbing, (2) high-pressure irrigation, (3) ultrasonication, or (4) soaking. The control animals' wounds were closed without debridement. At 7 days, each animal was evaluated for the presence of gross infection and wound induration. Ultrasound, with a 25% incidence of gross infection, compared with irrigation (75%), scrubbing (82%), and soaking (89%) provided significant protection from subsequent abscess formation. The control group uniformly developed infection (100%). The average amount of induration after ultrasonication (1.35 +/- 0.56 cm) was also significantly less than irrigation (2.07 +/- 0.75 cm), scrubbing (1.95 +/- 0.34 cm), and soaking (1.73 +/- 0.22 cm). Our data demonstrate that ultrasonic wound debridement has exciting potential as a new debridement technique for contaminated traumatic wounds.

Animals↗
PubMed1989

An unusual complication of an open-head injury: coccidioidal meningitis.

A case of coccidioidal meningitis following an open-head injury is presented. A 6-year-old boy was ejected from a motor vehicle as it was driven over a cliff, resulting in a severe open-skull fracture with grossly contaminated wounds. The accident occurred in an area in which coccidioidomycosis is endemic, and the causative agent, Coccidioides immitis, is found in high concentration in the soil. In addition to fracture reduction, the child received a course of intrathecal and intravenous amphotericin and achieved a satisfactory clinical response.

Amphotericin B↗
PubMed1989

Intralesional corticosteroid therapy for infantile hemangiomas.

Intralesional corticosteroid injections were performed in 31 hemangiomas in 30 infants aged 1 to 10 months at first injection. One to five injections were given, spaced 6 weeks apart. Lesions were located throughout the head and neck region, except one that was on the buttock. A mixture of betamethasone acetate and triamcinolone acetonide was used. Four lesions (13 percent) virtually disappeared, ten (32 percent) showed greater than 50 percent reduction in volume, ten (32 percent) showed definite but less than 50 percent reduction in volume, and seven (23 percent) showed little or no decrease in size. None showed further growth. All injections were performed without anesthesia, and there were not significant complications. We conclude that intralesional corticosteroid injections are safe and effective in properly selected infants with hemangiomas.

Betamethasone↗
PubMed1988

Cost of treating advanced leg ischemia. Bypass graft vs primary amputation.

We compared the hospital costs of 94 patients undergoing femoropopliteal bypass grafts with those of 53 patients undergoing primary amputation. The total cost of uncomplicated bypass surgery averaged +20,300, compared with +14,000 for uncomplicated below-knee amputation. However, including the cost of prosthesis and rehabilitation, the total cost of primary amputation was +20,400, equivalent to that of the bypass operation. Complications requiring revision of a bypass graft increased hospitalization by 4.5 days with the total cost rising to +28,700; complications that ended with major amputation added 15 hospitalization days and had an average cost of +42,200. In contrast, complicated below-knee amputation cost +40,600 and added 12.5 hospitalization days. There is therefore no cost-benefit in primary amputation when compared with arterial reconstruction, and cost should not be used to deny a patient the opportunity for limb salvage.

Amputation, Surgical↗
PubMed1988

Improving micrograft patency.

To help clarify many of the controversial issues affecting early microvascular graft patency, a series of experiments was performed comparing the relative importance of graft material used alone and in conjunction with antiplatelet agents. Using a rat carotid model employing 1 cm micrografts with 1 mm luminal diameter, this study demonstrated that 1) untreated 1 mm polytetrafluoroethylene (PTFE) and human umbilical vein (HUV) micrografts have unacceptably low patency rates; 2) treatment with the antiplatelet agents indomethacin, ibuprofen, and aspirin significantly improved micrograft patency; 3) differences in patency among the three agents were not significant; and 4) PTFE had higher patency rates than HUV, although this difference did not achieve significance.

Animals↗
PubMed1988

Ultrasonic wound debridement.

Current management of hand injuries includes debridement by abrasive scrubbing with anti-bacterial detergents, surgical excision, or pressure irrigation. A rat model with a contaminated laceration was used to study the efficacy of ultrasonic debridement to diminish bacterial counts and particulate matter in open wounds. Ultrasonic debridement of hand wounds has several advantages over the current methods of wound debridement. These include a technically simple procedure that is effective in the removal of particulate matter and the reduction of bacterial counts (p less than 0.005). In addition there was no blood loss and no detectable damage of viable tissues as evaluated by electron microscopy. This technique may prove to be a significant advance in the early management of hand wounds.

Animals↗