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Biomedical subjects

F Behrens

Publications and source records attributed to F Behrens.

At least 37 records · Page 2Linked to original sources
PubMed1989

Open-loop and closed-loop optokinetic nystagmus in squirrel monkeys (Saimiri sciureus) and in man.

Horizontal optokinetic nystagmus (OKN) was measured in 3 normal Squirrel monkeys by means of the electromagnetic search coil technique. Binocular and monocular stimulation of each eye to the left and right by moving vertical stripe patterns of 2.37 or 15 degree period were applied at angular velocities of 0.5 to 400 deg/s. After measurement of horizontal OKN under normal conditions, open-loop OKN gain was determined by monocular stimulation of an eyeball immobilized by means of retrobulbar injections of 11 units botulinum toxin (BoTx type A) and compared with the pre-injection data or with monocular stimulation of the other eye, which remained mobile. In normal Squirrel monkeys gain of optokinetic nystagmus reached values between 0.8 and 0.97 at angular velocities below 1.5 deg/s. Gain under these conditions was related to stimulus angular velocities Vs, i.e. Ge = Ve/Vs. A slightly higher gain was found for binocular than for monocular stimulation. No significant differences were found in OKN when monocular stimulation in the naso-temporal and in the temporo-nasal direction was applied. The upper cut-off angular velocity (-3 dB-point) reached values of 180-230 deg/s, significantly above those observed in man under similar stimulus conditions. Monocular optokinetic stimulation of an immobilized eye led to vigorous optokinetic nystagmus and OKAN of the other eye, whereby maximum gain (Gi = Ve/Vr) was found to be between 20 and 30 at lower retinal stimulus velocities (2-5 deg/s). Gain was related to retinal stimulus velocity Vr. Increase in Vr above 10 deg/s led to a decrease in gain with a slope of about 20 dB per decade. Measurement of gain of closed-loop OKN related to retinal stimulus velocity Vr (which was determined by the difference between Vs and Ve) led to a similar dependence of OKN as in closed-loop stimulus conditions. Differences in sensitivity between the temporal and the nasal visual hemifield stimulation evoking horizontal open-loop OKN are described. Directional selectivity appeared in these experiments. Open-loop OKN data from a human subject are reported. With highly attentive horizontal optokinetic gaze nystagmus, Ve depended on the duration of the pursuit phases of OKN. Ve accelerated with the duration of the individual slow phase of OKN and was reset by each backward saccade (of the covered mobile eye). OKN gain was considerably smaller when the subject intentionally pursued as many stripes as possible of the 1.15 degree period stripe pattern (gain related to Vr about 1.5-3).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

General theory and principles of external fixation.

Starting with a review of the capabilities and main complications of external fixators, this paper shows how advances made during the past two decades have rendered the method safe, reliable, and predictable. Improved component designs, new techniques of pin care, the discovery of three basic concepts that govern the safe and effective application of pin and ring fixators, and the recognition that preoperative and long-term planning are crucial to the success of the method have made external fixation the most adaptable, versatile, and gentle method for stabilizing complex injuries of soft tissue and bone.

Bone Nails↗
PubMed1989

Unilateral external fixation. Methods to increase and reduce frame stiffness.

Unilateral configurations with stiffness characteristics similar to those of the most rigid one- and two-plane bilateral constructs are easily built. Mechanically, most effective were two-plane unilateral frames with a short bone-rod distance. But single- and double-bar anterior unilateral frames had the best combination of clinical and mechanical features. To put gradual frame builddown on a rational basis, a sequence of stepwise frame reduction was developed. This sequence leads from the most rigid unilateral constructs to frames that allow almost complete force transmission across the fracture site while still providing adequate protection against the prevailing sagittal bending moments.

Elasticity↗
PubMed1989

A primer of fixator devices and configurations.

This paper gives a general introduction to the terminology, concepts, and classifications of external fixators. A clear distinction is made between characteristics typical of the three types of external fixators, simple, clamp, and ring, and those typical of the four standard frames that can be built with each of the devices. These four frames, the one-plane unilateral, two-plane unilateral, one-plane bilateral, and two-plane bilateral configurations, differ in the ease of wound access they allow and their mechanical balance, particularly toward bending moments. Hybrids of different devices and frames may prove beneficial for stabilizing complex injuries.

Bone Nails↗
PubMed1988

Use of vancomycin and tobramycin polymethylmethacrylate impregnated beads in the management of chronic osteomyelitis.

Over the past several years there has been a growing interest in the use of locally implanted beads containing antibiotics for the treatment of chronic osteomyelitis. This method has been popularized in Europe and, with few exceptions, gentamicin has been the only antibiotic used. There have been only a few reports from the U.S. and there is little information regarding the pharmacokinetics of antibiotics used in this fashion. To our knowledge this is the first report using vancomycin. Three patients with chronic osteomyelitis were treated with vancomycin and/or tobramycin polymethylmethacrylate beads. These beads were extemporaneously compounded and implanted for up to six weeks. From the site of bead implantation local fluid aliquots were collected for the measurement of antibiotic concentrations. In two patients, initial tobramycin concentrations exceeded 400 mg/L. In one patient receiving vancomycin, initial localized concentrations were approximately 100 mg/L. In all three patients therapeutic concentrations of localized antibiotic were maintained with immeasurable systemic concentrations throughout the period of bead placement. Localized antibiotic therapy for the management of chronic osteomyelitis represents a potential therapeutic alternative to long-term parenteral therapy. Data presented here suggest that other antibiotics, such as vancomycin and tobramycin, can be used successfully in polymethylmethacrylate beads and provide preliminary facts for future investigations of such applications.

Adult↗
PubMed1986

External fixation of the tibia. Basic concepts and prospective evaluation.

External fixation of fractures of the leg may give uneven results and a high rate of complications. We postulate that three basic principles can govern the optimal use of these devices. The external fixation frame should avoid damage to vital anatomical structures, it should allow access to the injured area and it should meet the mechanical demands of the patient and the injury. From 1978 to 1981 these principles were evaluated prospectively in 75 consecutive cases of complex tibial injury treated with an external frame. Most were open fractures. The study confirmed that the principles were safe and effective; they have general application and do not depend on the use of a particular frame or device. By following them we have eliminated the majority of complications seen after traditional methods of external fixation.

Adolescent↗
PubMed1985

Velocity step responses of the human gaze pursuit system. Experiments with sigma-movement.

By means of d.c.-electrooculography or the electromagnetic search coil technique, horizontal and vertical eye position signals were recorded in subjects (head fixed) attentively pursuing a rotating dot circle (dot distance Ps = 0.8 or 1.0 deg). In addition, circular eye pursuit movements were evoked by sigma-movement seen when the stationary dot circle was illuminated stroboscopically (flash frequency fs). The rotation velocity Vs or the velocity of sigma-movement (Ps X fs) was changed in positive or negative steps, leading to acceleration or deceleration of pursuit eye velocity. This step response of eye velocity could be well described by a linear second-order differential equation with an additional dead time of about 80-100 msec. When gaze position error signals were larger than 0.3-0.5 deg, correcting saccades were superimposed on the step response of the smooth pursuit system. Voluntary saccades across the rotating or apparently rotating circle did not lead to any impairment in successive pursuit eye movements or an interruption in the sigma-movement. The gaze tracking command signals (smooth pursuit and saccadic responses) are evidently related to the stimulus movement in the extrapersonal space and not to retinal movement signals.

Adult↗
PubMed1985

Long-term results of displaced talar neck fractures.

Of 36 fractures of the talar neck without comminution of the body, eight were undisplaced, treated closed, and 28 were displaced and treated by open reduction. Twenty of the operations were less than 12 hours after injury. Nineteen of 20 were performed through a medial approach, six with a medial malleolar osteotomy. The long-term results were evaluated by a standard rating system based on classification by the fracture. A protective brace was developed for non-weight-bearing in two patients with complete avascular necrosis, and ankle protection with weight-bearing in ten with partial necrosis. Prompt open reduction and internal fixation, malleolar osteotomy, and protected weight-bearing are recommended in selected cases.

Adolescent↗
PubMed1984

Basic concepts and applications in open tibial fractures.

These data indicate that unilateral frames erected with rather stiff pins and rods carry few of the serious problems that were typical for the traditional half frames characterized by weak components, routine medial application, and limited pin spread. In comparison with one- and two-plane bilateral fixator configurations, unilateral frames are safer and more versatile, provide better access to limb and injury, do not interfere with knee and ankle motion, facilitate patient mobility, allow full unsupported weight bearing, and have a low rate of serious complications. While the successful and effective use of unilateral half frames is predicated on the use of relatively stiff components, they can be erected with most presently available devices. If a modular fixator is employed, long clamps, which allow for an extended pin spread, are desirable. The routine use of partial and full weight bearing increases patient comfort and mobility and may have beneficial effects on the healing process. In order to have the fracture site accept larger loads toward the end of the treatment period, we have recently started to sequentially decrease the rigidity of our fixator frames by moving the longitudinal rods further away from the tibia and selectively loosening the two clamps closest to the fracture site. This allows for the transmission of almost all compressive and transverse bending loads across the fracture site but provides considerable protection from sagittal bending moments, which often cause anterior bowing late in the healing period.

Adolescent↗
PubMed1983

Bladder problems in pelvic injuries treated with external fixator and direct urethral drainage.

In the treatment of unstable pelvic fractures, external fixators provide the advantages of substantial pain relief, easier nursing care, early mobilization, decreased hospital stay, and direct access to open wounds. Urethral catheter drainage alone for ruptured bladders obviates the need for open surgical repair in a critically injured patient and reduces morbidity and pain. Three cases are reported with bladder complications arising from these recently advocated methods of management; two with external fixators and one with urethral catheter drainage. In one patient with an external fixator, stretching of the bladder over a bone fragment resulted in transient hematuria with activity. In a second patient, the protruding bladder wall was caught between opposing pubic rami. In an extraperitoneal bladder rupture with pubic rami fractures, urethral catheter drainage alone resulted in a pseudodiverticulum of the bladder with a bone fragment projecting through the hole in the bladder cavity. These cases illustrate some complications with these recently advocated methods of management of unstable pelvic fracture and ruptured bladder.

Adult↗
PubMed1983

Bending stiffness of unilateral and bilateral fixator frames.

The structural and geometric fixator properties that best neutralize the prevailing anteroposterior and transverse bending moments at a tibial fracture site were analyzed in anatomic specimens. Clinically and mechanically, anterior unilateral frames were most effective, particularly when applied with relatively stiff components with a maximal spread between the pins in each main bony fragment and with placement of the longitudinal rod close to the tibia.

Fracture Fixation↗
PubMed1983

Unilateral external fixation for severe open tibial fractures. Preliminary report of a prospective study.

In a prospective survey of severe open tibial fractures, the incidence of serious complications with relatively rigid one- or two-plane unilateral fixator frames was considerably lower than with internal fixation by plates and screws. Unilateral configurations that contain rigid components provide better wound access than bilateral frames and interfere less with knee and ankle motion; they allow unencumbered partial and even full weight-bearing. This increases comfort and mobility and may have a positive effect on fracture healing. No standard formula exists, however, for the application of an optimal unilateral frame. The clinical and mechanical demands of each patient and injury must be considered individually.

Adolescent↗