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Biomedical subjects

D C Meyer

Publications and source records attributed to D C Meyer.

At least 19 recordsLinked to original sources
PubMed2006

Materials: carbon nanotubes in an ancient Damascus sabre.

The steel of Damascus blades, which were first encountered by the Crusaders when fighting against Muslims, had features not found in European steels--a characteristic wavy banding pattern known as damask, extraordinary mechanical properties, and an exceptionally sharp cutting edge. Here we use high-resolution transmission electron microscopy to examine a sample of Damascus sabre steel from the seventeenth century and find that it contains carbon nanotubes as well as cementite nanowires. This microstructure may offer insight into the beautiful banding pattern of the ultrahigh-carbon steel created from an ancient recipe that was lost long ago.

Journal Article↗
PubMed2006

Ultrasonically implanted PLA suture anchors are stable in osteopenic bone.

We compared the in vitro pullout strengths of a metallic screw-type suture anchor (5-mm Corkscrew) and a new ultrasonically implanted absorbable pin from cadaveric humeral heads with different bone densities. They were assessed quantitatively using microcomputed tomography. Pullout tests were done at four standardized sites and then correlated with the local bone density. The mean pullout strengths for the 5-mm Corkscrew and the 3.5-mm polylactic pin were similar in weak bone (76 +/- 24 N versus 104 +/- 46 N), intermediate quality bone (194 +/- 81 N versus 218 +/- 76 N), and strong bone (349 +/- 127 N versus 325 +/- 100 N). Pullout strength correlated with bone density for both implants (r = 0.76 and r = 0.86 for the Corkscrew and polylactic pin, respectively). The ultrasonically implanted absorbable 3.5-mm polylactic pin achieved equal pullout strength in weak bone as the larger 5-mm titanium Corkscrew. Bone density is highly variable in humeral heads and influenced the pullout strength of both implants.

Absorbable Implants↗
PubMed2006

Tendon retracts more than muscle in experimental chronic tears of the rotator cuff.

We released the infraspinatus tendons of six sheep, allowed retraction of the musculotendinous unit over a period of 40 weeks and then performed a repair. We studied retraction of the musculotendinous unit 35 weeks later using CT, MRI and macroscopic dissection. The tendon was retracted by a mean of 4.7 cm (3.8 to 5.1) 40 weeks after release and remained at a mean of 4.2 cm (3.3 to 4.7) 35 weeks after the repair. Retraction of the muscle was only a mean of 2.7 cm (2.0 to 3.3) and 1.7 cm (1.1 to 2.2) respectively at these two points. Thus, the musculotendinous junction had shifted distally by a mean of 2.5 cm (2.0 to 2.8) relative to the tendon. Sheep muscle showed an ability to compensate for approximately 60% of the tendon retraction in a hitherto unknown fashion. Such retraction may not be a quantitatively reliable indicator of retraction of the muscle and may overestimate the need for elongation of the musculotendinous unit during repair.

Animals↗
PubMed2005

A new methodology for the planning of single-cut corrective osteotomies of mal-aligned long bones.

BACKGROUND: Corrections of combined torsional and angular deformities of long bones may be performed creating a single osteotomy which is oriented so that rotating the two fragments on the created osteotomy plane allows to correct all deformities in one step. A practical geometrical tool is presented to facilitate the difficult preoperative planning of such osteotomies. METHODS: The geometrical tool consists of two limbs connected by a mobile disk representing the osteotomy plane. This allows the two limbs to be deliberately bent and rotated against each other. Thereby, the mobile disk will change orientation in such a way that it will indicate the osteotomy plane needed in order to anatomically align the two limbs. The geometrical principle of the tool has been confirmed mathematically and compared with data from the literature. Five deformed test bones have been used to test the effectiveness of the tool. FINDING: . The geometrical principle of the tool is equivalent with the mathematical data from the literature. The maximal osteotomy angle which can be indicated by the tool is 65 degrees , with an error of +/-3 degrees compared to mathematically calculated values. The five test bones were all aligned anatomically with appropriate accuracy. INTERPRETATION: The presented tool can be easily used and facilitates largely the preoperative planning of a single cut osteotomy for complex deformities of long bones. It allows to avoid sophisticated mathematical calculations and helps to avoid the risk for errors in planning and performing correctional osteotomies.

Bone Malalignment↗
PubMed2004

In vivo tendon force measurement of 2-week duration in sheep.

Tendon tension in vivo may be determined indirectly by measuring intratendinous pressure, by using a buckle transducer or by measuring the tendon strain. All of these methods require appropriate calibration, which is highly dependent on various variables. To measure the tendon load in vivo during a period of 2 weeks in sheep, a measurement technique has been developed using a force sensor interposed serially between the humeral head and the tendon end. Within a supporting frame, a flexion-sensitive force transducer is subjected to three-point bending stress. The load is transmitted by sutures from the tendon end through a hole in the sensor frame, orthogonal to the force transducer. In this configuration, the sensor measures the tensile force acting on the tendon, largely independent of the loading direction. The sensor was screwed to the humeral head and connected to the tendon end which was previously released from its insertion site along with a bone chip, using sutures. Connecting wires passed subcutaneously to a skin outlet about 30 cm away from the transducer. The sensor output was linear to the measured load up to 300 N, with maximum hysteresis of 18% full scale. All sensors worked in vivo without drift over a period of up to 14 days with no change in the calibration data. Forces up to 310 N have been recorded in vivo with daily tension measurements. This study shows that serial tendon tension measurement is feasible and allows for reliable, repeatable recording of the absolute tendon tension at the expense of tendon integrity.

Animals↗
PubMed2004

Effect of tendon release and delayed repair on the structure of the muscles of the rotator cuff: an experimental study in sheep.

BACKGROUND: Ruptures of the tendons of the rotator cuff lead to profound and possibly irreversible changes in the structure and physiological properties of the rotator cuff muscles. Muscle atrophy and fatty infiltration are important prognostic factors that affect the natural history and outcome of treatment. The purpose of this study was to examine the amount of muscle atrophy and fatty infiltration in an animal model and to determine whether the repair of a long-standing tendon tear can reverse these changes. METHODS: The infraspinatus tendon in six sheep was released and encased in a silicone tube to prevent spontaneous healing. The musculotendinous unit was allowed to retract for forty weeks. Throughout this period, the muscular changes were studied with use of computed tomography, histological analysis, and electron microscopy. At forty weeks, the elasticity, intramuscular pressure, and perfusion were measured intraoperatively and a tendon repair was carried out. The structural changes of the muscle were studied for thirty-five weeks after the repair. The animals were then killed, and the musculotendinous units were examined macroscopically and by computed tomography, histological analysis, and electron microscopy. RESULTS: At the time of the tendon release, the infraspinatus showed no fatty changes. The force needed to cause a tendon excursion of 1 cm was a mean (and standard deviation) of 6.8 +/- 1 N. The application of tension on the tendon did not alter the perfusion and decreased the intramuscular pressure. After the tendon release, muscular atrophy developed and there was a significant increase (p < 0.001) in interfascicular and intrafascicular fat, representing fatty infiltration rather than fatty degeneration. Furthermore, there was an increase of interstitial connective tissue. At the time of the tendon repair, between forty and forty-two weeks after the release, there was a sevenfold poorer elasticity of the musculotendinous unit but preserved muscle perfusion. The structural changes increased six weeks after the repair and then recovered partially at twelve and thirty-five weeks thereafter but only to the amount demonstrated before the repair. CONCLUSIONS: Musculotendinous retraction induced by tendon release is associated with profound changes in the structure and function of the affected muscle. Vascularization, intramuscular pressure, and individual fiber composition are not markedly affected, and muscle fibers do not appear to degenerate. However, muscle atrophy, infiltration by fat cells, and an increase of interstitial connective tissue lead to impairment of the physiological properties of the muscle. These changes were irreversible under the conditions of this experiment with the repair technique used.

Adipose Tissue↗
PubMed2003

The use of acrylic bone cement for suture anchoring.

Healing of tendon or ligament sutured to bone depends among other parameters on the mechanical stability of the suture fixation in or to the bone. The authors propose a method of anchoring suture material using bone cement as a substitute for conventional suture anchors. Conditions for secure fixation of suture material in bone cement were assessed and the technique of anchoring suture material with acrylic cement in bone was developed. Mechanical testing and microcomputed tomography of the suture-cement-bone compound were done. It was found that the suture always should be knotted before embedding it at least 2 mm deep in the bone cement. The holes drilled into the bone in which the sutures are secured with cement should be at least 3.5 mm in diameter and 10 mm deep; in cortical bone a tapped thread is required. Sutures can be secured safely using cement anchors which provide higher pull-out strength of a factor two to five than conventional metallic suture anchors of comparable size. They also adapt to anatomic situations where conventional anchors cannot be used and are more favorable in osteoporotic bone. Cement anchoring of sutures seems to be a cost-effective and valuable alternative when there is poor bone quality or extraordinarily high mechanical load.

Bone Cements↗
PubMed2001

Software based digital signal processing and spectrum deconvolution in X-ray spectroscopy.

Approaches for software based digital signal processing and numerical deconvolution of measured signals which overcome limitations of state-of-the-art systems are described. The basic technical equipment for digital signal processing consists of an energy resolving detector with a preamplifier followed by a fast sampling analogue-to-digital converter (ADC). The main idea is the numerical decomposition of the measured signal into contributions caused by single photon absorption using standard pulses. The latter can be obtained by measurements under definite conditions. The maximum pulse rate is then limited only by the ratio of sampling time to the time between two pulses which should be attributed to single events. Thus pulse overlaps do not require pulse rejection. At sampling rates of 10(8) samples per second theoretically a comparable photon rate can be detected at throughputs of 100%. Beyond that it is outlined that in a comparable manner a numerical deconvolution of measured energy spectra (statistic distribution functions of single events) into combinations of standard spectra, which can likewise be determined by measurement, offers outstanding possibilities, too. On the one hand the energy resolution attainable for individual events for a given detector can be improved drastically by the statistical treatment of spectra. On the other hand an energy resolving work principle becomes possible for certain detectors, which do not permit this conventionally due to their poor signal to noise ratio.

Journal Article↗
PubMed1998

DAFS experiments with non-centrosymmetric single crystals.

Diffraction anomalous fine structure (DAFS) experiments were applied to an epitaxially grown (Ga,In)P layer on a [001] GaAs substrate as a single-crystalline model substance. The requirements for the reliable measurement of reflection intensities as a function of photon energy, as well as the quantitative DAFS analysis resulting in the complex-valued fine-structure function of the scattering factor, are described. In the case of single crystals, effort had to be put into performing the DAFS measurements in order to hold the position of the Bragg reflection exactly during the energy scan. Using the zinc-blende-type structure as an example, it is shown for the first time that, similar to single-crystal structure analysis, the lack of inversion symmetry has a significant impact on the DAFS signal, so that DAFS may contribute to structure analysis as well.

Journal Article↗
PubMed1993

GABA control of LHRH release is dependent on the steroid milieu.

The effect of GABA in controlling luteinizing hormone releasing hormone (LHRH) release from isolated hypothalamic fragments containing the mediobasal hypothalamus, suprachiasmatic nucleus, and the preoptic area (MBH-SCN-POA) was tested under different hormonal conditions with an in vitro superfusion method. GABA significantly decreased LHRH release under conditions of low, chronic levels of estradiol (E2) treatment but had no effect on tissue obtained from animals in proestrus. This suggests that the inhibitory effect of GABA is only manifested during certain stages of the estrous cycle characterized by negative feedback and low E2.

Animals↗
PubMed1992

Role of 5-hydroxytryptamine receptors on luteinizing-hormone-releasing hormone release in the ovariectomized, estradiol-treated rat.

The present experiments examined the effect of ketanserin [5-hydroxytryptamine-2 (5-HT2) antagonist] and 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) (5-HT1 agonist) on the in vitro release of luteinizing-hormone-releasing hormone (LHRH) from the medial basal hypothalamus-preoptic area-suprachiasmatic nucleus region (MBH-POA-SCN) of ovariectomized (OVX), estradiol-(E2) treated rats using in vitro superfusion techniques. Regularly cycling female Holtzman rats (250-300 g) were maintained on a photoperiod of 0500-1900 h light at 22 +/- 2 degrees C. Rats were ovariectomized (25-30 days) and received Silastic E2 implants (150 micrograms E2/ml sesame oil) SC 48 h prior to the in vitro superfusion. Following a control period of Krebs-Ringer Phosphate (KRP) superfusion, ketanserin (5-HT2 receptor antagonist, 1 x 10(-6) M) significantly increased LHRH release (p less than 0.05). Subsequent superfusion of 5-HT (1 x 10(-8) M) significantly decreased (p less than 0.05) the effect of ketanserin on LHRH release. The 5-HT2 antagonist Lilly 53857 (1 x 10(-6) M or 1 x 10(-5) M) did not increase LHRH release above control levels. Neither 5-HT nor quipazine had a significant effect on LHRH release at 1 x 10(-6) M. Superfusion of 8-OH-DPAT (5-HT1 receptor agonist 1 x 10(-5) M) significantly (p less than 0.01) increased LHRH release but subsequent superfusion of 8-OH-DPAT + pindolol (mixed 5-HT1a,1b and a beta-adrenergic receptor antagonist, 1 x 10(-6) M) or pindolol alone had no effect on LHRH release. These results suggest that the 5-HT1 receptor plays a role in LHRH release and this effect may be related to the opposing effects of postsynaptic and autoreceptors. However, the failure of Lilly 53857 to reproduce the stimulatory effect of ketanserin on LHRH release suggests that 5-HT2 receptors in the MBH-POA-SCN may not modify LH release during the estrous cycle.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1990

In vivo 5-HIAA release from the anterior hypothalamus in the ovariectomized and estradiol treated rat following perfusion with progesterone.

In the present study the frequency and magnitude of the release of 5-Hydroxyindoleacetic Acid (5-HIAA) was measured from the anterior hypothalamus of ovariectomized (OVX) and OVX rats treated with estradiol (E2). Female, Holtzman strain rats were maintained on a photoperiod of 14 H light from 0100 to 1500 H and experiments performed from 0900 to 1700 H. Animals exhibiting four-day estrous cycles (250-300 gms) were OVX (20 days recovery) and a push-pull-cannula (PPC) implanted and stereotaxically aimed at the SCN region in the anterior hypothalamus. Following a 7-10 day recovery push-pull-perfusion (PPP) experiments were performed on either OVX females or on OVX females in which a silastic E2 implant (150 micrograms E2/ml. sesame oil), was placed sc 48 H prior to PPP. In other experiments progesterone (P4) was perfused in a pulsatile manner over the SCN region of the anterior hypothalamus. The overall average 5-HIAA release in the OVX treated rats (548 +/- 358 pg/10 min.) was similar to that in the OVX E2 group (694 +/- 148 pg/10 min). The average period of 5-HIAA release was (48.2 +/- 5.5 min) in the OVX group and (56.0 +/- 9.8 min) in the OVX E2 group. These results indicate that exposure of long term OVX rats (20 days) to E2 has no effect on the release or period of 5-HIAA release from serotonergic terminals concentrated in the SCN of the anterior hypothalamus.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

No safe place: parental alcoholism and adolescent suicide.

A child growing up in an alcoholic home develops either little self-consolidation (I-ness) and efficacy (I can) or a distorted self (I am insignificant). This results in a desperate search for a soothing-object (We-ness). The sadomasochistic behaviors, which a youth witnesses and is subjected to, become internalized as survival skills, but ultimately fail. These factors set the stage for a destructive modus operandi. When there is peer group attachment pressure, this teen does not find security when questioning, "Who am I?" because there is no "I" and no "We". Instead, this adolescent experiences fear, anxiety, and range, and wonders, "What's going to happen to me?" This propels the youth into frantic behaviors that are meant to confirm a sense of "We-ness" and competence. The result, however, is greater frustration and a mirroring of the opposite. Also, since there is a diminutive capacity for trust and an exiguous chance to reach out or respond to significant others, external soothingness becomes unobtainable. When the adolescent is confronted with aloneness, helplessness, and hopelessness, desperation results and a search for a safe place ensues. Suicide holds such an illusion. It is the embodiment of sadomasochism and permits the cognition "I am capable." A case study illustrates the problems.

Adolescent↗
PubMed1989

Serotonin stimulation of the period of in vitro LHRH release is estradiol dependent.

The neurotransmitter serotonin (5-HT) has well known effects on the release of luteinizing hormone (LH) which may be estrogen and photoperiod dependent. An in vitro superfusion system was used to assess the potential role of 5-HT and photoperiod in modulating the release of luteinizing hormone releasing hormone (LHRH) from the mediobasal-suprachiasmatic-preoptic area (MBH-POA-SCN) in the ovariectomized (OVX) and OVX estradiol (E2) implanted rat model of LH release. Regularly cycling female Holtzman strain rats, maintained on a photoperiod of 0500-1900 or 0100-1500 hr light were OVX, and silastic capsules containing estradiol-17 beta (150 micrograms/ml) or sesame oil implanted SC. Two days later the rats were killed at 1000 hr and the MBH-POA-SCN isolated. Tissue was superfused in vitro with Krebs-Ringer-Phosphate buffer (KRP) for 2 hours followed by 3 hours of KRP with intermittent superfusion of 5-HT at increasing concentrations: 1 X 10(-10) M (1st hour); 1 X 10(-8) (2nd hour); 1 X 10(-6) M (3rd hour). Superfusate was collected every 10 min for the entire 5 hour incubation period and LHRH measured by RIA with the following results. In the OVX rat 5-HT significantly (p less than 0.05) increased the period of LHRH pulses and decreased the release of LHRH compared to control superfusions, while in the OVX E2 rat 5-HT significantly (p less than 0.05) decreased the period of LHRH release and increased the release of LHRH.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

In-vitro pulsatile luteinizing hormone-releasing hormone output is dependent on hypothalamic region and the stage of the estrous cycle.

In the following experiments, the role of the preoptic-suprachiasmatic area (POA-SCN) in the control of luteinizing hormone-releasing (LHRH) release was examined by in vitro superfusion of either mediobasal hypothalamus (MBH) or MBH-POA-SCN fragments obtained from cycling rats killed on various days of the estrous cycle. The lowest level of LHRH output occurred during estrus, highest levels during diestrus, and intermediate levels on proestrus in the MBH-POA-SCN preparation. As expected, significant decreases in LHRH output from the MBH alone occurred during both days of diestrus and on proestrus, as compared to output from the MBH-POA-SCN tissue, since this structure contains most of the LHRH perikarya. However, similar LHRH secretion patterns were detected in estrus from both preparations. The average period of the LHRH pulses for the estrous cycle in the MBH-POA-SCN was 30.9 +/- 1.2 min compared to 97.7 +/- 25.1 min in the MBH, with significant differences occurring on diestrus 2. The increase and extreme variability of the period of LHRH pulses in the MBH region, compared to the MBH-POA-SCN region, suggests that it is the latter region that contains the neural circuits that control the LHRH pulse generator. The LHRH pulse amplitudes from both hypothalamic regions were similar during all phases of the estrous cycle, except diestrus 2, when the LHRH pulse amplitude from the MBH region was significantly lower than the LHRH pulse amplitude from MBH-POA-SCN. The percentage of LHRH released in the MBH did not vary with the estrous cycle, however, in the MBH-POA-SCN significant changes were observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

The nature and magnitude of in vivo 5-hydroxyindoleacetic acid output from 5-hydroxytryptamine terminals is related to specific regions of the suprachiasmatic nucleus.

Eight cycling female rats were implanted with push-pull cannulae over the region of the suprachiasmatic nuclei (SCN) and allowed 7-10 days for recovery. Perfusion of the SCN continued in these freely behaving rats for 5-6 h of the light period and the subjective scotophase. The release of 5-hydroxyindoleacetic acid (5-HIAA) ranged from 10 to 350 pg 5-HIAA/min. Significantly, the amplitude and characteristics of the output of 5-HIAA were highly location dependent in that rostral cannulae placements revealed high amplitude changes with initial mean values of 40 pg 5-HIAA/min, which increased toward the dark phase to mean peak values of 195 pg 5-HIAA/min. Caudal cannulae placements revealed a low amplitude, high frequency, basal type of 5-HIAA release which did not increase toward the dark period (approximately 5 pg/min). 5-Hydroxytryptophan infusion resulted in a significant marked increase in the basal release of 5-HIAA confirming the biochemical viability of the area undergoing perfusion. These results suggest that the in vivo measurement of 5-HIAA from 5-hydroxytryptamine (5-HT) terminals in the region of the SCN could reflect discrete functional activity of serotonergic terminals within specific regions of the SCN in a freely behaving rat. Furthermore, the biochemical viability of these 5-HT terminals and the ability of the rat's SCN to exhibit marked differential changes in 5-HT activity emphasizes the physiological relevance of this model system to study neuroendocrine events in freely behaving animals.

Animals↗