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Biomedical subjects

J A Clark

Publications and source records attributed to J A Clark.

At least 109 records · Page 6Linked to original sources
PubMed1989

Stereotactic neurosurgery planning on a personal-computer-based work station.

Stereotactic surgery requires knowledge of cerebral structures derived from more than one image source. We have developed a PC-AT-based workstation that accepts patient images, made with the stereotactic frame in place, from CT, MRI, and DSA modalities. Reference markers on the frame are identified in the images to establish the coordinate geometry for each modality. Target points may be identified on each image type and trajectories of probe paths to these points defined. Targets identified on one set of images may be transferred automatically to other images of the same patient in order to guarantee a vessel-free path of approach to a target point deep within the brain. To date several hundred patients have had stereotactic surgery performed on the basis of plans using this system. Procedures included biopsy and aspiration of lesions, implantation of electrodes for the recording of deep EEG signals, and radiosurgical techniques. We present clinical examples of the use of this system in typical stereotactic neurosurgery procedures, address stereoscopic applications, and discuss the results of intermodality tests to establish the accuracy of the technique.

Angiography, Digital Subtraction↗
PubMed1989

Blood and component wastage report. A quality assurance function of the hospital transfusion committee.

The transfusion service of a regional referral medical center issues a monthly blood and component wastage report to the Hospital Transfusion Committee. The report includes the amount and type of units wasted, who is responsible, and the cost incurred by the wastage. The individuals responsible for wastage include physicians, nurses, and laboratory personnel. Physicians are responsible for most wastage, principally by failing to administer thawed or pooled blood products. The Hospital Transfusion Committee initiated a wastage-reduction program that included a letter to physicians indicating the patient's name and the type of blood and/or components that the addressed physicians was responsible for wasting. Simple corrective actions results in a 73 percent reduction in our blood and component wastage. Monitoring of blood and component wastage should be routine quality assurance function of the Hospital Transfusion Committee.

Blood Transfusion↗
PubMed1989

Quantitative muscle strength testing: a comparison of job strength requirements and actual worker strength among military technicians.

In this study the authors investigate the percentage of mismatch between job demands and worker physical capacity in Utah National Guard mechanics. This population had demonstrated a higher incidence of low back trouble than other job descriptions reviewed. The authors utilized onsite still and videotape photography and a computerized biomechanical strength prediction model to assess loads on the lumbosacral spine due to various job tasks. Job demands were then compared to the actual physical capacity of the individual workers based on static strength testing in job-related positions. A load cell on the testing apparatus entered the force generated into a computer which averaged the force of the last three seconds of a five-second lift. It was determined that as much as a 38% mismatch existed within this population for some job tasks which these workers were exposed to. Suggestions for preventing job-related low back cumulative trauma disorders are presented, including: engineering redesign, worker selection programs, work hardening, and others.

Back Pain↗
PubMed1989

Kappa opiate receptor multiplicity: evidence for two U50,488-sensitive kappa 1 subtypes and a novel kappa 3 subtype.

Kappa receptor multiplicity is a complex area. We now present evidence from binding studies suggesting the existence of four kappa receptor subtypes. The guinea pig cerebellum contains high levels of U50,488-sensitive, or kappa 1, receptors. Kappa opiates (U50,488, tifluadom, Mr2034, Mr2266 and Win44,441) compete [3H]ethylketocyclazocine binding to kappa 1 receptors with kappa, values under 10 nM and Hill coefficients of approximately one, as does dynorphin A (kappa 1, 0.27 +/- 0.05 nM; Hill coefficient, 0.83 +/- 0.20, n = 4). However, competition studies with dynorphin B yield a Hill coefficient of 0.46 +/- 0.03 (n = 5) and nonlinear regression analysis of the competition curve is best fit by two sites. alpha-Neoendorphin Neoendorphin competition curves (Hill coefficient, 0.46 +/- 0.07; n = 3) also were best fit with two components. Competition studies with both alpha-neoendorphin and dynorphin B together suggest that both compounds label the same site with high affinity. Similar results were obtained using [3H]U69,593. Dynorphin B and alpha-neoendorphin competed binding with Hill coefficients of 0.45 +/- 0.04 (n = 3) and 0.59 +/- 0.09 (n = 3), respectively. These data suggest two subtypes of kappa 1 receptors in the guinea pig cerebellum: kappa 1a and kappa 1b. Classical kappa opiates and dynorphin A have high affinity for both subtypes whereas dynorphin B and alpha-neoendorphin label kappa 1b over 50-fold more potently than kappa 1a sites. [3H]Naloxone benzoylhydrazone [( 3H]NalBzoH) labels a novel, U50,488-insensitive kappa receptor subtype, kappa 3, in membranes from calf striatum, rat and mouse brain. We now have developed a relatively selective assay in calf striatum.(ABSTRACT TRUNCATED AT 250 WORDS)

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1989

Successful implementation of Maximum Surgical Blood Order Schedule.

A Maximum Surgical Blood Order Schedule (MSBOS) is a schedule of commonly performed elective surgical procedures listing the maximum number of units of blood to be crossmatched preoperatively. A MSBOS reduces the preoperative crossmatching of blood in surgical cases in which there is less likelihood of blood transfusion. The reduction in crossmatched units of blood saves hospital time and money. This study presents the steps required to institute a MSBOS. Savings in reduced crossmatch charges were calculated. After a review of 1400 operations, a MSBOS listing 35 operative procedures was established at the Medical Center of Central Georgia. Staff compliance was greater than 99%, crossmatch to transfusion ratio was reduced from 5:1 to 2:1, and our annual savings was greater than $110,000 in reduced crossmatch charges.

Blood Grouping and Crossmatching↗
PubMed1989

Reduction of fresh frozen plasma use with a simple education program.

Fifty-six charts of patients who received 307 units of fresh frozen plasma (FFP) were audited to determine the transfusion practice of this component at our 550-bed regional referral hospital. Forty-six patients (82%) were on the surgical service. Indications for FFP transfusion were poorly documented. Forty-nine patients (87%) lacked evidence of a coagulopathy. An educational program addressing appropriate use of FFP was initiated. Over the course of two years, FFP usage dropped by over 1,000 units annually (46%).

Blood Transfusion↗
PubMed1988

Loss of striatal mu1 opiate binding by substantia nigra lesions in the rat.

Opiate receptors have been identified within the striatum and some have been localized presynaptically to nigrostriatal neurons. Using unilateral ablative lesions of the substantia nigra, we examined binding in the ipsilateral and contralateral striata. Lesions significantly lowered both 3H[D-Ala2,MePhe4,Gly(ol)5]enkephalin (DAGO) and 3H[D-Ala2,Leu5]enkephalin (DADL) binding. The inclusion of competitors in these assays revealed a decrease in both mu1 and mu2 receptors. Mu1 binding was slightly more sensitive to the lesioning than mu2 binding. Selective mu1 and mu2 binding assays supported these observations. No change in delta binding was observed in the lesioned striata. These studies raise the possibility that both mu1 and mu2, but not delta, receptors are localized presynaptically on nigrostriatal neurons.

Animals↗
PubMed1988

U50,488: a kappa-selective agent with poor affinity for mu1 opiate binding sites.

Although a number of potent kappa ligands have been reported, virtually all also label mu receptors with very high affinity. In contrast, we found that U50,488 is highly selective for kappa sites (Ki 12 nM) when compared to both morphine-selective (mu2) or delta receptors (both Ki values greater than 500 nM) confirming earlier reports. However, these reports did not examine interactions with mu1 receptors. In marked distinction to all other kappa-active agents examined which typically compete mu1 binding with Ki values under 1 nM, U50,488 competed mu1 binding quite poorly (Ki 370 nM). Thus, U50,488 is a highly selective kappa agent with very poor affinity for both subtypes of mu and delta receptors.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1988

Opiate binding in calf thalamic membranes: a selective mu 1 binding assay.

In the present study, we examined the binding of [3H][D-Ala2,D-Leu5]enkephalin ([ 3H]DADL) to bovine thalamic membranes. Scatchard plots were linear with a KD of 0.7 nM. However, competition experiments suggested binding heterogeneity. Approximately 20% of [3H]DADL binding was easily inhibited by [D-Pen2,D-Pen5]enkephalin (DPDPE) and was insensitive to morphine, implying labeling of delta receptors. The remaining 80% of binding was quite sensitive to both morphine and [D-Ala2,MePhe4,Gly(ol)5]enkephalin (DAGO) and insensitive to DPDPE, consistent with a mu receptor. However, this binding did not correspond to classical morphine-selective mu receptors. Unlike morphine-selective receptors, this binding had similar affinities for morphine, DAGO, DADL and [D-Ser2,Leu5]enkephalin-Thr6 (DSLET). In addition, it was far more sensitive to naloxonazine's wash-resistant inhibition and magnesium-induced enhancement of binding than either the morphine-selective (mu 2) or delta sites. [3H]DSLET binding yielded results very similar to those using [3H]DADL. In conclusion, approximately 80% of [3H]DADL binding in thalamus corresponds to a mu receptor distinct from the classical morphine-selective site. Based upon the results of our studies, we feel that this binding represents mu 1 receptors. DPDPE (10 nM) can effectively inhibit the binding of [3H]DADL to delta receptors, leaving a relatively homogeneous labeling of mu 1 sites. The availability of this selective binding assay should facilitate additional studies of mu 1 receptors.

Animals↗
PubMed1988

Nd: YAG laser iridectomies: 100 consecutive cases.

We reviewed the patient charts of our first 100 consecutive Nd:YAG laser iridectomies. Our success rate (99%) is the same as that reported by others. Iris bleeding was not problematic. We did find that relative pupillary block may still be present with a patent but very small Nd:YAG iridectomy; that transillumination is not an adequate criterion for assessing patency; and that a Nd:YAG laser iridectomy, probably in part because of its small size, frequently closes with chronic inflammation.

Aged↗
PubMed1988

Common artifacts encountered in magnetic resonance imaging.

Magnetic resonance imaging has rapidly become a widely accepted and clinically useful imaging modality primarily because of its excellent contrast resolution, ability to perform multiplanar acquisition, and the lack of ionizing radiation. However, the nuances of image acquisition are not trivial. Many technical factors must be considered and understood in order to knowledgeably choose sequence parameters that suppress artifacts and optimize the diagnostic quality of a particular MR examination. Even then, residual artifacts may persist. The presence of the artifacts and their technical basis must be understood before completely accurate MR interpretation can be rendered.

Brain↗
PubMed1987

Morphine-6-glucuronide, a potent mu agonist.

The 3- and the 6-glucuronides of morphine have been examined in binding studies and in vivo. The 3-glucuronide had poor affinity in all binding studies whereas the 6-glucuronide potently labeled mu, but not delta or kappa receptors with affinities similar to morphine. Microinjections of the 3-glucuronide directly into the periaqueductal gray were without effect. The 6-glucuronide, on the other hand, was up to 20-fold more potent than morphine following microinjections in the same region. High doses of the 6-glucuronide produced profound seizure activity. All 6-glucuronide actions were sensitive to the opiate antagonist naloxone.

Animals↗
PubMed1987

Mechanical characterisation of human postburn hypertrophic skin during pressure therapy.

Postburn hypertrophic scar commonly occurs among the Chinese resulting from serious burn injuries. A non-invasive method of preventing and controlling such scars is using pressure therapy. Its mechanical properties are used as a quantitative indicator for scar assessment and maturation. The non-linear properties of the skin tissue are characterised in this study by a modulus of elasticity and a percentage extension (strain) at load intensities of 20, 40 and 100 g. The latter is a measure of the scar extensibility while the former the scar stiffness. A correlation is obtained between the clinical scar grading and these mechanical properties. Altogether 300 individual measurements were made on fifteen Chinese patients of ages ranging from 18 to 44 with burn injuries of superficial to whole skin thickness burns which necessitated surgical graft procedures. This in vivo study of the mechanical properties of hypertrophic scar tissue lasted 2 yr.

Adolescent↗
PubMed1987

[Integration of digital angiography, magnetic resonance, x-ray computed tomography and positron emission tomography in stereotaxy].

Consecutively to drastic changes which occurred in cerebral imagery techniques, we have developed a stereotactic apparatus and system based on the integration of several new techniques allowing visualisation of the brain: tomodensitometry (TDM), digital subtraction angiography (DSA), magnetic resonance (MR) and positron emission tomography (PET). TDM, DSA and MR can be performed in stereotactic conditions with the apparatus in situ. They give the computer the anatomic references necessary for all calculations. MR and PET images obtained without stereotactic apparatus can also be integrated into the stereotactic study at the condition that DSA was formerly performed in stereotactic conditions, i.e. with the apparatus in situ. The visualisation of the corpus callosum makes this integration possible. An optimal definition of cerebral tumors or target-structures for intracerebral electrode recording is thus obtained.

Brain Diseases↗
PubMed1986

Naloxonazine actions in vivo.

Naloxonazine is a relatively selective mu 1 affinity label in binding studies. Like naloxazone, naloxonazine has proven valuable in vivo in establishing a role for mu 1 sites in specific opiate actions. We now report a detailed characterization of naloxonazine's actions in mice and rats. Naloxonazine antagonized morphine analgesia for greater than 24 h without altering lethality. This prolonged action could not be easily explained by a slow rate of elimination since the terminal elimination half-life was estimated at less than 3 h. Furthermore, these actions were associated with a wash-resistant inhibition of binding lasting 24 h which was relatively selective for mu 1 sites. At a fixed morphine dose, increasing naloxonazine doses lowered peak tailflick latencies in a biphasic manner, suggesting that morphine analgesia consisted of both mu 1 (naloxonazine-sensitive) and a non-mu 1 (naloxonazine-insensitive) components. The ratio of mu 1 to non-mu 1 analgesia was greater at low morphine doses, implying that morphine activated mu 1 analgesic mechanisms with higher affinity. Our studies also emphasized that naloxonazine has reversible actions similar to those of naloxone; only its irreversible actions are relatively mu 1-selective. In addition, the selectivity of naloxonazine's irreversible actions is dose-dependent. High naloxonazine doses will irreversibly antagonize receptors other than mu 1.

Animals↗