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Biomedical subjects

D Burke

Publications and source records attributed to D Burke.

372 records · Page 21Linked to original sources
PubMedDate not supplied

Sequence-dependent deterioration in the visual evoked potential in the absence of drowsiness.

When visual evoked potentials (VEPs) are tested patients are often expected to focus on a pattern screen for prolonged periods of time. This may lead to fatigue, failure of concentration and drowsiness, and consequently to a deterioration in the recorded VEP. To determine whether there may be time-dependent changes in the VEP of normal subjects independent of the degree of alertness, attention and altertness were controlled using a reaction time (RT) task in which the subjects were required to re-illuminate the fixation point in the middle of the stimulating screen for the VEP. It was first established that the switching of the fixation point produced little contamination of the background VEP to pattern reversal and that the latency and amplitude of P100 to pattern reversal were identical whether or not the subject was engaged in the RT task. A sequence of 16 averages of the VEP to 256 pattern reversals was recorded, alternately with or without the RT task. The measured RTs decreased during the sequence, presumably due to practice. There was a progressive decrease in the amplitude N70-P100, accompanied by an increase in the variability of the latency of P100. These changes cannot be attributed to lack of alertness, given the improvement in RT. Clinicians should be aware of the possibility of a deterioration in the VEP due to physiological mechanisms when the testing protocol involves multiple averages.

Adult↗
PubMedDate not supplied

Exotic mice as models for aging research: polemic and prospectus.

Most gerontological research using rodent models employs inbred strains, or F1 hybrids derived from them, rather than populations of genetically heterogeneous individuals. This study presents the argument that reliance on genetically homogeneous rodents, though sanctioned by tradition, may not be ideal for many sorts of investigations, and that use of heterogeneous mice and rats would allow researchers to reach robust conclusions that were less likely to reflect strain-specific idiosyncrasies. Segregating stocks, bred by backcross, F2 cross, or four-way cross procedures, would be an improvement over inbred and F1 stocks, providing inexpensive, arbitrarily large, and reproducible populations of genetically diverse test subjects. These stocks would not, however, recapture allelic variations that are likely to have been lost when wild-trapped mice and rats are selected inadvertently over dozens of generations for breeding success in laboratory conditions. Development of specific pathogen free stocks from wild-trapped progenitors particularly from populations selected for relevant evolutionary history and physiological characteristics, may be of great value for analysis of aging and late-life pathophysiology.

Aging↗
PubMedDate not supplied

Spinal anesthesia with 0.5% S(-)-bupivacaine for elective lower limb surgery.

BACKGROUND AND OBJECTIVES: This study examines the clinical effects of the subarachnoid administration of levobupivacaine, the S(-)-enantiomer of racemic bupivacaine. METHODS: An open, noncomparative study was performed on 20 patients undergoing elective lower limb surgery. Three milliliters of a plain solution of 0.5% S(-)-bupivacaine ( 15 mg) was administered via the L2 or L3 interspace with the patient in the sitting position. Following injection, the patients were immediately placed supine. Spread of sensory analgesia, degree of motor block, and hemodynamic parameters were recorded. RESULTS: Satisfactory surgical anesthesia was achieved in 18 patients. The median time to onset of analgesia was 2 minutes (ranging 2-10 minutes) and the median duration of analgesia was 388 minutes (range, 295-478 minutes). This group of patients achieved complete motor block, with a median onset time of 5 minutes (2-10 minutes) and duration of 266 minutes (range, 170-415 minutes). Sensory block height was inadequate for surgery in 2 patients, who received supplemental anesthesia. CONCLUSIONS: The results suggest that S(-)-bupivacaine can provide satisfactory surgical anesthesia, but the spread of the plain solution is unpredictable.

Adult↗
PubMedDate not supplied

Circumcision supplemented by dorsal penile nerve block with 0.75% ropivacaine: a complication.

BACKGROUND AND OBJECTIVES: Dorsal penile nerve block is a common procedure and can provide effective analgesia after penile surgery. Ischemic complications are rare and generally result from trauma or inadvertent administration of vasoconstrictive solutions. CASE REPORT: We describe a period of temporary ischemia of the glans penis occurring 40 minutes after dorsal penile nerve block with 0.75% ropivacaine. This was successfully treated with an intravenous infusion of iloprost (a PGI2 analogue), and at 43 hours appearances were normal. CONCLUSION: Theoretical concerns over the vasoconstrictive properties of ropivacaine may be sufficient to avoid its use where the potential for ischemia to end organs is present.

Adolescent↗
PubMedDate not supplied

Skin blood flow changes in response to intradermal injection of bupivacaine and levobupivacaine, assessed by laser Doppler imaging.

BACKGROUND AND OBJECTIVES: The vascular effects of local anesthetics are important determinants of their therapeutic activity. Drugs that vasoconstrict have the potential clinical advantages of limited systemic uptake and prolonged duration of effect. The aim of this study was to assess quantitatively the cutaneous vasoactivity of racemic bupivacaine and one of its enantiomers, levobupivacaine. METHODS: Four concentrations of each drug (0.1 mL each of 0.125%, 0.25%, 0.5%, and 0.75%), as well as normal saline, were injected intradermally into randomly assigned sites on the forearms of 10 volunteers. We measured skin blood perfusion using laser Doppler imaging before injection and at 2.5, 10, 20, 40, 60, and 90 minutes thereafter. RESULTS: Both drugs produced a rapid, dose-dependent increase in skin perfusion (P <.001). Saline also caused an increase in perfusion, although less sustained. By 40 minutes, most responses had returned to baseline levels. However, after this time, perfusion continued to decrease, below baseline, for both bupivacaine and levobupivacaine. The exception to this was 0.75% bupivacaine, the response to which was significantly higher than the same concentration of levobupivacaine over this later period (P <.05). CONCLUSIONS: Bupivacaine and levobupivacaine both have a biphasic effect on skin microvessels. The vasoconstriction observed after 40 minutes may occur when the quantity of drug remaining at the administration site has decreased to a lower level. The continued vasodilatation caused by bupivacaine is more difficult to interpret. The results suggest that these local anesthetics cause vasodilatation at high doses and vasoconstriction at lower, subclinical doses. This hypothesis and the clinical relevance of these effects warrant further investigation.

Administration, Cutaneous↗
PubMedDate not supplied

Biomechanics of cemented and cementless prostheses.

The success of the cemented arthroplasty is due primarily due to excellent initial stability, intimate contact with the prepared bone and the isoelastic properties provided by the cement. In an experimental in vitro study, the initial stability of both the cemented and uncemented femoral components was measured and it was found that they were both very stable in simulated single limb stance (maximum motion of less than fifty microns). However, in simulated stair climbing, the uncemented components were more unstable than the cemented components (maximum micromotion of 76 microns for cemented and 280 microns for uncemented), and this relative instability of the uncemented femoral components could compromise the bone ingrowth. Studies on femurs retrieved at autopsy from patients who underwent cemented total hip arthroplasty two week sup to seventeen years earlier and were functioning well, have shown that the failure of cemented femoral components is initiated primarily by mechanical factors, consisting of debonding at the cement-prosthesis interface and fractures of the cement rather than lack of bone ingrowth or fibrous tissue formation at the interface. Thus the problems with using cemented femoral components involve the poor strength of the cement-prosthesis interface and the cement, while the problems with cementless components involve the difficulties in precisely machining the femoral canal, and providing rigid stability as well as accurate fit.

Adult↗
PubMedDate not supplied

Total parenteral nutrition: iatrogenic immunosuppression.

It may be necessary for future formulations of TPN to encompass functions other than mere provisions of nutrients. Although current solutions of TPN are well tolerated in most patients for short periods and remain an important adjunct to modern surgical therapy, these solutions have significant room for improvement. Designing the ideal artificial gut for the highly stressed patient may include reproduction of the neurological, endocrine, and immune responses that occur after the oral presentation of foodstuffs.

Animals↗
PubMedDate not supplied

Ulna neuropathy after elbow injury in children.

Six children developed seven cases of ulna neuropathy between 7 days and 6 years after significant elbow injury. None had evidence of acute nerve damage at the time of initial trauma. This complication, which develops soon after injury, has not been well documented. For this reason, the mode of presentation, treatment options, and review of the literature is presented.

Adolescent↗