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Biomedical subjects

L L Davis

Publications and source records attributed to L L Davis.

At least 55 records · Page 3Linked to original sources
PubMed1993

Autorotation test of the horizontal vestibulo-ocular reflex in Menière's disease.

Sixty-four patients with the diagnosis of Menière's disease were tested at the House Ear Clinic with an active head-rotation test system, the Vestibular Autorotation Test (VAT). The VAT is a portable, computerized test that measures the horizontal vestibulo-ocular reflex (VOR) with the use of high-frequency (2 to 6 Hz) active head movements to obtain gain and phase. The purpose of this study was to characterize the horizontal VOR at high frequencies in patients with Menière's disease. At frequencies from 5 to 6 Hz, all patients demonstrated horizontal phase greater than 180 degrees and 85% showed abnormal VAT results. The most common patterns were decreased gain or increased phase values, or both, relative to normative data. No significant differences in the degree of abnormality in gain and phase were noted among groups of patients when the patients were clinically staged. We conclude that, in our test population of patients with Menière's disease, the VAT shows common gain and phase patterns and abnormalities of the horizontal VOR. This may contribute to high retinal image velocities, which render the patient unable to stabilize retinal images during locomotion (visual field image slip), in as many as 85% of the patients tested, regardless of clinical stage. Such high-frequency testing can reveal abnormalities of the horizontal VOR not apparent from conventional vestibular testing. Thus VAT provides additional information about the functioning VOR when combined with the present vestibular test battery.

Adult↗
PubMed1993

Criteria for critiquing clinical nursing research reports.

The primary goal of nursing research is to develop a scientific knowledge base for practice. Postanesthesia nurses are expected to critique nursing research before applying findings to clinical practice. As consumers of research, postanesthesia nurses must be able to employ critical evaluation skills to judge the merit and relevance of research to their clinical practice. This article presents criteria for critiquing clinical nursing research reports to determine their relevance to practice.

Evaluation Studies as Topic↗
PubMed1992

Family nursing research: precepts from paragons and peccadilloes.

The authors present 10 precepts that address the successes, as well as complexities and shortcomings, found in family nursing research as it has been conducted over the past decade. Problems with methodology, data collection and aggregation, random variables, and consistency with the unit of analysis all present challenges to the proper conduct of family nursing research. The authors cite these and other concerns in a critical analysis illustrated by examples from the growing body of family nursing literature.

Data Collection↗
PubMed1992

Carvedilol, a new vasodilator and beta adrenoceptor antagonist, is an antioxidant and free radical scavenger.

The antioxidant effect of carvedilol, a new vasodilating, beta adrenoceptor blocker was studied and compared with five other beta blockers. Carvedilol rapidly inhibited Fe(++)-initiated lipid peroxidation, measured as thiobarbituric acid reactive substance (TBARS), in rat brain homogenate with an IC50 of 8.1 microM. Under the same conditions, the IC50 values of atenolol, pindolol propranolol, celiprolol and labetalol were over 1.0 mM. Carvedilol protected against Fe(++)-induced alpha-tocopherol depletion in rat brain homogenate with an IC50 of 17.6 microM; propranolol, celiprolol and labetalol, up to 200 microM, did not show any effect. Using dihydroxyfumarate/Fe(++)-ADP as a OH.radical generating system and 5,5-dimethyl pyrroline-N-oxide (DMPO) as a trapping agent, the characteristic DMPO-OH signals were monitored by electron paramagnetic resonance. Carvedilol dose-dependently decreased the intensity of the DMPO-OH signal, with an IC50 of 25 microM, whereas propranolol, at 500 microM, and U74500A, a 21-aminosteroid, at 100 microM, had no effect. The antioxidant effect of carvedilol mainly resides in the carbazole moiety, and the substitution of a hydroxyl group at certain positions on the phenyl ring of either carbazole or the ortho-substituted phenoxylethylamine part of carvedilol resulted in an increase in antioxidant activity. Furthermore, the protective effect of carvedilol analogs against OH.-mediated neuronal death positively correlated to their antioxidant effect. We conclude that carvedilol is a far more potent antioxidant than other commonly used beta blockers. The apparent mechanism of carvedilol's inhibition of lipid peroxidation is mainly via scavenging free radicals. This novel property of carvedilol may contribute to the known cardioprotective activity of this compound.

Adrenergic beta-Antagonists↗
PubMed1991

Vestibular autorotation test asymmetry analysis of acoustic neuromas.

The vestibular autorotation test (VAT) measures the vestibulo-ocular reflex (VOR) response from 2 to 6 Hz, during 18 seconds of active head movements, while the patient attempts to fixate on a wall-mounted target. A new method of measuring eye velocity asymmetry from VAT data is presented, based on computer estimation of the 0th harmonics of discrete Fourier spectra over short segments of digital eye and head velocity records. Eye asymmetries greater than a 3% normal range are shown to be directionally correlated with the side of the lesions in patients with unilateral labyrinthectomies. Among patients with a diagnosis of acoustic neuroma, who were tested preoperatively with the VAT, nine of nine patients showed eye asymmetries greater than 3% toward the side of the neuroma. Those patients with acoustic neuromas who have sufficiently vigorous high-frequency head responses showed mean percentages of eye asymmetry that were linearly correlated with the size of the acoustic neuroma. These results suggest that VAT high-frequency asymmetry provides a useful method of diagnostic evaluation of the side and extent of unilateral peripheral lesions.

Aged↗
PubMed1990

Vestibular autorotation testing of Menière's disease.

Ten patients with previously confirmed diagnosis of acute-stage Meniere's disease were tested with the Vestibular Autorotation Test (VAT), a portable computerized test that measures the higher-frequency vestibulo-ocular reflex (VOR) to compute gain and phase. Patients were asked to fixate on a target and move their heads in synchrony with a computer-generated, sweep-frequency audible cue (0.5 to 6.0 Hz) through an 18-second test epoch. Head movements in both horizontal (yaw) and vertical (pitch) planes were used separately to test horizontal and vertical VORs, respectively. All subjects easily performed the VAT. Results of the horizontal tests were within normal limits for both gain and phase. The vertical gain was markedly high throughout the 2 to 6 Hz range. Mean vertical phase lags were reduced at higher frequencies. These results imply that the vertical VORs of acute-stage Meniere's patients are hypersensitive to the faster vertical head movements that occur commonly in daily activities.

Adult↗
PubMed1990

High-frequency autorotational testing of the vestibulo-ocular reflex.

Rotational testing is useful for clinical evaluation of vestibular dysfunction affecting the vestibulo-ocular reflex (VOR). Early applications relied on visual observation of nystagmus following turning. In modern use, control theory descriptors (e.g., gain and phase) are applied to patient data for comparisons with normal values. Motorized rotational chairs are used to passively oscillate patients with sinusoidal harmonic acceleration (SHA) stimulus profiles, usually at low frequencies (0.02 to 0.2 Hz). Changes in low-frequency phase and asymmetry, relative to normal values, provide useful indications of pathology. Vestibular autorotation testing (VAT) is a new, portable testing technique that utilizes microcomputers and patients' active head movements at high frequencies (2 to 6 Hz) to test both horizontal and vertical VOR responses. A head strap contains sensors and microelectronics for monitoring both head and eye movements. Higher-frequency VOR testing offers the advantages that the VOR is most active during locomotion at these frequencies and that other ocular motor systems are functionally insensitive above about 1 Hz. Results from VAT evaluation of patients with acute-stage Ménière's disease showed high vertical VOR gains, whereas patients receiving cisplatin chemotherapy showed pronounced low horizontal VOR gains and reduced phase lags. Practical experience in 4 years' clinical testing with the VAT has shown that this test is comfortable, efficient, clinically accurate, portable, and low cost, without requiring the dedicated, installed facility characteristic of other vestibular tests.

Eye Movements↗
PubMed1989

Fibronectin and postpartum infection in rabbits: an animal model.

A rabbit model was explored in preliminary studies of uterine colonization and infection, following cesarean section (CS), by toxigenic Staphylococcus aureus (Harrisburg) and other bacterial species known to be isolated from traumatized human uteri; effects on host susceptibility of fibronectin prophylaxis were studied. Histological characteristic and plasma fibronectin levels were recorded in double-blinded studies of four groups of rabbits (55 total), all sacrificed 96 h after CS performed at term. Animals which were inoculated without fibronectin prophylaxis, showed stable or slightly elevated plasma fibronectin levels through 96 h. Rabbits inoculated with nontoxigenic S. aureus (Wiley) exhibited stable fibronectin levels and less microscopic evidence of infection. All inoculated animals were colonized, but those that received fibronectin cryoprecipitate intravenously at CS showed less microscopic evidence of infection. Fibronectin levels for rabbits scores as 'seriously infected' were nearly 1.5 times that of controls. This is in contrast to other clinical studies in which chronic infections and poor clinical outcome have been strongly correlated with decreased plasma fibronectin levels. Histochemical studies of antifibronectin binding suggested that less fibronectin is deposited throughout the endometrial stroma of animals that received fibronectin prior to bacterial challenge. An increased polymorphonuclear leukocytic reaction in the stroma near the incisions was observed in animals that received fibronectin prophylaxis, with or without bacterial challenge. This reaction may be characterized as an acute-phase reaction.

Acute-Phase Reaction↗
PubMed1989

Mental health problems in primary care: a study of nurse practitioners' practice.

The purpose of this study was to explore whether NPs see clients for mental health problems in the primary care setting and the strategies NPs use to manage such problems. The results of a survey of 110 nurse practitioners suggest that NPs regularly encounter clients with mental health problems, use a wide variety of individual and family-focused strategies in caring for such clients and typically refer clients who have multiple problems/diagnoses.

Counseling↗
PubMed1988

Postcesarean section plasma fibronectin levels.

Decreases in plasma fibronectin levels following surgery and subsequent to trauma and sepsis have been previously reported. There have been no reports, however, regarding plasma fibronectin levels following cesarean section. Plasma fibronectin levels were followed for 3 days postpartum in 49 patients including cesarean section control patients, patients with cephalopelvic disproportion, pregnancy-induced hypertension, and endometritis. Cesarean section and cephalopelvic disproportion were not associated with a change in postpartum fibronectin levels. Pregnancy-induced hypertension and endometritis did show a significant increase (p less than 0.05) in plasma fibronectin levels. These levels are probably not decreased because of the large fibronectin pool in these otherwise healthy women.

Cesarean Section↗
PubMed1988

Active head-movement analysis of cisplatin-induced vestibulotoxicity.

The vestibulo-ocular reflex (VOR) acts to maintain a clear and stationary image of the visual world during movements of the head. Accurate measurement of the VOR is therefore an important clinical method for evaluation of the vestibular system. We applied a new method of computerized vestibular testing, the Vestibular Autorotation Test (VAT), which is based on 18 seconds of active head movements. The VAT was used to prospectively study the horizontal VOR of nine patients with cancer who were being treated with cisplatin. Patients were instructed to move their heads in the horizontal plane in synchrony with audible clicks of a linearly increasing frequency range, from 0.5 to 6.5 Hz. Electro-oculographic (EOG) eye movements and head velocity were monitored and digitized to compute horizontal VOR gain and phase from 2 to 6 Hz. Patients were tested with the VAT before the initial cisplatin treatment, and then before each subsequent cisplatin treatment. The pretreatment gains and phases were compared with those obtained after the final cisplatin treatment. Results showed decreased VOR gains at 3.1 Hz, 3.9 Hz, and 5.1 Hz, and increased phase lags at 3.1 Hz and 3.9 Hz. We conclude that VAT analysis of the horizontal VOR at frequencies 3 to 5 Hz is useful for detection and monitoring of cisplatin vestibulotoxicity.

Adult↗