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Biomedical subjects

J W Davis

Publications and source records attributed to J W Davis.

At least 343 records · Page 19Linked to original sources
PubMedDate not supplied

Arterial windkessel parameter estimation: a new time-domain method.

We developed and validated a new, more accurate, and easily applied method for calculating the parameters of the three-element Windkessel to quantitate arterial properties and to investigate ventriculoarterial coupling. This method is based on integrating the governing differential equation of the three-element Windkessel and solving for arterial compliance. It accounts for the interaction between characteristic impedance and compliance, an important phenomenon that has been ignored by previously implemented methods. The new integral method was compared with four previously published methods as well as a new independent linear least-squares analysis, using ascending aortic micromanometric and volumetric flow measurements from eight dogs. The parameters calculated by the new integral method were found to be significantly different from those obtained by the previous methods but did not differ significantly from maximum likelihood estimators obtained by a linear least-squares approach. To assess the accuracy of parameter estimation, pressure and flow waveforms were reconstructed in the time domain by numerically solving the governing differential equation of the three-element Windkessel model. Standard deviations of reconstructed waveforms from the experimental ensemble-averaged waveforms, which solely reflect the relative accuracy of the Windkessel parameters given by the various methods, were calculated. The new integral method invariably yielded the smallest error. These results demonstrate the improved accuracy of our new integral method in estimating arterial parameters of the three-element Windkessel.

Animals↗
PubMedDate not supplied

Assessment of the Frank-Starling relationship by two-dimensional echocardiography.

The Frank-Starling relationship between left ventricular stroke work and end-diastolic minor-axis cross-sectional area was evaluated as a load-insensitive measure of inotropic state by two-dimensional echocardiography in 10 conscious dogs. Stroke work was calculated as the product of systolic change in cross-sectional area and either (1) beat-to-beat mean arterial pressure or (2) initial systolic blood pressure. Both Frank-Starling relationships were highly linear during preload variation (mean r = 0.96), sensitive to the inotropic state (slope increase with calcium 51% +/- 43% and 62% +/- 53%, respectively), and insensitive to afterload (r < 0.4, slope or x intercept versus afterload). Thus the Frank-Starling relationships derived from two-dimensional echocardiographic images and peripheral arterial pressure may be a useful and practical means of assessing inotropic state with minimally invasive measurements.

Animals↗
PubMedDate not supplied

Alcohol use inventory: screening and assessment of first-time driving-while-impaired offenders. II. Typology and predictive validity.

This study evaluated the use of Alcohol Use Inventory (AUI) for driving-while-impaired (DWI) screening, by determining whether DWI offenders (n = 1644), grouped according to their reported alcohol involvement on the AUI, would have different rates of recidivism in a 5-year follow-up. Cluster analysis using the six second-order scales produced six groups (clusters 1-6) described as the Low-Profile (50%), Alcohol-Preoccupation (14%), Enhanced (22%), Enhanced-Disrupt (9%), Anxious-Disrupt (3%), and High-Profile (1%) types. They were characterized by different sociodemographic profiles. Members of cluster 4 were associated with the highest DWI recidivism rate (40%), committing one or more further DWI, and clusters 5 and 6 were associated with the highest rate of committing two or more DWIs. Rates of subsequent traffic convictions and crashes were, however, not statistically different among the clusters. Predictors of DWI recidivism included male gender, young age, less-educated, high blood-alcohol concentration at arrest, and clusters of 3 and 4. Different typologies indicated that the needs for treatment might be different. Evaluators should keep in mind the strength of AUI, use risk factors identified in the study, and take measures of test-taking defensiveness to enhance overall predictive validity.

Adolescent↗
PubMedDate not supplied

Acute effect of tobacco cigarette smoking on the platelet aggregate ratio.

The purpose of this study was to determine whether cigarette smoking acutely increased circulating platelet aggregates as detected by lowering of the platelet aggregate ratio. Eighteen (11 male and 7 female) volunteers ranging from 16 to 47 years of age rested during a 20-minute control period and smoked two unfiltered tobacco cigarettes during another 20-minute period. Platelet aggregate ratios (mean +/- SD) before and after the control period were 0.86 +/- 13 and 0.82 +/- 0.12 respectively (p greater than 0.05) and before and after smoking were 0.84 +/- 0.14 and 0.66 +/- 0.18 respectively (p less than 0.01). The mean plasma nonesterified fatty acid concentration was not significantly different before and after smoking suggesting that the decrease in platelet aggregate ratio was not mediated through elevation of the plasma nonesterified fatty acid concentration. Our results are consistent with the theory that platelet aggregates contribute to the increased incidence of myocardial infarction and sudden death from coronary artery disease observed among cigarette smokers.

Adolescent↗
PubMedDate not supplied

Use of overhead hooks in burn surgery.

An overhead "hook-and-pulley" system installed in the burn operating room can facilitate patient positioning and increase efficiency of the surgical team. This system can be installed easily and inexpensively; its use is recommended.

Burns↗
PubMedDate not supplied

The use of the bone curet in debridement of the burn wound and graft recipient sites.

We describe the use of the simple bone curet for the purpose of scraping and debriding partial-thickness burn wounds and other chronic wounds encountered by the burn surgeon before autograft placement. In our experience the instrument allows more efficient and safer operating room debridement than does the standard scalpel blade.

Burns↗
PubMedDate not supplied

Base deficit as an indicator or resuscitation needs in patients with burn injuries.

The utility of base deficit (BD) as a marker of shock and as an indicator of resuscitation requirements has been recognized in the trauma population. Base deficit in thermally injured patients has not been closely examined. The purpose of this study was to evaluate the usefulness of initial BD related to other resuscitation parameters in thermally injured patients. Burn center records over a 2-year period were reviewed; patients who survived at least 24 hours and had initial arterial blood gases were included. Parkland estimated fluid requirements underestimated actual volume requirements, but Parkland-calculated fluid requirements were related (p < 0.01) to actual volume requirements. BD had a better correlation to actual volume requirements, and a BD of -6 or less correlated with larger burn size (23% +/- 2% vs 47% +/- 9% total body surface area), and markedly increased mortality rate (9% vs 72%, p < 0.001).

Acidosis↗
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S-(1,2-dichlorovinyl)-L-cysteine-induced nephrotoxicity in the New Zealand white rabbit: characterization of proteinuria and examination of the potential role of oxidative injury.

S-(1,2-dichlorovinyl)-L-cysteine (DCVC)-induced nephrotoxicity in vivo was investigated in New Zealand White rabbits. A primary emphasis in these studies was further characterization of DCVC-induced nephrotoxicity using a variety of serum and urinary analytes, including sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Additionally, the role of oxidative injury was assessed to address the dichotomy between reports indicating that such a mechanism is important in vivo and those indicating that such mechanisms do not contribute substantially to the mechanism of effects observed in vitro. Urine was collected prior to and at 8 and 24 hr after iv administration of DCVC. Serum was collected 15 min prior to and 24 hr after DCVC administration. Rabbits were euthanized 24 hr post-DCVC administration, and kidneys were fixed in formalin and further processed for light microscopic examination. DCVC (10 mg/kg, iv) induced a 45-50-fold increase in total urinary protein excretion, a 10-15-fold increase in urinary N-acetyl-beta-D-glucosaminidase concentration, plus a marked glucosuria by 24 hr postadministration. Additionally, DCVC increased serum creatinine levels by about 2-fold, with a trend toward increased blood urea nitrogen. SDS-PAGE analysis of rabbit urine confirmed the clinical finding of marked proteinuria in DCVC-treated animals, which in contrast to previously reported data was due to the presence of both low and high molecular weight proteins. Antioxidants had no significant effect on DCVC-dependent renal injury, nor was there evidence for DCVC-induced lipid peroxidation, as measured by either thiobarbituric acid-reactive substances or a commercial assay for malondialdehyde and hydroxalkenals.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylglucosaminidase↗
PubMedDate not supplied

Appropriate clinical application of bone density measurements.

When bone mass is properly evaluated as a risk factor, as opposed to a diagnostic test, its relationship to fracture risk is apparent. There is now substantial agreement among several prospective studies relating bone mass of the radius and calcaneus to fractures of the wrist, spine, hip, and other sites. Thus, selection of menopause-age women for preventive measures, including estrogen replacement, can be guided by measurements of bone mass. Although levels of bone mass can indicate the presence of fracture risk, they are insufficient measures of disease severity, and additional information is required for clinical decision making. It is possible to estimate Remaining Lifetime Fracture Probability (RLFP) based upon current bone mineral content (BMC), current age, life expectancy, and anticipated rate of bone loss. Objective estimates such as RLFP can be used to determine which patients may benefit from drug treatment of osteoporosis. The ultimate objective is to match the level and intensity of treatment to the actual level of fracture risk.

Aged↗
PubMedDate not supplied

Augmentation of in vitro lymphocyte blastogenesis and cytotoxicity responses by tumor cells modified with dodecanoyl cytochrome C.

In a model testing the immune responsiveness of allogeneic lymphocytes against the human cervical cancer cell line SW756, tumor cells coupled to dodecanoyl cytochrome C (D-cyt C) demonstrated augmented immunogenicity. The coupling was noncovalent; the D-cyt C spontaneously associated with the SW756 cells during mixing. Augmented immunogenicity was shown in both in vitro blastogenesis and cytotoxicity assays. The extent of cell-associated D-cyt C, which influenced the in vitro responsiveness, was easily controlled. Increased lipoprotein concentrations and increased lipid substitution of the cyt Cs led to greater cell uptake. Under the maximum conditions, 60-80 micrograms D-cyt C were bound/10(7) SW756 cells. In the blastogenesis assay, augmented immunogenicity was observed on days 3 and 4 after cocultivation of the allogeneic lymphocytes with the modified SW756 cells. When cells modified by the optimal D-cyt C preparations (as determined in the blastogenesis assay) were tested in the cytotoxicity assay, augmented responses were observed across a range of lymphocyte:tumor cell ratios. Our results demonstrate that the modification of SW756 cells with D-cyt C can augment the immune responses detected in in vitro assays.

Adhesiveness↗