Search PubMed⌕ Search

Biomedical subjects

R Greene

Publications and source records attributed to R Greene.

At least 73 records · Page 4Linked to original sources
PubMed1994

Methodological challenges and innovations in patient outcomes research.

Between 1989 and 1992, the Agency for Health Care Policy and Research (AHCPR) awarded funding to 14 special projects known as Patient Outcomes Research Teams (PORTs). These large, complex projects form the centerpiece of the first generation of research under the Medical Treatment Effectiveness Program. In carrying out their individual 5-year research plans, and through collaborative work of six Inter-PORT Work Groups, PORTs have contributed to methodological advances related to their specific clinical focus and to outcomes research in general. Each of the PORTs has followed a standard research model, involving the application of: systematic literature review, measurement of outcomes, analysis of cost and claims data, decision analysis, and strategies for disseminating findings. This article reports what has been learned by individual PORTs, and by AHCPR, regarding the usefulness of each of these methodologies, both for the ongoing projects and for the next generation of effectiveness research. Example from individual PORTs and work groups illustrate some of the methodological gains that have been made in effectiveness research and provide a glimpse of the work that remains to be done.

Analysis of Variance↗
PubMed1994

The national medical effectiveness research initiative. The search for what really works in treating common clinical conditions.

In 1989, Congress established the Agency for Health Care Policy and Research within the U.S. Public Health Service and gave it the lead in a national effort to produce reliable evidence of which medical treatments are effective and which are not. The research program addresses the effectiveness of different available strategies for diagnosis, prevention, treatment, and management of common conditions, including diabetes, and emphasizes outcomes that matter to patients. The modest size of this program and the eagerness for its results have led to the development and use of innovative research methods. Illustrations of these methods and early findings are provided.

Aged↗
PubMed1993

Application of finite-element analysis with optimisation to assess the in vivo non-linear myocardial material properties using echocardiographic imaging.

An application of finite-element analysis with an optimisation technique to assess the myocardial material properties in diastasis in vivo is described. Using the data collected from an animal model, the three-dimensional geometry of the left ventricular chamber, at several times in diastole, was reconstructed. From the measurement of the ventricular chamber pressure during image acquisition, finite-element analysis was performed to predict the expansion during diastasis. Initially, by restricting the motion of the epicardial nodes and computing the reaction forces, an 'equivalent pericardial pressure' was determined and applied in subsequent analysis. The duration of diastasis was divided into three or four intervals and the analysis was performed at each interval to assess the material properties of the myocardium. Using such a step-wise linear approach, the non-linear material properties of the myocardium during passive expansion was determined. Our results demonstrated that the computed 'equivalent pericardial pressure' increased with and was smaller than the corresponding left ventricular chamber pressure. The passive myocardium exhibited a linear tangent modulus against chamber pressure relationship which is equivalent to an exponential stress/strain relationship, similar to those suggested by in vitro studies.

Animals↗
PubMed1993

Acute electrical stimulation increases extramyocardial collateral blood flow after a cardiomyoplasty.

We hypothesized that acute electrical stimulation of a latissimus dorsi cardiomyoplasty would augment the collateral blood flow delivered by the skeletal muscle to the heart. This hypothesis was tested in an animal model (13 goats) of coronary artery disease. Six weeks after a cardiomyoplasty was performed, myocardial collateral blood flow derived from the latissimus dorsi muscle was measured with colored microspheres when the muscle was at rest and during electrical stimulation of the thoracodorsal nerve at 1.25 Hz. The area at risk for ischemia averaged 13.37 +/- 2.08 g (mean +/- standard error), or 18.4% of left ventricular mass (n = 13). At rest, significant skeletal muscle-derived collaterals developed in 9 animals, and formed predominantly to chronic ischemic myocardium (mean +/- standard error, 0.07 +/- 0.02 mL.g-1 x min-1; n = 9), rather than infarct (0.03 +/- 0.02 mL.g-1 x min-1; n = 5), or normal myocardium (0.0005 +/- 0.0001 mL.g-1 x min-1; n = 9). Stimulation increased skeletal muscle-derived collateral blood flow to chronic ischemic areas to 0.38 +/- 0.09 mL.g-1 x min-1 (n = 9) (p < 0.05). During stimulation, the collateral flow was greater in the epicardium (0.46 +/- 0.11 mL.g-1 x min-1) than in endocardium (0.14 +/- 0.09 mL.g-1.min-1) (p < 0.05). This study demonstrates that electrical stimulation of a latissimus dorsi cardiomyoplasty increases extramyocardial collateral blood flow to chronic ischemic myocardium.

Animals↗
PubMed1993

Optimal pleurodesis: a comparison study.

With the resurgence of thoracoscopy, there is renewed interest in less invasive methods of pleurodesis. We wished to compare in an animal model a variety of methods suggested in reports. The purpose of the study was to rank the effectiveness of each procedure against the standard mechanical pleurodesis. Twenty-five mongrel dogs (weight, 25 to 35 kg) underwent bilateral thoracotomy. Each animal was randomly assigned to receive two of the following methods of pleurodesis: tetracycline, talc, mechanical abrasion, neodymium: yttrium-aluminum garnet (Nd:YAG) laser (Hereus Inc, E. Rutherford, NJ) photocoagulation, and argon beam coagulator (ABC) (Beacon Lab, Bloomfield, CO) electrocoagulation of the parietal pleura. At evaluation at 30 +/- 2 days, the efficacy of pleurodesis was graded on a scale of 0 to 4, with 0 representing a complete absence of pleural symphysis and 4 the adhesion of more than one lobe to both the chest wall and mediastinum. Mean grade and standard deviation of each method were: talc, 3.0 +/- 0.67; mechanical, 3.0 +/- 0.82; tetracycline, 2.3 +/- 1.4; ABC, 1.5 +/- 0.97; and Nd:YAG laser, 0.7 +/- 0.95. Both the talc and mechanical methods were superior to either the Nd:YAG laser or the ABC (p < 0.01). In this study, neither the Nd:YAG laser nor the ABC proved efficacious in producing pleurodesis. Talc poudrage is the only method of pleural symphysis comparable with mechanical abrasion.

Animals↗
PubMed1993

Chest "gestalt" and detectability of lung lesions.

Image perception in chest radiography is thought to occur on two levels, (a) a fast global response based on learned templates ("gestalt") and, (b) a slower systematic scan process. The relative importance of "gestalt" on the detection of nodular lung cancers was studied by disturbing the "gestalt" through rotation of the radiograph but not actually diminishing the image content available for viewing. Sixty chest radiographs (20 normals, 21 with subtle lung cancers, 19 with obvious lung cancers) were presented to three readers in normal and abnormal (rotated randomly in 90 degree increments) orientation for varying durations (0.25 s, 1 s, 4 s and unlimited viewing time). The results indicate that the detectability of obvious and subtle lung lesions was degraded by the disturbed "gestalt" for both short and long viewing times. The readers did not significantly increase their unlimited viewing time when faced with rotated images (4.4 +/- 3.4 s) as opposed to non-rotated images (4.0 +/- 3.2 s). We conclude that the detection of lung lesions relies heavily on the chest "gestalt" and that systematic scanning cannot fully compensate for an impaired global response due to a disturbed "gestalt."

Humans↗
PubMed1992

Successful extended lung preservation with UW solution.

Maximum preservation times of 4-6 hr continue to plague lung transplantation. The high-potassium colloid University of Wisconsin solution (UWS) has proved superior to the crystalloid modified Eurocollins' solution (ECS) for preservation of the liver, kidney, and pancreas. The purpose of this study was to compare UWS and ECS for extended lung preservation using a technique of combined pulmonary and bronchial artery perfusion. Simultaneous pulmonary artery and bronchial artery (via a closed aortic segment) perfusion was employed to harvest the lungs of ten mongrel dogs (wt 25-35 kg) using either UWS (n = 5) or ECS (n = 5) preservation solutions. Following 17 hr of cold (4 degrees C) pulmoplegic storage, the lungs were placed in an isolated perfused working lung (IPWL) apparatus. Seven freshly harvested lungs served as a control group (CON). Lung aerodynamics and gas exchange were evaluated at standard intervals until failure of the lung on the IPWL apparatus. Time until failure (mean +/- SEM) for each group was: CON = 209 +/- 14 min; UWS = 227 +/- 26 min; and ECS = 123 +/- 29 min. Only one of the ECS lungs lasted longer than 90 min. UWS-preserved lungs displayed a gas exchange efficiency equal to the CON group and better than that in the ECS-preserved lungs (lower A-aDO2, lower intrapulmonary shunt), suggesting better protection of the alveolar capillary membrane. Although the UWS lungs were initially less compliant than the ECS lungs, at no time was there a significant difference in the total work of respiration between the two groups. We conclude that UWS provides superior protection of the alveolar capillary membrane. The aerodynamic disadvantages of UWS preservation did not effect lung survival or total work of respiration.

Adenosine↗
PubMed1992

Lactic acidosis: effect of treatment on intracellular pH and energetics in living rat heart.

Systemic acidemia may impair cardiac contractility and predispose to arrhythmias. Moreover, bicarbonate treatment may further depress cardiac performance and increase mortality. Whether changes in myocardial intracellular pH or energy metabolism underlie this diminished performance has not been clarified in the in vivo setting. Thus we investigated the effect of lactic acidosis and two proposed treatments on myocardial energetics and intracellular pH in anesthetized living rats. A previously validated 31P-labeled nuclear magnetic resonance (31P-NMR) spectroscopic technique using saturating pulses was used to follow myocardial intracellular pH, phosphocreatine (PCr), ATP, and inorganic phosphate (Pi). After obtaining baseline values, we infused lactic acid to achieve a level greater than 5 mM. We then added an infusion of either bicarbonate (n = 7) or saline (n = 5). During lactic acid infusion, arterial pH declined (from 7.27 to 7.07, P less than 0.0001), but myocardial intracellular pH did not change (7.13 vs. 7.07, P not significant). The ratio of PCr to Pi, however, decreased with acidemia (from 3.13 to 2.24, P = 0.004), suggesting impaired energy metabolism. Compared with saline, bicarbonate infusion restored systemic pH (from 7.08 to 7.29), but myocardial pH was unaltered. In addition, PCr/Pi declined further following bicarbonate treatment (1.41 vs. 2.42, P = 0.08) but not following saline. Thus, despite reversal of systemic acidemia, bicarbonate treatment was associated with more severe impairment of energy metabolism than saline. This suggests a mechanism for previously reported adverse cardiac effects of bicarbonate treatment.

Acidosis, Lactic↗
PubMed1992

Fleischner Lecture. Imaging the respiratory system in the first few years after discovery of the X-ray: contributions of Francis H. Williams, M.D.

Imaging of the respiratory system developed with exceptional rapidity in North America during the spring of 1896, after Roentgen's discovery of X-rays in November 1895, largely because of the efforts of a unique physicians, Francis H. Williams. With great zeal, this pioneer used fluoroscopy for early detection of tuberculosis and other life-threatening chest disorders. By the summer of 1896, he had accumulated more than 100 volumes containing tracings of clinical chest fluoroscopy. As a result of his extensive clinical experience, his dedication to patients' welfare, and his sense of scientific inquiry, several inventions and many landmark clinical observations were made in the first few years after the discovery of the X-ray. These included (1) the invention of a "densitometer" for standardized measurements of relative X-ray attenuation of the lung, (2) the invention of a "seehear" device to correlate auscultative findings and fluoroscopic observations, (3) the recognition that fluoroscopy was more accurate than percussion for estimating mediastinal displacement, (4) the discovery that clinically occult tuberculosis and congestive heart failure could be detected with fluoroscopy, (5) the documentation that unilateral chest disease caused decreased ipsilateral ventilatory compliance and increased contralateral ventilation, (6) the identification of the classical imaging characteristics of tuberculosis, pneumonia, pneumothorax, tension pneumothorax, pleural effusion, hydropneumothorax, emphysema, congestive heart failure, and air trapping. In April 1896, Dr. Williams described the "air bronchogram" in a radiograph of a patient with pneumonia.

History, 19th Century↗
PubMed1992

Short-term and long-term results of experimental wrapping techniques for bronchial anastomosis.

Major complications of bronchial anastomoses for either transplantation or sleeve resection include early leak, fistula formation, granulation tissue, and stenosis. To evaluate the impact of technique on these complications, we designed a nonimmunocompromised canine model with a totally ischemic bronchial segment. We wished to discover the prevalence of early and late complications of a telescoping anastomosis and if wrapping techniques modify them. We autotransplanted 25 mm of left main-stem bronchus by telescoping 1 mm of proximal into distal bronchus sutured with interrupted 4-0 polyglactin sutures. The animals were divided into four groups: no wrap; omental pedicle wrap; detached-free omental wrap; and Gelfoam sponge soaked in porcine omental extract. Weekly bronchoscopic studies assessed airway patency. After the animals were put to death at 70 days, the luminal areas of the proximal anastomoses were compared with the origin of the left main bronchus. No air leak, bronchial disruption, or infection occurred in any group at any time. Luminal narrowing occurred in all four groups but was most pronounced in the three groups in which wrapping techniques were used. We conclude that wrapping of a telescoped anastomosis is not necessary to prevent early complications. However, no method completely eliminates stenosis. Further experiments should determine the effects of immunomodulation in this model.

Anastomosis, Surgical↗