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Biomedical subjects

R B Dunn

Publications and source records attributed to R B Dunn.

At least 19 recordsLinked to original sources
PubMed1998

Follow-up assessment of standing mobility device users.

The use of standing devices by spinal cord-injured subjects was investigated through a national survey of a sample of individuals who returned their manufacturer's warranty card to two companies. We obtained a 32% response rate (99/310). The majority of respondents were male (87%) with a median age between 41 and 50 years. Seventy-seven percent were paraplegic and 21% were quadriplegic. Forty percent had between 1 and 5 years experience with their device, and 84% of those responding were currently using their standing device. Forty-one percent used their standing device one to six times a week; two-thirds stood between 30 minutes and 1 hour for each use. Less than 10% of subjects experienced any side effects, such as nausea or headaches, from standing. Twenty-one percent of subjects reported being able to empty their bladder more completely. There was also a favorable response by some individuals on the effects of the standing devices on bowel regularity, reduction of urinary tract infections, leg spasticity, and number of bed sores. Finally, 79% of subjects highly recommended use of standing devices to other people with spinal cord injury. The positive responses of individuals using standing devices is a strong recommendation for the assistive technology community to make these devices more available to individuals with spinal cord injury.

Adult↗
PubMed1997

Plasma renin activity in heart failure-prone SHHF/Mcc-facp rats.

Plasma renin activity (PRA) increases during heart failure; however, PRA is altered by drug therapy, and it is difficult to study the natural progression of elevated PRA in humans and the possible factors that contribute to its rise. This study evaluated PRA in a drug-naive hypertensive rat model (SHHF/Mcc-facp) that has a genetic program resulting in heart failure (HF). Mean arterial blood pressure and PRA were determined and correlated to heart weight index in conscious normotensive, spontaneously hypertensive rats and HF rats of various ages. PRA, atrial natriuretic peptide, and aldosterone levels progressively increase with age in male HF rats. PRA and blood pressure are independently correlated to cardiac hypertrophy in male HF rats. Atrial natriuretic peptide was elevated in spontaneously hypertensive compared with normotensive rats. Female HF rats have elevated PRA, but the increase is temporally delayed compared with that in male HF rats. Hypertension, PRA, and male gender are independent factors contributing to cardiac hypertrophy and heart failure in the HF model. The HF rat model may prove useful in determining the contribution of these factors in the progression from cardiac hypertrophy to heart failure.

Aging↗
PubMed1995

Diaphragm and accessory respiratory muscle stimulation using intramuscular electrodes.

We tested the hypothesis that electrical stimulation of respiratory muscles can be obtained from intramuscular electrodes. In acute anesthetized dogs, suture-type intramuscular electrodes were placed in each hemidiaphragm and needle electrodes were placed in various intercostal regions of the thorax. During a hyperventilation induced period of apnea a 2-second stimulation was applied to the diaphragm or to the thoracic electrodes, followed by a combined thoracic-diaphragm stimulation period. Thoracic expansion and tidal volumes were measured as indices of inspiratory effort. We found that diaphragm stimulation produced tidal volumes between 104% and 180% of spontaneous breathing. Electrodes in the upper thorax produced chest expansion and when combined with diaphragm stimulation increased tidal volumes (p < .05). We conclude that intramuscular electrodes represent a feasible method for long-term electrogenic ventilation. Also, thoracic support for diaphragm pacing in quadriplegics could produce a more effective long-term system that is less prone to fatigue and failure.

Animals↗
PubMed1994

Dynamic bulbocavernosus reflex: dyssynergia evaluation following SCI.

High urethral resistance caused by detrusor-sphincter dyssynergia (DSD) occurs following spinal cord injury (SCI) and results in poor voiding. A major pelvic floor reflex that may be involved in DSD is the bulbocavernosus reflex (BC) and evaluation of this reflex during the micturition cycle may provide additional information regarding this role. The periodic BC observed during micturition via cystometry is described as a dynamic bulbocavernosus reflex (DBC). The DBC was induced in upper motor neuron SCI patients using periodic dorsal penile nerve stimulation; the evoked reflex response was recorded with an anal sphincter pressure sensing balloon. Stimulation of 15-50 mA was applied at the base and dorsal side of the penis with surface electrodes, pulsed at a rate of 0.25 Hz. By applying the stimulation during cystometry, the BC reflex could be evaluated throughout the entire micturition cycle. Results showed that the DBC increased during bladder filling and bladder contractions. These findings indicate that an enhanced BC reflex is a major factor causing increased urethral resistance during micturition.

Adult↗
PubMed1991

The hepatocellular thyroid status of uremic rats estimated from the abundances of thyroid hormone-dependent nucleoplasmic proteins.

Although the serum thyroxine (T4) and triiodothyronine (T3) concentrations of uremic rats are commensurate with moderate hypothyroidism, their thyroid status at the tissue level remains controversial. To help establish the hepatocellular thyroid status of uremic rats, a novel tissue marker (nuclear protein abundances) was evaluated in uremic rats (U), hypothyroid rats (H), and hypothyroid uremic rats (HU). Uremia was established by five-sixths nephrectomy. Moderate hypothyroidism was established by partial thyroidectomy or by provision of drinking water supplemented with propylthiouracil and T4. Normal rats (N) and pair-fed, sham-operated rats (1 to 3 weeks after surgery) served as controls. Animals were killed 1 to 5 weeks postoperatively. The following values were obtained 5 weeks after surgery, at which time the total and free serum T4 and T3 levels of the hypothyroid rats (H) were equivalent to those of the uremic rats (U). Total T4 (micrograms/dL +/- 1 SD): N, 5.4 +/- 1.7; H, 2.2 +/- 0.5; U, 1.9 +/- 1.5; HU, 0.5 +/- 0.0. Free T4 (ng/dL +/- 1 SD): N, 535 +/- 165; H, 126 +/- 37; U, 135 +/- 89; HU, 26 +/- 1. Total T3 (ng/dL +/- 1 SD): N, 63 +/- 20; H, 39 +/- 14; U, 38 +/- 18; HU, 13 +/- 4. Free T3 (ng/dL +/- 1 SD): N, 7.83 +/- 3.00; H, 3.87 +/- 1.05; U, 3.47 +/- 1.73; HU, 0.94 +/- 0.47. Hepatocellular thyroid status was estimated from the relative abundances of two nucleoplasmic proteins on polyacrylamide gel electrophoregrams.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Medical audit in geriatric medicine.

A form developed to audit the case notes of general medical patients was modified for use in geriatric medicine. The case notes of 41 admissions to the geriatric wards of a teaching hospital were audited with the new form and their contents did not come up to the standard set. Deficiencies were found in those parts of the notes considered to reflect the distinctive features of the specialty, e.g. the functional history, the assessment of mobility and the recording of multidisciplinary case conferences. The introduction of a standard history and examination form to meet the needs of patients admitted to geriatric wards, better training in geriatric medicine for junior doctors and closer scrutiny of medical records by consultants are suggested as ways of improving documentation in the case notes.

England↗
PubMed1986

Regional blood flow and metabolite levels in the left ventricular free wall and septum during aortic insufficiency: implications for the development of asymmetric septal hypertrophy.

Asymmetric septal hypertrophy is considered by many to be pathologic but its presence in a number of states associated with left ventricular overload indicates that it may develop as an adaptive feature in the overloaded heart. This hypothesis implies that initially in these states a greater systolic stress and thus energy metabolism occurs in the ventricular septum than in the left ventricular free wall. It was previously demonstrated that in the early stages of ischemia regional differences in energy metabolism could be determined by comparisons of tissue high energy phosphate depletion and lactate accumulation. In the present study these measurements were made in an animal model of left ventricular overload. In open chest dogs aortic insufficiency was produced, which served to provide both volume overload to the left ventricle and regional myocardial ischemia. In addition to regional metabolite levels, measurements of regional blood flow were determined using radioactive microspheres. Tissue samples were taken from the left ventricle and interventricular septum, freeze clamped, divided transmurally into thirds and analyzed for creatine phosphate, adenosine triphosphate and lactate. Animals with myocardial ischemia after aortic insufficiency were classified into two groups: those in which ischemia was limited to the inner left ventricle and left side of the septum and those with more extensive ischemia transmurally. In the latter group, creatine phosphate depletion and lactate accumulation were greater in the septum, but myocardial blood flow was also more depressed in the septum than in the left ventricle. In the former group, where ischemia was more restricted, metabolite changes were also more severe in the left septum than in the inner left ventricle.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1984

Transmural changes in porcine and canine hearts after circumflex artery occlusion.

The distribution of the coronary collateral circulation is an important determinant of the myocardial response to acute coronary artery occlusion. The dog shows an unequal response across the ventricular wall, whereas the pig seems to have more uniform transmural changes. This study was undertaken to compare the metabolic and blood flow response in pigs and dogs to acute occlusion of the circumflex artery. Microspheres (8-10 micron) were used to determine control blood flow and flow 5 min after occlusion. A transmural tissue sample from the center of the ischemic zone was taken at 8 min after occlusion, and inner, middle, and outer layers were analyzed for high-energy phosphates and lactate. The remainder of the heart was analyzed for microsphere distribution. The epicardium in the dog showed less severe damage than the subendocardium. High-energy phosphates were higher and lactate lower in this region. In the pig high-energy phosphates and lactate were the same in the subepicardium and subendocardium. Blood flow to regions surrounding the central ischemic zone in pigs was generally uniform across the ventricular wall or greater in the inner wall than in the outer wall. These results verify that dogs as a group have a greater subepicardial protection during coronary artery occlusion. Pigs, however, demonstrate uniform ischemia or even slightly less severe ischemia in the subendocardium in regions of restricted blood flow.

Adenosine Triphosphate↗
PubMed1984

High energy phosphate depletion and lactate accumulation in the interventricular septum and left ventricular free wall of the dog after total coronary occlusion.

We measured indices of energy metabolism in tissue samples taken from the interventricular septum and left ventricular free wall of open-chest dogs under control conditions and after a 20-second period of no coronary inflow. The heart was paced at 150 beats/min, and arterial pressure was controlled by aortic constriction. Each tissue sample was divided into three transmural regions and analyzed for creatine phosphate, adenosine triphosphate, and lactate. Data were also obtained in animals subjected to ventricular fibrillation, with ventricular pressures reduced to atmosphere and sampling delayed to 70 seconds, and with the pulmonary artery constricted prior to coronary artery occlusion. In control animals, there were no metabolite differences between the free wall and septum. Coronary occlusion produced a lactate gradient across both the free wall and septum, with the highest lactate concentrations occurring in the regions adjacent to the left ventricular cavity. The increase in tissue lactate above control was greater in the septum than in the free wall. Coronary occlusion decreased tissue creatine phosphate but not adenosine triphosphate. The decrease in creatine phosphate was greater in the septum than in the free wall. Coronary occlusion and ventricular fibrillation, or coronary occlusion and ventricular pressures reduced to atmosphere, produced neither transmural metabolite differences nor differences between the free wall and septum. Pulmonary artery constriction increased right and decreased left ventricular pressures.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1983

Respite admissions and the disabled elderly.

A retrospective descriptive study of the elderly patients served by a respite admission program in a teaching hospital is described. Data were collected by health record review and interviews with the program social worker. In the three years covered by the study there were 28 patients, with a mean age of 80.5 years. Fifty-seven per cent were male, 68 per cent, married, 29 per cent, widowed, and 3 per cent, single. When first admitted they were all living in their own homes or the home of a child. Seventy-nine per cent of the patients had moderate or severe dementia, with or without physical disability. Family members were the main caregivers and home care services provided support in 54 per cent of cases. Ninety-three per cent of the patients attended the geriatric day hospital. The patients received respite admissions for a mean of 10.8 months. At the end of the study more than a third of the patients were still living at home and half had entered long-term care facilities. By means of respite admissions supplemented by day hospital attendance it has been possible to maintain in the community disabled elderly patients who might otherwise have required immediate institutionalization. The need for more respite care and in-home services is discussed and a role for long-term care facilities as major providers of respite care suggested.

Aftercare↗
PubMed1983

Ventricular filling pressure as a determinant of coronary blood flow during ischemia.

The role of ventricular filling pressure (VFP) as a determinant of coronary blood flow (CBF) in the acutely ischemic ventricle was examined in the open-chest dog under conditions of a reduced, constant coronary artery pressure and an unstable VFP. Blood delivery to different layers of the ventricle and ischemic metabolic changes occurring in these layers were also determined and compared with appropriate control data. A close, inverse, linear relationship between VFP and CBF was found in animals exhibiting a progressive rise in VFP from 6 +/- 0 to 25 +/- 1 mmHg (r = 0.99). A lower endocardial-to-epicardial ratio of delivered blood and a steeper transmural gradient in ischemic metabolic changes were noted in these animals compared with similarly prepared animals exhibiting a stable VFP. The findings demonstrate the importance of VFP as a determinant of CBF during ischemia, and they lend support to the concept that blood flow in the ischemic ventricle is regulated by a preload-dependent transmural gradient in coronary driving pressure.

Animals↗
PubMed1983

Cardiovascular responses of the dog to acute smoke toxicity.

Cardiovascular function and metabolism were investigated during and after an acute bout of smoke inhalation in dogs anesthetized with morphine-chloralose. Smoke was generated from burning charcoal briquets layered with hardwood sawdust. By the end of 8 min of smoke inhalation significant increases occurred in left and right ventricular dP/dt, heart rate, and respiratory rate while aortic blood pressure underwent little or no change. These hemodynamic changes were paralleled by marked increases in carboxyhemoglobin, lactate, plasma epinephrine, and norepinephrine. Arterial blood gases showed significant decreases in PO2 and pH accompanied by a rise in PCO2. The presence of hypoxic hypoxia and hypercapnia was reversed during the postinhalation period, while catecholamines, carboxyhemoglobin, and lactate remained significantly above control. The ECG recorded throughout the experiment generally showed ventricular premature beats, atrioventricular conduction abnormalities, and increases in T wave amplitude. The above data led to the conclusion that acute smoke toxicity causes cardiac and metabolic alterations resulting from widespread stimulation of the sympathetic nervous system.

Animals↗
PubMed1979

High energy phosphate stores and lactate levels in different layers of the canine left ventricle during reactive hyperemia.

To study postischemic recovery of myocardial energy metabolism in relation to the reactive hyperemic response, the tissue levels of creatine phosphate (CP), adenosine triphosphate (ATP), and lactate were estimated in the outer, middle, and inner layers of the left ventricle before, during, and at several times after a 20-second bilateral coronary arterial occlusion in the open-chest dog. The reactive hyperemic response was characterized by monitoring blood flow in the cannulated coronary sinus in a separate group of dogs. Substantial changes in myocardial CP and lactate, but not ATP, were produced by the occlusion and reciprocal transmural gradients in CP and lactate occurred such that CP was lowest and lactate was highest in the inner layer. Recovery of high energy phosphate stores (CP + ATP) occurred long before blood flow returned to the preocclusion level, this being achieved in two of the three layers after completion of only 29% of the reactive hyperemic response when the blood flow debt repayment was 151%. Lactate returned to control levels during the response, but recovery times in the different layers were delayed compared to those for the high energy phosphate stores. A transmural lactate gradient was maintained as the regional levels declined, and recovery times were different for each of the three layers, being longest in the inner layer. The results suggest that during the reactive hyperemic response (1) kinetically different processes are involved in the repletion of energy stores and the removal of anaerobically produced metabolites, and (2) metabolic vasodilation of coronary vessels probably is more pronounced and sustained longer in the inner than in the outer ventricular layer.

Adenosine Triphosphate↗
PubMed1975

Uptake of lactate by dog skeletal muscle in vivo and the effect of free fatty acids.

These experiments were designed to determine: 1) if lactate can be extracted from the arterial blood and utilized by resting skeletal muscle of the dog, and 2) if lactate uptake or production by skeletal muscle is influenced by the level of circulating free fatty acids. Skeletal muscle arteriovenous differences in lactate were measured at several arterial lactate and free fatty acid concentrations. With sodium pentobarbital anesthesia and a low concentration of free fatty acids, arterial lactate concentrations of 1-2 mM were associated with extraction of lactate; however, when circulating free fatty acids were elevated (greater than 1 mM), no extraction of lactate occurred at these lactate concentrations. The relationship between arterial free fatty acids and uptake or release of lactate demonstrated in these in vivo studies suggest that the inhibition of free fatty acid release from adipose tissue that occurs when the arterial lactate concentration increases may function facilitate the metabolism of lactate by skeletal muscle.

Albumins↗
PubMed1975

Effect of circulating FFA on lactate production by skeletal muscle during stimulation.

The present experiments were undertaken to study the effects of FFA on lactate production by skeletal muscle during stimulation. In the first group, dogs were anesthetized with sodium pentobarbital and given no anticoagulant. The second group was also anesthetized with sodium pentobarbital but in addition given heparin and a fat-albumin infusion to elevate FFA. Stimulating the nerves to a group of skeletal muscles in the hindlimb (1.5/s) increased muscle blood flow 2.4-fold in both groups. In the first group stimulation did not alter the arteriovenous difference of lactate across the muscles. The difference was close to zero before and during stimulation. However in the second group, in which FFA were elevated, stimulation produced a large increase in muscle lactate production. In both groups there were no differences in the L/P ratio of muscle venous blood during stimulation. These results indicate that an increase in lactate production following muscle stimulation is not necessarily related to a state of tissue hypoxia.

Anesthesia, General↗