Biomedical subjects

E S Clark

Publications and source records attributed to E S Clark.

At least 19 recordsLinked to original sources

PubMed1996

Delrin material characteristics.

Delrin acetal resin, a product of DuPont, is formed from the polymerization of formaldehyde. The tightly interlocked helical molecules and high crystallinity result in excellent mechanical properties. Its superiority in tensile strength, stiffness, creep resistance, and fatigue classify it as an "engineering resin', a term used for plastics which can compete with metals in many applications. One of the important characteristics separating Delrin from other engineering plastics such as polyamides (nylons) is its very low water absorption and the small effect of aqueous solutions on its properties. The structure of Delrin is reviewed on several levels: chemical, crystallographic, lamellar, and spherulitic. The relationship of the structure to the properties of moldings of Delrin is discussed.

Crystallography↗

PubMed1996

Surface and edge wear of Björk-Shiley Delrin heart valve discs.

BACKGROUND AND AIMS OF THE STUDY: Wear of Björk-Shiley Delrin (BSD) heart valve discs is known to have occurred in some patients, possibly contributing to increased regurgitation. This paper specifically addresses surface and edge wear that have been observed on some discs of explanted BSD valves after implant durations up to 22.4 years. METHODS: The wear patterns have been documented using either photographic or scanning electron microscopic methods for 42 out of 73 explanted BSD valve discs. The remainder of the 73 discs were not available for analysis. RESULTS: One form of surface wear found on 18 out of 42 of the Delrin discs was the concentric wear of mild abrasive origin along the surface near the disc edge due to contact with the inlet and outlet struts. In five instances, surface anomalies were observed, primarily in the areas of high velocity blood flow. This paper also describes two Delrin discs with non-concentric edge wear patterns: (a) one which appears to be due to fatigue micro-chipping and abrasive wear of the disc of a 20 year BSD explant, which had fibrous tissue ingrowth, causing abnormal rotation of the disc during valve closure, and (b) a second one which is thought to have been caused by a cutting action of the knife-like stub of one inlet strut leg which had separated. Cross-sectional analyses of two explanted BSD discs, with full indent grooves on the inflow side, indicated that the Delrin material was primarily compressed under these wear grooves, rather than removed by abrasion. Hardness profiles indicated that the Delrin 150 microns below the surface was harder and would tend to prevent further deformation. A simple model describing the compound impact (impact with sliding) phenomenon is introduced to explain abrasive wear found on some explanted BSD discs. CONCLUSION: Based on the studies here and reports in the literature, the BSD heart valve appears to present a design which provides many years of service and, when wear occurs, it occurs in a manner that provides easily recognized clinical symptoms, which allow time for diagnosis and treatment.

Aortic Valve↗

PubMed1991

Ocular pharmacology.

Application of sound ocular therapeutic principle is more difficult in food animals than most other species. Financial or husbandry constraints limit the practitioner's ability to use the entire range of ocular drugs available or to use them with adequate frequency. These problems may be dealt with by using systemically administered drugs when effective or by employing vehicles or delivery techniques that necessitate minimal dosing frequency. By far the most important medically treatable eye disease encountered in food animal practice is IBK. Effective therapies include systemic administration of long-acting oxytetracycline, subconjunctival administration of a variety of antibiotics, or topical application of benzathine cloxacillin. Infectious conjunctivitis in sheep and goats due to a variety of agents may be treated successfully with tetracycline in most cases. Conjunctivitis and keratitis secondary to IBR virus usually are given supportive therapy only, although specific antiviral drugs have been used in the treatment of herpetic eye disease in other species. Anterior uveitis is best treated by corticosteroid and mydriatic therapy in addition to treatment of the underlying cause, if identified.

Animals↗

PubMed1991

Effects of slow infusion of a low dosage of endotoxin on systemic haemodynamics in conscious horses.

The effects of intravenous (iv) infusion of endotoxin for 60 mins at a cumulative dosage of 0.03 micrograms/kg bodyweight on systemic arterial, right atrial and pulmonary arterial pressures, heart rate, cardiac output, and derived pulmonary vascular resistance and total peripheral vascular resistance were compared to the effects of iv infusion of saline solution in four healthy horses. Heart rate was increased significantly after endotoxin infusion, although diastolic arterial pressure, systolic arterial pressure, electronically averaged arterial pressure, cardiac output, total peripheral resistance, and right atrial pressure did not change significantly. Average pulmonary arterial pressure was increased significantly by endotoxin infusion. This was accompanied by a trend toward increased diastolic pulmonary arterial pressure (P = 0.1), systolic pulmonary arterial pressure (P = 0.08) and pulmonary vascular resistance (P = 0.07). These results suggest that low dosages of endotoxin produce pulmonary hypertension without causing hypotensive, hypodynamic shock.

Animals↗

PubMed1990

Septicemia, atrial fibrillation, cardiomegaly, left atrial mass, and Rhodococcus equi septic osteoarthritis in a foal.

A foal with vegetative bacterial endocarditis affecting the wall of the left atrium was treated successfully with cefotaxime, erythromycin, and rifampin. Bacterial isolates included Escherichia coli from blood and Rhodococcus equi from a P-type osteomyelitic lesion of the left third metatarsal bone and from synovial fluid from the left metatarsophalangeal joint. Cardiac complications included cardiomegaly and atrial fibrillation, which responded to treatment with digoxin and quinidine sulfate. Cardiac function was considered normal 18 months after treatment. Bacteriologic cure of osteoarthritis was achieved by use of surgical debridement, lavage, and local and systemic antimicrobial treatment; however, lameness developed 18 months after treatment when training for flat racing was begun. Radiography revealed chronic degenerative joint disease.

Actinomycetales Infections↗

PubMed1990

Pericarditis in horses: six cases (1982-1986).

Records of 6 horses with pericarditis were reviewed. Septic pericarditis was suspected in all horses, based on historic and clinical findings. In horses 1, 2, and 4, cytologic examination of the pericardial effusion revealed acute inflammation with severe neutrophil degeneration. In horses 3 and 5, cytologic examination of pericardial fluid revealed subacute inflammation with degenerated neutrophils, and in horse 6, chronic active inflammation, with well preserved neutrophils. In horses 1 and 3, bacteria were identified on cytologic examination of pericardial fluid. Results of microbiologic cultures of pericardial fluid were positive in horse 3. All horses were treated with broad-spectrum antibiotics. An indwelling pericardial catheter was used to lavage and directly administer antibiotics into the pericardial sac. Horses 1, 4, 5, and 6 survived, horse 2 died of unrelated causes, and horse 3 was euthanatized at the owner's request. Surviving horses returned to athletic performance.

Animals↗

PubMed1990

Oxidant-induced increases in mucosal permeability in developing piglets.

Reactive oxygen metabolites have been implicated in the pathogenesis of mucosal injury induced by ischemia-reperfusion in adult animals, with recent interest centering on the capacity of polymorphonuclear neutrophil-derived oxidants to mediate this injury. A role for oxidants has also been postulated in the etiology of neonatal necrotizing enterocolitis. Based on evidence that the intrinsic capacity of the neonatal piglet intestine to detoxify hydrogen peroxide (H2O2) is minimal relative to that of older piglets, we characterized the changes in mucosal permeability induced by luminal perfusion with H2O2 and hypochlorous acid at concentrations that can be produced physiologically by activated neutrophils (0.05 mmol/L, 0.1 mmol/L, and 0.5 mmol/L), in the distal ileum of 1-d- and 1-mo-old piglets. Mucosal permeability was quantitated by measurement of blood-to-lumen clearance of 51-labeled chromium EDTA. Luminal perfusion with either H2O2 (0.05 mmol/L and 0.1 mmol/L) or hypochlorous acid (0.1 mmol/L and 0.5 mmol/L) significantly increased mucosal permeability in newborn piglets but did not affect mucosal permeability in 1-mo-old animals. Perfusion with 0.5 mmol/L H2O2 significantly increased mucosal permeability over control values in both age groups, but injury in the newborn intestine was significantly greater than that observed in 1-mo-old animals. Thus, as predicted by the reduced intrinsic capacity of the mucosa of neonatal piglets to detoxify H2O2, the ileum of newborn piglets is more vulnerable to oxidant-induced mucosal injury than is the ileum of older animals.

Age Factors↗

PubMed1990

Evaluation of equine digital Starling forces and hemodynamics during early laminitis.

A carbohydrate overload model was used in 8 horses to evaluate Starling forces and hemodynamics of the digit during the prodromal stage of acute laminitis. A pump-perfused extracorporeal digital preparation was used to evaluate blood flow, arterial pressure, venous pressure, capillary pressure, isogravimetric capillary filtration coefficient, osmotic reflection coefficient, and vascular compliance. From these data, pre- and postcapillary resistances and pre- to postcapillary resistance ratios were determined. Vascular and tissue oncotic pressures were estimated from plasma and lymph protein concentrations, respectively. The osmotic reflection coefficient, an estimation of capillary permeability, was determined by means of the lymph protein wash-down technique. Using the collected data, tissue pressure in the digit was calculated by use of the Starling equation. In the isolated digit, mean isogravimetric capillary pressure was 55.13 mm of Hg, mean plasma and lymph oncotic pressures were 22.29 mm of Hg and 7.2 mm of Hg, respectively, the mean osmotic reflection coefficient was 0.66, the mean capillary filtration coefficient was 0.003 ml/min/mm of Hg/100 g, and mean interstitial fluid pressure was 44.82 mm of Hg. The high capillary pressure appeared to be caused by high vascular resistance from the venous side, predisposing to enhanced capillary filtration and interstitial fluid accumulation.

Animals↗

PubMed1990

Hypoperfusion of the small intestine during slow infusion of a low dosage of endotoxin in anesthetized horses.

The effects of intravenous infusion of endotoxin for 30 minutes at a cumulative dosage of 0.03 micrograms/kg on average carotid arterial pressure, and on average arterial pressure, capillary pressure, venous pressure, total vascular resistance, precapillary resistance, postcapillary resistance, and capillary filtration coefficient in the jejunum were compared to the effects of intravenous infusion of 0.9% sodium chloride solution in 6 anesthetized horses. Endotoxin significantly reduced intestinal venous blood flow by inducing vasoconstriction. Increased vascular resistance resulted from increased precapillary resistance. The capillary filtration coefficient was unchanged by endotoxin. These results suggest that intestinal vasoconstriction occurs during the compensatory stages of endotoxemia.

Animals↗

PubMed1989

Pathophysiology of acute laminitis.

This article reviews research findings relating to the pathophysiology of acute laminitis in horses. The data presently available suggest that the onset of the condition may be due to constriction of the postcapillary vessels in the digit, leading to increased capillary hydrostatic pressure and movement of fluid into the interstitial space.

Acute Disease↗

PubMed1989

The effects of slow infusion of a low dosage of endotoxin in healthy horses.

The effects of slow intravenous (i.v.) infusion of a very low dosage of endotoxin (a cumulative dosage of 0.03 microgram/kg bodyweight [bwt] infused over 60 mins) were evaluated in six conscious healthy horses. Duodenal, right ventral colon, and caecal contractions were detected with strain gauge force transducers. Lateral caecal arterial blood flow was measured using transit time ultrasonic blood flow probes. Duodenal contractile activity was not significantly altered by infusion of endotoxin. In contrast, the contractile activity of the right ventral colon 90 and 270 mins after infusion of endotoxin was less than after infusion of saline solution (control). The contractile activity of the caecal body 30, 60, 90, 120 and 240 mins after infusion of endotoxin was significantly less than control. The contractile activity of the caecal apex 60, 90, 120, 240 and 270 mins after termination of endotoxin infusion was significantly less than control. Lateral caecal arterial blood flow was significantly less than control at the end of endotoxin infusion and at 30, 45, 60, 90, 105 and 120 mins afterwards. Average carotid arterial pressure was significantly greater than control at 210, 225, 240, 255 and 270 mins after endotoxin infusion. Infusion of endotoxin increased heart rate, respiratory rate and body temperature significantly. The decrease in caecal contractile activity occurred before the increase in body temperature. All horses became depressed and developed injected mucous membranes. Signs of abdominal pain (including stretching, pawing, kicking at abdomen) were seen in four of the six horses.

Abdominal Pain↗

PubMed1989

Renal effects of dopamine infusion in conscious horses.

An ultrasonic flow probe was implanted around a branch of the left renal artery in five horses. The effects of dopamine were studied in the unsedated horses 10 days after surgery. Three experiments, separated by at least two days, were performed in random order on each horse. In two experiments, dopamine was infused intravenously for 60 mins at either 2.5 and 5.0 micrograms/kg bodyweight (bwt)/min. Saline was infused for 60 mins before and after each infusion, and for 180 mins in the third experiment as a control. Renal blood flow increased during administration of dopamine at both dose rates (P = 0.0001). Urine volume increased (P = 0.055), and osmolality decreased (P < 0.05), with infusion of dopamine at 5.0 micrograms/kg bwt/min. Arterial blood pressure and heart rate were not significantly affected. Fractional excretions of sodium and potassium were not significantly changed with dopamine infusion. The higher dopamine dose rate was accompanied by dysrhythmias in some horses.

Animals↗

PubMed1989

Effects of fenoldopam on cecal blood flow and mechanical activity in horses.

Lateral cecal arterial blood flow, carotid arterial pressure, heart rate, and mechanical activity in the duodenum, right ventral colon, cecal body, and cecal apex were measured in 6 conscious healthy horses for 60 minutes during and for 120 minutes after IV infusion of 0.9% NaCl solution (control) or fenoldopam. There were no significant changes in these measurements during or after infusion of 0.9% NaCl (saline) solution. Fenoldopam, a selective dopamine-1 receptor agonist, was administered in saline solution at dosages of 0.01, 0.05, and 0.1 micrograms/kg/min. Intravenous infusion of fenoldopam at 0.01 microgram/kg/min significantly increased heart rate, but did not change average carotid arterial pressure or lateral cecal arterial blood flow. Intravenous infusion of fenoldopam at both 0.05 and 0.1 microgram/kg/min significantly increased heart rate, significantly decreased average carotid arterial pressure, and significantly increased lateral cecal arterial blood flow. Intravenous infusion of fenoldopam at 0.01, 0.05, and 0.1 microgram/kg/min did not significantly change the mechanical activity measured by the area under the strain gauge deflection curve for the duodenum, right ventral colon, cecal body, or cecal apex. These results suggest that dopaminergic-1 receptors are present on the colonic vasculature of horses. There was no evidence, however, that dopaminergic-1 receptors exist on the visceral smooth muscle of the duodenum, right ventral colon, cecal body, or cecal apex of horses.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1989

Effects of dopamine administration on cecal mechanical activity and cecal blood flow in conscious healthy horses.

Lateral cecal arterial blood flow, carotid arterial pressure, heart rate, and mechanical activity of the circular and longitudinal muscle layers of the cecal body were measured in 7 conscious healthy horses during IV infusion of physiologic saline solution for 60 minutes (control), during a 60-minute IV infusion of dopamine (at dosages of 1, 2.5, and 5 micrograms/kg/min), and for 60 minutes after IV infusion of dopamine. The mean values for lateral cecal arterial blood flow during IV infusion of dopamine at a dosage of either 1 or 2.5 micrograms/kg/min were not significantly different from the mean values for lateral cecal arterial blood flow during IV infusion of saline solution. The mean values for lateral cecal arterial blood flow, however, were significantly greater during IV infusion of dopamine at a dosage of 5 micrograms/kg/min than the mean values for lateral cecal arterial blood flow during IV infusion of saline solution. Intravenous infusion of dopamine at 1 and 2.5 micrograms/kg/min did not significantly change the mean values for carotid arterial pressure. In contrast, the mean values for carotid arterial pressure were significantly less during IV infusion of dopamine at dosages of 2.5 and 5 micrograms/kg/min than during infusion of saline solution. The mean values for heart rate were not significantly altered by infusion of dopamine at a dosage of either 1 or 2.5 micrograms/kg/min, but infusion of dopamine at a dosage of 5 micrograms/kg/min significantly increased heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Omphalophlebitis and osteomyelitis associated with Klebsiella septicemia in a premature foal.

Gram-negative neonatal septicemia was diagnosed in a premature Standardbred colt. Clinical signs included lethargy, weakness, loss of suckle reflex, tachypnea, and injected mucous membranes. Sequelae included pneumonia, omphalophlebitis, septic arthritis, and osteomyelitis. Prepartum maternal uterine infection, premature delivery, abnormal parturition with premature fetal membrane separation, and failure of passive transfer of colostral immunoglobulins increased the foal's risk for developing sepsis. Treatment included administration of moxalactam disodium and cefadroxil. The clinical efficacy of cephalosporin antibiotics in the treatment of gram-negative sepsis is discussed.

Animals↗

PubMed1988

Lymphocytic enteritis in a filly.

A yearling Hanoverian filly had intermittent colic for 6 weeks, chylous peritoneal effusion, and a firm mass palpable per rectum. Exploratory laparotomy revealed mesenteric lymphadenopathy, adhesion of the mesenteric root to the duodenum and jejunum, distention of the mesenteric veins and lymphatic vessels, and increased jejunal venous pressure. Lesions in the duodenum, jejunum, and colon included infiltration of lymphocytes and plasma cells in the lamina propria.

Animals↗

PubMed1988

Effects of fenoldopam on feline intestinal microcirculation.

Experiments were performed to evaluate the effects of the specific dopamine-1-receptor agonist, fenoldopam, on the feline intestinal microcirculation. Cranial mesenteric arterial pressure, cranial mesenteric vein pressure, cranial mesenteric vein blood flow, venous occlusion capillary pressure, pre- and postcapillary resistances, total mesenteric vascular resistance, lymph flow, lymph and plasma protein concentrations, the capillary osmotic reflection coefficient, and the capillary filtration coefficient were determined in an isolated autoperfused jejunal segment in anesthetized fasted cats during intra-arterial administration of saline or fenoldopam mesylate in saline. Fenoldopam significantly increased mean cranial mesenteric vein blood flow from 26.8 +/- 3.4 to 33.7 +/- 2.8 ml.min-1.100 g-1. This increase in blood flow was due primarily to a significant decrease in mean intestinal vascular resistance from 3.14 +/- 0.32 to 2.54 +/- 0.2 mm Hg.ml-1.min-1.100 g-1, since cranial mesenteric arterial pressure during fenoldopam infusion was not different from the value obtained during control studies. Mean capillary pressure during fenoldopam infusion (17.2 +/- 0.5 mm Hg) was significantly greater than mean capillary pressure during control studies (15.6 +/- 0.3 mm Hg). The mean lymph flow during fenoldopam infusion (0.186 +/- 0.083 g/dl) was significantly greater than the value obtained during saline infusion (0.08 +/- 0.009 g/dl). Fenoldopam infusion significantly increased the mean capillary filtration coefficient from 0.135 +/- 0.021 to 0.275 +/- 0.035 ml.min-1.100 g-1.mm Hg-1 without altering the capillary osmotic reflection coefficient. These results suggest that specific dopamine-1-receptor stimulation in the small intestine increases the perfused capillary density without altering capillary permeability.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Capillary permeability to endogenous macromolecules in the equine digit.

Microvascular permeability characteristics were evaluated in digits of 7 adult horses. After capillaries were isolated and an extracorporeal perfusion circuit for the digit was established, a lymphatic vessel draining the distal portion of the phalangeal region was cannulated at the level of the coronary band. Venous pressure was increased in a stepwise manner, and lymph flow, lymph protein concentration (Cl), and plasma protein concentration (Cp) were determined after measured variables were allowed to reach steady state. Lymph-to-plasma protein concentration ratios (Cl/Cp) and lymph and plasma oncotic pressures were determined from samples collected during steady state. The osmotic reflection coefficient was determined after Cl/Cp became constant, regardless of increasing lymph flow, and was expressed as 1--Cl/Cp. The osmotic reflection coefficient for the digit was 0.67. Seemingly, the microvasculature bed of the digit was relatively permeable and could maintain only 67% of the endogenous macromolecules within the vasculature.

Animals↗