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Biomedical subjects

M King

Publications and source records attributed to M King.

At least 271 records · Page 15Linked to original sources
PubMed1991

Soft filamentous woven polyester arterial prosthesis from China.

Woven polyester arterial prostheses have traditionally been known for their tight construction and smooth surface which has limited their healing capacity and resulted in poor attachment of their internal and external capsules. A new woven prototype has recently been developed in the Peoples' Republic of China. Among its unique features are its high physical porosity, softness and flexibility. This study undertook a series of in vitro tests to characterize its structure and physical properties in comparison with four commercial polyester grafts of North American origin. In addition, an animal trial was completed in which the new prototype was implanted as an infrarenal aortic substitute in 20 dogs for periods ranging from 4 h to 12 month. The in vitro tests confirmed a unique lightweight, highly porous, satin weave construction. Because of its high water permeability, preclotting was necessary before implantation. Once preclotted and installed, no significant blood loss was observed, and 19 of the 20 grafts remained patent at the sacrifice. Rapid full-width healing was achieved with tightly bound capsules, and more extensive tissue ingrowth was observed. Further work is needed to evaluate its long-term durability as an arterial substitute.

Animals↗
PubMed1991

Percutaneous transhepatic biliary drainage for malignant biliary obstruction: a report of two cases with five year survival.

We report two cases of malignant biliary obstruction in whom percutaneous transhepatic biliary drainage has contributed to patient survival of more than 5 years. To our knowledge, this represents the first such case report in the literature. Both patients suffered biliary obstruction from poorly differentiated adenocarcinoma, in all likelihood from the head of the pancreas. Morbidity has been low with only two episodes of significant sepsis and one episode of GI haemorrhage in one patient and both patients were able to enjoy an excellent quality of life. These cases demonstrate that percutaneous biliary drainage has a place not only in the short term palliation of patients with malignant biliary obstruction, but in the long term as well.

Adenocarcinoma↗
PubMed1991

Neonatal capsaicin treatment alters basal pulmonary mechanics and response to methacholine in F344 rats.

Full methacholine dose-response curves were performed on anesthetized tracheostomized Fischer 344 adult rats treated neonatally with capsaicin (50 mg/kg) or with vehicle alone. Capsaicin, the hot extract of pepper, releases substance P (SP) from nonmyelinated sensory nerve endings and causes acute bronchoconstriction and airway microvascular leakiness. Chronic treatment with capsaicin leads to depletion of SP and other tachykinins from afferent C-fibers and can therefore be used as a tool to investigate the contribution of SP innervation to airway responses. The rats (9 controls and 6 treated with capsaicin) were paralyzed with succinylcholine and mechanically ventilated at a constant tidal volume and frequency. Airway resistance (RL) and dynamic compliance (Cdyn) were determined at each dose of methacholine from measurements of volume, flow, and transpulmonary pressure. Capsaicin-treated rats were found to have a significantly reduced baseline RL [0.150 +/- 0.039 (SD) vs. 0.225 +/- 0.050 cmH2O.ml-1.s, P = 0.009] and a correspondingly significantly elevated Cdyn (0.371 +/- 0.084 vs. 0.268 +/- 0.053 ml/cmH2O, P = 0.012). There was no significant difference in sensitivity to methacholine, but the maximal response to methacholine was significantly greater in the capsaicin-treated rats. In terms of RL, the maximal response for capsaicin-treated rats was 6.03 x baseline +/- 0.98 vs. 4.30 x baseline +/- 1.80 (P = 0.05) for controls, and for Cdyn changes the maximal decrease was 5.75 x baseline +/- 1.22 vs. 3.83 +/- 0.69 (P = 0.002). The observed differences in RL and Cdyn coupled with the differences in maximal responses can be attributed to the selective destruction of a subpopulation of pulmonary afferent C-fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1991

In vivo glucocorticoid modulation of guinea pig splenic macrophage Fc gamma receptors.

Although glucocorticoids are widely used in the treatment of immunohematologic disease, their relative efficacy is uncertain. We used an animal model, which has helped to elucidate the role of splenic macrophage Fc gamma receptors in the clearance of IgG-coated cells, to investigate whether each Fc gamma receptor is modulated by glucocorticoids to the same extent and to examine the relative potency of three commonly used glucocorticoids. Cortisol, prednisone, and dexamethasone all impaired the clearance of IgG-coated erythrocytes. However, dexamethasone was more effective than either prednisone or cortisol (P less than 0.001). Furthermore, splenic macrophages isolated from glucocorticoid-treated animals expressed impaired Fc gamma receptor function. This effect was greater in macrophages isolated from dexamethasone-treated animals, as compared to either cortisol- or prednisone-treated animals (P less than 0.001). To assess the effect of glucocorticoids on the two types of guinea pig splenic macrophage Fc gamma receptors, Fc gamma R1,2 and Fc gamma R2, specific immunoglobulin isotypes were used to measure macrophage binding of IgG-sensitized erythrocytes. Cortisol and prednisone primarily affected Fc gamma R2, whereas dexamethasone inhibited the function of both guinea pig Fc gamma receptors. Furthermore, dexamethasone was more effective (P less than 0.01) than either prednisone or cortisol in inhibiting the ability of both receptors to bind IgG-sensitized cells. Fluorescence-activated cell sorter analysis and fluorescence microscopy with monoclonal antibodies specific for each of these two receptors demonstrated that essentially all splenic macrophages expressed both receptors, and that these glucocorticoids decreased the level of each Fc gamma receptor protein expressed, rather than altering receptor mobility and clustering in the macrophage membrane. The effect on both Fc gamma receptors was greatest with dexamethasone and least with cortisol. These studies demonstrate the significant role of guinea pig splenic macrophage Fc gamma R2 in immune clearance and in the binding of IgG-coated cells. They demonstrate a differential effect of glucocorticoid hormones on Fc gamma receptor function and on surface receptor protein. Furthermore, they suggest that dexamethasone may be a more effective glucocorticoid than either prednisone or cortisol in inhibiting the clearance of IgG-coated cells by its effect on splenic macrophage Fc gamma receptors.

Animals↗
PubMed1991

Quality assurance in MRI.

"With the prospect of the federal government waiting in the wings to mandate and oversee quality assurance in radiology, managers should waste no time in establishing adequate quality assurance programs for MRI, the latest new technology," declare the authors. Determining standards for quality assurance is certainly a difficult task, considering all the stakeholders involved, say the authors. They focus on evaluating the appropriateness of the imaging test and insuring the accuracy of the diagnosis as the key elements to be monitored.

Centers for Medicare and Medicaid Services, U.S.↗
PubMed1991

Role of simulated repetitive coughing in mucus clearance.

The role of repetitive simulated coughing on the clearance of gel mucus simulant was investigated in vitro, by using a simulated cough machine. The repetition of cough induced a significant increase (p less than 0.01) in mucus simulant clearance (139.3 +/- 78.7 mm) in comparison to a single cough (24.9 +/- 27.5 mm). Moreover, the increase in frequency of the repetitive coughing induced a marked and significant increase in mucus simulant clearance (75.4 +/- 51.1 mm and 139.3 +/- 78.7 mm at 0.1 Hz and 1.6 Hz frequency, respectively). A significant (p less than 0.05) correlation was observed between the percentage increase of clearance and both shear-thinning index (r = 0.62) and the thixotropic index (r = 0.63). These results suggest that the shear-dependent properties of mucus, associated with a repetitive coughing, may increase the efficiency of mucus clearance by air flow mechanisms.

Cough↗
PubMed1991

Night-to-night variability of disturbed breathing during sleep in an elderly community sample.

Night-to-night variability of breathing and oxygenation during sleep was examined with portable monitoring equipment in 30 residents of a retirement village. Subjects had a variety of health problems as might be expected in the elderly, but all were living independently in self-contained units. None had clinical features to suggest obstructive sleep apnea. Two pairs of consecutive nights were studied, separated by 4-6 months. Satisfactory recordings on all four nights were obtained in 15 subjects, and in these subjects variability of measurements was examined across nights 1-4 using the kappa (K) statistic. There was low but significant agreement in estimated total sleep time (K = 0.23, p less than 0.01) and estimated wakefulness after sleep onset (K = 0.18, p less than 0.05) as assessed with a wrist actigraph. Good agreement was found among measures of disturbed breathing during sleep whether expressed in terms of numbers of events [respiratory disturbance index (RDI), K = 0.62, p less than 0.0001], their duration (event minutes, K = 0.53, p less than 0.0001), or associated disturbance of oxygenation (% cumulative time less than 90% SaO2, K = 0.50, p less than 0.001, n = 9). Twenty-eight subjects had at least two nights' satisfactory recordings. Although some of these individuals showed considerable variation in RDI, this had little overall effect on classification of them into normal (RDI less than or equal to 15) and abnormal groups. The accuracy of the first night's recording in predicting classification derived from recording on three or four nights was 83%.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1991

The reversibility of impaired mucociliary function after lung transplantation.

Impairment of mucociliary function occurs after lung transplantation and may predispose patients to repeated pulmonary infections. The purpose of this study is to determine whether and how soon such mucociliary function may recover. Ten dogs underwent left lung autotransplantation. Within 3 weeks five of these dogs underwent study for proximal airway clearance by observation through a bronchoscope of the movement of carbon particles placed at different locations on the tracheobronchial mucosa. The mechanical properties of collected mucus from specific sites were determined by magnetic rheometry. The right lung, which was not operated on, served as a paired control. Similar studies were conducted in the remaining five dogs at 12 weeks after autotransplantation. Lung autotransplantation caused significant depression of proximal airway clearance and a 35% increase in mucous rigidity (p = 0.05) soon after operation. At 12 weeks after operation, there was a partial recovery of proximal airway clearance. Mucous changes were no longer consistent. Histologic and electron microscopic examinations initially revealed focal denudation of ciliated cells and loss of the bronchial glands. At 12 weeks there was a regeneration of cilia and a reappearance of the bronchial glands. We conclude that the mucociliary function, observed to be depressed early after lung autotransplantation, recovers partially during the late postoperative period. Thus the mucociliary functional recovery should be attributed to revascularization rather than to reinnervation, since the latter is unlikely to occur during this period.

Anastomosis, Surgical↗
PubMed1991

Etiology of prosthetic anastomotic false aneurysms: pathologic and structural evaluation in 26 cases.

To determine the etiology of anastomotic false aneurysms (AFAs), 26 textile graft specimens, removed because of AFA, were studied morphologically, histologically and by scanning electron microscopy. No cases of suture-related failures leading to AFA were found. Nine cases of frayed grafts were documented but were not the cause of AFA formation. In three cases, chemical degradation of the fibres, which may have been secondary to lipid infiltration, may have contributed to AFA formation. There were no cases of overt clinical infection, but the presence of bacteria was documented by scanning electron microscopy in 20 cases. The role of bacteria is not well defined, but they may be a factor in host arterial-wall degeneration as a cause for AFA formation.

Adult↗
PubMed1990

A pilot study of aerosolized amiloride for the treatment of lung disease in cystic fibrosis.

Excessive active absorption of sodium is a unique abnormality of the airway epithelium in patients with cystic fibrosis. This defect is associated with thickened mucus and poor clearance of airway secretions and may contribute to the pulmonary disease in these patients. To study whether the inhibition of excessive absorption of sodium might affect the course of lung disease in cystic fibrosis, we performed a double-blind, crossover trial comparing aerosolized amiloride (5 mmol per liter; 3.5 ml four times daily), a sodium-channel blocker, with vehicle alone. Fourteen of the 18 adult patients initially enrolled in the study completed the one-year trial (25 weeks for each treatment). The mean (+/- SEM) loss of forced vital capacity (FVC) was reduced from 3.39 +/- 1.13 ml per day during treatment with vehicle alone to 1.44 +/- 0.67 ml per day during treatment with amiloride (P less than 0.04). A measured index of sputum viscosity and elasticity was abnormal during treatment with vehicle alone and improved during treatment with amiloride. Calculated indexes of mucociliary and cough clearance also improved during amiloride treatment. No systemic, respiratory, or subjective toxic effects of amiloride were noted. We conclude from this preliminary study that aerosolized amiloride can be safely administered to adults with cystic fibrosis. The slowing of the loss of FVC and the improvement in sputum viscosity and elasticity suggest a beneficial clinical effect. Aerosolized amiloride deserves further evaluation in the treatment of lung disease in patients with cystic fibrosis.

Absorption↗
PubMed1990

The disulphide-bond content and rheological properties of intestinal mucins from normal subjects and patients with cystic fibrosis.

The disulphide/thiol (S-S/SH) content and rheological properties of highly purified small-intestinal mucins from normal (N) subjects and patients with cystic fibrosis (CF) were investigated. (1) An assay was developed to measure free SH groups (before reduction) and total SH content (after reduction) using 4,4'-dipyridyl disulphide. S-S bonds were calculated by difference. Experimental values for the S-S and SH contents of well-characterized proteins obtained with the assay showed good agreement with expected values. (2) The S-S and free SH contents of nine N and six CF mucins were variable: 44.4 +/- 5.4 nmol of S-S and 4.3 +/- 1.1 nmol of free SH per mg of N mucin and 31.7 +/- 7.6 nmol of S-S and 7.5 +/- 3.7 nmol of SH per mg of CF mucin. N and CF mucins were not statistically different. In most mucins, approximately 90% of the SH groups were involved in S-S bonds. (3) Gels were reconstituted from the same N and CF mucins at concentrations between 8 and 25 mg/ml and their rheological properties were assessed by using a magnetic microrheometer. (4) Once formed, mucin gels were stable and maintained the same mechanical properties over a long period of time (3-14 days). (5) The rheological profiles of both N and CF samples did not vary with the concentration of mucin present and were characteristic of weak, visco-elastic gels. (6) Although variations were seen in the visco-elastic properties of individual mucins, no systematic differences were detected between N and CF preparations. (7) There was no apparent correlation between the rheological properties of a mucin and its S-S/SH content.

Cysteine↗