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Biomedical subjects

J Couture

Publications and source records attributed to J Couture.

At least 55 records · Page 3Linked to original sources
PubMed1986

Load compensation during positive pressure breathing in anesthetized man.

To investigate the mechanisms by which human subjects prevent or compensate for the change in respiratory muscle length imposed by applying continuous positive pressure to the airways, six men were studied under general anesthesia with methoxyflurane at the end of a minor surgical procedure (rhinoplasty). Ventilatory and occlusion pressure response to carbon dioxide was measured by a rebreathing technique with no bias pressure, or with 16 cm H2O positive pressure produced by adding weights to a spirometer bell. Static pressure-volume curves of the respiratory system were obtained while the subjects were paralyzed with succinyl choline. In contrast to awake subjects described in other studies, the anesthetized patients did not activate expiratory muscles to combat the rise in end-expiratory level caused by pressure, and showed little evidence of enhanced activation of inspiratory muscles that in the conscious state compensates for the disadvantage of their shorter length. A change in the shape of the occlusion pressure wave, however, suggested that positive pressure had some effect on the neural discharge to inspiratory muscles. The mechanisms by which the respiratory system defends itself against a pressure load that tends to change end-expiratory level are sensitive to anesthesia and may require consciousness.

Adult↗
PubMed1986

The production of high affinity monoclonal antibodies to human chorionic gonadotropin and their application to immunoradiometric assay.

Production of monoclonal antibodies against hCG has been studied using hCG as the antigen. This study reports the successful isolation of hybrid clones secreting monoclonal antibodies specific for hCG with an affinity constant higher than 10(10) M-1. Of 23 fusions, only 17 fusions have produced positive clones which secrete antibodies giving high levels of binding with 125I-labelled hCG in the supernatant. Finally, 6 different monoclonal antibodies have been isolated; 4 of them, specific for the beta-subunit, with a Ka approximately 1.1-4.0 X 10(11) M-1 and 2 others, specific for the alpha-subunit, presenting an affinity of 2.5 X 10(10) M-1. When the antibodies specific for the beta-subunit are used, specific and highly sensitive radioimmunoassays are obtained after only 3 hrs of incubation. Using iodinated monoclonal antibodies specific for the alpha-subunit and tubes coated with antibodies against the beta-subunit, we have developed sensitive immunoradiometric assays.

Animals↗
PubMed1986

Prolonged hyporesponsiveness of airway smooth muscle to histamine following general anesthesia.

The prolonged effect of barbiturates and inhalation anesthesia on airway response to histamine was studied in five groups of dogs. Group B (n = 10), H24 (n = 5), and H72 (n = 5) were anesthetized with sodium thiamylal (B) or halothane and N2O (H24, H72) for 3 h, during which a dose-response curve to histamine was obtained. The animals were then allowed to recover; 24 h (B and H24) or 72 h later, the animals were killed and an in vitro dose-response curve to histamine was obtained on a tracheal smooth muscle (TSM) specimen. Group C (n = 5), the control group, had no prolonged exposure to anesthesia. The dogs were immediately killed and the in vitro histamine response of the TSM was measured. The results (mean +/- SE) showed that the smooth muscle contractile properties (i.e., the maximum contraction to electrical field stimulation) were comparable in all four groups: 111 +/- 12 g (B); 168 +/- 23 g (H24); 106 +/- 32 g (H72); and 107 +/- 31 g (C). The maximum response (mean +/- SE) to histamine (as % of maximum electrical contraction) was: 15 +/- 6% (B), 30 +/- 9% (H24), 32 +/- 12% (H72), and 50 +/- 8% (C). Statistical analysis of the data showed that the histamine response of Group B and Group H24 was significantly decreased compared to Group C (P less than 0.01 and less than 0.05, respectively); in Group H72 the results were not significantly different from Group C (0.1 greater than P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, General↗
PubMed1984

Textile Teflon arterial prostheses: how successful are they?

Today the woven and knitted Teflon vascular prostheses developed over 25 years ago by Edwards are of only minor clinical interest. The literature contains a chronology of postoperative complications critical of textile Teflon as a prosthetic material, and this led to its discontinuance as a commercial product. Recent evidence from pathologic and material analyses of three grafts removed from patients after implantation for 11, 19 and 19 years, respectively, suggests that the previously reported complications were more likely to have been related to the use of silk sutures, the fraying and ravelling of the woven and weft-knitted constructions and local or systemic reactions than to degradation of the Teflon. Experimental studies of grafts implanted in the thoracic and abdominal aortas of dogs for periods of up to 6 months support these findings. Because of the apparent long-term stability of textile Teflon as an implantable material, the authors see merit in its reintroduction as a warp-knitted vascular prosthesis.

Aged↗
PubMed1983

Experimental colonization of vascular grafts with Staphylococcus aureus.

In an attempt to solve the problem of infection of arterial grafts, the authors designed an experimental model to reproduce, in vitro, hematogenous seeding of grafts with Staphylococcus aureus. The inoculum, containing an average of 10(7) viable bacterial cells per millilitre, was circulated through grafts of various types. Normal dog aortas were used as controls. They entrapped a mean of 8 bacteria/cm2. The prosthetic grafts, previously placed in dogs as femorofemoral arteriovenous bypasses for 2 hours, trapped many more cells: expanded polytetrafluoroethylene, 23 cells/cm2; bovine heterograft, 607 cells/cm2 and Dacron velour, 2801 cells/cm2. All cell counts were significantly (p less than 0.001) different from control values. Thoracoabdominal aortic bypass grafts implanted in dogs 2 months previously gave the following mean numbers of trapped bacteria: expanded polytetrafluoroethylene, 19 122 cells/cm2; bovine heterograft, 863 cells/cm2 and Dacron velour, 3500 cells/cm2. Polytetrafluoroethylene had significantly (p less than 0.001) higher numbers of trapped bacteria than any other type of prosthesis. The bacteria were located mainly on irregular fibrin strands and on surface defects of the grafts. The addition of cefazolin during the seeding process at concentrations 10 to 25 times the minimal inhibitory concentration did not decrease the numbers of bacteria in any graft. Bacterial colonization of prosthetic arterial grafts depends on the graft material and on the duration of implantation, but this study provided no answer to the controversial question of how to prevent arterial graft infections with antimicrobial agents in patients who undergo vascular procedures that expose them to bacteremia.

Animals↗
PubMed1982

Melanoma: the management of local recurrence and in-transit metastasis.

Following the primary treatment of melanoma, subsequent appearance of local recurrence and in-transit metastasis remains one of the most difficult problems faced by surgeons. In managing the disease at this stage, it is important to realize that, because of a favourable immune reaction in some patients, the disease may remain localized for many months or years. Consequently, local control should be attempted in the best possible manner when the disease is confined to a specific region and there are no signs of dissemination. Methods of local control include local surgical procedures, local and systemic chemotherapy, immunotherapy, radiotherapy, amputation and isolation-perfusion. After reviewing the literature and based upon personal experience, the author found that hyperthermic isolation-perfusion can be effective in the management of local recurrences of melanomas and in-transit metastasis.

Humans↗
PubMed1976

Occlusion pressures in men rebreathing CO2 under methoxyflurane anesthesia.

The effect of general anesthesia on control of breathing was studied by CO2 rebreathing and occlusion pressure measurements in six normal human subjects under methoxyflurane anesthesia. CO2 was found to increase the amplitude of the occlusion pressure wave without changing its shape, so that CO2 responses in terms of the occlusion pressure developed 100 ms after the onset of inspiration (Po/0.1) gave results equivalent to the responses in terms of Po/1.o or any other parameter of the pressure wave. Methoxyflurane depressed the ventilatory response to CO2 but not the occlusion pressure response, implying that the most important action of the anesthetic was to increase the effective elastance of the respiratory system rather than to depress the respiratory centers. The elastance was further increased by CO2, and this mechanical change had the effect of shifting the "apneic threshold" extrapolated from the ventilatory response curve to a lower PAco2. Frequency of breathing, inspiratory and expiratory times were not altered by CO2 in anesthetized subjects.

Adult↗
PubMed1976

Adaptation of anesthetized men to breathing through an inspiratory resistor.

Normal men anesthetized with methoxyflurane rebreathed carbon dioxide under two conditions. In one case they breathed most of the time through a low-resistance circuit and an inspiratory resistor of 40.4 cmH2O/1-s-1 was applied at intervals. In another case they breathed most of the time through the resistor and were allowed occasional free breaths. There were no differences between the two types of runs in tidal volume, respiratory frequency, duration of inspiration of loaded or unloaded breaths, or in amplitude or shape of occlusion pressure waves. It is concluded that the reaction of conscious men to an inspiratory resistive load, consisting of a compensatory augmentation of neural drive to respiratory muscles that does not depend on a chemical stimulus, is absent in anesthetized men.

Adult↗
PubMed1975

Growth and development of the fetal Rhesus monkey. VI. Morphometric analysis of the developing lung.

Groups of fetal monkeys were studied at 50, 75, 100, 125 and 150 days gestational age, and postnatal monkeys were studied at 175 days gestational age and in adult life (full term gestation is 168 plus or minus 4 days). The ratios between the various tissues of which lung is composed were determined by light and electronmicroscopy. Characteristic changes in ratios were noted at each developmental age. Primitive bronchioles increased from 50 to 75 days, decreased as permanent bronchioles, alveolar ducts and alveoli developed, and were absent after 150 days. Mesenchymal tissue decreased progressively from 50 to 150 days. Alveoli were present at 100 days gestational age; alveolar lumens accounted for approximately 1/2 the volume of peripheral lung by 150 days, and 2/3 the volume of lung in adult animals. By 150 days alveolar epithelial cells could be identified as Type I (membranous) or Type II (granular) on the basis of the characteristic cytoplasmic lamellar inclusion bodies of the latter. The ratios of the Type II/Type I cells were .21-.23 at 150 and 175 days, and fell to approximately half that value in adult lungs.

Animals↗