A number of combinations of anionic and cationic polymers, the majority being polysaccharides, were screened to determine their suitability for the development of alternative microcapsule formulations capable of supporting cells. The capsules were taken through a limited optimization and then evaluated on the bases of rupture strength, permeability to albumin, and ability of their components to promote the attachment, aggregation, and function of encapsulated rabbit hepatocytes. The widely used alginate-polylysine capsules were employed as a comparative standard in all tests. A number of the new formulations compared favorably with the standard, and some exhibited superior performance in specific areas. Hepatocyte function, as evaluated by the rate of urea synthesis, showed no significant differences between formulations over a 24-h test period. One formulation, composed of the polysaccharides (carboxymethyl)cellulose, chondroitin sulfate A, chitosan, and polygalacturonate, was found to be superior to alginate-polylysine capsules in the areas investigated and supported the long-term survival and growth of liver endothelial cells.

Animals↗

PubMedDate not supplied

Regional blood flow during extracorporeal membrane oxygenation in lambs.

To determine changes in blood flow to different organs during extracorporeal membrane oxygenation (ECMO), the authors performed venoarterial ECMO in four young lambs for 71-96 hr (Group 1). Macroaggregated albumin microspheres labeled with technetium 99m were injected through the perfusion cannula before termination of ECMO to determine percent of blood flow by measuring radioactivity from the microspheres lodged in specific organs. The control group (Group 2) consisted of three animals not on bypass; injections were made through a catheter placed in the left ventricle. Relative coronary blood flow from the perfusion cannula was significantly less than relative coronary blood flow in the control group, possibly because of cannula location. Renal flow from the perfusion cannula also was decreased. Contrary to observations in rabbits, cerebral perfusion did not decrease in the bypass group despite ligation of the carotid artery and the external jugular vein. There were no statistically significant differences between the two groups in the relative blood flow to other organs. The authors conclude that ECMO may significantly alter myocardial and renal perfusion, with minimal effects to other organs.

Animals↗

PubMedDate not supplied

Effect of extracorporeal membrane oxygenation on body water content and distribution in lambs.

Water content of the various body compartments were estimated immediately after beginning extracorporeal membrane oxygenation (ECMO), and daily thereafter for 3 days, in seven healthy 2-month-old lambs. Total body water, extracellular water, and plasma volume were estimated simultaneously by 18O, bromide, and T-1824 dilution, respectively. Volumes of intracellular water, interstitial water, blood, and red cells were calculated from the experimental estimates. No statistically significant changes occurred in the water content of the various body compartments in relation to duration of ECMO. The data suggest that water retention, clinically noted in human neonates treated with ECMO for persistent pulmonary hypertension, may be related to the primary disease process and/or its medical management, rather than to ECMO.

Animals↗

PubMedDate not supplied

Thermal, operational, and storage stability of immobilized carbonic anhydrase in membrane lungs.

The significant improvement in CO2 removal rates from blood through membrane lungs with EMCO and ECCO2R is achievable by means of the immobilization of carbonic anhydrase (CA) onto the membrane surface. The practical application of this technology requires that the enzyme be maintained for long periods without loss of activity. Thus, studies were performed to evaluate the thermal, operational, and storage stability of CA in a cellulose nitrate-encapsulated, silicone rubber membrane-immobilized form. Cellulose nitrate microcapsules containing 1000 micrograms/ml CA were prepared using a modified version of the method of Chang, and immobilized onto a 0.06 m2 section of commercial silicone rubber membrane material. The extent of enzyme activity in free solution and in the encapsulated form was determined after long-term storage at 4 degrees C, 37 degrees C, and 50 degrees C. Likewise, in an in vitro test circuit, CO2 removal efficiency in both CA treated and untreated membrane lungs was measured for extended time periods of 10 hr over a 10 day period. The thermal stability tests showed a significantly greater degree of retained enzyme activity in the encapsulated form, over the free enzyme in solution, at all temperatures. This was especially evident at higher temperatures and when the enzyme was stored for extended periods. In the operational stability tests, the CO2 removal efficiency of the treated membrane was not degraded, and stayed significantly higher than the untreated membrane for extended time periods. This further illustrates the potential for the use of the immobilized enzyme, carbonic anhydrase, for improved CO2 removal efficiency.

Acetazolamide↗

PubMedDate not supplied

Feasibility studies for a photosynthetic artificial lung. Optimization of parameters affecting photosynthesis.

As an alternative to conventional extracorporeal membrane oxygenation (ECMO) hardware, preliminary studies were conducted toward the development of a life support system based on biologic processes for the direct generation of O2 and removal of CO2 by the action of a photosynthetic organism. A high temperature strain of Chlorella pyrenoidosa, which functions optimally at 37 degrees C and pH 7.4, was cultured in a 3 I fermenter with artificial lighting provided with Hg-metal halide lights. The pH, total CO2 and partial pressure of oxygen (PO2) of the system were monitored at regular intervals using flow-through microelectrodes. The degree of importance of light intensity, substrate concentration, and cell density in the photosynthetic ability of Chlorella in batch culture were assessed over a 2 hour period. At high light intensities, the O2 production, CO2 removal, and pH changes were significantly greater than those at low irradiance levels. Over the range of HCO3- concentrations used in these experiments, the initial HCO3- levels did not appear to have a significant effect on the rates of O2 production/CO2 removal. The total amount of O2 produced/CO2 removed and pH changes were found to be greater with higher cell densities. Under more optimal culture conditions, it may be feasible to eventually interface this photobioreactor with blood across a semipermeable membrane and catalytically convert blood CO2 to O2 directly, needing only an adequate light source.

Artificial Organs↗

PubMedDate not supplied

Ultrasound abnormalities in term infants on ECMO.

The charts and cranial ultrasounds of 29 infants treated with extracorporeal membrane oxygenation (ECMO) for respiratory insufficiency secondary to meconium aspiration syndrome, primary pulmonary hypertension, congenital diaphragmatic hernia and/or sepsis were examined to identify ultrasound abnormalities. Seventeen (58.6%) developed extra-axial fluid collections, only two of which were progressive. Ten (34.5%) developed evidence of intracranial hemorrhage (ICH): seven caudate, one each in the thalamus, parietal and occipital lobes. Eight (27.65%) of the neonates had seizures while on ECMO, 5 of whom had concurrent ICH.

Adolescent↗

PubMedDate not supplied

Immediate delivery room repair of fetal abdominal wall defects.

Eighteen patients with a prenatal diagnosis of fetal abdominal wall defect were delivered by cesarean section and repaired either immediately (begun within 15 min, n = 9), or by the traditional (delayed) method (n = 9, average delay = 4.4 h). Neonates repaired immediately had comparable gestational ages and birthweight, however, subjectively had less edematous bowel with less fibrous peel. These fetuses were more likely to be closed primarily (7/9 vs. 4/9), spent less time on a ventilator (8.1 vs. 17.9 days), seemed to be fed sooner (7.6 vs. 17.9 days), and discharged home earlier (14.3 vs. 24.0 days). Our results suggest that for fetuses delivered by cesarean section, early defect repair may reduce bowel edema and fibrous peel formation thus facilitating primary closure, with earlier ventilator weaning, feeding and discharge home.

Abdominal Muscles↗

PubMedDate not supplied

The metabolism of an exogenous lipid source during septic shock in the puppy.

Septic shock induces physiologic and hemodynamic responses that may alter the host's ability to metabolize an exogenous source of lipids. The present study examined the metabolic changes occurring during septic shock in the young animal receiving an intravenous fat emulsion. Five 8-wk-old male Beagle puppies were studied. Each animal served as his own control twice, during which time 14C-palmitic acid alone or with a 10% fat emulsion (Liposyn) was administered. Septic shock (cardiac output less than 50% of control) was induced with an intravenous bolus of live Escherichia coli. During shock the puppies received intravenous 14C-palmitic acid and Liposyn. The mean respiratory quotient for the shock dogs (0.96 +/- 0.01) was significantly (p less than 0.05) higher than that of the controls (0.83 +/- 0.06). The amount of expired 14CO2 was 25.0 +/- 15.9% for the shock animals, 53.9 +/- 28.1% for the Liposyn controls, and 75.7 +/- 30.5% for the controls receiving only 14C-palmitic acid (these differences are all significant, p less than 0.05). After the onset of shock, serum triglyceride levels peaked within 2 min at 851 +/- 540 mg/100 ml and remained elevated at 333 +/- 213 mg/100 ml. Triglyceride levels in the Liposyn control animals returned to baseline values (54 +/- 13 mg/100 ml) at the end of the 4-hr experimental period. Free fatty acids in the shock dogs reached a maximal level of 1.44 +/- 0.09 mEq/liter at 1 hr and remained at this elevated value for a significantly longer period of time than in the Liposyn control puppies. Glycerol value followed a similar pattern and cholesterol remain unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

A technique for tunneling central venous catheters.

Tunneling the central venous catheter from the venous insertion site in the subclavicular or cervical area to the exit site on the chest wall can be difficult, especially in small children with a very convex chest wall. We present a technique which avoids many of the problems encountered with previously described methods.

Catheterization↗

PubMedDate not supplied

Microencapsulated hepatocytes. Prospects for extracorporeal liver support.

To assess the potential for encapsulated hepatocytes as a bioartificial liver support system, rabbit hepatocytes were encapsulated within multicomponent capsules using a complex coacervation technique, and cultured both on plates and in a perfusion reactor. The urea synthesis rate and antipyrine and diazepam degradation rates were evaluated in each system over a 10 day period, and compared with standard plate-cultured hepatocyte efficacy. Urea synthesis rates were significantly higher in the perfusion cultures than in either of the plate culture environments, whereas drug degradation rates were not significantly different in any of the systems.

Animals↗

PubMedDate not supplied

Vascular access for extracorporeal circulation. Resistance in double lumen cannulas.

Double lumen catheters (DLCs) currently are being used for vascular access with extracorporeal circulation. Blood flow studies were done on various DLCs connected to a circuit made of polyvinyl chloride tubing. Sheep's blood was used with all catheters at flows of 200 and 400 ml/min. The inlet and outlet pressures were measured and resistances calculated. Modified versions of the Shiley and Kendall catheters, also were tested. In both catheters, resistance was reduced with the use of perfusion adaptors. Flow through catheters, with a diameter that exceeded the Luer fitting dimension, was compromised. The modified Shiley and unmodified Kendall catheters had the lowest resistance to flow, and they thus are best suited for extracorporeal circulation.

Animals↗

PubMedDate not supplied

Immobilized carbonic anhydrase in a membrane lung for enhanced CO2 removal.

The potential use of carbonic anhydrase (CA), immobilized within membrane lungs, to accelerate the removal of CO2 from blood was investigated. Using a variation on the technique of Chang, 500 micrograms/mL of CA was encapsulated in 5-20 microns cellulose nitrate microcapsules which were then immobilized onto a 0.1 m2 silicone rubber membrane. Using an in vitro test circuit, 0.68 mmol/m2/min of CO2 was removed from venous blood through an untreated membrane at steady state. With the CA-immobilized membrane, CO2 removal was enhanced to 1.09 mmol/m2/min. This technique has the potential of greatly improving the CO2 efficiency of commercial membrane lungs for ECCOR.

Carbon Dioxide↗

PubMedDate not supplied

CO2 removal for ventilatory support: a comparison of dialysis with and without carbonic anhydrase to a hollow fiber lung.

All CO2 in blood is in equilibrium, catalyzed by carbonic anhydrase (CA). This has prompted some investigators to consider treating ventilatory failure by using dialysis to remove HCO3-. Since there is at least 18 times more CO2 in the form of HCO3- than dissolved CO2, theoretically, lower blood flows could be used than with current extracorporeal support with artificial membrane lungs. HCO3- removal for ventilatory support has required alkalinization to compensate for the resulting acidosis and has been capable of removing 26 to 38 ml CO2/100 ml blood flow, compared to 14 ml CO2/100 ml for clinically employed silicone membrane lungs. We designed a HCO3- removal system using recirculation of dialysate through a membrane lung to remove CO2, rather than alkalinization of blood, and removed 8.8 ml CO2/100 ml. Adding CA improved this to 12.2 ml CO2/100 ml, but a conventional hollow fiber lung removed 30 ml CO2/100 ml. We conclude that the complexities of an HCO3- removal system may not be necessary with the advent of more efficient hollow fiber lungs.

Bicarbonates↗