Identifying a site for maximum delivery of oxygen to transplanted cells

For in vivo cell implantation techniques to be successful, the energy and metabolic substrate requirement of the cells being grown must be met. Certain cells with high-energy requirements (e.g., hepatocytes, pancreatic island cells) experience a high degree of cell death after implantation due to a limited supply of oxygen. We proposed that the pleural cavity might be an oxygen-rich environment and hence an excellent site for cell implantation. To test the hypothesis that the delivery of oxygen to the pleural cavity is directly proportional to the inspired oxygen concentration we measured the pO(2) of saline instilled in the pleural cavity as compared to that of the peritoneal cavity. We postulated that the physiologic basis for any difference was the result of direct diffusion of oxygen into the pleural space across the alveoli. The study was conducted on sheep (n = 6), after induction of general anesthesia, in two phases, control and experimental. Saline was instilled into the peritoneal and pleural cavities via catheters, after equilibration at given FiO(2), the pO(2) of the paline aspirated from the two cavities was compared. In the experimental group, animals were sacrificed (no circulation) and ventilated. The same sequence of steps as in the control phase were repeated. In the control group, the pO(2) of saline aspirated from the pleural cavity approached the arterial pO(2) at all FiO(2) levels. The pO(2) of the peritoneal saline aspirate fell over time. In the experimental phase (no circulation), the pO(2) of the pleural cavity saline rose to \u3e400 mm Hg. We conclude that this is a result of direct diffusion and is a potential source of unlimited oxygen supply not dependent on vascular supply

Diffusion of nitrous oxide into the pleural cavity

We postulated that nitrous oxide transfer into the pleural cavity can occur by diffusion from the alveoli, independent of vascular transport. Under general anaesthesia, six sheep were studied in two phases, a control and an experimental phase. The sheep were anaesthetized, intubated, and received positive pressure mechanical ventilation. A catheter was placed in the right pleural cavity and 150 ml air injected. The animals were ventilated with 100% oxygen. The inspired gas was changed to a mixture of 50% nitrous oxide and 50% oxygen, and the rate of increase of nitrous oxide concentration in the pleural space was measured. The animals were then ventilated with 100% oxygen and then killed by exsanguination while ventilation was continued. The inspired mixture was changed to 50% nitrous oxide and 50% oxygen and the rate of increase in nitrous oxide concentration was measured in the pleural space again. During venitilation with nitrous oxide in the living animals, the concentration of nitrous oxide in the pleural cavity increased rapidly and decreased to zero during ventilation with 100% oxygen. During ventilation without circulation, the rate of increase in the concentration of nitrous oxide in the pleural cavity was the same as in the control phase. This suggests that nitrous oxide enters the pleural space by diffusion, rather than by vascular delivery. This mechanism may explain the rapid increase in the volume of pneumothorax if nitrous oxide is given in the inspired gas

Third-degree heart block complicating supraclavicular brachial plexus block

Regional anesthesia is frequently administered to elderly patients and those with known cardiovascular disease in the hope of minimizing the cardiovascular complications associated with general anesthesia. Drug interactions between local anesthetics used in regional techniques and calcium channel blockers have been described. To date, however, potentially life-threatening dysrhythmias associated with brachial plexus blockade using the supraclavicular approach have not been reported. We now describe such a case

Characteristics of cartilage engineered from human pediatric auricular cartilage

In the repair of cartilage defects, autologous tissue offers the advantage of lasting biocompatibility. The ability of bovine chondrocytes isolated from hyaline cartilage to generate tissue-engineered cartilage in a predetermined shape, such as a human ear, has been demonstrated; however, the potential of chondrocytes isolated from human elastic cartilage remains unknown. In this study, the authors examined the multiplication characteristics of human auricular chondrocytes and the ability of these cells to generate new elastic cartilage as a function of the length of time they are maintained in vitro. Human auricular cartilage, harvested from patients 5 to 17 years of age, was digested in collagenase, and the chondrocytes were isolated and cultured in vitro for up to 12 weeks. Cells were trypsinized, counted, and passaged every 2 weeks. Chondrocyte-polymer (polyglycolic acid) constructs were created at each passage and then implanted into athymic mice for 8 weeks. The ability of the cells to multiply in vitro and their ability to generate new cartilage as a function of the time they had been maintained in vitro were studied. A total of 31 experimental constructs from 12 patients were implanted and compared with a control group of constructs without chondrocytes. In parallel, a representative sample of cells was evaluated to determine the presence of collagen. The doubling rate of human auricular chondrocytes in vitro remained constant within the population studied. New tissue developed in 22 of 31 experimental implants. This tissue demonstrated the physical characteristics of auricular cartilage on gross inspection. Histologically, specimens exhibited dense cellularity and lacunae-containing cells embedded in a basophilic matrix. The specimens resembled immature cartilage and were partially devoid of the synthetic material of which the construct had been composed. Analyses for collagen, proteoglycans, and elastin were consistent with elastic cartilage. No cartilage was detected in the control implants. Human auricular chondrocytes multiply well in vitro and possess the ability to form new cartilage when seeded onto a three-dimensional scaffold. These growth characteristics might some day enable chondrocytes isolated from a small auricular biopsy to be expanded in vitro to generate a large, custom-shaped, autologous graft for clinical reconstruction of a cartilage defect, such as for congenital microtia