Emulsion strategies in the microencapsulation of cells: Pathways to thin coherent membranes

Microencapsulation of cell spheroids in an immunoselective, highly biocompatible, biomembrane offers a way to create viable implantation options in the treatment of insulin-dependent diabetes mellitus (IDDM). Traditionally the encapsulation process has been achieved through the injection/extrusion of alginate/cell mixtures into a calcium chloride solution to produce calcium alginate capsules around the cells. A novel alternative is explored here through a procedure using an emulsion process to produce thin adherent calcium alginate membranes around cell spheroids. In this study, a thorough investigation has been used to establish the emulsion process parameters that are critical to the formation of a coherent alginate coat both on a model spheroid system and subsequently on cell spheroids. Optical and fluorescence microscopy are used to assess the morphology and coherence of the calcium alginate/poly-L-ornithine/alginate (APA) capsules produced.

Transesophageal echocardiographic features and management of retained intracardiac air in two patients after surgery

Intracardiac residual air after open-heart surgery may carry a significant risk of embolization with associated morbidity and death. We hereby report two cases of retained intracardiac air detected in an unusual location with transesophageal echocardiography in the superior aspect of the left atrium after completion of standard air-evacuation procedures. Characteristic echocardiographic features and the impact on immediate management are described along with a review of the literature.

Arterial lesions associated with medial disorganization and fibrosis in endomyocardial biopsies from human cardiac allografts

We describe distinctive arterial lesions in endomyocardial biopsies from patients with human cardiac allografts. The lesions affected principally the media of small arteries and consisted of misorientation of smooth muscle cells and fibrosis. This remodelling was most prevalent in the subadventitial zone, but sometimes extended to involve the full thickness of the media. In the most extreme cases medial smooth muscle cells ran parallel to the long axis of the vessel and were segregated into small bundles and single cells separated by collagen which merged with the adventitial fibrosis. The intima was always normal. Abnormal arteries were present in 16% of 603 consecutive biopsies from 44 patients, and 39% of lesions occurred in 16% of patients. No lesions were found in endomyocardial biopsies from 25 non-transplanted patients, nor in mucosal biopsies from both transplanted and non-transplanted patients, confirming that the appearances were not due to biopsy artefact. There was early arterial remodelling in biopsies within two weeks of transplantation and none of the stages resembled vascular rejection. Fifty per cent of biopsies from some patients contained arterial lesions, suggesting that in susceptible patients they are common.

Bandwidth-induced errors in parameters used for automated activation time determination during computerized intraoperative cardiac mapping: theoretical limits

Two parameters commonly used when determining the time of local activation during computerized intraoperative cardiac mapping are the time of the peak in bipolar electrograms (BP) and the time of the largest negative slope (LNS) in monopolar electrograms (MP). The dependence of these parameters upon bandwidth was studied. A database of fast MP and BP was compiled from intraoperative recordings collected from epicardial sock arrays in man. Based on 95%, 99% and 99.9% of total signal power, the bandwidths of each response were determined. After removing specified frequencies using the Fourier transform, errors in determining these parameters were computed and characterized with respect to mean square error (MSE), percent power bandwidth and frequency content. The Fourier transform was used to abruptly filter out undesired upper frequencies. Filtering BP at 200 Hz produced a 1-ms shift in the peak in 17.0% of the electrograms, 0.4% of the peaks shifted by 2 ms and none shifted by more than 2 ms. Comparable shifts in the LNS occurred when filtering MP at 400 Hz. Retention of 95% of the power in a BP rarely (0.9%) changed the time of its peak by more than 1 ms. For MP, retention of 99.9% of the power was required for similar performance (3.6%). Thus, although BP have greater signal power in the higher frequencies than MP, a greater bandwidth is required when recording monopolarly in order to preserve the small amount of power necessary to define the time of the LNS with accuracy comparable to determination of the peak in BP.

Intimal intussusception: unusual complication of dissecting aneurysm

A case is reported of a 65-year-old man operated on to relieve obstruction of the left common carotid and left subclavian arteries due to a dissecting aneurysm. At operation the obstruction was found to be due to detachment of the intima from the ascending aorta followed by intussusception into the distal aortic arch. Surgical correction consisted in resection of the ascending aorta and aortic arch and replacement with a Dacron graft. Certain technical aspects of the operation were considered important in achieving a successful outcome.