Recoverability of heat-injured Bacillus spores by lysozyme and EDTA or alkaline thioglycollate.

The D95°C value of Bacillus thuringiensis spores plated in the presence of lysozyme increased from 3.0 min to 3.6 min by post-treatment of heat-injured spores with 50MM EDTA. In the case of Bacillus alvei and Bacillus polymyxa spores D-values decreased from 4.9 to 4.3 min and from 4.7 to 4.1 min respectively. Post-treatment of heat-injured spores treated with alkaline thioglycollate increased D95°C values of Bacillus alvei from 4.2 to 5.3 min, B. thuringiensis 3.6 to 4.7 min, and Bacillus polymyxa from 4.2 to 5.0 min when spores were plated in the presence of lysozyme. Electron micrographs of heat-injured B. alvei spores treated with sodium thioglycollate indicated that the coat layers of the treated spores were granulated and less intact than the control spores.

Laser angioplasty: controlled delivery of argon laser energy.

A laser catheter system that integrates balloon and fiberoptic technologies was evaluated. In vitro tissue studies were conducted to compare the tissue response to laser irradiation from a bare optical fiber (undiverged light beam) and from a fiber with an optical assembly (diverged light beam). An in vivo study of occluded and unoccluded canine femoral arteries examined coaxial alignment of the diverged light beam and the resultant thermal effects. In the in vitro studies, a diverged laser light beam effected maximum tissue ablation (mean crater diameter, 1.81 mm +/- 0.44) at a distance of only 3 mm from the optical fiber tip. The in vivo study demonstrated the ability of a specially designed balloon catheter to align the diverged laser beam coaxially within the arterial lumen. This laser catheter system successfully avoids the risks of inadequate tissue removal and perforation.

Canine model for long-term evaluation of prosthetic mitral valves.

The evaluation of mechanical prosthetic heart valves would be aided by a more satisfactory animal model. For acute assessment, a variety of animals have been used, but for chronic studies, only larger animals (pigs, calves, baboons) have been employed, creating an expensive model with laboratory management difficulties. Previously, the use of dogs for chronic evaluation has been unsatisfactory because of the frequent occurrence of early sepsis and valve-related thrombotic deaths. We have modified our existing acute dog protocol to produce a successful chronic model. Our model employs perioperative systemic antibiotics, short cardiopulmonary bypass period (range 35-60 min), a minimum of perioperative intravenous lines, postoperative anticoagulation therapy, and strict postoperative antiseptic technique for blood sampling. To evaluate this model, 11 consecutive mongrel dogs underwent mitral valve replacement with either a standard Dacron sewing skirt or a newly devised carbon-coated Teflon sewing skirt No. 23 mm Bjork-Shiley Convexo Concave (CC) prosthetic valve. Nine animals (82%) survived and were evaluated after a predetermined observation interval of either 3 or 6 months for valve function, pannus formation, and possible carbon particle migration. At sacrifice, all animals had good hemodynamics and valve function, minimal pannus formation and no carbon washout. Consequently, this model provides a relatively inexpensive, reproducible method of chronic in vivo evaluation of prosthetic valve modifications.

Brain damage in profound hypothermia. Perfusion versus circulatory arrest.

To investigate brain changes in induced deep core hypothermia (18 degrees C) with or without circulatory arrest, four groups of dogs were subjected to cardiopulmonary bypass (CPB) under the following conditions: (1) differential head perfusion with pulsatile flow and simultaneous circulatory arrest to the rest of the body; (2) differential perfusion to the head with a nonpulsatile flow; (3) total circulatory arrest; and (4) continuous hypothermic perfusion. Parameters analyzed were: (1) blood flow distribution; (2) creatine kinase isoenzyme (CK-BB) elevation in the cerebrospinal fluid (CSF) and in the brain venous return; and (3) microscopy of the brain in animals killed at 30 minutes, 24 and 48 hours, 1 and 2 weeks, and 1 month. Although minor brain tissue flow differences were found at 37 degrees C among the groups, flows equalized at 18 degrees C. A significant seven-fold brain flow increase followed the period of circulatory arrest in Group III. Rise of CK-BB levels occurred in brain venous return but not in CSF in all groups. Microscopic cellular damage appeared in all groups with an equal degree of severity, regardless of the method of hypothermia and perfusion implemented.