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A new morphologic method is described for the simultaneous quantitation of porcine aortic valve collagen crimp length and the assessment of biomechanical properties. This method utilizes the simultaneous real-time video recording of collagen crimp morphology and acquisition of crimp length data through the combination of polarized light microscopy and morphometry. We felt that the development of this method was warranted, due to the fundamental role played by collagen in porcine aortic valve performance. The development of this method involved the design and fabrication of a uniaxial microtensile stage, suitable for mounting on a standard microscope stage. The validation of our test method was accomplished by a comparison of untreated and glutaraldehydetreated porcine aortic valve leaflet tissue, because the biomechanical and morphologic characteristics of the native and fixed aortic valve have been extensively studied. The method described in this communication enables the collection of morphologic and biomechanical data from a single tissue specimen, eliminating the need for independent studies of multiple specimens. Furthermore, this method obviates the need for making assumptions, which may be difficult to verify, concerning the homogeneity of different test specimens with respect to their morphology and corresponding mechanical response to different experimental conditions.

Twenty-five human cryopreserved valves with harvest-related warm ischemic times (WITs) ranging from 0 to 20 hours were studied using transmission electron microscopy to characterize the effects of harvesting and preservation on leaflet matrix cells. The valves were divided into seven groups on the basis of WIT and processed using standard transmission electron microscopic methods. Each cell (528 micrographs) was graded for reversible and irreversible cellular injury and subjected to a Cochran-Mantel-Haenszel trend analysis. Our results demonstrated a progression in cellular injury with increasing WIT. During the first 12 hours of warm ischemia, reversible cellular injury predominated (0.0%, 30.0%, 51.2%, 31.3%, 35.1%, 45.1%, and 40.0% at WITs of 0, 1, 2, 8, 12, 16, and 20 hours, respectively). A positive correlation (p < 0.0001) between increasing WIT and reversible cellular injury through the first 12 hours was observed. Minimal morphologic evidence of irreversible injury was noted in valves harvested with less than 12 hours of warm ischemia; however, after 12 hours there was a marked increase (0.0%, 0.0%, 4.7%, 2.4%, 2.7%, 31.4%, and 40.0% at WITs of 0, 1, 2, 8, 12, 16, and 20 hours, respectively) in irreversible cellular injury (p < 0.001 between 12 and 20 hours WIT). These data demonstrate a progression in cellular injury with increasing WIT. There was virtually no morphologic injury in valves with harvest-related WITs less than 2 hours and minimal irreversible cellular injury observed in valves exposed to 12 hours or less of warm ischemia. If cellular viability is critical to homograft durability then harvest-related warm ischemia may need to be restricted to 12 hours.

Cryopreserved allograft valves are increasingly being used as valvular replacements. Leaflet fibroblast viability has been suggested to influence clinical durability. The warm ischemic time is thought to be a critical determinant of this cell viability. The purpose of this study was to apply quantitative morphometric methods to characterize, by transmission electron microscopy, valvular cellular injury resulting from progressive warm ischemic time. Porcine aortic valves were harvested with a spectrum of warm ischemic times (40 minutes and 2, 6, 12, 24, and 36 hours; five valves per warm ischemic time; n = 30) and processed by standard electron microscopic methods. To ensure randomized tissue selection within each warm ischemic time interval, we randomly selected one thin section from each leaflet. The first ten cells in each thin section were photographed and cellular injury was assessed (cell disruption, dilation of endoplasmic reticulum, cytoplasmic edema, nuclear and mitochondrial changes). Nine hundred micrographs have been analyzed by Cochran-Mantel-Haenszel statistics to determine if a significant association between warm ischemic time and cellular injury exists. Our findings indicate a significant association between reversible cell injury through 24 hours of warm ischemic injury (p less than 0.0001). Furthermore, a significant association between irreversible cell injury and progressive warm ischemia through 36 hours was also found. These findings indicate that the ischemic interval after donor death is associated with progressive leaflet cell injury. Cellular damage begins shortly after donor death and continues incrementally throughout 36 hours. After 2 hours of warm ischemic injury 37% of the cells had morphologic evidence of injury. After 6 hours of warm ischemic injury the number of injured cells increased to 73%. By 36 hours 22% of the cells appeared normal. Irreversible cell injury increases with prolonged ischemia and becomes quantitatively impressive at 24 hours, by which time 26% of cells are so affected. Conversely, some cells are resistant to irreversible injury for a prolonged ischemic interval.

It has been suggested that the mechanical durability of glutaraldehyde-treated porcine aortic valve (PAV) bioprostheses (BPs) may be increased if collagen crimp approximating that observed in native valvular tissue is maintained during preimplantation processing. Among the factors affecting PAV fixation, the magnitude of the pressure applied to the aortic valve during fixation influences the extent of collagen crimp. Polarized light microscopy is useful for both the qualitative assessment of collagen morphology and the quantitative measurement of collagen crimp in BPs. The purpose of this study was to determine the feasibility of using this optical method to detect quantitative differences in PAV collagen crimp following zero-, low-, and high-pressure fixation. The results of this study demonstrate the following: 1) coupling polarized light microscopy and morphometric measurements provides a quantitative method for the evaluation of the relationship between fixation pressure and collagen crimp in PAVs; 2) a significant association between increasing fixation pressure and absence of collagen crimp was observed in cords and the mid-cusp region; 3) collagen crimp length in the cords is affected by fixation pressure; 4) the alteration of collagen crimp by low- and high-pressure fixation does not uniformly affect all regions of the cusp; and, 5) collagen crimp was consistently present in all cusp regions in zero-pressure fixed PAVs.

The overall and cause-specific mortality experience of male radiologists and a comparable group of medical specialists, pathologists, who were included in the Radiation Registry of Physicians, is presented. The study population consists of an early-entry cohort of physicians who were members of either the American College of Radiology or the College of American Pathologists as of Jan. 1, 1962, and a late-entry cohort of similar members who joined these societies between January 1962, and June 1972. The purpose of the study was to determine if occupational exposure to low levels of ionizing radiation resulted in excess mortality from all causes and specific causes, or decreased survival patterns for radiologists compared with pathologists over the 16-year period, 1962 to 1977. The data revealed that radiologists and pathologists were comparable regarding overall mortality experience for all entrants, the early-entry cohort, and the late-entry cohort. Further analyses revealed a gradient in mortality between the two specialties, with the largest differences in the earliest birth subcohorts for all three groups, and a significant excess in mortality among radiologists in those subcohorts of the late-entry cohort born before 1920. Such a gradient may indicate an exposure effect associated with time of first exposure or duration of exposure, but not associated with time of entry into a professional society. Nevertheless, overall age-specific and age-adjusted mortality rates among radiologists and pathologists were lower in the late-entry cohort compared with the early-entry cohort, thus indicating some effect of time of entry within each specialty.(ABSTRACT TRUNCATED AT 250 WORDS)

There are reports in the literature that the temporal peak intensity of pulsed ultrasound may be a better predictor of biological damage than is average intensity. The effects of temporal peak intensity on the survival of Drosophila melanogaster pupae exposed to pulsed ultrasound were investigated. Pulse average intensity and pulse repetition frequency were varied, while temporal average intensity and exposure duration were held constant. Thus, the total energy delivered was held constant. Survival was found to be directly dependent on pulse average intensity. We observed decreased survival at spatial average pulse average intensities as low as 0.5 W/cm2.

Criteria and evaluation procedures have been established to assess the measurement accuracy of Automated Microwave Oven Leakage Survey Systems. These criteria and procedures are based upon analytical characterizations of the oven leakage fields, measurement data and statistical analysis and experience gained from evaluation of hand-held oven survey instruments. Results of our evaluation of a typical survey system are presented.