Shell Thickening Research Articles

Left ventricular midwall mechanics in systemic arterial hypertension. Myocardial function is depressed in pressure-overload hypertrophy.

Left ventricular (LV) midwall geometry has been described conventionally as the sum of the chamber radius and half of the wall thickness; this convention is based on the assumption of uniform transmural thickening during systole. However, theoretical considerations and experimental data indicate that the inner half (inner shell) of the LV wall thickens more than the outer half (outer shell). Thus, an end-diastolic circumferential midwall fiber exhibits a relative migration toward the epicardium during systole. As a result, the conventional method provides an overestimate of the extent of the midwall fiber shortening. We developed an ellipsoidal model with a concentric two-shell geometry (nonuniform thickening) to assess midwall fiber length transients throughout the cardiac cycle. This modified midwall method was used in the analysis of LV cineangiograms from 15 patients with systemic arterial hypertension and 14 normal subjects. Study groups were classified according to LV mass index (LVMI): 14 normal subjects (group I), eight hypertensive patients with a normal LVMI (group II), and seven hypertensive patients with an increased LVMI (group III). There were no significant differences in LV end-diastolic pressure or volume among the three groups; the ejection fraction was slightly greater in group II (70 +/- 5%) than in groups I (65 +/- 8%) and III (66 +/- 4%), but this trend did not achieve statistical significance. Values for endocardial and conventional midwall fractional shortening (FS) were also similar in the three groups. By contrast, FS by the concentric two-shell geometry (modified midwall method) in group III (16 +/- 2%) was significantly less than that seen in groups I and II (21 +/- 4% and 21 +/- 5%, respectively; both p less than 0.05). This difference achieves greater importance when it is recognized that mean systolic circumferential stress was lower in group III (151 +/- 22 g/cm2) than in groups I and II (244 +/- 37 g/cm2 and 213 +/- 38 g/cm2, respectively; both p less than 0.01). The midwall stress-shortening coordinates in six of the seven group III patients were outside the 95% confidence limits for the normal (group I) subjects. Thus, despite a normal ejection fraction, systolic function is subnormal in hypertensive patients with LV hypertrophy. Chamber dynamics provide an overestimate of myocardial function, especially when LV wall thickness is increased. This is due to a relatively greater contribution of inner shell thickening in pressure-overload hypertrophy.

Metabolism of tributyltin by marine animals and possible linkages to effects

This paper summarizes recent work on the metabolism of tributyltin (TBT) by marine animals and how this metabolism may relate to some of the observed effects. Fish and crustaceans have an active cytochrome P-450 dependent mono-oxygenase system which oxidizes TBT to a series of hydroxylated derivatives. These hydroxylated derivatives are conjugated to sulfate or carbohydrate by phase 2 enzyme systems which facilitates the rapid elimination of TBT from the animal. Mollusks have low cytochrome P-450 content and mixed function oxygenase activity which results in TBT accumulation because of the low TBT metabolism rate. Some of the TBT effects observed for mollusks include imposex in stenoglossan gastropods, oyster shell thickening, reduced growth rates in mussels and breakdown of sexual differentiation, oogenesis and egg production in Ostrea edulis. We suggest that these effects are related to the binding of TBT metabolites to cellular proteins and inhibition of detoxifying enzyme systems, e.g., cytochrome P-450 systems and glutathione S-transferases, by TBT. All of the effects are hormonally regulated and TBT and hormones share common metabolic pathways.

Variation in composition and condition of the Pacific oyster, crassostrea gigas, along a pollution gradient in Manukau Harbour, New Zealand

Three physical and four biochemical condition indices were used to assess the condition of the Pacific oyster, Crassostrea gigas, down a pollution gradient in Wairopa Channel, Manukau Harbour, New Zealand. The channel receives inputs of industrial and municipal waste including various organochlorine compounds, metals and microbiological contaminants. Changes in condition along the channel agreed well with the known water quality/pollution gradient. All indices except one (based on protein content) clearly distinguished between polluted and unpolluted sites. Differences in condition were attributable principally to an increase in glycogen content down the pollution gradient. Whereas protein content varied insignificantly amongst sites, glycogen content was 1.5–1.8 times greater at the less polluted sites and accounted for much of the observed increase in dry flesh weight. Pronounced shell thickening, commonly associated with tributyl tin contamination, was also observed at the more polluted sites.

Large heteromorph ammonites from the Upper Cretaceous of Seymour Island, Antarctica

Two species of the heteromorph ammonite genus Diplomoceras Hyatt are described from the Upper Cretaceous of the James Ross–Seymour Islands area, Antarctica. The late Campanian–early Maastrichtian D. lambi Spath has a relatively high rib density, whereas D. maximum n. sp. has a lower rib density and is known only from the uppermost Maastrichtian of the Lopez de Bertodano Formation on Seymour Island. Both species attain an exceptionally large size with the body chamber of D. maximum n. sp. attaining a length in excess of one meter. The structure of the shell wall in Diplomoceras is characterized by the thickening of the nacreous layer below the ribs. The shell thickening results in an inner flat surface and a smooth phragmocone. Reconstruction of the shell suggests at least four parallel shafts and three U-connectives. Estimates of the total density, center of buoyancy, and center of mass in this reconstructed shell indicate a slightly positive buoyant shell with a relatively unstable floating position.

The accumulation of organotins in adult and seed oysters from selected estuaries prior to the introduction of U.K. regulations governing the use of tributyltin-based antifouling paints

Between April and November, 1985, a study of the levels of organotins in adult and seed Crassostrea gigas grown in the southwest and southeast of England was carried out. This work corresponds with a similar study of organotin water levels (reported separately). The analytical procedure used was directly coupled high performance liquid chromatography-flame atomic absorption spectrometry. Individual adult oysters and groups of 20–40 seed oysters were taken for analysis on a monthly basis. The profiles of tributylin (TBT), dibutyltin (DBT) and monobutyltin (MBT) are discussed in relation to each other and levels found in the waters. In general, levels of all three organotin species were found to be higher in the seed oysters. Mean levels of TBT reached 3.1 μg g −1 in seed oysters from the Exe, Devon, in October, whereas mean levels of DBT and MBT reached 16.1 and 16.7 μg g −1 in Teign, Devon, seed oysters in October. Bioconcentration factors of ∼ 10000 were found, but seem to be greater when lower levels of TBT were present in the water, perhaps indicating a more ‘efficient’ removal from the water. The degree of shell thickening was calculated for all oysters submitted for analysis. The highest percentage of adult oysters with severely thickened shells was found at Tollesbury Fleet, where 61% of oysters showed shell thickness index values of six or less. Generally, two peaks in TBT levels in the oysters were observed, in the late spring and early summer: these seem to correlate with peak levels of TBT in the waters immediately preceding these times. A large proportion of the DBT and MBT found in the oysters seems to come from the metabolism of the TBT ingested. It is suggested that high sediment loadings may contribute to the severe deformation of oysters grown at Tollesbury Fleet, but only in the presence of TBT.

Shell thickening in Anodonta cygnea by TBTO treatments

1. Low level TBTO (bis(tributyltin)oxide) treatments (0.2 μg/l) caused, in vivo, a secretion of a calcified organic matrix over the inner face of the shell of Anodonta cygnea after eight days. 2. Electrophysiological studies carried out on the outer mantle epithelium (OME) showed that the short-circuit current was strongly inhibited by TBTO from the shell side. On the contrary, the effect is very slow from the haemolymph side. 3. The TBTO effect on the proton and/or bicarbonate transport mechanisms across the OME can be a strong factor in the shell thickening.

Possible effects of organotins on scallop recruitment

The adult populations of the scallop ( Pecten maximus) and of flame shells ( Lima hians) have declined in the North Water of Mulroy Bay on the north coast of Ireland. Settlements of these and some other bivalve species either failed or were reduced. These events relate well to the first introduction and subsequent increased use of organotin net-dips on salmonid farms in this Bay. The last use of these net-dips was during the spring of 1985. In 1986 these was a good settlement of scallops, and settlements of other bivalves were recorded except for flame shells. Levels of TBT in adult scallop tissue in the North Water are high, 0.7 μg g −1 wet wt; levels determined in other species were much lower. Pacific oyster ( Crassostrea gigas) shell thickening was used to monitor the presence of organotins in a number of areas including Mulroy Bay. In Kilkieran Bay, an area having a scallop fishery, this was greatest at the innermost station, suggesting higher levels there. Shell thickening and organotins in Pacific oysters were also measured in Cork Harbour.

Structure, crystallography, and morphogenesis of the cryptic shell of the terrestrial slug Limax maximus (Mollusca, gastropoda).

The structure and crystallography of the internal shell of the pulmonate gastropod slug Limax maximus were studied at the levels of light and scanning electron microscopy, revealing patterns of shell ontogeny and morphogenesis. The calcified portion of the slightly convex ovoid shell is composed of a single palisade layer of calcitic crystals. Numerous projections, 100 μm in width at the dorsal tip, are found on the dorsal surface of the shell and coincide with local nucleation sites of primordial calcium salt deposition onto the periostracum. With continued calcification these projections coalesce ventrally, forming the single crystalline shell layer. The organic portion of the shell includes the periostracum and an extensive PAS-staining conchiolin. In EDTA-etched preparations, conchiolin appears as a spongy network of fibers throughout the shell. Both horizontal and vertical components of the conchiolin are present, the former of variable thickness and occurring in an intercrystalline manner, the latter always occurring normal to the horizontal set. Macromorphogenic growth is characterized by three distinct temporal stages. Primary growth occurs radially from the umbonal region. Secondary growth is synonymous with shell thickening. Tertiary growth is characterized by both a lateral component, in which the shell extends beyond the primary growth boundaries, and a ventral component, in which the shell continues to grow in thickness. SEM of the ventral shell surface reveals a pattern of growth at the crystalmatrix interface. Proteinaceous fibers of the conchiolin occur unidirectionally in horizontal rows. Zones of incipient calcitic crystallization onto these hypostracal fiber bundles are contrasted by zones of increasing crystallization until the fibrous template (reduced hypostracum) is completely covered by crystals.

Buckling of Cooling-Tower Shells: Bifurcation Results

This paper describes studies of bifurcation buckling of hyperboloids used for large-scale cooling towers. Those studies include the effects of flexible supports, combined loadings from wind, dead weight, and temperature, shell cracking, different variations in the wind pressure distribution, and changes in the shell thickening. Comparisons are made between numerical and wind-tunnel results. The finite element formulation used is examined and results are presented for the tower at the Trojan Nuclear Power Plant on the Columbia River, Oregon.