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E A Talman

Publications and source records attributed to E A Talman.

9 recordsLinked to original sources
PubMed1999

Quasi-Linear Viscoelastic theory applied to internal shearing of porcine aortic valve leaflets.

The elements of Quasi-Linear Viscoelastic (QLV) theory have been applied to model the internal shear mechanics of fresh and glutaraldehyde-fixed porcine aortic valve leaflets. A novel function estimation method was used to extract the material functions from experimental shear data obtained at one strain rate, and the model was used to predict the material response at different strain rates. In general, experiments and predictions were in good agreement, the larger discrepancies being in the prediction of peak stresses and hysteresis in cyclic shear. In shear, fixed tissues are stiffer (mean initial shear modulus, 13 kPa versus 427 Pa), take longer to relax to steady state (mean tau 2 4,736 s versus 1,764 s) with a slower initial relaxation rate (mean magnitude of G(0), 1 s-1 versus 5 s-1), and relax to a lesser extent than fresh tissues (mean percentage stress remaining after relaxation, 60 versus 45 percent). All differences were significant at p = 0.04 or less, except for the initial relaxation slope. We conclude that shear experiments can complement traditional tensile and biaxial experiments toward providing a complete mechanical description of soft biomaterials, particularly when evaluating alternative chemical fixation techniques.

Animals↗
PubMed1996

Internal shear properties of fresh porcine aortic valve cusps: implications for normal valve function.

BACKGROUND AND AIMS OF THE STUDY: Several types of stress act on aortic heart valve tissue during the cardiac cycle. When closed the valve is subjected to primarily tensile stress due to the diastolic pressure, and upon opening bending stress occurs near the attachment with the aortic root and throughout the body of the cusps. Smooth bending requires internal tissue shearing. To measure the internal shear properties of the tissue a testing device was created which combined a high-precision linear actuator with a sensitive load cell. MATERIALS AND METHODS: Circular punch biopsy specimens from fresh porcine aortic valve cusps (n = 32) were examined. The shear stress versus shear strain characteristics were measured both in the circumferential (n = 17) and the radial (n = 13) direction, and the stress relaxation characteristics were also examined circumferentially (n = 15) and radially (n = 15). In addition seven specimens were tested repeatedly in both radial and circumferential directions for tissue isotropy. RESULTS: The results from the shear stress versus strain tests showed the tissue to behave non-linearly over the strain range between -0.9 and 0.9. The average moduli at the near zero strains were less than 300 Pa and increased to over 20 kPa at the extreme strains. The circumferential direction yielded slightly higher average moduli than the radial direction but this difference was not significant. The stress relaxation results indicated that valve tissue relaxation occurs in two distinct phases, an initial low slope region and a second high slope region with respective values of -7.5 log(s)-1 and -15 log(s)-1 and with no significant difference between test directions. CONCLUSIONS: Our results define and describe the pattern of internal shear properties of the aortic valve that are particularly important during the transition between the open and closed positions. This behavior pattern has particular application in the creation of accurate mathematical models of the valve tissue and may be important in understanding the mechanism of tissue failure in bioprosthetic valves.

Animals↗
PubMed1995

Glutaraldehyde fixation alters the internal shear properties of porcine aortic heart valve tissue.

Glutaraldehyde fixation noticeably alters the mechanical properties of porcine aortic valve tissue, subsequently affecting the function and durability of these tissues when used as prosthetic heart valves. Traditional uniaxial tensile testing techniques do not fully define the mechanical properties and we have devised a new approach to examine the important shear properties of the tissue. Altered shear properties would change the response of the valve tissue as it flexes open and closed. An apparatus combining a high-precision linear actuator with a gram-sensitive load cell was used to measure the shear characteristics of circular punch specimens taken from the center of each valve cusp. The tissue parameters measured showed significant differences between the fixed and fresh tissues. Glutaraldehyde-fixed tissue (n = 16) was about 100 times as stiff as fresh tissue (n = 32) between shear strain values of 0 and 0.2. The fixed tissue also had stress relaxation rates about 60% those of the fresh cusps and had about 70% of the hysteresis loss seen in fresh tissue. These results demonstrated the significant effects of glutaraldehyde fixation on the properties of porcine aortic valve cusp when tested in shear. Such changes could lead to altered tissue function and may increase internal stresses during opening and closing, contributing to valve fatigue.

Animals↗
PubMed1991

Medial collagen organization in human arteries of the heart and brain by polarized light microscopy.

The mechanical properties of collagen as a biopolymer ensures that collagen has a significant influence on the mechanical behavior of the host tissue. Structural organization is a key to that influence. We have assessed this relationship quantitatively in the tunica media of arteries from the heart and brain, using the polarizing light microscope and Universal stage. Arteries from 22 autopsies were isolated, cannulated and fixed with 10% buffered formalin, at a distending pressure spanning normal values in vivo. We prepared the tissue for light microscopy, with paraffin embedding, sectioning at 7 microns, and staining with picrosirius red to enhance the natural birefringence of medial collagen. Individual measurements, 30 to 50 per arterial section, referenced against the central axis of the vessel segment, revealed a coherent organization, with an average orientation which was within 1 to 2 degrees of being perfectly concentric for all artery segments. Analysis was done with Lambert projections and circular statistics. We calculated the circular standard deviation, which was 5.2 degrees for 27 brain arteries (S.D. 1.9 degrees) and 5.6 degrees (S.D. 2.1 degrees), for 5 coronary arteries sectioned at less than 15 degrees. Our interpretation is that medial collagen can be strained even though highly aligned, revealing a mechanical property which contrasts that of type I collagen.

Azo Compounds↗
PubMed1983

A 25-year experience with total portosystemic shunts and reappraisal of colon exclusion.

The results of 43 total shunt procedures for bleeding esophageal varices performed consecutively at two community hospitals from 1956 to 1981 are reviewed. Of 15 patients with immediate preoperative bilirubins greater than 2.0 mg/dl, 11 died following shunt surgery. Of 28 other shunted patients with immediate preoperative bilirubins of less than 2.0 mg/dl, there was only one in-hospital death, thus substantiating the contention that the last preoperative serum bilirubin value is the best predictor of operative mortality. Of ten patients with appreciable ascites verified at the time of operation, there were only two survivors, and both of these had preoperative bilirubins of less than 2.0 mg/dl. Twenty-nine of the 31 patients who left the hospital were still living at least one year after operation. All 23 patients operated on prior to 1977 were available for 5-year follow-up, and there were 14 survivors (60%). Thirteen of the 31 patients (42%) manifested some degree of hepatic encephalopathy, as interpreted by necessity for protein restriction and either Neomycin or Lactulose. Incapacitating post-shunt hepatic encephalopathy developed in one patient who required recurrent hospitalizations for episodic coma. This patient underwent a total abdominal colectomy and ileorectal anastomosis, with elimination of all episodes of encephalopathy for the subsequent 4 1/2 years. The previous 16 cases in the literature of surgical treatment of post-shunt encephalopathy are reviewed, and the efficacy of such colon exclusion is reassessed.

Adult↗
PubMed1979

Role of arteriography in rectal hemorrhage due to arteriovenous malformations and diverticulosis.

Nine patients with arteriographic right colon arteriovenous malformations (AVM's) are reviewed. Even though five of the eight surviving patients had diverticulosis in remaining colon, right colectomy with removal of the AVM effectively controlled bleeding in seven of the eight patients in follow-up intervals of 14-66 months. Such results suggest that right colon AVM, rather than diverticulosis, may be the more common cause of chronic recurrent lower intestinal hemorrhage in the elderly. Rebleeding occurred in one patient and has heretofore been reported in seven cases. However, since AVM bleeding is rarely life-threatening, right colectomy for chronic recurrent rectal bleeding is justifiable as the initial operative procedure for an AVM, even in the presence of left colon or sigmoid diverticulosis. In the same five year period, 1973-1977, four additional patients with massive hemorrhage, characteristic of diverticulosis, had emergency arteriography with demonstration of a localized site of diverticular bleeding that was controllable by partial colon resection. Consequently, segmental resection of the colon, utilizing selective arteriography, has thus far eliminated bleeding in eight of nine patients with diverticulosis. The judicious use of arteriography in patients with diverticulosis and rectal bleeding substantially reduces the requirement for subtotal colectomy and ileoproctostomy.

Adult↗