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Biomedical subjects

J Fisher

Publications and source records attributed to J Fisher.

At least 271 records · Page 15Linked to original sources
PubMed1995

In vitro determination of the curvatures and bending strains acting on the leaflets of polyurethane trileaflet heart valves during leaflet motion.

Leaflet tears originating from the free leaflet edge and calcification around the commissural region are common modes of failure exhibited by explanted bioprosthetic trileaflet heart valves. These may be a result of the cyclic bending and high levels of curvature that affect the leaflets within these areas during normal valve operation. These high levels of curvature occur in a short time period (approximately 20 ms) during rapid leaflet opening and to a lesser degree during leaflet closure. The curvatures that occur at the free leaflet edge of two designs of polyurethane trileaflet heart valve were determined in vitro at various stages during a cardiac cycle using a high-speed video camera (1000 frames/s). Significant deformations at the free leaflet edge were observed and bending radii as low as 0.55 +/- 0.125 mm (mean +/- standard deviation) were present during leaflet opening, 0.76 +/- 0.24 mm during leaflet closure and 1.01 +/- 0.27 mm while the valve was fully open during peak systole. The values of curvature were used to determine the values of bending strain and bending stress acting at the free leaflet edge using thin shell bending theory. The calculated values of bending strain were a maximum during the leaflet flexure associated with valve opening. These high levels of bending strain, which occur for short periods of time, are likely to be an important determinant of the valve's durability. It has been shown that the method of manufacture significantly influenced the level of bending strain in the valve leaflets. Valves manufactured using a dip-casting technique resulted in open leaflet bending strains up to 31 per cent lower than valves manufactured from solvent-cast sheets of polyurethane.

Heart Valve Prosthesis↗
PubMed1995

The influence of scratches to metallic counterfaces on the wear of ultra-high molecular weight polyethylene.

A number of studies of explanted metallic femoral heads have shown scratches or damage caused by bone cement, bone or metallic particles. This damage has been cited as a cause of increased wear of ultra-high molecular weight polyethylene (UHMWPE) acetabular cups. In this laboratory study, small scratches 2 mu m deep were made on smooth stainless steel surfaces at a spacing of 10 mm. These individual scratches were found to increase the wear rate of UHMWPE by a factor of 30 in unidirectional sliding and a factor of 70 in reciprocating motion. It is of particular concern that a single small scratch, which is not detected by the average surface roughness measurement Ra can cause such a dramatic increase in the wear of ultra-high molecular weight polyethylene.

Biocompatible Materials↗
PubMed1995

Private health insurance and a healthy personality: new risk factors for obstetric intervention?

In this study 242 nulliparous pregnant women completed standardized psychometric questionnaires and semi-structured interviews in the latter half of pregnancy and again 4-6 weeks postpartum. Discriminant function analysis revealed that the use of operative obstetric interventions was measurably influenced by psychosocial factors. Privately insured women were significantly more likely to experience instrumentally assisted (relative risk = 1.53, 95% CI: 1.05, 2.25) and Caesarean (relative risk = 1.91, 95% CI: 1.05, 3.46) deliveries than those receiving care in the public hospital system. The likelihood of experiencing these procedures was increased further among those who in late pregnancy were thinking clearly, had high self-esteem, mature means of dealing with anxiety, were confident in their knowledge of childbirth procedures and in secure partnerships with highly educated men. There was no evidence that either elevated anxiety or abnormalities of personality contributed to obstetric outcome. These findings indicate that obstetric decision-making is significantly influenced by patient personality and socioeconomic circumstances. In particular, they suggest that fear of malpractice litigation, physician convenience factors and the response of obstetricians to assured, well pregnancy-educated pregnant women may be influencing the use of operative intervention in delivery.

Adult↗
PubMed1995

Oxygenation and exercise performance-enhancing effects attributed to the breathe-right nasal dilator.

Recently, many professional football players have elected to wear spring-loaded nasal dilators during competition. Many athletes believe that wearing the "Breathe-Right" nasal dilator will increase nasal gas conduction and oxygenation to their body, subsequently improving their performance. The purpose of this experiment was to investigate the advantages of wearing a nasal dilator while performing aerobic and anaerobic exercise, as opposed to not wearing a nasal dilator. It was hypothesized that the "Breathe-Right" nasal dilator, manufactured by CNS, Inc (Chanhassen, MN) would increase nasal gaseous conduction and increase oxygenation to the body. Nasal gaseous conduction and oxygenation are essential components for using aerobic power. We examined whether wearing a nasal dilator improves performance by using a ramped cycle ergometer stress test on athletes until they reached VO(2) maximum progressing from aerobic to anaerobic exercise. Baseline data were collected (ie, VO(2), VO(2)/Kg, respiratory exchange ratio, anaerobic threshold time, and onset of VO(2) max) using a MedGraphics CardiO(2) System. The subjects included 16 college-aged male athletes. Dependent t-tests implemented on each physiological response; VO(2) max, peak VO(2) kg, onset of anaerobic threshold, onset of VO(2) max, respiratory exchange ratio at VO(2) max, and maximum WATT output, showed there was no difference in the athletes' performance when they wore the nasal dilators and when they did not wear the dilators.

Journal Article↗
PubMed1995

A rat transverse rectus abdominis musculocutaneous flap model: effects of pharmacological manipulation.

A study was designed to attempt to develop an experimental animal model for the transverse rectus abdominis musculocutaneous (TRAM) flap. The rat has a well-formed superior epigastric artery with musculocutaneous perforators that have been shown to support a musculocutaneous flap on a single superior pedicle. Despite the anatomical differences between the dominance of the axial longitudinal cutaneous circulation in loose-skinned animals compared with humans, as well as a dominant superior intramuscular pedicle, the rat TRAM model appears to be reproducible and has predictable zones of viability as well as areas that typically do not survive when based on a single superior pedicle. These areas of nonviability correspond to those zones at high risk of nonviability in the human clinical situation: zone 3 and 4 on the contralateral side and zone 3 on the ipsilateral side (tissue lateral to the superficial inferior epigastric supply). Once the reliability and reproducibility of this model was demonstrated (coefficient of variation 18.9%), a study was undertaken to determine whether pharmacological manipulation of this flap altered survival in those areas that are inadequately perfused. The two agents tested were allopurinol (xanthine oxidase inhibitor, antioxidant) and pentoxifylline (microcirculatory rheological agents that is a xanthine analogue and is also believed to have antioxidant potential). The study involved creating right unipedicled TRAM flaps in 30 male specific pathogen-free Sprague-Dawley rats weighing 375 to 450 gm. The transverse skin paddle was centered over the umbilical dimple and measured 5.5 x 2 cm.(ABSTRACT TRUNCATED AT 250 WORDS)

Allopurinol↗
PubMed1995

A review of 5 existing guidelines for planning focus groups in GP research.

The use of a focus group as a research method has become increasingly common in general practice related studies. Although existing guidelines for planning focus groups are very useful, a review of these guidelines indicate that a few of them are vague and need further elaboration. The authors review five existing guidelines for planning focus groups. These are size, number, duration, format and composition of a focus group. Suggestions have been made to address the uncertainties in these areas when a focus group is used. This paper was a section of manuscript presented at the 2nd International Qualitative Health Research Conference on 11 June 1994, Hershey, Pennsylvania.

Family Practice↗
PubMed1994

Changes in radiation survival curve parameters in human tumor and rodent cells exposed to paclitaxel (Taxol).

PURPOSE: Late G2 and M are the most radiosensitive phases of the cell cycle. Cells exposed to paclitaxel develop a cell cycle arrest in G2/M. These studies were performed to assess the in vitro radiosensitization properties of paclitaxel in human tumor and rodent cell lines. METHODS AND MATERIALS: The effect of paclitaxel on the radiation sensitivity of human breast (MCF-7), lung (A549), ovary (OVG-1) adenocarcinoma and Chinese hamster lung fibroblast V79 cells was determined with clonogenic assays. DNA flow cytometry studies were performed to define the cell cycle characteristics of the cells during irradiation. Survival curve parameters for all cell lines were determined with the use of a computer program which represents cell survival after radiation by a linear-quadratic model. RESULTS: All cell lines developed a G2/M block after exposure to paclitaxel for 24 h. However, the degree of radiosensitization produced by paclitaxel varied among the cell lines. The maximal sensitizer enhancement ratio (SER) of paclitaxel was 1.8 in MCF-7 cells, 1.6 in OVG-1 cells, and 1.7 in V79 cells. However, no concentration of paclitaxel was able to enhance the radiation sensitivity of A549 cells. Paclitaxel increased the linear (alpha) component of the radiation survival curves in all cell lines. The quadratic (beta) component was unaffected by paclitaxel in the rodent cells. High concentrations of paclitaxel (> or = 1000 nM) increased beta slightly in the human cell lines but there was considerable variation in the effect of paclitaxel on beta. The cells which were sensitized to radiation by paclitaxel had a relatively small baseline alpha component, while A549 cells had a large alpha component. CONCLUSION: We conclude that paclitaxel is a modest radiosensitizer in some, but not all, human tumor cells. Paclitaxel appears to cause radiosensitization mainly by increasing the alpha component of radiation survival curves. Cells that normally have a relatively small alpha component should exhibit the most radiosensitization in response to paclitaxel while cells with a large alpha component should show little or no radiosensitization after paclitaxel treatment. Because the greatest effect of paclitaxel is on the linear component of radiation survival curves, these results indicate that paclitaxel may be an effective radiation sensitizer in many human tumors treated at clinically relevant radiation doses of 2 Gy or less.

Animals↗
PubMed1994

In vitro studies of Taxol as a radiation sensitizer in human tumor cells.

BACKGROUND: Cells exposed to paclitaxel (Taxol) develop a cell cycle arrest in G2/M. It has long been recognized that late G2 and M are the most radiosensitive phases of the cell cycle. PURPOSE: These studies were performed to assess the in vitro radiosensitization properties of paclitaxel in human tumor cell lines. METHODS: The effect of paclitaxel at concentrations ranging from 0 to 10,000 nM on the radiation sensitivity (from 0 to as much as 10 Gy in certain experiments) of human breast (MCF-7), lung (A549), ovary (OVG-1), and pancreas (PC-Sh) adenocarcinoma cells was determined using clonogenic assays. DNA flow cytometry studies were performed to define the cell cycle characteristics of populations of cells that had been treated for 6-72 hours with 0, 100, 1000, or 10,000 nM paclitaxel. RESULTS: All cell lines developed a G2/M block after exposure to 100-10,000 nM paclitaxel for 24 hours. However, the degree of radiosensitization produced by paclitaxel varied among the cell lines. The sensitizer enhancement ratio (SER) of paclitaxel at 10% survival was 1.8 in MCF-7 cells and 1.6 in OVG-1 cells. However, paclitaxel at any concentration was unable to enhance the radiation sensitivity of A549 cells. PC-Sh cells demonstrated a complex and inconsistent radiosensitization response to paclitaxel. At 10% survival, an SER of 1.5 was observed in PC-Sh cells. However, at 1% survival, no radiosensitization was observed in PC-Sh cells. Maneuvers that prevented paclitaxel from producing a G2/M block, including coincident treatment with cycloheximide or treatment of cells in plateau phase of growth, completely abrogated the radiosensitization afforded by paclitaxel in MCF-7 cells. CONCLUSIONS: Paclitaxel is a modest radiosensitizer in some, but not all, human tumor cells. The degree of radiosensitization that we have observed with paclitaxel is similar to what has been found with other chemotherapeutic agents. The absence of radiosensitization by paclitaxel in MCF-7 cells grown to plateau phase or treated with cycloheximide implies that the development of a G2/M block is a necessary condition for paclitaxel radiosensitization. However, the inability of paclitaxel to radiosensitize A549 cells despite the presence of a G2/M block in those cells demonstrates that a G2/M block is not a sufficient condition for paclitaxel radiosensitization. IMPLICATIONS: Paclitaxel can radiosensitize to a modest degree some, but not all, human cell lines by a mechanism that requires the production of a G2/M cell cycle block. Additional studies are needed to define more clearly the mechanism by which paclitaxel radiosensitizes cells.

Cell Cycle↗
PubMed1994

Anisotropic elasticity and strength of glutaraldehyde fixed bovine pericardium for use in pericardial bioprosthetic valves.

Uniaxial tensile tests were performed on glutaraldehyde fixed bovine pericardial strips prepared from chemically modified pericardial samples. These samples originated from an area which demonstrated anisotropic mechanical properties in the native material and which is suitable for the construction of leaflets for pericardial bioprostheses. After glutaraldehyde fixation the tissue had retained its anisotropicity in stiffness and strength in two orthogonal directions. In the range of the functional stresses for a heart valve leaflet (< 1 MPa) the unconstrained fixation regime had modified the initial anisotropic elastic behavior into a more isotropic one. The implications of these findings are that leaflets manufactured from bovine pericardium can be made to resemble, to a degree, the well known anisotropy found in two orthogonal directions in natural human heart valve leaflets, or porcine bioprosthetic heart valve leaflets.

Animals↗
PubMed1994

The influence of Cremophor EL on the cell cycle effects of paclitaxel (Taxol) in human tumor cell lines.

We have performed DNA flow analysis, mitotic index studies, time-lapse photography, and paclitaxel uptake studies of human tumor cell lines exposed to paclitaxel. DNA flow analysis demonstrated that cells began accumulating in G2/M within 6 hrs of exposure to paclitaxel; by 12 hrs over 50% of cells accumulated in G2/M at all concentrations tested. After 24 hrs of exposure to 10 nM paclitaxel, cells underwent non-uniform mitotic division resulting in multinucleated cells. Of cells treated with 30 nM to 1000 nM paclitaxel, 75% to 85% remained blocked in G2/M for up to 72 hrs. Although a large proportion of cells treated with higher concentrations of paclitaxel (10,000 nM) was blocked in G2/M, a significant proportion (10% to 40%) of these cells was also in G1. Cells exposed to lower concentrations of paclitaxel (10 nM to 1000 nM) in medium containing 0.135% (v/v) Cremophor EL also had a relatively large proportion in G1. Mitotic index studies demonstrated that the paclitaxel-induced G2/M block was initially a mitotic block and that cells remained in mitosis for up to 24 hrs. With additional time of exposure to paclitaxel, mitotic index and time-lapse studies indicated that cells attempted to complete mitosis; however, cytokinesis was inhibited and cells became multinucleated. Time-lapse photography revealed that paclitaxel markedly prolonged the time in mitosis from 0.5 hr to 15 hr. High levels of Cremophor EL (0.135% v/v) markedly reduced the number of cells in mitosis but did not alter the mitotic delay induced by paclitaxel. 3H-paclitaxel uptake studies revealed that high concentrations of Cremophor EL did reduce the rate of uptake of paclitaxel into cells but had little effect on total paclitaxel accumulation. These results confirm that paclitaxel has striking effects on the cell cycle and show that high concentrations of Cremophor EL are capable of inducing a cell cycle block distinct from the mitotic block seen with paclitaxel. These results also demonstrate that cells exposed to paclitaxel for longer than 24 hours attempt to complete mitosis but the process of cytokinesis is inhibited. Together with cytotoxicity data, these results indicate that entry into and exit out of mitosis are prerequisites for paclitaxel cytotoxicity.

Adenocarcinoma↗
PubMed1994

A parametric analysis of the contact stress in ultra-high molecular weight polyethylene acetabular cups.

It is well known that the wear factor for ultra-high molecular weight polyethylene (UHMWPE) sliding on metallic or ceramic counterfaces is largely independent of contact stress for modest loading conditions and sliding distances. However, it is now recognized that under more severe stress levels and with sliding distances comparable to those encountered in current replacement synovial joints, subsurface fatigue contributes to the volume of wear debris. Since the fatigue process is influenced by surface stress levels it is becoming increasingly important to limit the contact stress through design in order to minimize the volume of UHMWPE wear debris in implants. The contact pressure in UHMWPE acetabular cups has been predicted using both the simple elasticity analysis and the finite element method. It has been shown that the radial clearance between the femoral head and the socket is the dominant parameter in determining the contact stress. Thus, the radial clearance should be controlled so the contact half width is close to the femoral head radius (a total included angle of contact of 120 degrees) to minimize the contact pressure. There is little benefit to be gained by increasing the contact half width greater than the femoral head radius. This is consistent with the geometrical constraint of the anatomical position and the direction of loading. It has been shown that the radius of the femoral head has the most significant effect on the maximum contact pressure for these closely conforming contacts where the contact half width is close to the femoral head radius. The effect of the elastic modulus and the thickness of UHMWPE is relatively small under these contact conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetabulum↗
PubMed1994

A tribological study of a series of retrieved accord knee explants.

A tribological study of a series of 27 retrieved Accord meniscal bearing knee joints has been carried out. The roughness of the articulating surfaces of the meniscal and the femoral components was investigated, and the penetration into the polyethylene meniscal component was determined. There was generally little damage to the highly polished metallic femoral components. A general polishing and smoothing of the ultra high molecular weight polyethylene meniscal components was observed, although there was some subsequent deterioration of the polyethylene surfaces in certain cases. The penetration rate of the femoral components into the menisci was low, and was found to be similar to that reported for other meniscal knee joints.

Adult↗
PubMed1994

Comparative study of the wear of UHMWPE with zirconia ceramic and stainless steel femoral heads in artificial hip joints.

The wear of ultra high molecular weight polyethylene (UHMWPE) when sliding against zirconia ceramic and stainless steel counterfaces has been compared in a pin-on-plate reciprocator and in a hip joint simulator. A lower wear factor was found for the UHMWPE when sliding on the zirconia ceramic counterfaces in the pin-on-plate tests. In the hip joint simulator test, the acetabular cups articulating on zirconia heads showed consistently lower volume changes than the cups articulating on stainless steel heads. The higher volume changes found with the stainless steel heads were associated with an increased roughness of the femoral heads during the tests. This roughening was caused by the adherence of a rough polymer transfer film.

Biocompatible Materials↗
PubMed1994

A synthetic leaflet heart valve with improved opening characteristics.

A new geometry for the design of polyurethane leaflet heart valves has been investigated. The geometry termed the 'alpharabola' has a radius of curvature that increases from the centre of the leaflet at the free edge towards the base of the valve and perimeter of the leaflet. The hydrodynamic function and leaflet opening characteristics of the new valve design have been compared to a valve with a spherical leaflet geometry using the same material. The pressure and flow required to open alpharabola leaflets in steady flow tests was markedly lower than for spherical leaflets. Under pulsatile flow conditions with the valve leaflets fully open, the pressure drop across the alpharabola and spherical leaflets was similar, but much lower than in a porcine bioprosthesis. High speed photography showed that the alpharabola leaflets opened in less than 30 ms with the leaflet opening initiating in the base of the leaflet where the radius of curvature was larger. The synthetic leaflet valve has demonstrated short term durability in accelerated fatigue tests to 100 million cycles.

Biomechanical Phenomena↗
PubMed1994

Do surgical residents, emergency medicine physicians, and nurses experience significant radiation exposure during the resuscitation of trauma patients?

During this study we investigated the yearly risk of radiation exposure for surgical residents (group 1, n = 8), emergency department (ED) physicians (group 2, n = 6) and nurses (group 3, n = 97) participating in the resuscitation of trauma victims in the emergency department of a 500-bed teaching hospital. Dosimeter readings of the three study groups were recorded monthly over the 1-year study period. During the study interval, 758 patients underwent resuscitation following trauma; 2098 portable radiographs (758 chest films, 758 lateral cervical spine films, and 582 radiographs of the pelvis) were obtained during the resuscitation phase of these patients. The total radiation exposure for group 3 was significantly greater than that for groups 1 and 2 (340 +/- 50 vs. 160 +/- 112 and 20 +/- 14 mrem, respectively, p < 0.01). Individual residents received a significantly greater amount of radiation than ED physicians and nurses (20 +/- 28 vs. 3.3 +/- 2.0 and 3.5 +/- 2.0 mrem, respectively, p < 0.05). However, despite repeated exposure to radiation, individuals in the three groups did not exceed the safety limits of 0.05 Gy/year set by the National Council on Radiation Protection and Measurements. Based on the results of this study, we conclude that trauma resuscitation teams can provide quality care to their patients without concern over the detrimental effects of radiation exposure, provided that the basic principles of radiation protection are followed.

Emergency Medicine↗