Biomedical subjects

R C Quijano

Publications and source records attributed to R C Quijano.

27 records · Page 2Linked to original sources

PubMedDate not supplied

Sterilization of a small caliber vascular graft with a polyexpoxy compound.

Sterilization of tissue based medical devices via cold sterilization processes has been limited to formaldehyde, glutaraldehyde, and mixtures of the same with alcohols and surfactants. The authors report the sterilization of a small caliber vascular graft with a combination of diglycidyl ether and ethanol. The sterilant contains 1-4% diglycidyl ether and 10-20% ethanol as an aqueous solution. Sterilization is achieved after exposure of the graft to the sterilant solution for a period of 7 days at an elevated temperature (30 degrees - 40 degrees C). The biologic indicator selected for efficacy studies was Bacillus subtilis niger ATCC 9372 (endospores). The grafts were inoculated with a concentrated endospore suspension and immersed in the sterilant solution for increasing time periods. After extensive rinsing over membrane filters to remove any residual sterilant, the grafts and filters were cultured in tryptic soy broth. D10 values were calculated using a fraction-negative, most probable number technique. Additionally, many representative bacteria and fungi were tested and found to be susceptible to the new sterilant developed. The diglycidyl ether/alcohol sterilant developed was found to be efficacious for sterilization of the tissue based vascular grafts tested.

Bacteria↗

PubMedDate not supplied

In vitro evaluation of a stentless porcine aortic bioprosthesis. A preliminary study.

Currently available aortic bioprosthetic heart valves are all relatively suboptimal due to the constraints placed on leaflets by stenting. The constraints on the stenting mechanism may directly or indirectly cause turbulence in the orifice neighborhood, be nidi of tissue calcification, and impart transleaflet stress differentials. To address all these deficiencies, we undertook the development of a stentless porcine aortic bioprosthesis (SPAB). This study evaluates the hemodynamic performance and durability of this design in special chambers with near physiologic compliance. The results are compared to those shown by a stented porcine aortic bioprosthesis. The pressure measurements under steady flow conditions showed that the hemodynamic performance (including pressure gradient and effective orifice area) of SPAB is superior to that of its stented counterpart, especially in the smaller sizes. In addition, it is expected that this stentless design should minimize the mechanical stress to which the leaflets are subjected throughout the cardiac cycle, thus enhancing the durability of the bioprosthesis. In our accelerated durability study for up to 2 equivalent years, no valve failure has been observed. More in vitro studies under pulsatile flow conditions, including color Doppler flow visualization, are currently being conducted.

Aortic Valve↗

PubMedDate not supplied

In vitro testing of venous valves.

The need to test prosthetic venous valves led to the design of a hydraulic mock circuit that reliably mimics natural venous flow. Components of this system simulate calf muscle pump and thoracoabdominal suction pump action. Flow and pressures are serially measured along the circuit. Valve function can be observed and videotaped. Evaluation of biologic venous valves provides visual and quantitative assessment of venous valve function with respect to tissue processing, valve design, and implantation technique. Further improvement in this system in terms of more compliance and less rigidity of components is being pursued.

Blood Vessel Prosthesis↗

PubMedDate not supplied

Dynamic internal compliance of a vascular prosthesis.

A new technique was used to measure dynamic internal compliance of a blood vessel or vascular graft subjected to dynamic internal pressure. The internal compliance can be broken into three categories: the volumetric compliance (CV), defined as (dV/V)/dP; the longitudinal compliance (CL), defined as (dL/L)/dP; and radial compliance (CR), defined as (dR/R)/dP. It can be shown mathematically that CV = 2 CR + CL. Thus, measuring any two of the three entities will also give the value for the third. A Dynatek DCT1 dynamic compliance tester was used for measuring the compliance of DenaflexTM biologic grafts and fresh bovine internal thoracic arteries, from which the Denaflex grafts were obtained by fixation. Volumetric compliance was obtained with the test sample mounted in a loose loop that allowed the sample to move both radially and longitudinally. By mounting the sample in a straight fashion that limited longitudinal movement, the radial compliance was determined. The longitudinal compliance was then calculated from the above relationship. Test results show that the fresh bovine artery had an average volumetric compliance of 26.1%/100 mmHg, radial compliance of 9.5%/100 mmHg, and longitudinal compliance of 7.2%/100 mmHg. The Denaflex vascular graft showed a reduction in longitudinal and radial compliance, compared to the fresh raw artery, as a result of extensive fixation.

Animals↗

PubMedDate not supplied

In vitro pulsatile flow evaluation of a stentless porcine aortic bioprosthesis.

Suboptimal hemodynamic performance, tissue calcification, and limitation in long-term durability have been encountered clinically after aortic valve replacement with currently available bioprostheses. It is believed that some of these problems may be caused, directly or indirectly, by the stents of the bioprostheses. To address these deficiencies, the authors undertook the development of the Edwards Prima Stentless Bioprosthesis. This study was designed to evaluate the hemodynamic performance of the Edwards Prima Stentless Bioprosthesis in a pulse duplicator system. The stented Carpentier-Edwards Porcine Bioprosthesis (Baxter Healthcare Corp., Irvine, CA), which has been used in United States clinics for more than 10 years, was used as a control device. The flow fields in the vicinity of the test bioprostheses were inspected with color Doppler flow mapping. The transvalvular pressure gradients were measured invasively with a catheter and calculated with the Doppler determined velocity using a simplified Bernoulli equation. Additionally, the leakage volumes were determined with an electromagnetic flowmeter. In the Doppler flow mapping study, during systole, a central flow was observed distal to the stentless and stented bioprostheses. The central flow distal to the stentless bioprosthesis was broader than that observed distal to its stented counterpart. During diastole, no regurgitation was detected by color Doppler flow mapping in either the stentless or stented groups. The Doppler determined transvalvular pressure gradients correlated well with those measured by catheter (r = 0.990). Moreover, it was learned that the transvalvular pressure gradients of the stentless bioprosthesis were less than those of its stented counterpart, especially for the smaller sizes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

A newly developed porcine heart valve bioprosthesis fixed with an epoxy compound. An experimental evaluation.

Concerns with currently available bioprostheses are calcification, long-term durability, and functional and hemodynamic performance. It has been well known that these concerns are all more or less related to the fixatives, glutaraldehyde or formaldehyde, used in preserving bioprostheses. To address these concerns, we undertook the development of a porcine bioprosthesis fixed with an epoxy compound. It was discovered that the porcine leaflets fixed with the epoxy compound appeared more natural than those preserved with glutaraldehyde. The performance of this newly developed epoxy compound bioprosthesis (three samples) was evaluated in a juvenile sheep model. The results were compared to those of its glutaraldehyde counterpart (three samples). Two-dimensional echocardiographic inspection of the valvular leaflet motion indicated that the epoxy compound leaflets were more pliable than their glutaraldehyde counterparts. In addition, the epoxy compound valve appeared to open more widely than the glutaraldehyde valve. Color Doppler flow mapping demonstrated that the blood flow distal to the epoxy compound valve was slightly broader than that observed distal to the glutaraldehyde valve. Moreover, at retrieval, less calcium and pannus ingrowth were observed in the epoxy compound valve than its glutaraldehyde counterpart. The results of this preliminary evaluation indicated that the performance of this newly developed epoxy compound valve was at least equivalent to its glutaraldehyde counterpart, if not better.

Animals↗

PubMedDate not supplied

Comparison of the cross-linking characteristics of porcine heart valves fixed with glutaraldehyde or epoxy compounds.

The concerns about currently available bioprosthetic heart valves are calcification, long-term durability, and functional and hemodynamic performance. These concerns are all more or less related to the cross-linking reagents, glutaraldehyde or formaldehyde, used in fixing bioprostheses. To address these concerns, the authors undertook the development of a porcine heart valve cross-linked with an epoxy compound. This study compared the cross-linking characteristics, shrink temperature, and moisture content of porcine heart valves fixed with epoxy compounds or glutaraldehyde. Two types of epoxy compounds, Denacol EX-313 and EX-810, or a 0.625% glutaraldehyde were used to fix the porcine aortic valves procured from a slaughter house. Samples of each group were removed at various elapsed fixation times. The shrink temperature and moisture content of the valvular leaflet and distinct layers of aortic wall of each sample were measured. Fresh porcine aortic valve was used as a control. It was found that the shrink temperature of the glutaraldehyde leaflet was the highest, whereas the moisture content of the EX-313 leaflet was the greatest among the three test groups. No significant difference in shrink temperature was observed among the epoxy compound fixed inner, middle, outer, and entire aortic walls. This implied that the cross-linking density of the epoxy compound valve was uniform throughout the entire aortic wall. The same also was observed for the glutaraldehyde fixed aortic wall.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

A comparative study of complement activation by Denaflex, Bioflow, and BioPolyMeric vascular grafts.

This study was performed to evaluate the degree of complement activation by three bovine arterial graft materials: Bioflow (Bio-Vascular Inc., a bovine artery fixed with dialdehyde starch), BioPolyMeric (St. Jude Medical Inc., a collagen conduit of bovine arterial origin, tanned with glutaraldehyde and covered with a Dacron mesh), and Denaflex (Baxter Edwards CVS Division, a bovine artery fixed with polyepoxy compounds). The grafts were rinsed by following the manufacturer's recommended procedures and thereafter incubated with normal human serum. CH50 assays were performed on the serum after incubation, and the percentage of complement activation for each sample was calculated relative to its control serum. The results indicated that the BioPolyMeric grafts activated the most complement, with about a 48% decrease in the CH50. The BioPolyMeric graft is composed of an outer polyester mesh and an inner collagenous tubing, exhibiting a nonreversible negative surface charge. After the polyester mesh was removed, the BioPolyMeric graft showed the highest complement activation in this study, suggesting that the glutaraldehyde fixed graft is more prone to complement activation than either the polyepoxy compound or dialdehyde starch fixed grafts. The complement fragment, C5a, generated during complement activation is strongly chemotactic for polymorphonuclear leukocytes and monocytes, which likely play early and long-lasting roles in regulating tissue reaction to the implanted graft.

Bioprosthesis↗

PubMedDate not supplied

Evaluation of epoxy ether fixed bovine arterial grafts for mutagenic potential.

Two epoxy ether compounds [glycerol polyglycidyl ether (Denacol EX-313) and ethylene glycol diglycidyl ether (Denacol EX-810)] are under consideration as alternatives to glutaraldehyde for use in the processing of an arterial graft. The two are utilized as cross-linking and sterilant agents, respectively. Epoxy resins are multifunctional alkylating agents, and bifunctional alkylating epoxide solutions are known to be mutagenic. The correlation between mutagenic potential and carcinogenicity, in addition to evidence that diepoxides are carcinogenic in mice and rats, prompted the evaluation of the mutagenic potential of the epoxy treated, clinically rinsed graft. Ames and sister chromatid exchange (SCE) test procedures were used to assess mutagenic potential. Normal saline and distilled water were selected as the most physiologically representative and procedurally acceptable extraction mediums for the Ames and SCE tests, respectively. The results of the Ames and SCE tests in both the activated and non activated systems indicated that there were no statistically significant differences detected between various test article concentrates and the spontaneous mutation controls for both the activated and non activated systems. The epoxy treated graft was determined to be non mutagenic and demonstrated no dose related responses by these methods.

Animals↗