Biomedical subjects

Gillian M Bernacca

Publications and source records attributed to Gillian M Bernacca.

3 recordsLinked to original sources

PubMed2004

Comparison of prosthetic valve hydrodynamic function: objective testing using statistical multilevel modeling.

BACKGROUND AND AIM OF THE STUDY: The performance of novel prosthetic heart valves is assessed using in-vitro hydrodynamic function tests. The study aim was to examine the problem of objective discrimination of hydrodynamic performance to determine significant differences between valve designs, and illustrate proposed methodology using data collected from five different polyurethane tri-leaflet valve designs. METHODS: Two engineering designs were manufactured with leaflets of the same polyurethane (GE, LE); design L was manufactured using three further leaflet materials of differing material modulus (LL, L4, L5). Six valves were made in each design, each tested at five flow rates in a standard hydrodynamic test rig, with five test replications for each valve. The data were analyzed using multilevel statistical modeling methods, allowing simultaneous comparison of multiple regression lines describing valve performance. The multilevel model is hierarchical in structure, in this case with two levels of data, describing individual valves at level 2 and test replicates at level 1. In all cases, the multilevel model uses the hydrodynamic function measure of interest, e.g. mean pressure gradient or leakage, with logarithmic transformation as required as the dependent variable, Y. The independent variable, X, is, in all cases, the natural logarithm of the RMS flow measured through the valve. RESULTS: The two-design multilevel model enabled quantitative discrimination of designs GE and LE, showing that design GE had significantly better hydrodynamic function overall than design LE in this case (mean pressure gradient was estimated as 0.93 mmHg lower at low cardiac output, 14.74 mmHg lower at 9.6 l/min). The five-design multilevel model showed clearly the relatively poor hydrodynamic performance of designs L4 and L5 compared with others. The procedure was straightforward, and produced a statistical comparison among valve designs that is not easily achieved by other means. CONCLUSION: This methodology provides a useful means of objective assessment of valve function for valve developers. Variance estimates provided by the analysis also provide a basis for quality control of valve production and testing.

Equipment Failure Analysis↗

PubMed2002

Mechanical and morphological study of biostable polyurethane heart valve leaflets explanted from sheep.

Two novel biostable polyurethanes, designated EV3.34 and EV3.35, were used to manufacture a flexible trileaflet heart valve. The valves were implanted in the mitral position in young adult (18 month) sheep. Six valves were electively explanted at 6 months and the remaining six valves at 9 months follow-up. The leaflet material was examined by surface Fourier transform infrared spectrometry (ATR/FTIR) and scanning electron microscopy (SEM). The leaflet material was also subjected to cyclic mechanical testing and, compared with unimplanted control material, to demonstrate any change in mechanical properties during implantation. There was no degradation of functional groups detected by ATR/FTIR, although there was a slight surface enrichment of siloxane soft segment. Surface morphology of the explanted leaflet material was similar to unimplanted control material. EV3.34 demonstrated similar inelastic energy loss behavior, with no significant change in residual strain in explanted compared with control material. EV3.35 demonstrated a reduction in inelastic energy and residual strain in explanted compared with control material. There is no evidence of biodegradation of these siloxane-based polyurethanes, in functional valves up to 9 months implantation in sheep. The FTIR and SEM findings are supported by the retention of mechanical properties of the materials.

Animals↗

PubMed2002

Hydrodynamic function of polyurethane prosthetic heart valves: influences of Young's modulus and leaflet thickness.

The development of flexible polyurethane heart valves has been hindered by material degradation in vivo. Low modulus polyurethane leaflets are regarded as desirable to achieve good hydrodynamic function. However, low modulus materials may suffer high strain accumulation, hence poor durability. Higher modulus materials may improve durability, but may have poor hydrodynamic function. This study examines the hydrodynamic behaviour of biostable polyurethane valves, varying Young's modulus from 5 to 63.6 MPa and mean leaflet thickness from 48-238 microm. Parameters studied included mean pressure gradient, energy losses and regurgitation over 5 equivalent cardiac outputs (3.6, 4.9, 6.4, 8.0 and 9.61 min(-1)) At low cardiac output, modulus was not significantly correlated with any parameter of valve opening. At 9.61 min(-1), modulus significantly influenced mean pressure gradient (p = 0.033). Mean leaflet thickness significantly correlated with mean pressure gradient and energy losses during forward flow at all cardiac outputs (p<0.001). This study demonstrates that, over a wide range of moduli, valve hydrodynamic function is not affected significantly by the material modulus. Leaflet thickness is a highly significant factor. Higher modulus elastomers in a range up to 32.5 MPa may be useful in prosthetic heart valve leaflet manufacture, retaining good hydrodynamic function while potentially extending the lifetime of the valve.

Heart Valve Prosthesis↗