1000 resultados para Bed dip direction
Resumo:
Collection : Collection d'instructions et de manuels pédagogiques
Resumo:
Collection : Collection d'instructions et de manuels pédagogiques
Resumo:
Échelle(s) : 1:800 000
Resumo:
Échelle(s) : [ca 1:175 500], échelle de 20000 mètres [= 11,4 cm]
Resumo:
Échelle(s) : 1:600 000
Resumo:
Adequate in-vitro training in valved stents deployment as well as testing of the latter devices requires compliant real-size models of the human aortic root. The casting methods utilized up to now are multi-step, time consuming and complicated. We pursued a goal of building a flexible 3D model in a single-step procedure. We created a precise 3D CAD model of a human aortic root using previously published anatomical and geometrical data and printed it using a novel rapid prototyping system developed by the Fab@Home project. As a material for 3D fabrication we used common house-hold silicone and afterwards dip-coated several models with dispersion silicone one or two times. To assess the production precision we compared the size of the final product with the CAD model. Compliance of the models was measured and compared with native porcine aortic root. Total fabrication time was 3 h and 20 min. Dip-coating one or two times with dispersion silicone if applied took one or two extra days, respectively. The error in dimensions of non-coated aortic root model compared to the CAD design was <3.0% along X, Y-axes and 4.1% along Z-axis. Compliance of a non-coated model as judged by the changes of radius values in the radial direction by 16.39% is significantly different (P<0.001) from native aortic tissue--23.54% at the pressure of 80-100 mmHg. Rapid prototyping of compliant, life-size anatomical models with the Fab@Home 3D printer is feasible--it is very quick compared to previous casting methods.
Resumo:
The time constant of cerebral arterial bed (in brief time constant) is a product of brain arterial compliance (C(a)) and resistance (CVR). We tested the hypothesis that in normal subjects, changes in end-tidal CO(2) (EtCO(2)) affect the value of the time constant. C(a) and CVR were estimated using mathematical transformations of arterial pressure (ABP) and transcranial Doppler (TCD) cerebral blood flow velocity waveforms. Responses of the time constant to controlled changes in EtCO(2) were compared in 34 young volunteers. Hypercapnia shortened the time constant (0.22 s [0.17, 0.26] vs. 0.16 s [0.13, 0.20]; p = 0.000001), while hypocapnia lengthened the time constant (0.22 s [0.17, 0.26] vs. 0.23 s [0.19, 0.32]; p < 0.0032). The time constant was negatively correlated with changes in EtCO(2) (R(partial) = -0.68, p < 0.000001). This was associated with a decrease in CVR when EtCO(2) increased (R(partial) = -0.80, p < 0.000001) and C(a) remained independent of changes in EtCO(2). C(a) was negatively correlated with mean ABP (R(partial) = -0.68, p < 0.000001). In summary, the time constant shortens with increasing EtCO(2). Its potential role in cerebrovascular investigations needs further studies.