The Importance of Venous Return in Starling‐Like Control of Rotary Ventricular Assist Devices

Rotary ventricular assist devices (VADs) are less sensitive to preload than the healthy heart, resulting in inadequate flow regulation in response to changes in patient cardiac demand. Starling‐like physiological controllers (SLCs) have been developed to automatically regulate VAD flow based on ventricular preload. An SLC consists of a cardiac response curve (CRC) which imposes a nonlinear relationship between VAD flow and ventricular preload, and a venous return line (VRL) which determines the return path of the controller. This study investigates the importance of a physiological VRL in SLC of dual rotary blood pumps for biventricular support. Two experiments were conducted on a physical mock circulation loop (MCL); the first compared an SLC with an angled physiological VRL (SLC‐P) against an SLC with a vertical VRL (SLC‐V). The second experiment quantified the benefit of a dynamic VRL, represented by a series of specific VRLs, which could adapt to different circulatory states including changes in pulmonary (PVR) and systemic (SVR) vascular resistance versus a fixed physiological VRL which was calculated at rest. In both sets of experiments, the transient controller responses were evaluated through reductions in preload caused by the removal of fluid from the MCL. The SLC‐P produced no overshoot or oscillations following step changes in preload, whereas SLC‐V produced 0.4 L/min (12.5%) overshoot for both left and right VADs. Additionally, the SLC‐V had increased settling time and reduced controller stability as evidenced by transient controller oscillations. The transient results comparing the specific and standard VRLs demonstrated that specific VRL rise times were improved by between 1.2 and 4.7 s ( = 3.05 s), while specific VRL settling times were improved by between 2.8 and 16.1 seconds ( = 8.38 s) over the standard VRL. This suggests only a minor improvement in controller response time from a dynamic VRL compared to the fixed VRL. These results indicate that the use of a fixed physiologically representative VRL is adequate over a wide variety of physiological conditions.     

县级医院医疗仪器管理对策

医疗仪器在疾病诊断和医疗中的作用越来越大,完善的管理不仅可提高仪器的使用寿命和安全性,关系到医院的经济效益和社会效益,更关系到患者的利益.文章结合实际,提出县级医院医疗仪器管理对策.     

口腔修复临床电刀龈成形术的效果观察

现察口腔修复临床电刀龈成形术的效果。方法：对81例口腔修复门诊牙体缺损患者用电刀进行牙龈成形术并定期复诊观察。结果：81例术后牙龈全部达到修复要求而立即修复，其中70例术后牙龈稳定，占总数的86．4％。结论：电刀龈成形术是口腔修复临床上一种可行的治疗手段。     

Learning root debridement with curettes and power-driven instruments in vitro: the role of operator motivation and self-assessment

The influence of systematic dummy-head training with Periopolishe (PP, group A) and Gracey instruments (GRA, group B) on the effectiveness of root debridement was evaluated by Rühling et al., 2002 (9). Their results indicate that independent of the instrument used, untrained operators were only able to debride root surfaces at low levels of effectiveness. It was possible to increase effectiveness to a high level through systematic training in both groups. The aim of the present study was to assess the role of operator motivation and self-assessment on scaling effectiveness. Before baseline, operators were asked to answer a questionnaire rating the expectation of the instrument performance. Four groups of inexperienced operators (n = 11 each) received 10 weeks dummy-head training. In groups A (GRA) and B (PP), training was combined with a motivational programme. Groups C (GRA) and D (PP) received the same training, but no additional motivational programme. In a dummy-head, 10 test teeth were debrided and operators were asked to estimate their effectiveness of debridement at each test day. Effectiveness was calculated as percentage of debrided root area on 10 test teeth at different time points with an image analysis programme (NIH Image) and ANOVA. Two groups were compared using the Mann-Whitney U-test (unpaired) and the Wilcoxon signed ranks test (paired). Motivated groups (A and B) reached about 25% higher debridement results (p < 0.001) and were able to estimate their effectiveness more precisely compared to groups C and D. In the low motivation groups (C and D), overestimation of more than 20% was evident (p < 0.001). The questionnaires revealed underestimation of the GRA instruments and overestimation of PP instruments. Operator motivation and self-assessment greatly influence learning of effective root debridement.     

Image size magnification and power and dilation factors for optical instruments in general

Traditional treatments of spectacle magnification for distant objects consider only stigmatic spectacle lenses and they compare the retinal image size in a refractively fully compensated eye with the image size in the uncompensated eye. Spectacle magnification is expressed as a product of two factors, the power and shape factors of the lens. The power factor depends on the position of the entrance pupil of the eye. For an eye with an astigmatic cornea, however, the position of the entrance pupil is not well defined. Thus, the traditional approach to spectacle magnification does not generalize properly to allow for astigmatism. Within the constraints of linear optics and subject to the restriction that the eye's iris remains the aperture stop, this paper provides a complete, unified and exact treatment for optical instruments in general. It compares retinal image size in a generalized sense (including image shape and orientation) for any instrument in front of an eye with that of the eye alone irrespective of whether the instrument compensates or not. The approach does not make use of the concept of the entrance pupil at all and it allows for astigmatism and for non-alignment of refracting elements in the instrument and in the eye. The concept of spectacle magnification generalizes to the concept of instrument size magnification. Instrument size magnification can be expressed as the product of two matrix factors one of which can be interpreted as a power factor (as back-vertex power) and the other factor for which the name dilation factor is more appropriate in general. The general treatment is then applied to a number of special cases including afocal instruments, spectacle lenses (including obliquely crossing thick bitoric lenses), contact lenses, stigmatic systems and stigmatic eyes. In the case of spectacle lenses, the dilation factor reduces to the usual shape factor.     

普理灵疝装置和疝塞在无张力腹股沟疝修补中的对比研究

目的探讨更为合理的无张力疝修补方法。方法分别应用普理灵疝装置 (polyprop ylene proleneherniasystem ,PHS )和疝塞 (MeshPlug&Patch)作为疝修补材料行疝修补术 ,将 10 0例腹股沟疝患者随机分为PHS组和Plug组 2组 ,每组各 5 0例 ,对 2组的临床资料进行对比。 结果随访 6～ 10个月 ,PHS组与Plug组手术时间平均为 35min和 4 0min ;术后并发症发生率为 2 % (1 5 0 )和 8% (4 5 0 ) ;平均住院日 2d和 3d ;均无复发。Plug组 1个月内 6例 (PHS组 0例 )有异物感 ,两组差异有显著意义 (P <0 0 5 )。结论普理灵疝装置和疝塞均能较好地修补腹股沟疝 ,普理灵疝装置尤其适用于消瘦和疝环或腹横筋膜缺损较大的腹股沟疝患者 ,而疝塞在肥胖和疝环或腹横筋膜缺损不太大的腹股沟疝患者更有优势。     

脊柱后入路显微内窥镜下手术治疗侧隐窝狭窄

目的 探讨脊柱后入路显微内窥镜下手术治疗侧隐窝狭窄的手术方法。方法 采用自行研制的异型骨凿，于显微内窥镜下手术治疗38例确诊为侧隐窝狭窄的患。结果 经6～12个月随访，所有患均无神经损伤等并发症；疗效评价：32例，良5例，可1例。结论 本术式具有创伤小，对术后脊柱的稳定性破坏小，疗效确切等优点。     

A comparison of the relative risk of vessel injury with conical versus pyramidal laparoscopic trocars in a rabbit model

OBJECTIVE: Our purpose was to compare the relative risk of vessel injury after use of a 5 mm conical-tipped trocar, a 5 mm pyramidal-tipped trocar, and a 10 mm pyramidal-tipped trocar in a rabbit vessel model.STUDY DESIGN: Plastic templates were placed in front of and behind 108 mesenteric vessels in 11 anesthetized New Zealand White rabbits. Laparoscopic trocars were inserted through the templates and mesentery. The incidence of vessel injury was determined at distances from the vessels ranging from 0 to 5 mm.RESULTS: The 5 mm conical trocar resulted in a vessel injury rate of 88% at 0 mm from the vessel but 0% at 1 or 2 mm. The 5 mm pyramidal trocar resulted in 100%, 88%, and 62% injury rates of 0, 1, and 2 mm from the vessels, respectively. The 10 mm pyramidal trocar resulted in a 100% injury rate at 0, 1, 2, or 3 mm from the vessels and 80% and 40% at 4 mm and 5mm, respectively.CONCLUSION: The relative risk of vessel injury is significantly increased by the use of pyramidal-tipped trocars when compared with conical-tipped trocars, especially if larger diameter trocars are used.