Validation of open-surgery VR trainer.

VREST (Virtual Reality Educational Surgical Tools) is developing a universal and autonomous simulation platform which can be used for training and assessment of medical students and for continuing education of physicians. With the VREST - Virtual Lichtenstein Trainer, simulating the open surgery procedure of the inguinal hernia repair according to Lichtenstein, the validation of the simulator is ongoing. Part of this trajectory is the evaluation of the transfer of training of the virtual incision making. One group of students trained incision making on the VREST platform where the control group did not. In an experiment both groups has to perform several incision tasks on a manikin. The results are not available yet but will be presented at the MMVR14 conference.

Open surgery in VR: inguinal hernia repair according to Lichtenstein.

VREST (Virtual Reality Educational Surgical Tools) is developing a universal and autonomous simulation platform which can be used for training and assessment of medical students and for continuing education of physicians. A workstation consisting of two haptic devices and a 3D vision system is part of the VREST platform. Another part of the platform is a generic software environment in which lessons can be built by the teacher and performed by their students. Using the platform one can see, feel and decide as in reality. With the assessment tool the progress and skills of the students can be supervised. The first lesson build on the VREST platform is an inguinal hernia repair according to Lichtenstein. This is an open surgery procedure. The VREST platform is used prior to the first operating room surgery of the resident. Interactive models and case dependent feedback is used to enlarge the residents' cognition. This should reduce the training time in the operating room.

The VREST learning environment.

The VREST learning environment is an integrated architecture to improve the education of health care professionals. It is a combination of a learning, content and assessment management system based on virtual reality. The generic architecture is now being build and tested around the Lichtenstein protocol for hernia inguinalis repair.

The EAG tool: a decision support system for selection of abdominal aorta aneurysm endografts.

This article describes a decision support system (the EAG tool = Effective AAA Graftmanship) that assists the vascular surgeon in deciding whether a patient is fit for an endograft procedure and that assists the vascular surgeon in selecting the proper graft and in planning the endograft procedure. The EAG tool is the first step in the development of a learning environment for AAA procedures. As such the EAG tool is part of the VREST development project aiming to create a complete set of Virtual Reality Educational Surgical Tools. The EAG tool has been validated by using the expert knowledge of five experienced AAA physicians: three vascular surgeons and two interventional radiologists. In over 3,000 assessments, the EAG tool showed a false-positive rate of 0.2%, or in other words: in only 1 out of 500 cases the EAG tool indicated the possible use of an endograft, whereas the combined group of experts believed that it was not possibe. The EAG tool proved to be more prudent than the group of experts in having a false-negative rate of 3.7%. The EAG tool thus proved to be useful in daily clinical practice. Further developments are ongoing to use the EAG tool in a learning environment, specifically for unexperienced physicians.

Dynamic pumping characteristics of the Hemopump.

While pumping blood with the Hemopump in sheep, the ability of predicting the instantaneous pump flow from the pressure difference over the pump system and pump parameters was investigated. For rotational speed n between 300 and 475 revolutions per second (rps), maximum pump flow QO(n) at zero pressure difference, internal pump resistance R(n), and inertia parameter Lc were found to be suitable parameters for Hemopump characterization. The instantaneous pump flow could be estimated with an accuracy of approximately 1.0 [ml/s]. The values of the pump source parameters (+/- sd) were: (the figures in parentheses represent earlier reported values found while pumping water) Lc was a constant of 21.4 +/- 6.4 [Pa.s2/ml] (in water: 10.8). QO(n) is linearly related to rotational speed n according to: QO(n) = QO(ncen) + CQ(n-ncen), with QO(ncen) = 49.4 +/- 4.5 [ml/s] (in water: 60.3), CQ = 142 +/- 22.4 [10(-3) ml] (in water: 146), and ncen = 387.5 [rps]. R(n) is linearly related to rotational speed n according to: R(n) = R(ncen) + CR(n-ncen), with R(ncen) = 556 +/- 124 [Pa.s/ml] (in water: 502) and CR = 1.47 +/- 0.83 [Pa.s2/ml] (in water: 1.67).

Characterization of left ventricle function by analysis of pressure responses to steps in rotational speed of the Hemopump.

Optimizing the procedure of weaning the left ventricle from a left ventricular assist device requires the determination of the momentaneous condition of the left ventricle. In sheep, a method was developed to momentaneously quantify the left ventricular condition. The left ventricular pump condition was quantified by the time-varying parameters elastance and resistance. They were determined from perturbations in the left ventricular pressure of two subsequent beats induced by changes in flow of the assist device. The end-diastolic volume of the ventricle was estimated without directly measuring ventricular volume. Maximum elastance and resistance were 201.3 +/- 32.7 [Pa/ml] and 12.3 +/- 1.6 [Pa.s/ml], respectively (mean +/- SE). The ventricular time constant, defined by the ratio of resistance of elastance, was 84.6 +/- 17.1 [ms] (mean +/- SE).

Dynamic pumping performance of the Hemopump--a small intraventricular blood pump.

We studied the pumping characteristics of the Hemopump, a commercially available miniature intraventricular blood pump for temporary support of failing hearts. The Hemopump is an axial flow pump of which the characteristics can be described by turbomachine theory. Experiments with water and a mock circulation verified that the pumping characteristics of the Hemopump in terms of both pressure head and flow as a function of rotational speed, very well can be described by a first order differential equation. The influence of blood with its non-Newtonian character is being investigated.