Does virtual reality training make sense in interventional radiology? Training skill-, rule- and knowledge-based behavior.
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Animals↗
Biomedical subjects
H G Stassen
Publications and source records attributed to H G Stassen.
Rasmussen's model of human behavior in laparoscopy training.
AIMS: Compared to aviation, where virtual reality (VR) training has been standardized and simulators have proven their benefits, the objectives, needs, and means of VR training in minimally invasive surgery (MIS) still have to be established. The aim of the study presented is to introduce Rasmussen's model of human behavior as a practical framework for the definition of the training objectives, needs, and means in MIS. METHODS: Rasmussen distinguishes three levels of human behavior: skill-, rule-, and knowledge-based behaviour. The training needs of a laparoscopic novice can be determined by identifying the specific skill-, rule-, and knowledge-based behavior that is required for performing safe laparoscopy. Future objectives of VR laparoscopy trainers should address all three levels of behavior. RESULTS: Although most commercially available simulators for laparoscopy aim at training skill-based behavior, especially the training of knowledge-based behavior during complications in surgery will improve safety levels. However, the cost and complexity of a training means increases when the training objectives proceed from the training of skill-based behavior to the training of complex knowledge-based behavior. CONCLUSION: In aviation, human behavior models have been used successfully to integrate the training of skill-, rule-, and knowledge-based behavior in a full flight simulator. Understanding surgeon behavior is one of the first steps towards a future full-scale laparoscopy simulator.
Algorithms↗
Peroperative analysis of the surgical procedure.
The increased technological complexity of surgery and the growing importance of quality assessment demand objective analysis of the surgical process. However, until now no standard method existed for analyzing the peroperative process. In this article, a methodology is discussed to describe and to analyze the surgical process. A method is given to measure the correctness and efficiency of task performance, protocols, and instruments used. In addition, reference values are defined so as to compare new instruments, alternative protocols, and the performance of new tasks with a standard. Finally, recommendations are given for improving new surgical tasks, the development of clinically driven instrument design, and new protocols.
Algorithms↗
Observation in laparoscopic surgery: overview of impeding effects and supporting aids.
Within a Dutch research program on minimally invasive surgery, a large literature survey has been carried out. This article describes the state of the art in research on observation in laparoscopy. It gives an overview of factors impeding the surgeon and technical developments designed to overcome these problems. A large number of journals, proceedings, patents, and books starting from the year 1991 have been consulted. The survey was completed with a thorough MEDLINE search. The survey showed that many authors have an incomplete background in the fundamentals of visual perception. This leads to a lack of understanding and to the design of supporting aids that often are not very useful. The new aspect of this study is that it gives a complete and structured overview of laparoscopic observation problems and current solutions. The observation problems are structured according to visual perception theory. The solutions are critically considered, and their benefits and drawbacks are identified. The study shows that the benefits of stereo-endoscopes and motorized endoscope positioners are questionable. The addition of shadows and movement parallax is still a very important research topic.
Humans↗
Myogenic reactivity and resistance distribution in the coronary arterial tree: a model study.
The objectives of this study were to evaluate the myogenic behavior of blood vessels and their interaction within the coronary arterial tree and to evaluate the possible role of the myogenic response in autoregulation. The model consists of 10 compartments in series, each representing a class of vessel sizes. Diameter and resistance in each class are determined by their value at full dilation (d(p,) R(p)) and by the myogenic response. Three distributions of R(p) and three distributions of myogenic strength, M(i) (slope of pressure-diameter curve, range -0.05 to -0.4%/mmHg) were evaluated (9 cases). It was found that larger vessels attenuate the myogenic activity of smaller vessels and that myogenic responsiveness is sufficient to achieve autoregulation. When M(i) has a maximum in vessels of 84 microm, the maximum effect of perfusion pressure on active diameter occurs in vessels between 123 and 181 microm, depending on the distribution of R(p). Distribution of resistance and control mechanisms in the coronary arterial tree are important for interpretation of individual vessel responses as observed in vivo.
Algorithms↗
Interaction between Gregg's phenomenon and coronary flow control: a model study.
Coronary perfusion pressure, Pp, affects coronary arterial resistance, Ra, (autoregulation) as well as myocardial oxygen consumption, MVO2 (Gregg's phenomenon). The interaction between the effects of Pp and MVO2 on coronary flow control was investigated using a coronary flow control model. Model analysis predicts that response of the pressure-flow ratio, p/q(t), following a change in Pp depends on the sensitivity of Ra to a change in tissue oxygen concentration (tone sensitivity) and on the sensitivity of MVO2 to a change in capillary pressure (Gregg's sensitivity). At high tone sensitivity Gregg's effect is small, whereas at high Gregg's sensitivity autoregulation is attenuated. In experiments glibenclamide decelerated the p/q(t) in response to a pressure step by a factor of four. However, the proposed model demonstrates that this is compatible with a reduction in rate of change of Ra by a factor of ten. This is due to the interaction of negative and positive feedback gains in the model. Model analysis demonstrates that autoregulation and Gregg's phenomenon compete with each other in controlling coronary flow.
Animals↗
Sensitivity of laparoscopic dissectors. What can you feel?
BACKGROUND: Sensory feedback is reduced considerably in minimally invasive procedures by the interposition of instruments, causing loss of direct manual contact with the tissue. The purpose of this study was to evaluate the feedback quality of commercially available reusable and disposable laparoscopic dissectors. METHODS: A total of 31 participants were asked to feel a simulated arterial pulse with their bare fingers and through laparoscopic dissectors, tweezers, an orthopedic forceps, and a laparoscopic low-friction prototype. The absolute sensory threshold was determined by the psychophysical method of limits. RESULTS: The sensory feedback quality was significantly better for the reusable dissectors tested than for the disposable dissector (p < 0.001). Nevertheless, the reusable dissectors were at least eight times less sensitive than bare fingers. Furthermore, sensitivity qualities were highly variable, depending on the dissector tested. CONCLUSIONS: This study showed that the overall sensitivity loss through instruments could be accurately assessed, proving that the sensory feedback for commercially available instruments was low compared to bare fingers. The good sensory feedback results of the prototype indicated that careful design could decrease the overall sensitivity loss.
Adult↗
Manipulation in laparoscopic surgery: overview of impeding effects and supporting aids.
Within a Dutch research program on minimally invasive surgery, a large literature survey has been carried out. This article describes the state of the art in research on manipulation in laparoscopy. It gives an overview of factors impeding the surgeon and technical developments designed to overcome these problems. Starting from the year 1991, a large number of journals, proceedings, patents, and books have been consulted. The survey was completed with a thorough MEDLINE search. The impeding effects have been subdivided into two groups: transformation of spatial and grasping movements of the hand. The article gives an overview of these effects and of supporting aids that have been developed. The studies show that many aids are based on a technology-driven rather than a clinically-driven approach. The development of simple instruments that can be used for a large range of tasks instead of only one is still a very important topic of research.
Ergonomics↗
Comparison of different oxygen exchange models.
A functional distribution of coronary volume can be estimated from the response of arterio-venous O2 content difference (AVO2) to a flow step. However, the results depend on the assumed O2 exchange model. The previously used model consisted of a single mixed compartment with O2 exchange (reference model). The purpose of this study is to provide an estimate of the errors made in the volume estimations by not taking into account factors as flow heterogeneity, different mixing sites or Krogh-like O2 exchange. The approach is indirect: the response of the AVO2 to a flow step has been calculated with alternative O2 exchange models in which factors mentioned are incorporated. These transients are fitted with the reference model. The resulting estimated volumes are different from the volumes assumed in the alternative models. Large differences are obtained with some of the alternative models, e.g. the model with Krogh characteristics. However, these models seem unrealistic because capillary pO2 is higher than venous pO2. Only small differences in volume are obtained with the more realistic models. Therefore, these results indicate that the coronary volumes are approximated well by the estimations obtained with the reference model. These volume estimations were 9.9 and 3.8 ml 100 g-1 for the O2 exchange vessels and the distal venous volume, respectively.
Blood Volume↗
Computer assisted diagnosis and treatment planning of brachial plexus injuries.
PLEXUS is a computer program which has been developed to provide recommendations for diagnosis and treatment planning of brachial plexus injuries. This computer program is meant for neurologists, neurosurgeons and orthopaedic surgeons who are not experienced in the field of brachial plexus injuries. The system detects the locations and severity of brachial plexus lesions. PLEXUS also indicates whether the patient may be referred to a specialist centre for nerve surgery. In order to determine whether the advice given by the system is of expert quality, a study of its recommendations is being carried out in cooperation with four international brachial plexus experts. To investigate if the system does indeed have the capability to assist physicians in the area of brachial plexus injuries, it is being tested clinically in four hospitals in The Netherlands.
Adult↗
Oxygen diffusion in a network model of the myocardial microcirculation.
Oxygen supply was studied in a three-dimensional capillary network model of the myocardial microcirculation. Capillary networks were generated using one common strategy to locate the capillary branchings and segments, arterioles and venules. Flow paths developed with different capillary flow velocities. All pressure-flow relationships were linear. The model includes free diffusion of oxygen within tissue slices that are perpendicular to the main capillary orientation. Oxygen pressure distributions were calculated and correlated to oxygen delivery by small capillary segments. It was shown that intercapillary diffusion is important for reducing PO2 heterogeneity. The absence of this feature leads to an oxygen distribution that has similar heterogeneity characteristics as the capillary flow heterogeneity. Such situations may also occur during simulated, elevated metabolic activity in a network model that allows intercapillary diffusion. On the basis of our simulations of metabolic vasoactivity we concluded that the venous PO2 is a misleading quantity to indicate tissue oxygenation. The venous PO2 in our model was not a good measure for the mean tissue or capillary PO2, and for the low oxygen pressures that exist at some locations in the network model. Moreover, the venous PO2 may remain constant despite considerable changes on the tissue PO2 distribution induced by metabolic activity.
Blood Flow Velocity↗
Evaluation of the control function of interstitial osmolarity in coronary autoregulation.
A control mechanism for the control of coronary blood flow (especially coronary autoregulation), presuming that interstitial osmotic pressure determines vascular resistance, was critically examined. A theoretical model of the control mechanism was made and the most important parameters of this theoretical model were estimated from published data. The parameters are the slope of coronary autoregulation curves, the sensitivity of coronary resistance to plasma oncotic pressure and capillary resistance. It appeared that the gains of this control loop were not large enough to allow for a dominant role of interstitial osmolarity in coronary autoregulation.
Coronary Circulation↗
System analysis of the dynamic response of the coronary circulation to a sudden change in heart rate.
In this study the response of driving pressure/flow ration on an abrupt change in heart rate was analysed. The difference between the response obtained with constant pressure and constant flow perfusion was also studied. The responses show a fast initial reversed phase followed by a slow phase caused by regulation. To test whether the initial phase could be the result of mechanical changes in the coronary circulation, a model for regulation was extended by the addition of four different mechanical models originating from the literature. These extended models were able to explain the fast initial phase. However, the mechanical model consisting of an intramyocardial compliance (C = 0.08 ml mm Hg-1 100 g-1) with a variable venous resistance, and the model consisting of a waterfall and a small compliance (C = 0.007 ml mm Hg-1 100g-1) both explained these responses best. The analysis showed that there is no direct relationship between rate of change of vascular tone and rate of change of pressure/flow ratio. However, on the basis of the two extended models, it can be predicted that the half-time for the response of regulation to be complete is about 9s with constant pressure perfusion and 15 s with constant flow perfusion.
Blood Pressure↗
Dynamics of coronary adjustment to a change in heart rate in the anaesthetized goat.
1. We have previously shown that steady-state coronary flow during auto-regulation and metabolic rate changes is predicted by a mathematically expressed theory which assigns control of coronary vascular resistance to tissue PO2. Our present purpose was to test the applicability of this theory to the non-steady state as exemplified by a sudden step change in heart rate. 2. The theory predicted that the response time of change of resistance in these circumstances would be slower with constant-flow perfusion of the coronary bed than with constant-pressure perfusion, and that with constant-pressure perfusion only, the rate of adaption of resistance would be dependent on the level of pressure used. 3. These predictions were tested in open-chest goats with cannulation of the left main coronary artery and perfusion with alternately constant pressure or constant flow. Sudden step changes in heart rate were induced by pacing to induce rapid transients in myocardial metabolic rate. 4. The half-time of subsequent change in perfusion pressure-flow ratio, which in the dynamical state is not equal to resistance, was 15.7 +/- 0.4 s (mean +/- S.E.M.), which was statistically shorter than for constant flow (22.2 +/- 0.5 s, P less than 0.001). 5. The half-time of subsequent change in perfusion pressure-flow ratio with constant-pressure perfusion was 14.4 +/- 0.6 s at low pressure and 17.0 +/- 0.6 s at high pressure (P less than 0.001). 6. The results differed from those predicted by the theory, in that the changes described above were preceded by a rapid (5 s) step change in pressure-flow ratio, up with an increase in heart rate and down with a decrease in heart rate. We postulated that this was a mechanical effect due to greater compression of the coronary microvasculature with more frequent contractions. 7. To test this hypothesis, we measured changes in coronary blood volume by integrating the difference between arterial inflow and venous outflow. These experiments showed a decrease in coronary blood volume with heart rate increase and vice versa. 8. Abolition of autoregulation and metabolic regulation was achieved with maximum vasodilatation of the coronary bed with adenosine. A sudden switch in heart rate then produced the initial step change in pressure-flow ratio, but not the subsequent adaptation over 13-25 s. This confirmed that the former effect is attributable to a passive mechanical mechanism.
Animals↗
Quantification of arteriolar density and embolization by microspheres in rat myocardium.
We developed a technique for in vitro determination of arteriolar densities. Hearts, obtained from anesthetized rats and perfused by the Langendorff method, were fully dilated with adenosine and were arrested with an elevated potassium concentration. After a stabilization period, the hearts were perfused with a buffered fixative for some minutes to obtain a nonvital vasculature. After fixation, perfusion was switched back to control for some minutes. The hearts were then perfused with a medium containing a low concentration of microspheres: either pollen grains [Urtica dioica (15.4 microns), Betula (23.5 microns), or Phleum pratense (36.5 microns)] or polystyrene microspheres (15 microns). The perfusion was switched back to the standard medium after flow had been reduced to between 83 and 57% of control flow. Microscopic observations of microsections revealed that the percentages of arterioles embolized by one microsphere were 64% for the 15.4-microns, 74% for the 15-microns, 78% for the 23.5-microns, and 72% for the 36.5-microns microspheres. The percentages of arterioles embolized with two microspheres were 20, 15, 15, and 16%, respectively. The arteriolar densities were calculated from the total fractional reduction in coronary flow, the amount of microspheres injected, the wet heart weight, and the degree of occupancy, which corrects for the multiple embolization of the arterioles. The arteriolar densities in the rat hearts were 162.4 +/- 54.9 mg-1 (N = 6) for polystyrene microspheres of 15 microns, 161.5 +/- 81.1 mg-1 (N = 15) for 15.4-microns microspheres, 31.6 +/- 7.8 mg-1 (N = 9) for 23.5-microns microspheres, and 13.0 +/- 2.4 mg-1 (N = 8) for 36.5-microns microspheres.
Animals↗
Heterogeneous pO2 distribution as a consequence of the capillary network.
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Capillaries↗
A field evaluation of arm prostheses for unilateral amputees.
A post-clinical investigation has been carried out among 42 unilateral amputees who lost their hand due to an accident. The investigation was directed at two main topics of interest. Firstly the amputee, the problems he has to cope with, and the role the prosthesis plays in his life; and secondly the prosthesis, its use and its potential benefits and burdens. The group of amputees consisted of above-elbow and below-elbow amputees. Body powered as well as myoelectric prostheses were represented in the group. Most of the information was obtained during a two-day home visit where a semi-structured interview was conducted, and where a number of daily life activities were observed. The information thus obtained has led to a number of conclusions and recommendations with respect to the rehabilitation of this category of amputees, and with respect to the design criteria of prostheses for unilateral amputees.
Activities of Daily Living↗
The lightspot operated typewriter: a communication aid for severely bodily handicapped patients.
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Communication Devices for People with Disabilities↗