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Biomedical subjects

J Dankelman

Publications and source records attributed to J Dankelman.

At least 19 recordsLinked to original sources
PubMed2007

Relation between branching patterns and perfusion in stochastic generated coronary arterial trees.

Biological variation in branching patterns is likely to affect perfusion of tissue. To assess the fundamental consequences of branching characteristics, 50 stochastic asymmetrical coronary trees and one non-stochastic symmetrical branching tree were generated. In the stochastic trees, area growth, A, at branching points was varied: A = random; 1.00; 1.10; 1.13 and 1.15 and symmetry, S, was varied: S = random; 1.00; 0.70; 0.58; 0.50 and 0.48. With random S and A values, a large variation in flow and volume was found, linearly related to the number of vessels in the trees. Large A values resulted in high number of vessels and high flow and volume values, indicating vessels connected in parallel. Lowering symmetry values increased the number of vessels, however, without changing flow, indicating a dominant connection of vessels in series. Both large A and small S values gave more realistic gradual pressure drops compared to the symmetrical non-stochastic branching tree. This study showed large variations in tree realizations, which may reflect real biological variations in tree anatomies. Furthermore, perfusion of tissue clearly depends on the branching rules applied.

Arteries↗
PubMed2006

Friction dynamics of trocars.

BACKGROUND: In minimally invasive surgery, force feedback information on tissue manipulation is altered by friction between the instrument and the sealing mechanism of the trocar. It is unknown how the different sealing mechanisms of currently available trocars influence the friction forces. The current study investigated the dynamic changes in friction for various trocars at different instrument velocities. METHODS: The friction characteristics for six common types of trocars were determined. A force sensor was attached to the shaft of a standard 5-mm disposable grasper to measure the forces required to move it through the trocars. Movement velocity and direction of the shaft were controlled by a servomotor. In addition, whether moistening the shaft reduced friction was tested. RESULTS: The friction depended on the type of trocar, the movement velocity, and the movement direction, and varied between 0.25 and 3.0 N. Specifically, trocars with narrow sealing caps (i.e., high normal force onto the shaft) and trocars with thick sealing caps (i.e., large contact area) generate a high amount of friction. Moistening the shaft reduced friction 15% to 45%. For most trocars, large fluctuations in forces occur when the movement starts or when the direction reverses. The magnitude of these fluctuations varied between 0.2 and 2.5 N. CONCLUSIONS: For some trocars, friction can be as great as the forces associated with instrument-tissue interaction. At movement reversals, friction fluctuates due to deformations of the rubber and silicon parts of the sealing mechanism. Such high variance can deteriorate surgical performance during high precision tasks (e.g., tissue manipulation) that typically involve many changes in movement direction. Comparisons of the investigated trocars indicate that the friction magnitude and variance can be reduced easily by changing the properties of the sealing cap or by lubricating the instruments.

Equipment Design↗
PubMed2006

The influence of different training schedules on the learning of psychomotor skills for endoscopic surgery.

BACKGROUND: Psychomotor skills for endoscopic surgery can be trained with virtual reality simulators. Distributed training is more effective than massed training, but it is unclear whether distributed training over several days is more effective than distributed training within 1 day. This study aimed to determine which of these two options is the most effective for training endoscopic psychomotor skills. METHODS: Students with no endoscopic experience were randomly assigned either to distributed training on 3 consecutive days (group A, n = 10) or distributed training within 1 day (group B, n = 10). For this study the SIMENDO virtual reality simulator for endoscopic skills was used. The training involved 12 repetitions of three different exercises (drop balls, needle manipulation, 30 degree endoscope) in differently distributed training schedules. All the participants performed a posttraining test (posttest) for the trained tasks 7 days after the training. The parameters measured were time, nontarget environment collisions, and instrument path length. RESULTS: There were no significant differences between the groups in the first training session for all the parameters. In the posttest, group A (training over several days) performed 18.7% faster than group B (training on 1 day) (p = 0.013). The collision and path length scores for group A did not differ significantly from the scores for group B. CONCLUSION: The distributed group trained over several days was faster, with the same number of errors and the same instrument path length used. Psychomotor skill training for endoscopic surgery distributed over several days is superior to training on 1 day.

Adult↗
PubMed2006

Problems with technical equipment during laparoscopic surgery. An observational study.

BACKGROUND: This study was designed to investigate the incidence of technical equipment problems during laparoscopic procedures. METHODS: A video-capturing system was used, consisting of an analog video recorder with three camera image inputs and a microphone. Problems with all technical equipment used by the surgical team, such as the insufflator, diathermy apparatus, monitors, light source, camera and camera unit, endoscope, suction devices, and instruments, were registered. RESULTS: In total, 30 procedures were randomly videotaped. In 87% (26/30) of the procedures, one or more incidents with technical equipment (49 incidents) or instruments (9 incidents) occurred. In 22 of those incidents (45%) the technical equipment was not correctly positioned or not present at all; in the other 27 (55%), the equipment malfunctioned as a result of a faulty connection (9), a defect (5), or the wrong setting of the equipment (3). In 10 (20%) cases the exact cause of equipment malfunctioning was unclear. CONCLUSIONS: The incidence of problems with laparoscopic technical equipment is high. To prevent such problems, improvement and standardization of equipment is needed, combined with the incorporation of checklist use before the start of a surgical procedure. Future research should be aimed at development, implementation, and evaluation of these measures into the operating room.

Adult↗
PubMed2006

Validation of a new basic virtual reality simulator for training of basic endoscopic skills: the SIMENDO.

BACKGROUND: The aim of this study was to establish content, face, concurrent, and the first step of construct validity of a new simulator, the SIMENDO, in order to determine its usefulness for training basic endoscopic skills. METHODS: The validation started with an explanation of the goals, content, and features of the simulator (content validity). Then, participants from eight different medical centers consisting of experts (> or =100 laparoscopic procedures performed) and surgical trainees (<100) were informed of the goals and received a "hands-on tour" of the virtual reality (VR) trainer. Subsequently, they were asked to answer 28 structured questions about the simulator (face validity). Ratings were scored on a scale from 1 (very bad/useless) to 5 (excellent/very useful). Additional comments could be given as well. Furthermore, two experiments were conducted. In experiment 1, aimed at establishing concurrent validity, the training effect of a single-handed hand-eye coordination task in the simulator was compared with a similar task in a conventional box trainer and with the performance of a control group that received no training. In experiment 2 (first step of construct validity), the total score of task time, collisions, and path length of three consecutive runs in the simulator was compared between experts (>100 endoscopic procedures) and novices (no experience). RESULTS: A total of 75 participants (36 expert surgeons and 39 surgical trainees) filled out the questionnaire. Usefulness of tasks, features, and movement realism were scored between a mean value of 3.3 for depth perception and 4.3 for appreciation of training with the instrument. There were no significant differences between the mean values of the scores given by the experts and surgical trainees. In response to statements, 81% considered this VR trainer generally useful for training endoscopic techniques to residents, and 83% agreed that the simulator was useful to train hand-eye coordination. In experiment 1, the training effect for the single-handed task showed no significant difference between the conventional trainer and the VR simulator (concurrent validity). In experiment 2, experts scored significantly better than novices on all parameters used (construct validity). CONCLUSION: Content, face, and concurrent validity of the SIMENDO is established. The simulator is considered useful for training eye-hand coordination for endoscopic surgery. The evaluated task could discriminate between the skills of experienced surgeons and novices, giving the first indication of construct validity.

Adult↗
PubMed2005

Systems approach to reduce errors in surgery.

Reducing the number of medical errors significantly is the challenge for the coming decade. In medicine and in surgery, in particular, errors are traditionally treated as being committed by individuals. To reduce human errors, two approaches can be used: the person approach and the systems approach. In the systems approach, the operator is not blamed, but the system is analyzed in order to find the causes of errors. Furthermore, defenses are built into the system so that errors will not result in an adverse outcome anymore. This article aims to provide insight into the systems approach.

Humans↗
PubMed2005

Fundamental aspects of learning minimally invasive surgical skills.

With the introduction of minimally invasive surgery (MIS) the necessity to develop training methods to learn skills outside the operating room (OR) became clear. Several training simulators have become commercially available. However, fundamental research into the requirements for effective and efficient training in MIS is still lacking. Yet in the literature several learning models have been described that may be used when designing the structure of a training program. While learning skills, three stages can be observed: cognitive, associative and autonomous. The learning cycle also includes different learning styles and, moreover, every trainee has his/her preferred learning style. Furthermore, training should be adapted to the level of behaviour: skill-based, rule-based or knowledge-based. Training of complex skills should include multiple performance objectives, such as just-in-time supportive information and part-task practice. Finally, motivation for training can be created by assessment. In conclusion, several theories on learning can be found in the literature. These theories may help in the development of effective training programs for training MIS skills outside the OR.

Journal Article↗
PubMed2005

Fenestrations in the jaws of laparoscopic graspers.

Laparoscopic graspers used for manipulating delicate tissue generally possess jaws with fenestrations (windows). The fenestrations should enhance the grip on the tissue; however, fenestrations reduce the contact area between jaws and tissue, leading to higher local pressures and possibly tissue damage. Experiments were performed to determine the effect of a fenestration on the pinch force needed to prevent slip of tissue and on the pinch force leading to tissue damage. In addition, the size and position of the fenestration were determined. Fenestrated jaws resulted in increased tissue damage, without affecting the pinch force needed to prevent slip. These negative effects increased with increasing fenestration size and when the fenestration was located toward the tip of the jaws. Therefore, fenestrated jaws had a smaller safe working range than the jaws without fenestrations.

Journal Article↗
PubMed2004

The optimal mechanical efficiency of laparoscopic forceps.

BACKGROUND: Laparoscopic forceps have a large amount of friction in the mechanism, leading to a limited mechanical efficiency, which impairs the pinch force feedback. The advantage of a small amount of friction is that it is easier to maintain a constant pinch force on the tissue. Therefore, to obtain the optimal mechanical efficiency of the forceps, the influence of mechanical efficiency on the performance of several static and dynamic operative tasks, such as grasping tissue and estimating pressure, is quantified. METHODS: A grasper with adjustable mechanical efficiency and a load cell to measure the pinch force on the tissue was developed. Using this grasper, subjects performed several tasks on pig bowel tissue and simulation tissue: grasping tissue, reproducing a requested constant or variable pinch forces, and estimating the pressure in a tube. RESULTS: With increasing mechanical efficiency, a variable pinch force could be reproduced more accurately (deviation from the requested pinch force decreased from 34.4 to 24.9%, p = 0.016). The performance on the grasping tissue, reproducing a constant pinch force, and estimating pressure tasks did not improve with increased mechanical efficiency. CONCLUSIONS: The optimal mechanical efficiency of laparoscopic forceps is dependent on the task that is performed. For tasks requiring little movement of the forceps, such as grasping and holding tissue, a low mechanical efficiency is sufficient, whereas for tasks requiring repeated movement of the forceps to feel tissue, a high mechanical efficiency is required.

Animals↗
PubMed2004

Slip and damage properties of jaws of laparoscopic graspers.

BACKGROUND: The optimal jaws of laparoscopic graspers can be used to manipulate the tissue properly with minimal damage. The criteria jaws should satisfy are investigated. METHODS: The cecum of pigs was clamped between 13 pairs of jaws differing in size and profile. Various pinch and pull forces were applied. At 5 N pull force, the minimally required pinch force to prevent slip and the pinch force that is maximally allowable without causing damage were obtained. RESULTS: With increasing size of the jaws, the contact area with the tissue increases. With increasing contact area, the pinch force leading to tissue damage was increased from 15 to 37 N. A profile of the jaws decreased the pinch force needed to prevent slip of tissue from 22 to 3 N. CONCLUSION: An optimal jaw possesses a large contact area to prevent tissue damage and a slight profile to prevent tissue slip.

Animals↗
PubMed2004

The influence of force feedback and visual feedback in grasping tissue laparoscopically.

BACKGROUND: Due to the limited force feedback provided by laparoscopic instruments, surgeons may have difficulty in applying the appropriate force on the tissue. The aim of this study was to determine the influence of force feedback and visual feedback on the exerted pinch force. METHODS: A grasper with a force sensor in the jaws was developed. Subjects with and without laparoscopic experience grasped and pulled pig bowel with a force of 5 N. The applied pinch force was measured during tasks of 1-s and 1-min duration. Visual feedback was provided in half the measurements. Force feedback was adjusted by changing the mechanical efficiency of the forceps from 30% to 90%. RESULTS: The mean pinch force applied was 6.8 N (+/-0.5), whereas the force to prevent slippage was 3.0 N (+/-0.4). Improving the mechanical efficiency had no effect on the pinch force for the 1-s measurements. The amount of excessive pinch force when holding tissue for 1 min was lower at 30% mechanical efficiency compared with 90% (105% vs 131%, p = 0.04). The tissue slipped more often when the subject had no visual feedback (2% vs 8%, p = 0.02). CONCLUSION: Force feedback and visual feedback play a more limited role than expected in the task of grasping tissue with laparoscopic forceps.

Animals↗
PubMed2003

Inter- and intraindividual variabilities of perforation forces of human and pig bowel tissue.

BACKGROUND: A laparoscopic bowel grasper should be suitable for safely grasping the bowel in a wide variety of patients. Therefore, the inter- and intraindividual variabilities in the strength of bowel tissue to resist perforation force should be analyzed. METHODS: The large and small bowels of pigs ( n = 14) and the human small bowel ( n = 7) were clamped between two hemispheres 1.5 mm in diameter. The pinch force was increased until the tissue was perforated. RESULTS: The perforation force for the pig large bowel was higher than for the small bowel (13.5 +/- 3.7 vs 11.0 +/- 2.5 N; p = 0.014). No difference was found between the human and pig small bowel (10.3 +/- 2.9 vs 11.0 +/- 2.5 N). The intercoefficient of variation varied between 22% and 28%, and the intracoefficient of variation varied between 14% and 18%. CONCLUSIONS: The strength of the pig bowel is approximately comparable to the strength of the human bowel, and, therefore, testing of graspers on pig bowel is justified. However, due to the large interindividual variation, large safety margins should be taken into account.

Adult↗
PubMed2002

Effectiveness of grasping and duration of clamping using laparoscopic graspers.

BACKGROUND: Manipulating tissue with laparoscopic forceps is more difficult than using the hands. This study investigates the effectiveness of grasping and the duration of tissue-clamping using laparoscopic forceps. METHODS: Video recordings of 10 laparoscopic colectomies and 15 cholecystectomies were analyzed using time-action analysis. RESULTS: The results indicated that 62% of the grasping actions were successful: the tissue was clamped sufficiently to perform an action. Of all the clamping actions on the colon, 10% were repeated actions. On the gallbladder 7% were repeated actions. The bowel slipped out of the grasper in 7% of the clamping actions, whereas the gallbladder slipped in 17%. In 89%, the colon was clamped less than 1 min. The maximum clamping time for colon clamps was 7 min for the colon, and 55 min for the gallbladder. CONCLUSION: The low percentage of successful grasping actions indicates that the design of laparoscopic graspers is not optimal.

Cholecystectomy, Laparoscopic↗
PubMed2002

The perspective effect of wide-angle lenses in laparoscopes.

PURPOSE: To evaluate the effect of perspective distortion of wide-angle lenses in laparoscopes on hand-eye coordination during endoscopic manipulation. METHODS: Sixteen subjects repeatedly performed a standardized positioning task in a pelvi-trainer under two conditions. The subjects had no prior experience with endoscopic manipulation. In one condition, a wide-angle lens with considerable perspective distortion was used; in the other, a telephoto lens without perspective distortion was used. Task time and number of errors were measured. RESULTS: Task time and the number of errors did not significantly increase in the condition with a wide-angle lens. CONCLUSIONS: The perspective effect did not influence task performance in endoscopic manipulation in this experiment. Subjects indicated that they even preferred the wide-angle lens because its extreme perspective improved their perception of depth.

Adult↗
PubMed2001

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↗
PubMed2001

Time-action analysis of instrument positioners in laparoscopic cholecystectomy.

BACKGROUND: Instrument positioners can position and lock a laparoscopic instrument. This study uses time-action analysis to evaluate objectively whether IPs can substitute for a surgical assistant efficiently and safely. METHODS: In four hospitals, 78 laparoscopic cholecystectomies were randomly assisted by a surgical assistant or an instrument positioner (AESOP and PASSIST) The efficiency and safety of laparoscopic cholecystectomies were analyzed with respect to time, number and type of actions, positioning accuracy, and peroperative complications. A questionnaire evaluated the difficulties for each operation and the comfort of instrument positioner use. RESULTS: The PASSIST and AESOP were able to replace the surgical assistant during laparoscopic cholecystectomies without significantly changing either the efficiency or the safety of the operation. The questionnaire showed that the surgeons preferred to operate with an instrument positioner. CONCLUSION: This study assessed objectively that instrument positioners can substitute for a surgical assistant efficiently and safely in elective laparoscopic cholecystectomies.

Cholecystectomy, Laparoscopic↗
PubMed2001

Analysis of the quality and efficiency in learning laparoscopic skills.

OBJECTIVES: This study demonstrates the application of time-action analysis to the evaluation of task performance of diagnostic laparoscopy with laparoscopic ultrasonography. METHODS: The first 25 diagnostic laparoscopies with laparoscopic ultrasonography performed by a surgical resident were analyzed and compared with the outcomes of these procedures performed by an experienced surgeon. The time, actions, and correctness of task performance were evaluated. Furthermore, outcome correctness and postoperative complications were assessed. RESULTS: No postoperative complications occurred. The resident made one wrong diagnosis, for which the cause was detected by peroperative analysis. Additionally, 1% of the subtasks were performed only partially, 4% not at all, and 2% using the wrong technique. The efficiency for most diagnostic tasks remained significantly lower than that of the experienced surgeon (p < 0.001). CONCLUSIONS: Time-action analysis can be used to provide detailed insight into the quality and efficiency of learning surgical skills. It enables objective measurement of correctness in task performance as well as time and action efficiency.

Ampulla of Vater↗