Force model for laparoscopic graspers: implications for virtual simulator design.

INTRODUCTION: Laparoscopic graspers limit haptic perception, which in turn leads to tissue damage. Using virtual simulators to train surgeons in handling these instruments would ensure safer grasp. The design of a laparoscopic virtual simulator with force feedback depends on effective implementation of the grasper force model. OBJECTIVE: To develop a laparoscopic grasper tip force model theoretically from grasper mechanics and validate the same experimentally during laparoscopic pinching. MATERIALS AND METHODS: We developed a force model for double and single jaw action graspers using grasper mechanics. For experimental validation, the handle angle and the forces at the tip and the handle of the instrumented graspers during laparoscopic pinching of porcine abdominal tissues were measured. The intra-class correlation coefficient (ICC) between experimental and calculated tip force was calculated. RESULT: Excellent ICC (ICC ≥0.8, p<.001) between calculated and experimental tip force was obtained for both graspers for all grasped tissues. Mean absolute forces for all trials while using double and single jaw action graspers were ((FTc = 1.7N, FTe = 1.8N) and (FTc = 2.2N, FTe = 2.8N)) for gall bladder, ((FTc = 3.4N, FTe = 4.4N) and (FTc = 3.3N, FTe = 3.4N)) for liver and ((FTc = 4.2N, FTe = 4.5N) and (FTc = 2.3N, FTe = 2.6N)) for spleen, respectively. CONCLUSION: The proposed model may be used for the design of laparoscopic pinching action in a virtual simulator with force feedback and also for better ergonomic design of laparoscopic graspers.

Factors influencing forces during laparoscopic pinching: Towards the design of virtual simulator.

BACKGROUND: The design of good virtual simulators for laparoscopic training requires realistic visual and tactile perception. This is a study to characterize the factors that contribute to forces during laparoscopic pinching. METHODS: Surgeons were divided into four groups according to years of experience in laparoscopic surgery. They were asked to grasp six different types of porcine abdominal tissue in a randomly sequenced manner, using two different types of sensorized graspers, under two regimes of perceptual feedback (with and without visual feedback). The forces (grasper handle force and grasper tip force) and grasper handle angle were recorded and analyzed. RESULTS: The factors that determine forces during laparoscopic pinching can be ranked as follows: surgical experience (p < .001), tissue type (p = .007) and visual feedback (p = .033), but not grasper type (p = .071). Handle force depends significantly on surgical experience (p < .001), tissue type (p = .001) and visual feedback (p = .019), but not on grasper type (p = .203). Tip force depends significantly on surgical experience (p < .001) and marginally on tissue type (p = .082) and visual feedback (p = .053) but not on the grasper type (p = .180). CONCLUSION: Forces during laparoscopic pinching depend on surgical experience, tissue type and presence of visual feedback but not on grasper type. Our data can be an input in the design of virtual simulators with force feedback, for training laparoscopic pinching.

Neuromodulation by surface electrical stimulation of peripheral nerves for reduction of detrusor overactivity in patients with spinal cord injury: A pilot study.

OBJECTIVES: To demonstrate reduction in detrusor overactivity using surface electrical stimulation of posterior tibial nerve (PTN) or dorsal penile nerve (DPN) in patients with spinal cord injury (SCI). DESIGN: Patients with SCI with symptoms of urinary urgency/leaks, with cystometrogram (CMG) proven detrusor overactivity were recruited in this study. Ten persons with observable F-wave from tibial nerve were included in the PTN group. Five persons who had F-wave absent but preserved bulbocavernosus reflex were included in the DPN group. Stimulation was given at 20 Hz, 10-40 mA for 20 minutes/session/day for 14 consecutive days. Detrusor overactivity was recorded using CMG on days 1 and 15. SETTINGS: Rehabilitation Institute, Department of Physical Medicine and Rehabilitation, Christian Medical College and Hospital, Vellore, TN, India. PARTICIPANTS: Patients with SCI. INTERVENTIONS: Surface stimulation of peripheral nerves for reduction of detrusor overactivity. OUTCOME MEASURES: Qualitative analysis using voiding diary data and quantitative analysis using CMG data comparing pre- and post-intervention. RESULTS: P value obtained from voiding chart was 0.021 for PTN and 0.062 for DPN. P value obtained from CMG data was not significant in both groups. In one subject, treatment was extended to 4 weeks and further improvement in voiding diary was seen. CONCLUSIONS: In this pilot study of 15 patients, voiding chart data showed statistically significant improvement following PTN stimulation and trend of improvement following DPN stimulation. However, the CMG data were not statistically significant in this sample population. Further studies with larger, appropriately powered sample size would be helpful to demonstrate the associations of symptoms with CMG data. Trial registration CTRI no.; CTRI/2012/12/003234; CMCH Approval no.: CMC/IRB/6735/2008/12/18.

A palmar pressure sensor for measurement of upper limb weight bearing by the hands during transfers by paraplegics.

Paraplegic patients have to effect transfer from one seat to another by using their upper limbs. In this process the hands bear almost the entire weight of the body in at least some phases of the transfer. It is desirable to train patients, especially those who are elderly and otherwise weak, to distribute their weight so as to avoid large forces being sustained on any one hand for an extended period. It is also desirable to evaluate the effectiveness of assistive devices like lower limb FES in sharing the load on the hand. This study presents a simple and versatile method of measuring palmar hand force during transfers by paraplegic patients. It is important that this force sensor should not interfere with the grasping and stabilizing properties of the hands and should permit normal transferring. The force sensor comprises an air-filled pouch or pillow that can be placed on any surface. This pneumatic sensor feels like upholstery padding on the surface on which it is placed. The sensor integrates the total pressure applied to the surface of the pouch, thereby obtaining the total force exerted by the palm/hand. The fabrication of the sensor is described, as well as the associated measurement circuit. The static calibration shows that the sensor is linear up to 350 N and the dynamic calibration shows that it has a bandwidth of 13 Hz. The sensor was fabricated using an inflated inelastic airbag attached to a pressure transducer. An automatic offset correction circuit in the preamplifier module ensures that any offset due to initial pressure or sensor drift is removed and the output is zero under no load condition. The key to this sensor arrangement is the ease of fitting it into the intended location without disturbing the existing arrangement for the subject's activities of daily living (ADL).

Utility of multi-channel surface electromyography in assessment of focal hand dystonia.

INTRODUCTION: Surface electromyography (SEMG) allows objective assessment and guides selection of appropriate treatment in focal hand dystonia (FHD). METHODS: Sixteen-channel SEMG obtained during different phases of a writing task was used to study timing, activation patterns, and spread of muscle contractions in FHD compared with normal controls. Customized software was developed to acquire and analyze EMG signals. RESULTS: SEMG of FHD subjects (20) showed "early onset" during motor imagery, rapid proximal muscle recruitment, agonist-antagonist co-contraction involving proximal muscle groups, "delayed offset" after stopping writing, higher rectified mean amplitudes, and mirror activity in contralateral limb compared with controls (16). Muscle activation latencies were heterogenous in FHD. CONCLUSIONS: Anticipation, delayed relaxation, and mirror EMG activation were noted in FHD. A clear pattern of muscle activation cannot be ascertained. Multi-channel SEMG can aid in objective assessment of temporal-spatial distribution of activity and can refine targeted therapies like chemodenervation and biofeedback.

Motor recovery following olfactory ensheathing cell transplantation in rats with spinal cord injury.

BACKGROUND: Olfactory ensheathing cells (OEC) are considered to be the most suitable cells for transplantation therapy in the central nervous system (CNS) because of their unique ability to help axonal regrowth and remyelination in the CNS. However, there are conflicting reports about the success rates with OEC. AIM: This study was undertaken to evaluate the therapeutic effect of OEC in rat models using different cell dosages. MATERIAL AND METHODS: OECs harvested from the olfactory mucosa of adult white Albino rats were cultured. Spinal cord injury (SCI) was inflicted at the lower thoracic segment in a control and test group of rats. Two weeks later, OECs were delivered in and around the injured spinal cord segment of the test group of the rats. The outcome in terms of locomotor recovery of limb muscles was assessed on a standard rating scale and by recording the motor-evoked potentials from the muscles during transcranial electrical stimulation. Finally, the animals were sacrificed to assess the structural repair by light microscopy. STATISTICAL ANALYSIS: Wilcoxon signed rank test and Mann-Whitney U-test were used to compare the data in the control and the test group of animals. A P value of <0.05 was considered significant. RESULTS: The study showed a moderate but significant recovery of the injured rats after OEC transplantation (P=0.005). CONCLUSION: Transplantation of OECs along with olfactory nerve fibroblasts improved the motor recovery in rat models with SCI.