Haptic based fundamentals of laparoscopic surgery simulation for training with objective assessments.

Force is crucial for learning psychomotor skills in laparoscopic tissue manipulation. Fundamental laparoscopic surgery (FLS), on the other hand, only measures time and position accuracy. FLS is a commonly used training program for basic laparoscopic training through part tasks. The FLS is employed in most of the laparoscopic training systems, including box trainers and virtual reality (VR) simulators. However, many laparoscopic VR simulators lack force feedback and measure tissue damage solely through visual feedback based on virtual collisions. Few VR simulators that provide force feedback have subjective force metrics. To provide an objective force assessment for haptic skills training in the VR simulators, we extend the FLS part tasks to haptic-based FLS (HFLS), focusing on controlled force exertion. We interface the simulated HFLS part tasks with a customized bi-manual haptic simulator that offers five degrees of freedom (DOF) for force feedback. The proposed tasks are evaluated through face and content validity among laparoscopic surgeons of varying experience levels. The results show that trainees perform better in HFLS tasks. The average Likert score observed for face and content validity is greater than 4.6 ± 0.3 and 4 ± 0.5 for all the part tasks, which indicates the acceptance of the simulator among subjects for its appearance and functionality. Face and content validations show the need to improve haptic realism, which is also observed in existing simulators. To enhance the accuracy of force rendering, we incorporated a laparoscopic tool force model into the simulation. We study the effectiveness of the model through a psychophysical study that measures just noticeable difference (JND) for the laparoscopic gripping task. The study reveals an insignificant decrease in gripping-force JND. A simple linear model could be sufficient for gripper force feedback, and a non-linear LapTool force model does not affect the force perception for the force range of 0.5-2.5 N. Further study is required to understand the usability of the force model in laparoscopic training at a higher force range. Additionally, the construct validity of HFLS will confirm the applicability of the developed simulator to train surgeons with different levels of experience.

Robust Method to Determine Critical Micelle Concentration via Spreading Oil Drops on Surfactant Solutions.

The spreading of a liquid on another is often encountered in oil spills and coatings and is also of industrial relevance in pharmaceuticals and petrochemicals. In this study, the spreading of oil drops on aqueous solutions containing cationic, anionic, and nonionic surfactants over a wide range of surfactant concentrations is investigated. The spreading behavior quantified by measuring the time evolution of the projected area of the oil lens reveals the occurrence of a maximum, which is strongly dependent on the concentration of the surfactant in the aqueous solution. Our experiments show that this dependence is different at concentrations above and below the critical micelle concentration (CMC) of the surfactant and can be captured by two straight lines of different slopes. Interestingly, these two straight lines intersect at a concentration that coincides with the CMC of the surfactants in solution. We find that this behavior is universal as shown by performing experiments with different types of surfactants, their purity, and other system variables. Thus, we propose a method to unambiguously determine the CMC of surfactant solutions compared to the conventional techniques. The proposed method is simple, versatile, and applicable for the determination of CMC of both ionic and nonionic surfactants.

Volumetric and Morphometric Analysis of Pineal and Pituitary Glands of an Indian Inedial Subject.

BACKGROUND: Inedia (Latin for "fasting") is the ability of a person to live without consuming food and water and to sustain solely by prana, the vital life force in Hinduism. According to Ayurveda, sunlight is one of the main sources of prana, and some practitioners believe that it is possible for a person to survive on sunlight alone. PURPOSE: In this study, we report the unusual sizes and volumes of both the pineal and pituitary glands in a subject with inedia state for nearly 70 years. METHODS: The pineal and pituitary glands were located in the MRI of the subject from coronal, axial, and sagittal images. Segmentation of the pineal and pituitary glands was performed using level set active contours method. RESULTS: The overall volume, size, and shape of the glands were calculated as 38.7604 mm3 for the pineal gland and 272.552 mm3 for the pituitary gland and compared with that of the normal volumes (94.2 ± 40.65 mm3 and 320-718 mm3 , respectively). CONCLUSION: It was found that the subject has significantly low pineal and pituitary volumes, which fall under the category of normal young child and we could show that the neurohormonal morphology of inedia subject is within childhood range.

Computer-Based CPR Simulation Towards Validation of AHA/ERC Guidelines.

As per the AHA 2015 and ERC 2015 guidelines for resuscitation, chest compression depth should be between 5 and 6 cm with a rate of 100-120 compressions per minute. Theoretical validation of these guidelines is still elusive. We developed a computer model of the cardiopulmonary resuscitation (CPR) system to validate these guidelines. A lumped element computer model of the cardiovascular system was developed to simulate cardiac arrest and CPR. Cardiac output was compared for a range of compression pressures and frequencies. It was observed from our investigation that there is an optimum compression pressure and rate. The maximum cardiac output occurred at 100 mmHg, which is approximately 5.7 cm, and in the range of 100 to 120 compressions per minute with an optimum value at 110 compressions per minute, validating the guidelines. Increasing the pressure or the depth of compression beyond the optimum, limits the blood flow by depleting the volume in the cardiac chambers and not allowing for an effective stroke volume. Similarly increasing the compression rate beyond the optimum degrades the ability of the chambers to pump blood. The results also bring out the importance of complete recoil of the chest after each compression with more than 400% increase in cardiac output from 90% recoil to 100% recoil. Our simulation predicts that the recommendation to compress harder and faster is not the best counsel as there is an optimum compression pressure and rate for high-quality CPR.

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.

Morphological analysis of pressure wave in the arterial tree with stenosis - a modeling approach.

This paper describes the morphological changes in peripheral signals due to arterial diseases with various severity conditions and site of stenosis using modeling approaches, and its effect in the morphological parameters of radial artery. As stenosis induces abrupt change in geometry and elastic properties of arterial tree (constitutes major reflection sites), hybrid model is well suited for studying the changes in shape of the pressure and flow wave transmitted through the stenosis. These morphological changes in wave shape of peripheral signal have significant diagnostic value in both modern and traditional medicine systems. It can be used for the quantitative assessment of the severity of the arterial diseases.

Effects of laparoscopic instrument and finger on force perception: a first step towards laparoscopic force-skills training.

BACKGROUND: In laparoscopic surgery, no external feedback on the magnitude of the force exerted is available. Hence, surgeons and residents tend to exert excessive force, which leads to tissue trauma. Ability of surgeons and residents to perceive their own force output without external feedback is a critical factor in laparoscopic force-skills training. Additionally, existing methods of laparoscopic training do not effectively train residents and novices on force-skills. Hence, there is growing need for the development of force-based training curriculum. OBJECTIVE: As a first step towards force-based laparoscopic skills training, this study analysed force perception difference between laparoscopic instrument and finger in contralateral bimanual passive probing task. METHODS: The study compared the isometric force matching performance of novices, residents and surgeons with finger and laparoscopic instrument. Contralateral force matching paradigm was employed to analyse the force perception capability in terms of relative (accuracy), and constant errors in force matching. RESULTS: Force perception of experts was found to be better than novices and residents. Interestingly, laparoscopic instrument was more accurate in discriminating the forces than finger. The dominant hand attempted to match the forces accurately, whereas non-dominant hand (NH) overestimated the forces. Further, the NH of experts was found to be most accurate. Furthermore, excessive forces were applied at lower force levels and at very high force levels. CONCLUSIONS: Due to misperception of force, novices and residents applied excessive forces. However, experts had good control over force with both dominant and NHs. These findings suggest that force-based training curricula should not only have proprioception tasks, but should also include bimanual force-skills training exercises in order to improve force perception ability and hand skills of novices and residents. The results can be used as a performance metric in both box and virtual reality based force-skills training.

Vibrotactile sensitivity threshold: nonlinear stochastic mechanotransduction model of the Pacinian Corpuscle.

Based on recent discoveries of stretch and voltage activated ion channels in the receptive area of the Pacinian Corpuscle (PC), this paper describes a two-stage mechanotransduction model of its near threshold Vibrotactile (VT) sensitivity valid over 10 Hz to a few kHz. The model is based on the nonlinear and stochastic behavior of the ion channels represented as dependent charge sources loaded with membrane impedance. It simulates the neural response of the PC considering the morphological and statistical properties of the receptor potential and action potential with the help of an adaptive relaxation pulse frequency modulator. This model also simulates the plateaus and nonmonotonic saturation of spike rate characteristics. The stochastic simulation based on the addition of mechanical and neural noise describes that the VT Sensitivity Threshold (VTST) at higher frequencies is more noise dependent. Above 800 Hz even a SNR = 150 improves the neurophysiological VTST more than 3 dBµ. In that frequency range, an absence of the entrainment threshold and a lower sensitivity index near the absolute threshold make the upper bound of the psychophysical VTST more dependent on the experimental protocol and physical set-up. This model can be extended to simulate the neural response of a group of PCs.

Multiscale layered biomechanical model of the pacinian corpuscle.

This paper describes a multiscale analytical model of the lamellar structure and the biomechanical response of the Pacinian Corpuscle (PC). In order to analyze the contribution of the PC lamellar structure for detecting high-frequency vibrotactile (VT) stimuli covering 10 Hz to a few kHz, the model response is studied against trapezoidal and sinusoidal stimuli. The model identifies a few generalizable features of the lamellar structure which makes it scalable for different sizes of PC with different number of lamellae. The model describes the mechanical signal conditioning of the lamellar structure in terms of a recursive transfer-function, termed as the Compression-Transmittance-Transfer-Function (CTTF). The analytical results show that with the increase of the PC layer index above 15, the PC inner core (IC) relaxes within 1 ms against step compression of the outermost layer. This model also considers the mass of each PC layer to investigate its effect on the biomechanical response of the lamellar structure. The interlamellar spacing and its biomechanical properties along with the model response are validated with experimental data in the literature. The proposed model can be used for simulating a network of PCs considering their diversity for analyzing the high-frequency VT sensitivity of the human skin.

Morphological analysis of peripheral arterial signals in Takayasu's arteritis.

Takayasu's arteritis disease (TA) remains a rarely studied chronic inflammatory disease. Our objective is to analyze peripheral pulse using photoplethysmography (PPG) as a new assessment method for diagnosing TA. So far no literature reports detailed morphological analysis of TA PPG signals. PPG signals of twenty normal and twenty TA patients at five different regions such as left and right thumbs, left and right toes and neck have been acquired simultaneously. Morphological parameters of peripheral signals such as peak-to-peak time, the crest time (CT), reflection index (RI), maximum systolic slope (MSS), maximum diastolic slope, pulse height, area under pulse and pulse transit time are obtained from PPG and electro cardiogram of normal and TA patients. Surprisingly RI is different in all the five locations of TA patients, whereas it is same for normal in all five locations. Mean MSS are significantly lesser than normal subjects. Mean CT of normal subjects is always lesser than normal subject. Morphological parameters based classification method has sensitivity of 80-100 and specificity of 86-100 in all limbs/all parameters. Bilateral dissimilarity in morphological parameters of multi site peripheral signals in the TA patients can be used to diagnose TA patients and find the pathological site. Less population is studied which reflects the rarity of the TA disease.

On the somatosensation of vision.

The interconnection between vision and somatosensation is already well-established and is further supplemented by the evolutionary link between eyes and photoreceptors, and the functional connection between photosensation and thermoreception. However, our analysis shows that the relation between vision and somatosensation is much deeper and suggests that somatosensation may possibly be the basis of vision. Surprisingly, our photoreceptor itself needs somatosensory proteins for its functioning, and our entire visual pathway depends on somatosensory cues for its functioning.

Reconstruction of gastric slow wave from finger photoplethysmographic signal using radial basis function neural network.

Extraction of extra-cardiac information from photoplethysmography (PPG) signal is a challenging research problem with significant clinical applications. In this study, radial basis function neural network (RBFNN) is used to reconstruct the gastric myoelectric activity (GMA) slow wave from finger PPG signal. Finger PPG and GMA (measured using Electrogastrogram, EGG) signals were acquired simultaneously at the sampling rate of 100 Hz from ten healthy subjects. Discrete wavelet transform (DWT) was used to extract slow wave (0-0.1953 Hz) component from the finger PPG signal; this slow wave PPG was used to reconstruct EGG. A RBFNN is trained on signals obtained from six subjects in both fasting and postprandial conditions. The trained network is tested on data obtained from the remaining four subjects. In the earlier study, we have shown the presence of GMA information in finger PPG signal using DWT and cross-correlation method. In this study, we explicitly reconstruct gastric slow wave from finger PPG signal by the proposed RBFNN-based method. It was found that the network-reconstructed slow wave provided significantly higher (P < 0.0001) correlation (≥ 0.9) with the subject's EGG slow wave than the correlation obtained (≈0.7) between the PPG slow wave from DWT and the EEG slow wave. Our results showed that a simple finger PPG signal can be used to reconstruct gastric slow wave using RBFNN method.

On non-invasive measurement of gastric motility from finger photoplethysmographic signal.

This article investigates the possibility of extracting gastric motility (GM) information from finger photoplethysmographic (PPG) signals non-invasively. Now-a-days measuring GM is a challenging task because of invasive and complicated clinical procedures involved. It is well-known that the PPG signal acquired from finger consists of information related to heart rate and respiratory rate. This thread is taken further and effort has been put here to find whether it is possible to extract GM information from finger PPG in an easier way and without discomfort to the patients. Finger PPG and GM (measured using Electrogastrogram, EGG) signals were acquired simultaneously at the rate of 100 Hz from eight healthy subjects for 30 min duration in fasting and postprandial states. In this study, we process the finger PPG signal and extract a slow wave that is analogous to actual EGG signal. To this end, we chose two advanced signal processing approaches: first, we perform discrete wavelet transform (DWT) to separate the different components, since PPG and EGG signals are non-stationary in nature. Second, in the frequency domain, we perform cross-spectral and coherence analysis using autoregressive (AR) spectral estimation method in order to compare the spectral details of recorded PPG and EGG signals. In DWT, a lower frequency oscillation (≈0.05 Hz) called slow wave was extracted from PPG signal which looks similar to the slow wave of GM in both shape and frequency in the range (0-0.1953) Hz. Comparison of these two slow wave signals was done by normalized cross-correlation technique. Cross-correlation values are found to be high (range 0.68-0.82, SD 0.12, R = 1.0 indicates exact agreement, p < 0.05) for all subjects and there is no significant difference in cross-correlation between fasting and postprandial states. The coherence analysis results demonstrate that a moderate coherence (range 0.5-0.7, SD 0.13, p < 0.05) exists between EGG and PPG signal in the "slow wave" frequency band, without any significant change in the level of coherence in postprandial state. These results indicate that finger PPG signal contains GM-related information. The findings are sufficiently encouraging to motivate further exploration of finger PPG as a non-invasive source of GM-related information.

Hybrid cardiopulmonary model for analysis of valsalva maneuver with radial artery pulse.

A comprehensive model, which has the advantages of both lumped parameter and distributed parameter, has been developed with the objective of investigating the respiratory influences in radial artery pressure pulse as in photoplethysmography (PPG). It integrates lumped parameter cardiopulmonary (CP) model and transmission line arterial tree model from aorta to radial artery. The cardio-pulmonary interaction is realized by incorporating respiratory-induced variations in intrapleural pressure (Ppl) in circulatory system. The PPG signal of the model is considered as the radial artery pulse. To investigate the interaction Valsalva Maneuver (VM) condition has been simulated for different Ppl magnitude (10, 20, 30, and 40 mmHg) and for different time duration (5, 10, 15, and 20 s), and validated with PPG signal recorded in 10 normal subjects performing VM. The effects of test duration and VM pressure are studied in both the simulation and the experiments with specific focus on the maximal (%∆) changes in Heart Rate (HR), and Mean Arterial Pressure (MAP) during phases II and IV of VM. The correlation coefficients derived from model result have good agreement with experimental results. As radial artery pulse plays important role in both allopathy and alternate medicine systems, this model can serve to study its clinical importance in detecting cardiac and respiratory pathologies.

Effect of upper arm cuff pressure on pulse morphology using photoplethysmography.

Study of Arterial pressure and flow variation when external pressure applied is critical in understanding clinical relevance of pulse. We propose a distributed model of entire human arterial tree to describe the hemodynamic changes due to pressure applied on the brachial artery. Input to this distributed model is from a four element Windkessel model. We measured the blood volume during brachial occlusion in six healthy subjects using finger photoplethysmography (PPG). We analyzed the morphological changes in both the model and the experiment. We found that both the model pressure pulse and the finger volume pulse morphology changing with the applied pressure. We calculated the normalized values of pulse height, maximum systolic slope, maximum diastolic slope and peak to peak interval (PPI) for each beat. Mean values of all the morphological parameters show an initial rise and in the model the maximum occurs at 60-80mmHg while in the experiments it occurs at 40mmHg. The predicted model parameters are positively correlated with measured parameters (for maximum systolic slope r = 0.54; for maximum diastolic slope r = 0.77; for pulse height r = 0.89 when P < 0.05). The PPI variation is different for each subject reflecting the reflex properties of the individual. Variable elastance and reflex system should be incorporated in the model to accurately predict the experimental results.

Pulse rate variability and gastric electric power in fasting and postprandial conditions.

Photoplethysmography (PPG) is typically used to extract cardiac-related information like heart rate and cardiac output, though extra-cardiac information like respiratory rate can also be extracted from PPG. The aim of the current study is to advance this approach further and investigate existence of gastric-related activity in PPG. To this end, we consider pulse rate variability (PRV), which provides information analogous to heart rate variability (HRV). Finger PPG and electrogastrography (EGG) signals were recorded from 8 healthy volunteers in fasting and postprandial state for 30 minutes. Peak-to-peak interval (PPI) analysis shows that the power of high frequency (HF) component in fasting and postprandial state changes significantly. The power ratio (PR), which is the ratio between powers of low frequency band (LF, 0.04-0.15 Hz) to that of high frequency band (HF, 0.15-0.4 Hz) and the EGG power were calculated in fasting and postprandial state. PR was positively correlated with EGG power (r = 0.46; P< 0.05). PR indicates the balancing sympathovagal modulation and vagal nervous activity. The significance of this study is that PR from PRV analysis could be used as a tool for diagnosing gastric system instead of the present invasive/cumbersome methods.

Vibration perception threshold and the law of mobility in diabetic mellitus patients.

BACKGROUND: Diabetic neuropathy is a family of nerve disorders with progressive loss of nerve function in 15% of diabetes mellitus (DM) subjects. Vibration Perception Threshold (VPT) is one of the modalities of testing loss of protective sensation. Law of mobility for VPT is well known for normal subjects, but not for diabetic subjects. This is a pilot study to evaluate and plot the law of mobility for VPT among DM subjects. METHODS: We used biothesiometer to find the VPT of several areas in upper and lower extremities for normal and diabetic subjects. VPT of normal and diabetic subjects for different foot areas from proximal to distal is evaluated for 30 subjects. All the subjects are screened for peripheral artery occlusive disease with ankle brachial pressure index (0.9 or above). VPT values of different areas are arranged in a proximal to distal order for the analysis. RESULTS: VPT values monotonically decrease from proximal to distal areas. Vierodt's law of mobility holds well for normal subjects in both feet areas. The law of mobility does not hold good for the DM subjects in one or both feet areas. CONCLUSIONS: The VPT value of diabetic subjects reveals that the law of mobility do not holds good for diabetic subjects in foot areas. Though the number of subjects is small, all the subjects defied the law.

Haptic guided laparoscopy simulation improves learning curve.

Haptic fidelity has been increasingly emphasized in MIS simulators however the real benefits of the simulated environments are mostly under-exploited for MIS Simulation and Training. In this paper we discuss the use of augmented forces such as haptic guidance in our laparoscopic simulator for improving learning curve. A simple virtual environment has been designed to simulate advanced MIS tasks such as cutting. A simple haptic guidance system has been implemented to provide a guiding force pulling a novice trainee along the ideal motion path for manipulating the laparoscopic tools. An experiment has been designed to compare the time taken by two groups of participants with and without guidance for the cutting procedure. The results indicate that the haptic guidance has assisted participants in learning of motor skills in its cognitive and associative stage of learning.

Changes in two point discrimination and the law of mobility in diabetes mellitus patients.

BACKGROUND: Diabetic neuropathy is a family of nerve disorders with progressive loss of nerve function in 15% of diabetes mellitus (DM) subjects. Two-point discrimination (TPD) is one method of quantitatively testing for loss of nerve function. The law of mobility for TPD is known for normal subjects in earlier studies but has not been studied for diabetic subjects. This is a pilot study to evaluate and plot the law of mobility for TPD among DM subjects. METHODS: The Semmes Weinstein monofilament (SWMF) was used to measure the loss of protective sensation. An Aesthesiometer was used to find the TPD of several areas in upper and lower extremities for normal and diabetic subjects. All the subjects were screened for peripheral artery occlusive disease with ankle brachial pressure index (0.9 or above). RESULTS: TPD of normal and diabetic subjects for different areas of hands and legs from proximal to distal is evaluated for 18 subjects. TPD values decrease from proximal to distal areas. Vierodt's law of mobility for TPD holds good for normal subjects in the hand and foot areas. The law of mobility for TPD in DM subjects holds well in the hand but doesn't hold well in foot areas with or without sensation. CONCLUSION: TPD is a quantitative and direct measure of sensory loss. The TPD value of diabetic subjects reveals that the law of mobility do not hold well for Diabetic subjects in foot areas. The significance of this result is that the TPD of the diabetic subjects could provide direct, cost effective and quantitative measure of neuropathy.

Correlation between two-point discrimination with other measures of sensory loss in diabetes mellitus patients.

Diabetic neuropathy is one of the most important factors for foot ulceration in diabetes mellitus (DM) patients. Among different sensibility measures of neuropathy, two-point discrimination (TPD) has been suggested as a reliable method; however, the correlation of TPD with other well-known measures is not known. We measured the loss of protective sensation using Semmes-Weinstein Monofilaments (SWMF), hardness of the foot sole using shore meter (sh), power ratio (PR) using pedopowergraph and TPD using esthesiometer in foot areas of both left and right legs in 14 DM subjects. We have found no correlation either between TPD and shore values (sh) or between TPD and PR. The SWMF (10 g) is found not to provide any additional value in measuring loss of sensation in comparison to TPD. The TPD appears to be measuring different property of the foot compared to other measures. The mechanism of this independence is not well understood and more investigation is required to understand the mechanism.