A Negative-Pressure Face-Mounted System Reduces Aerosol Spread during Endonasal Endoscopic Surgery.

Purpose Due to the potential risk of COVID-19 transmission during endonasal surgery, we studied methods to reduce droplet and aerosol generation during these procedures. Methods Droplet spread was assessed using ultraviolet light and a camera that detected fluorescence in the operative field and surgeon's personal protective equipment. Density of aerosols sized <10 µm was measured using a photometric particle counter. We designed a face-mounted negative-pressure mask placed on the patients' face during endoscopic endonasal surgery. Sixteen patients were recruited between October 2020 and March 2021 and randomly assigned to the mask and no-mask groups. We compared droplet spread and aerosols generated in both groups, with copious irrigation and continuous suction during drilling forming the mainstay of surgical technique in all cases. Results Droplet contamination due to direct spillage of fluorescein from the syringe was noted in two patients. Aerosol density rose during sphenoid drilling in both groups, with no significant difference when continuous suction and irrigation were employed (1.27 times vs. 1.07 times the baseline, p = 0 .248 ). Aerosol density rose significantly when suction and irrigation were interrupted in the no-mask group (44.9 times vs. 1.2 times, p = 0 .028) , which was not seen when the mask was used. Conclusion Aerosol generation increases during drilling in endonasal procedures and is a concern during this pandemic. The use of a rigid suction close to the drill along with copious irrigation is effective in reducing aerosol spread. The use of a negative pressure mask provides additional safety when inadvertent blockage of suction and inadequate irrigation occur.

Intra-arterial blood pressure measurement: sources of error and solutions.

Intra-arterial blood pressure measurement is the cornerstone of hemodynamic monitoring in intensive care units (ICU). Accuracy of the measurement is dependent on the dynamic response of the measuring system, defined by its natural frequency (fnatural) and damping coefficient (Zdamping). Gardner's plot (1981) has long been the only way to determine the accuracy of the pressure measurement. Specific objectives: (i) estimation of the amplitude of error in pressure measurement through simulations based on real-world data, (ii) a novel method to correct the error. Simulated blood pressure waveforms of various heart rates were passed through simulated measurement systems with varying fnatural and Zdamping. The numerical errors in systolic and diastolic pressures and mean error in the measured pressure were used to generate heat maps for the various recording conditions, in the same plot as that by Gardner (1981). fnatural and Zdamping from 121 patient recordings are plotted on these heat maps to demonstrate the fraction of unacceptable recordings. Performance of a tunable filter to correct the error is demonstrated. In many clinical settings, the measurement of intra-arterial pressure is prone to significant error. The proposed tunable filter is shown to improve the accuracy of intra-arterial pressure recording.

Electrical modelling of tissue experiments confirms precise locations of resistance and compliance in systemic arterial tree-they are mutually exclusive.

This study presents electrical modelling of the arterial system to understand the effect of adrenaline on the aortae and small arteries in terms of their resistance and compliance. There is no categorical documentation in the current literature on the precise locations of arterial resistance (R) and compliance (C) in vasculature. Knowledge of their exact locations in the arterial tree enables re-assessment of the differential action of vasoactive drugs on resistance versus compliance vessels once we resolve beat-to-beat changes in R and C in response to these drugs. Isolated goat aortae and small arteries were perfused with a pulsatile pump and lumen pressures were recorded before and after addition of adrenaline. Equivalent electrical models were simulated, and biological data was compared against the electrical equivalents to derive interpretations. In the aortae, systolic pressure increased, diastolic pressure decreased, pulse pressure increased (P = .018); but the mean pressure remained the same (P = .357). Whereas in small artery, vasoconstriction caused an increase in systolic, diastolic, and mean pressures (P = .028). Simulations allow us to infer that vasoconstriction in the aorta leads to a reduction in compliance, but an increase in resistance if any, is not sufficient to alter the mean aortic pressure. Whereas vasoconstriction in small arteries increases resistance, but a decrease in compliance, if any, does not affect any of the pressure parameters measured. The presented study is first of its kind to give experimental evidence that large arteries and aorta are the only compliance vessels and small arteries are the only resistance vessels.

Affordable passive 3D-printed prosthesis for persons with partial hand amputation.

BACKGROUND AND AIM: Partial hand amputations are common in developing countries and have a negative impact on patients and their families' quality of life. The uniqueness of each partial hand amputation, coupled with the relatively high costs of prostheses, makes it challenging to provide suitable prosthetic solutions in developing countries. Current solutions often have long lead times and require a high level of expertise to produce. The aim of this study was to design and develop an affordable patient-specific partial hand prosthesis for developing countries. TECHNIQUE: The prosthesis was designed for a patient with transmetacarpal amputation (i.e. three amputated fingers and partial palm). The final design was passive, controlled by the contralateral hand, and utilized the advanced flexibility properties of thermoplastic polyurethane in a glove-like design that costs approximately 20 USD to fabricate. Quantitative and qualitative tests were conducted to assess performance of the device after the patient used the final design. A qualitative assessment was performed to gather the patient's feedback following a series of tests of grasp taxonomy. A quantitative assessment was performed through a grasp and lift test to measure the prosthesis' maximum load capacity. DISCUSSION: This study showed that the prosthesis enhanced the patient's manual handling capabilities, mainly in the form of grasp stability. The prosthesis was light weight and could be donned and doffed by the patient independently. Limitations include the need to use the contralateral hand to achieve grasping and low grasp strength. CLINICAL RELEVANCE: Persons with partial hand amputation in developing countries lack access to affordable functional prostheses, hindering their ability to participate in the community. 3D-printed prostheses can provide a low-cost solution that is adaptable to different amputation configurations.

Biomechanical assessment of an alternative method of staple fixation for anchoring the Bone Patellar Tendon Bone graft to the tibia.

INTRODUCTION: The Anterior cruciate ligament (ACL) is the most commonly injured ligament around the knee and is best reconstructed with a biological graft. For ideal graft fixation, there should be sufficient initial strength to avoid failure of fixation and sufficient stiffness to restore the stability of the knee and to avoid gradual loosening in the post-operative period.When considering fixation of Bone Patellar Tendon Bone (BPTB) grafts to the tibia, the interference screw is considered to be the gold standard. As an alternative, we have used of staples and stainless steel (SS) wire to anchor the BPTB graft to the tibia and femur. The aim of this study was to assess the biomechanical efficacy of this fixation technique for anchoring the BPTB graft to the proximal tibia. We used a bovine model to compare three fixation techniques -interference screw, braided polyester sutures tied to a screw post and SS wire tied to a staple. MATERIALS AND METHODS: Fifteen fresh bovine knees specimens were used for the study. The patella was fixed to a load cell and the construct was pre-tensioned to 40N to allow for creep of the tendon. The BPTB graft was fixed to the tibia using the three fixation techniques - the interference screw, polyester suture tied to a post, and SS wire anchored to a staple. After fixation, the graft was subjected to a single load to failure test, and the forces generated were recorded. The ultimate failure load (the pullout strength), stiffness, and mode of failure were noted. RESULTS: In the single load-to-failure biomechanical testing, the ultimate failure load and stiffness for Staple with SS wire were 726.40N and 61.9N/mm respectively. For the screw post and polyester suture, it was 733.20N and 53.22N/mm, and for Interference screw - 594.00N and 79.50 N/mm respectively. There was no statistically significant difference in the stiffness or ultimate failure load between the three fixation techniques. The graft fixation using interference screws failed at the bone- tunnel interface by slippage of the bone block from the tunnel in all 5 specimens. In all 5 of the specimens fixed with polyester suture and the screw post, the fixation failed when the polyester suture snapped. When the SS wire and staple construct was stressed, the graft failed as the SS wire cut through the graft in 4 specimens, and in the fifth construct, the knot over the staple unraveled as the load was applied. CONCLUSION: The biomechanical properties of BPTB graft fixation with SS wire tied to a staple is similar to that of other fixation devices like the interference screw and suture post. This technique provides a simple, yet effective fixation for the graft - but needs further clinical assessment.

The Spectrum of Autonomic Dysfunction in Myasthenic Crisis.

BACKGROUND: Autoimmune autonomic dysfunction is described in Myasthenia Gravis. In myasthenic crisis, the spectrum of autonomic dysfunction is hitherto uncharacterized. OBJECTIVE: The objective of this study is to describe the spectrum of autonomic dysfunction in myasthenic crises using the composite autonomic symptom scale 31 (COMPASS 31) autonomic symptom questionnaire and power spectral analysis of heart rate variability (HRV), which is a simple way of estimating general autonomic dysfunction. METHODS: Adult patients with myasthenic crisis from January 1, 2014 to March 15, 2015, were prospectively included in this study. The COMPASS 31 questionnaire for symptoms of autonomic dysfunction and power spectral analysis of HRV were assessed. These were compared with the patient's demographic and clinical parameters and with previous literature. IRB approval was obtained. RESULTS: Sixteen patients were included (M:F 3:1). 15/16 patents (93%) had autonomic dysfunction on COMPASS 31 questionnaire. The domains of involvement were gastrointestinal (80%), orthostatic (67.7%), pupillomotor (67.7%); sudomotor (33.3%), and vasomotor (13.3%). Parasympathetic dysfunction predominance was suggested by the symptom profile. HRV analysis showed a low frequency (LF) spectral shift suggesting slowed parasympathetic responsiveness (LF normalized unit (nu): high frequency [HF] nu mean 8.35, standard deviation ± 5.4, 95% confidence interval 2.2-12.5), which significantly exceeded the mean LF nu: HF nu ratios of the majority of previously reported noncrises myasthenic populations. CONCLUSIONS: Myasthenic crisis has autonomic dysfunction involving multiple organ systems. Increased latency of parasympathetic reflexes is suggested. A comprehensive management protocol addressing different autonomic domains is required for holistic patient care.

Design and evaluation of cryodevice, an easy to use apparatus for maintenance of optimum temperature during cryoglobulin assay.

INTRODUCTION: Maintenance of temperature during collection and transport of blood is an important pre-requisite for cryoglobulin assays. In this manuscript, we describe 'cryodevice', a low-cost device for transportation and/or incubation of vials of whole blood at 37°C. Such a device would reduce false negatives in cryoglobulin assays. METHOD: The 'cryodevice' takes the embodiment of a portable, light, insulated water bath, which can be used as an incubator in a plugged-in state, or as a transport container after it is set up and disconnected from the power supply. The design of the cryodevice is described here, with focus on its construction and electronic control circuit. Computer simulations and in vitro trials were performed to study the temperature drop in the blood samples placed in the device. Subsequently, the cryodevice was also used with actual patient blood samples. RESULTS: Thermal simulations and in vitro testing of the cryodevice predicted that the design would meet the temperature maintenance goals. When the cryodevice was put in to use for screening 45 patient blood samples, it helped identify positive cryoglobulinemia in three of the samples. CONCLUSION: The description of the cryodevice envisions enabling the construction of a low-cost device in resource-limited healthcare settings in India created with locally available resources. On testing, the device was found to be satisfactory in performance and is expected to bring down incidences of false negatives in cryoglobulin tests.

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.

Phase changing material: an alternative method for cooling babies with hypoxic ischaemic encephalopathy.

BACKGROUND: Therapeutic hypothermia for hypoxic ischaemic encephalopathy (HIE) has been proved effective. Standard equipment is expensive, while ice packs used in low resource settings are labour intensive and associated with wider temperature fluctuations. OBJECTIVES: To assess the feasibility of using phase changing material (PCM) as an alternative method for providing therapeutic hypothermia. METHODS: We retrospectively analysed 41 babies with HIE who had been cooled with PCM (OM 32 or HS 29) to a target rectal temperature of 33-34°C. Rectal temperature was continuously monitored and recorded every hour. If the rectal temperature was >33.8°C, cool gel packs were applied, and if the temperature was <33.2°C, the baby was covered with sheets and the warmer output turned on till the temperature stabilized at 33.5°C. The unit's standard protocol for cooling was followed for monitoring and treatment. The outcome measures were stability and fluctuation of the rectal temperature and the need for interventions to maintain the target temperature. RESULTS: The mean (±SD) temperature during the cooling phase was 33.45 ± 0.26°C. Throughout the cooling phase, the target temperature range was maintained in 96.2% of the time. There was no temperature reading <32°C. With HS 29, ice packs were not used in any baby, and the warmer was used for a median of 7 h (interquartile range 1.5-14). CONCLUSIONS: PCM provides a low cost and effective method to maintain therapeutic hypothermia. However, careful monitoring is required during induction and the rewarming phase to avoid hypothermia outside the therapeutic range.

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.

Dimensions of the foveal avascular zone using the Heidelberg retinal angiogram-2 in normal eyes.

PURPOSE: The purpose was to study the dimensions of the foveal avascular zone (FAZ) using Heidelberg Retinal Angiogram-2 (HRA-2; Heidelberg Engineering GmBH, Dossenheim, Germany). MATERIALS AND METHODS: An observational study of the FAZ area and circumference was done with fundus fluorescein angiography (FFA) using HRA-2 in 31 normal individuals. The FAZ was studied using both contrast-adjusted and nonadjusted methods. Contrast adjustment was done to obtain better visualization of the finer capillaries around the fovea enabling more precise measurements of the FAZ in normal eyes. RESULTS: The mean area of the FAZ calculated by the contrast-adjusted method was 0.2753 mm 2 (±0.074) and the mean circumference was 2.22 mm (±0.048). By the conventional method, the area and circumference of the FAZ were 0.6241 mm 2 (±0.177) and 3.23 mm (±0.454), respectively. CONCLUSION: The measurements of area and circumference of FAZ using contrast-adjusted methods were significantly smaller than the conventional method.