Mechanical impact of epiretinal membranes on the retina utilizing finite element analysis.

BACKGROUND AND OBJECTIVE: Epiretinal membrane (ERM) is a transparent membrane that forms on the surface of the neurosensory retina, causing tangential traction on the retinal surface, which may contribute to cell proliferation and contraction. Epiretinal membranes (ERMs) may be asymptomatic in some patients, while in others the membranes can progress, resulting in macular thickening and macular traction, thus distorting and inducing loss of central visual function and metamorphopsia. Currently, treatment options include follow-up or pars plana vitrectomy with an ERM peel, aiming to relieve the macular traction and improve vision and metamorphopsia. No specific criteria exist for predicting which patients might progress and need early surgery to improve and maintain good vision. The decision for surgery is based on the individual's symptoms and the physician's judgment. This study aimed to evaluate the mechanical impact in terms of stress and deformations of the ERM and to qualitatively compare them with the clinical progression of fovea thickening observed through optical coherence tomography (OCT) images. METHODS: Numerical simulation on a three-dimensional geometrical retina and ERM model was applied to isolate factors that can be used to predict its progression and prognosis. OCT images of 14 patients with ERM were used to derive the fovea thickness progression before and after vitrectomy surgery with ERM peeling. RESULTS: The results clearly show that the increase in ERM contractility level increases the developed stress at the fovea, which spreads and advances toward its base. The highest stress level (2.1 kPa) was developed at the highest and asymmetric contractility, producing non-uniform distributed deformations that distort the fovea structure. CONCLUSIONS: These findings imply that high and asymmetric ERM contractility should be evaluated clinically as a factor that might signal the need for early vitrectomy surgery to avoid irreversible visual loss. Moreover, the OCT images revealed that in some cases, the thickness of the fovea indeed remains high, even after ∼12 months postoperatively, which also indicates that the deformation of the fovea in these cases is irreversible.

A novel approach based on machine learning analysis of flow velocity waveforms to identify unseen abnormalities of the umbilical cord.

INTRODUCTION: A Doppler ultrasound (DUS) is essential for detecting blood flow abnormalities in the umbilical cord (UC). Any morphological abnormalities of the UC may lead to morbidity and stillbirth. Some abnormalities such as torsion, strictures and true-knot, however, may only be discovered at birth. This study proposes a novel approach of using machine learning analysis of flow velocity waveforms to improve the diagnosis of UC abnormalities. METHODS: A dynamic in-vitro simulator for DUS and three UC models, each representing a different morphology: true-knot, straight and coiled, were designed. DUS flow field images were captured from four cases of flow through the models: straight, coiled, at mid- and exit of the UC true-knot. The images were transformed into vector profiles of average flow signals that were segmented into 250 flow waves, each comprising 120 samples, for each of the four cases. Three sets of features were extracted from each flow wave and different machine learning algorithms were used for dimensional reduction and binary and multiclass classification. RESULTS: Significant differences were obtained between flow signals measured at the mid-knot compared to all other cases, which were also reflected in the average high accuracy rates of 97.5%-99.2%. Good accuracy rates of ∼80% and up were also generated, allowing the differentiation between the straight, coiled and exit true-knot. DISCUSSION: Our dynamic simulator can produce an unlimited database, and combined with the proposed machine learning analysis, may be used as decision support system and increase the ability to diagnose unseen pathologies of the UC.

Analysis of skeletal muscle performance using piezoelectric film sensors.

A flexible piezoelectric thin film sensor has been proposed recently in several studies for detection of muscle movements. The objective of this study was to investigate the ability of this sensor to assess skeletal muscle performance and fatigue under isokinetic contractions. Simultaneous noninvasive measurements of muscles activity were done using surface electromyography (EMG) electrodes and two thin film piezoelectric sensors. Measurements were taken from the biceps during slow and fast elbow flexion with and without strong grip, during different weight lifting and from the gastrocnemius during treadmill marching at speeds of 4 and of 10 kph. The results shows correlation between the onset of EMG and the piezoelectric sensors (Piezo) signals during muscle contraction. Increasing contraction intensity increase significantly both EMG and Piezo signals. Higher contractions velocity increased Piezo signal. Opposite linear relation was found between the average maximal EMG envelope amplitudes and the average maximal Piezo peaks with increasing loads. The significant decrease in the maximal Piezo peaks with time of all 3 subjects during elbow flexion while holding weight suggests the ability of piezoelectric thin film sensor to track muscle fatigue during isokinetic contractions.

The impact of breathing pattern and rate on inspiratory muscles activity.

Different rehabilitation programs are used to relieve dyspnea for hyper-inflated lung patients. In this study, a new approach, based on integrated changes in respiratory rate and pattern, for inspiratory muscles rehabilitation and training was examined utilizing noninvasive measurements of the two inspiratory muscles (rib cage inspiratory and neck inspiratory muscles) activity during controlled breathing in healthy subjects. Muscles activity was measured using electromyography, while subjects, breathed at different combinations of respiratory rate (6, 10, 16 breath per minutes) and inspiratory duty cycles (TI/Ttot). The results clearly show that both muscles were most active at the lowest evaluated respiratory rate, and that alteration of the duty cycle at the lowest rate significantly (p< 0.05) changes their electrical activity. Breathing at low respiratory rate RR is recommended for hyper-inflated lung patients in order to improve their gas exchange, therefore, it is recommended for these patients to find their most effective combination of RR and TI/Ttot and to use control breathing to practice their breath at optimum combination.

Mechanical properties of different airway stents.

Airway stents improve pulmonary function and quality of life in patients suffering from airway obstruction. The aim of this study was to compare main types of stents (silicone, balloon-dilated metal, self-expanding metal, and covered self-expanding metal) in terms of their mechanical properties and the radial forces they exert on the trachea. Mechanical measurements were carried out using a force gauge and specially designed adaptors fabricated in our lab. Numerical simulations were performed for eight different stent geometries, inserted into trachea models. The results show a clear correlation between stent diameter (oversizing) and the levels of stress it exerts on the trachea. Compared with uncovered metal stents, metal stents that are covered with less stiff material exert significantly less stress on the trachea while still maintaining strong contact with it. The use of such stents may reduce formation of mucosa necrosis and fistulas while still preventing stent migration. Silicone stents produce the lowest levels of stress, which may be due to weak contact between the stent and the trachea and can explain their propensity for migration. Unexpectedly, stents made of the same materials exerted different stresses due to differences in their structure. Stenosis significantly increases stress levels in all stents.

Physical stresses at the air-wall interface of the human nasal cavity during breathing.

The nose is the front line defender of the respiratory system and is rich with mechanoreceptors, thermoreceptors, and nerve endings. A time-dependent computational model of transport through nasal models of a healthy human has been used to analyze the fields of physical stresses that may develop at the air-wall interface of the nasal mucosa. Simulations during quiet breathing revealed wall shear stresses as high as 0.3 Pa in the noselike model and 1.5 Pa in the anatomical model. These values are of the same order of those known to exist in uniform large arteries. The distribution of temperature near the nasal wall at peak inspiration is similar to that of wall shear stresses. The lowest temperatures occur in the vicinity of high stresses due to the narrow passageway in these locations. Time and spatial gradients of these stresses may have functional effects on nasal sensation of airflow and may play a role in the well-being of nasal breathing.

The air-conditioning capacity of the human nose.

The nose is the front line defender of the respiratory system. Unsteady simulations in three-dimensional models have been developed to study transport patterns in the human nose and its overall air-conditioning capacity. The results suggested that the healthy nose can efficiently provide about 90% of the heat and the water fluxes required to condition the ambient inspired air to near alveolar conditions in a variety of environmental conditions and independent of variations in internal structural components. The anatomical replica of the human nose showed the best performance and was able to provide 92% of the heating and 96% of the moisture needed to condition the inspired air to alveolar conditions. A detailed analysis explored the relative contribution of endonasal structural components to the air-conditioning process. During a moderate breathing effort, about 11% reduction in the efficacy of nasal air-conditioning capacity was observed.

Air-conditioning characteristics of the human nose.

Nasal inspiration is important for maintaining the internal milieu of the lung, since ambient air is conditioned to nearly alveolar conditions (body temperature and fully saturated with water vapour) upon reaching the nasopharynx. This literature review of the existing in vivo, in vitro and computational studies on transport phenomena that take place within the human nasal cavity summarizes the current knowledge on air-conditioning characteristics of the human nose.