Chuong Ngo

RWTH Aachen University · Helmholtz Institute of Biomedical Engineering

Background and objectiveSickle cell disease (SCD) is a very common autosomal recessive hemoglobinopathy leading to multiple pulmonary complications that are closely associated with mortality. The pathophysiology of chronic pulmonary involvement is not yet fully understood and no specific therapies are available.Methods The aim of this cross-section...

Electrical impedance tomography (EIT) is an imaging modality that can estimate a visualization of the conductivity distribution inside the human body. However, the spatial resolution of EIT is limited because measurements are sensitive to noise. We investigate a technique to incorporate a priori information into the EIT reconstructions of the D-Bar...

Introduction Aging is accompanied by changes in muscle mass, strength and loss of sensory, visual and auditive functions. However, these changes do not occur linearly, most spatiotemporal gait parameters change with aging. Age simulation suits have been invented to give young people an impression of the implications of being older and may be a usef...

For many elderly, wheeled rollators play an essential role in everyday life’s mobility. In addition, exoskeletons are increasingly used in daily mobility as well as in rehabilitation therapy. We present a motorized rollator to combine the advantages of both support devices. Based on the developed hardware, we design two model-based control concepts...

Active lower limb exoskeletons are increasingly used in rehabilitation therapy. An important aspect and ongoing research topic in developing such assistive devices is safe human–machine interaction. Another major challenge in the control of exoskeletons is determining the subject's intention to move for providing cooperative assistance. To address...

Walking gait correction is fundamental to restoring body motion function for patients. Functional Electrical Stimulation (FES) is regarded as a promising method and essential to Neurotherapy, and the exoskeleton is fast becoming a key instrument in rehabilitation. Applying FES or exoskeleton alone, however, has its inherent disadvantages. Therefore...

Lyapunov exponent is a promising parameter to ascertain the stability of the human gait. In this work, we use a time-series model based on a second-order delay-system with inertial measurement units placed on the foot and wrist. Stability is analyzed in a localized sense, with the Lyapunov exponent computed in the temporal region between two heel-s...

In this work, we evaluated the possibility to use synthesized IMU data for training a deep neural network to generate a more complex, full-body description of the human gait in terms of joint angle trajectories from a sparse sensor setup. In this context, a sparse sensor setup consists of a few sensors attached to human body segments in an unobtrus...

Gait behavior is considered an important indicator for the assessment of the general health status and provides a diagnostic observation for neuro-degenerative and musculo-skeletal diseases. Individual changes in gait behavior often reflect a deterioration of the current health status in a general sense and therefore provide significant information...

Step Length is an important metric that can be used for the analysis and assessment of the gait. Proper dynamical models are not available in current literature associated with the wrist that can adequately determine the step length using recursive estimation techniques. This study presents a method to estimate the step length using angular velocit...

Electrical Impedance Myography (EIM) is a painless and non-invasive approach for quantitative assessment of muscle-condition of the limbs, which is based on consideration of dielectric tissue properties. The purpose of this work is to analyse the impact of isometric (constant muscle length) and isotonic (constant muscle force) contraction on the re...

The determination of step length, an important gait parameter, has been a challenging task. Although unobtrusive sensors (inertial measurement units) have been developed recently, they cannot facilitate the automatic estimation of step length. In this article, we use a model-based technique to determine the step length using the Unscented Kalman Fi...

Background: Electrical Impedance Tomography (EIT) is a radiation-free technique for image reconstruction. However, as the inverse problem of EIT is non-linear and ill-posed, the reconstruction of sharp conductivity images poses a major problem. With the emergence of artificial neural networks (ANN), their application in EIT has recently gained inte...

The detection of muscle contraction and the estimation of muscle force are essential tasks in robot-assisted rehabilitation systems. The most commonly used method to investigate muscle contraction is surface electromyography (EMG), which, however, shows considerable disadvantages in predicting the muscle force, since unpredictable factors may influ...

Creating highly functional prosthetic, orthotic, and rehabilitation devices is a socially relevant scientific and engineering task. Currently, certain constraints hamper the development of such devices. The primary constraint is the lack of an intuitive and reliable control interface working between the organism and the actuator. The critical point...

The electrical impedance myography method is widely used in solving bionic control problems and consists of assessing the change in the electrical impedance magnitude during muscle contraction in real time. However, the choice of electrode systems sizes is not always properly considered when using the electrical impedance myography method in the ex...

The step length is an important parameter in gait analysis. Long-term monitoring applications for gait analysis are often based on inertial measurement units (IMUs) due to their low-cost and unobtrusive nature. Spatial gait parameters, such as step or stride length, are therefore not directly accessible. In this contribution, we focus on model-base...

The goal of this work is to design a Finite Element Method model enabling the simulation of the impact of muscle activity onto current density distribution, which is established by far-current electrode placement. Here assumed as an alteration in el. conductivity within specific muscle groups, coupled to increasing perfusion during repetitive tasks...

The control of the ankle joint induced by functional electrical stimulation (FES) is especially for paraplegic patients of high interest as it allows to partly re-gain the functionality of the lower limb. For this reason, we developed a Simulink model of the ankle joint which describes the dynamic behavior regarding the activation and force develop...

The lower limb exoskeleton investigated in this work actively supports the knee and hip and is intended to provide full motion support during gait. Parallel elastic actuators are integrated into the hip joints to improve the energy efficiency in gait. The prototype was tested in sit-to-stand and gait trials, in which the actuators were cascade-cont...

Body sensor networks (BSNs) represent an important research tool for exploring novel diagnostic or therapeutic approaches. They allow for integrating different measurement techniques into body-worn sensors organized in a network structure. In 2011, the first Integrated Posture and Activity Network by MedIT Aachen (IPANEMA) was introduced. In this w...

This paper investigates a closed-loop torque-controlled variable stiffness actuator (VSA) combined with a disturbance observer for enhancing low output impedance. We implement the generalized extended state observer (GESO) for conveniently testing the stability of the time-varying VSA system. In our application, the GESO is also required to serve t...

Compliant actuators have been increasingly used for active joints in lower-limb exoskeletons or orthoses because they help to guarantee a safe human interaction. One example of such compliant motors is the variable stiffness actuator (VSA). The design of a torque controller for such an actuator is a crucial task in order to provide patients with ph...

Parallel-elastic actuators (PEA) can provide efficiency advantages. In current designs clutches can fix or release the neutral position of the elasticity. The presented actuator combines a direct actuator with a serial-elastic actuator (SEA) in parallel. In addition to the efficiency advantages of a PEA, both actuators can also actively cooperate o...

Stride time variability is an important indicator for the assessment of gait stability. An accurate extraction of the stride intervals is essential for determining stride time variability. Peak detection is a commonly used method for gait segmentation and stride time estimation. Standard peak detection algorithms often fail due to additional moveme...

Variable stiffness actuators help to guarantee a safe human interaction when it is used as the active joints in lower-limb exoskeletons. Therefore, we designed a unilateral exoskeleton consisting of a mechanical-rotary variable impedance actuator (MeRIA) assisting the human knee. In this paper, a first walking trial with a healthy, human subject ha...

We present a novel application of the variable stiffness actuator (VSA)-based assistance/rehabilitation robot-featured impedance control using a cascaded position torque control loop. The robot follows the adaptive impedance control paradigm, thereby achieving an adaptive assistance level according to human joint torque. The feedforward human joint...

Various actuator topologies are discussed for the purpose of powering periodic processes and particularly walking robots. The Clutched Parallel Elastic Actuator (CPEA) is proposed to reduce the energy consumption of active exoskeletons. A nonlinear model of the CPEA is presented in addition to the mechanical design. The CPEA prototype is operated w...

Variable impedance actuators are widely used in tasks with an interaction between human and machine. In this paper, a mechanical-rotary variable impedance actuator (MeRIA), designed for knee or hip joint of a lower limb exoskeleton, is investigated. In the torque control loop of the MeRIA, a zero-torque controller is designed to achieve a low outpu...

Background and objective: This work introduces an object-oriented computational model to study cardiopulmonary interactions in humans. Methods: Modeling was performed in object-oriented programing language Matlab Simscape, where model components are connected with each other through physical connections. Constitutive and phenomenological equatio...

Background: Electrical impedance tomography (EIT) provides information on global and regional ventilation during tidal breathing and mechanical ventilation. During forced expiration maneuvers, the linearity of EIT and spirometric data has been documented in healthy persons. The present study investigates the potential diagnostic use of EIT in pedia...

This paper describes a novel extension of the Forced Oscillation Technique (FOT), namely the volume-dependent Forced Oscillation Technique (v-FOT). This extension is based on the measurement of the respiratory impedance over the whole lung volume. A new measurement protocol was introduced: subjects breathe slowly from residual volume to total lung...

There is a lack of noninvasive pulmonary function tests which can assess regional information of the lungs. Electrical impedance tomography (EIT) is a radiation-free, non-invasive real-time imaging that provides regional information of ventilation volume regarding the measurement of electrical impedance distribution. Forced oscillation technique (F...

The forced oscillation technique (FOT) is a non-invasive pulmonary function test which is based on the measurement of respiratory impedance. Recently, promising results were obtained by the application of FOT on patients with respiratory failure and obstructive sleep apnea (OSA). By using a nasal mask instead of a mouthpiece, the influences of the...

Electrical impedance tomography (EIT) provides global and regional information about ventilation by means of relative changes in electrical impedance measured with electrodes placed around the thorax. In combination with lung function tests, e.g. spirometry and body plethysmography, regional information about lung ventilation can be achieved. Imped...

We introduce a novel comprehensive model of the cardiopulmonary system with emphasis on perfusion and ventilation distribution along the vertical thorax axis under the gravity effect. By using an object-oriented environment, the complex physiological system can be represented by a network of electrical, lumped-element compartments. The lungs are di...

Background: Electrical impedance tomography (EIT) delivers information about global and regional ventilation. Linearity of EIT during tidal breathing is known. We investigated the feasibility of EIT during lung function tests in pediatric patients with cystic fibrosis (CF) and healthy controls. Methods: Eleven CF patients and 11 age-matched cont...

Introduction: Electrical Impedance Tomography (EIT) is a tomographic, radiation-free technique based on the injection of a harmless alternating current. Objective: As electrical impedance strictly correlates with the variation of air content, EIT delivers highly dynamic information about global and regional ventilation. We want to demonstrate th...

Respiratory impedance was measured in healthy subjects using Forced Oscillation Technique (FOT). Measurements with a FOT system were performed for five healthy male adults. Based on these measurements, we compared parameter estimation approaches in frequency and time domain. In frequency domain, the fast Fourier transform and windowed cosine fittin...

We introduce a new sophisticated model of the cardiopulmonary system. The model consists of the heart, circulation and respiration systems with emphasis on the cardiopulmonary interaction. Heart and lungs are anatomically and physically coupled through the intra-thoracic pressure since they are both located in the same chest cavity. A novel extende...

Zusammenfassung Das Ziel der ereignisbasierten Regelung ist die Verringerung des Kommunikationsaufwands innerhalb eines Regelkreises, indem die Rückführung nur dann geschlossen wird, wenn ein Ereignis eine hinreichend große Regelabweichung anzeigt. In diesem Beitrag werden Bedingungen für die Struktur einer ereignisbasierten Regelung gekoppelter Sy...