Publications
The use of actograph in the assessment of fetal wellbeing
J Lai, R Vaidyanathan, NC Nowlan, CC Lees
The Journal of Maternal-Fetal & Neonatal Medicine
DOI: 10.1080/14767058.2018.1540584
Publication Year: 2019 , Page(s): 1-6 vol.
Tags: Fetal health; prenatal care; medical instrumentation; signal processing; c
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Purpose: Third trimester maternal perception of fetal movements is often used to assess fetal well-being. However, its true clinical value is unknown, primarily because of the variability in subjective quantification. The actograph, a technology available on most cardiotocograph machines, quantifies movements, but has never previously been investigated in relation to fetal health and existing monitoring devices. The objective of this study was to quantify actograph output in healthy third trimester pregnancies and investigate this in relation to other methods of assessing fetal well-being.

Methods: Forty-two women between 24 and 34 weeks of gestation underwent ultrasound scan followed by a computerized cardiotocograph (CTG). Post capture analysis of the actograph recording was performed and expressed as a percentage of activity over time. The actograph output results were analyzed in relation to Doppler, ultrasound and CTG findings expressed as z-score normalized for gestation.

Results: There was a significant association between actograph output recording and estimated fetal weight Z-score (R¼0.546, p  .005). This activity was not related to estimated fetal weight. Increased actograph activity was negatively correlated with umbilical artery pulsatility index Z-score (R ¼ 0.306, p ¼ .049) and middle cerebral artery pulsatility index Z-score.

Conclusion: Fetal movements assessed by the actograph are associated both with fetal size in relation to gestation and fetoplacental Doppler parameters. It is not the case that larger babies move more, however, as the relationship with actograph output related only to estimated fetal weight z-score. These findings suggest a plausible link between the frequency of fetal movements and established markers of fetal health.

Rationale: The objective of this study was to quantify actograph output in healthy third trimester pregnancies and investigate this in relation to other methods of assessing fetal well-being. This is a widely available method of assessing fetal movements objectively, which has been shown to be an important marker of fetal health. This research is novel in the fact that actograph has never been truly investigated in relation to fetal well-being, despite being available on most cardiotocograph (CTG) machines. Our results show that fetal movements assessed by the actograph are associated both with fetal size in relation to gestation and fetoplacental Doppler parameters. If this proves to be true, smaller babies that move less maybe at particular perinatal risk.

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Segmenting Mechanomyography Measures of Muscle Activity Phases Using Inertial Data
RB Woodward, MJ Stokes, SJ Shefelbine, R Vaidyanathan
Nature: Scientific Reports
DOI: 10.1038/s41598-019-41860-4
Publication Year: 2019 , Page(s): 1-10 vol.9 (1)
Tags: Inertial Measurement, Physiological Monitoring, Fatigue Monitoring, Medical Instrumentation, MMG, EMG, Wearable Sensors,
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Electromyography (EMG) is the standard technology for monitoring muscle activity in laboratory environments, either using surface electrodes or fine wire electrodes inserted into the muscle. Due to limitations such as cost, complexity, and technical factors, including skin impedance with surface EMG and the invasive nature of fine wire electrodes, EMG is impractical for use outside of a laboratory environment. Mechanomyography (MMG) is an alternative to EMG, which shows promise in pervasive applications. The present study used an exerting squat-based task to induce muscle fatigue. MMG and EMG amplitude and frequency were compared before, during, and after the squatting task. Combining MMG with inertial measurement unit (IMU) data enabled segmentation of muscle activity at specific points: entering, holding, and exiting the squat. Results show MMG measures of muscle activity were similar to EMG in timing, duration, and magnitude during the fatigue task. The size, cost, unobtrusive nature, and usability of the MMG/IMU technology used, paired with the similar results compared to EMG, suggest that such a system could be suitable in uncontrolled natural environments such as within the home.

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Formulation of a new gradient descent MARG orientation algorithm: Case study on robot teleoperation
S Wilson, H Eberle, Y Hayashi, S O.H. Madgwick, A McGregor, X Jing, R Vaidyanathan
Mechanical Systems and Signal Processing
DOI: 10.1016/j.ymssp.2019.04.064
Publication Year: 2019 , Page(s): 183-200 vol.130
Tags: Inertial Measurement, Robot Teleportation, Manipulation, Physiological Monitoring, MMG, EMG, Wearable Sensors
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We introduce a novel magnetic angular rate gravity (MARG) sensor fusion algorithm for inertial measurement. The new algorithm improves the popular gradient descent (Ê»Madgwick’) algorithm increasing accuracy and robustness while preserving computational efficiency. Analytic and experimental results demonstrate faster convergence formultiple variations of the algorithm through changing magnetic inclination.  Furthermore, decoupling of magnetic field variance from roll and pitch estimation is proven for enhanced robustness. The algorithm is validated in a human-machine interface (HMI) case study. The case study involves hardware implementation for wearable robot teleoperation in both Virtual Reality (VR) and in real-time on a 14 degree-of-freedom(DoF) humanoid robot. The experiment fuses inertial (movement) and mechanomyography(MMG) muscle sensing to control robot arm movement and grasp simultaneously, demonstrating algorithm efficacy and capacity to interface with other physiological sensors. To our knowledge, this is the first such formulation and the first fusion of inertial measurement and MMG in HMI. We believe the new algorithm holds the potential to impact a verywide range of inertial measurement applications where full orientation necessary. Physiological sensor synthesis and hardware interface further provides a foundation forrobotic teleoperation systems with necessary robustness for use in the field.

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Fusion of Enhanced and Synthetic Vision System Images for Runway and Horizon Detection
A F Fadhil, R Kanneganti, L Gupta, H Eberle, R Vaidyanathan
Sensors
DOI: 10.3390/s19173802
Publication Year: 2019 , Page(s): 1-17 vol.19
Tags: unmanned air vehicles (UAV); sensing; intelligent transportation; image fusion; signal alignment; runway detection; image registration; wavelet transform; Hough transform
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Networked operation of unmanned air vehicles (UAVs) demands fusion of information from disparate sources for accurate flight control. In this investigation, a novel sensor fusion architecture for detecting aircraft runway and horizons as well as enhancing the awareness of surrounding terrain is introduced based on fusion of enhanced vision system (EVS) and synthetic vision system (SVS) images. EVS and SVS image fusion has yet to be implemented in real-world situations due to signal misalignment. We address this through a registration step to align EVS and SVS images. Four fusion rules combining discrete wavelet transform (DWT) sub-bands are formulated, implemented, and evaluated. The resulting procedure is tested on real EVS-SVS image pairs and pairs containing simulated turbulence. Evaluations reveal that runways and horizons can be detected accurately even in poor visibility. Furthermore, it is demonstrated that different aspects of EVS and SVS images can be emphasized by using different DWT fusion rules. The procedure is autonomous throughout landing, irrespective of weather. The fusion architecture developed in this study holds promise for incorporation into manned heads-up displays (HUDs) and UAV remote displays to assist pilots landing aircraft in poor lighting and varying weather. The algorithm also provides a basis for rule selection in other signal fusion applications.

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Performance of a wearable acoustic system for fetal movement discrimination
Jonathan Lai, Richard Woodward, Yuriy Alexandrov, Qurratul ain Munnee, Christoph C. Lees, Ravi Vaidyanathan , Niamh C. Nowlan
PLOS One
DOI: 10.1371/journal.pone.0195728
Publication Year: 2018 , Page(s): 1-14 vol.13
Tags: Wearable Sensors, Inertial Measurement, Fetal Health, Sensor Fusion
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Fetal movements (FM) are a key factor in clinical management of high-risk pregnancies such as fetal growth restriction. While maternal perception of reduced FM can trigger self-referral to obstetric services, maternal sensation is highly subjective. Objective, reliable monitoring of fetal movement patterns outside clinical environs is not currently possible. A wearable and non-transmitting system capable of sensing fetal movements over extended periods of time would be extremely valuable, not only for monitoring individual fetal health, but also for establishing normal levels of movement in the population at large. Wearable monitors based on accelerometers have previously been proposed as a means of tracking FM, but such systems have difficulty separating maternal and fetal activity and have not matured to the level of clinical use. We introduce a new wearable system based on a novel combination of accelerometers and bespoke acoustic sensors as well as an advanced signal processing architecture to identify and discriminate between types of fetal movements. We validate the system with concurrent ultrasound tests on a cohort of 44 pregnant women and demonstrate that the garment is capable of both detecting and discriminating the vigorous, whole-body ‘startle’ movements of a fetus. These results demonstrate the promise of multimodal sensing for the development of a low-cost, non-transmitting wearable monitor for fetal movements.

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A biomimicking design for mechanical knee joints
Felix Russell, Yipeng Zhu, William Hey, Ravi Vaidyanathan, Peter Ellison
Bioinspration and Biomimetics
DOI: 10.1088/1748-3190/aad39d
Publication Year: 2018 , Page(s): 1-13 vol.13:5
Tags: biomimetics, biomechanics, robotics, ligaments, above knee prostheses, condylar knee, lower limb
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We present a new bioinspired bicondylar knee joint that requires a smaller actuator size when compared to a constant moment arm joint. Unlike existing prosthetic joints, the proposed mechanism replicates the elastic, rolling and sliding elements of the human knee. As a result, the moment arm that the actuators can impart on the joint changes as function of the angle, producing the equivalent of a variable transmission. By employing a similar moment arm—angle profile as the human knee the peak actuator force for stair ascent can be reduced by 12% compared to a constant moment arm joint addressing critical impediments in weight and power for robotics limbs. Additionally, the knee employs mechanical 'ligaments' containing stretch sensors to replicate the neurosensory and compliant elements of the joint. We demonstrate experimentally how the ligament stretch can be used to estimate joint angle, therefore overcoming the difficulty of sensing position in a bicondylar joint.

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A Kinematic Model for the Design of a Bicondylar Mechanical Knee
Felix Russell, Ravi Vaidyanathan, Peter Ellison
2018 7th IEEE International Conference on Biomedical Robotics and Biomechatronics (Biorob)
DOI: 10.1109/BIOROB.2018.8487734
Publication Year: 2018 , Page(s): 750-755 vol.
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In this paper we present a design methodology for a bicondylar joint that mimics many of the physical mechanisms in the human knee. We replicate the elastic ligaments and sliding and rolling joint surfaces. As a result the centre of rotation and moment arm from the quadriceps changes as a function of flexion angle in a similar way to the human knee. This leads to a larger moment arm in the centre of motion, where it is most needed for high load tasks, and a smaller moment arm at the extremes, reducing the required actuator displacement. This is anticipated to improve performance:weight ratio in legged devices for tasks such as stair accent and sit-to-stand. In the design process ligament attachment positions, femur profile and ligament lengths were taken from cadaver studies. This information was then used as inputs to a simplified kinematic computer model in order to design a valid profile for a tibial condyle. A physical model was then tested on a custom built squatting robot. It was found that although ligament lengths deviated from the designed values the robot moment arm still matched the model to within 6.1% on average. This shows that the simplified model is an effective design tool for this type of joint. It is anticipated that this design, when employed in walking robots, prostheses or exoskeletons, will improve the high load task capability of these devices. In this paper we have outlined and validated a design method to begin to achieve this goal.

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Unilateral Inertial and Muscle Activity Sensor Fusion for Gait Cycle Progress Estimation
Christopher Caulcrick, Felix Russell, Samuel Wilson, Caleb Sawade, and Ravi Vaidyanathan
2018 7th IEEE International Conference on Biomedical Robotics and Biomechatronics (Biorob)
DOI: 10.1109/BIOROB.2018.8487936
Publication Year: 2018 , Page(s): 1151 - 1156 vol.
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This paper introduces a method which uses feedforward neural networks (FNNs) for estimating gait cycle progress using data recorded from inertial and muscle activity sensors attached to one side of the lower body. Three-axis inertial measurement unit (IMU) readings from accelerometers and gyroscopes located above the outer ankle and knee were fused with mechanomyogram (MMG) sensor readings from across major muscle groups on the left leg. Validation was against ground truth gathered concurrently with VICON motion capture. The performance was characterised by rms error (Erms) and max error (Emax), averaged across four cross-validated trials, and enhanced by adjusting number of sliding window frames and hidden layer neurons. The final configuration estimated gait cycle progress with Erms of 1.6% and Emax of 6.8%. This demonstrates promise for such a method to be used for control of unilateral robotic prostheses and exoskeletons, providing state estimation of gait progress from low power sensors limited to one side of the lower body.

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Gait Analysis Using Pervasive Motion Tracking and Mechanomyography Fusion
R Woodward, S Shefelbine, R Vaidyanathan
IEEE Transactions on Mechatronics
DOI: 10.1109/TMECH.2017.2715163
Publication Year: 2017 , Page(s): 2022-2033 vol.22
Tags: Gait Analysis, Wearable Sensors, Mechanomyography, Inertial Measurement Unit, Pervasive Monitoring, Heterogeneous Sensing
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Muscle activity and human motion are useful parameters to map the diagnosis, treatment, and rehabilitation of neurological and movement disorders. In laboratory and clinical environments, electromyography (EMG) and motion capture systems enable the collection of accurate, high resolution data on human movement and corresponding muscle activity. However, controlled surroundings limit both the length of time and the breadth of activities that can be measured. Features of movement, critical to understanding patient progress, can change during the course of a day and daily activities may not correlate to the limited motions examined in a laboratory. We introduce a system to measure motion and muscle activity simultaneously over the course of a day in an uncontrolled environment with minimal preparation time and ease of implementation that enables daily usage. Our system combines a bespoke inertial measurement unit (IMU) and mechanomyography (MMG) sensor, which measures the mechanical signal of muscular activity. The IMU can collect data continuously, and transmit wirelessly, for up to 10 hours. We describe the hardware design and validation and outline the data analysis (including data processing and activity classification algorithms) for the sensing system. Furthermore, we present two pilot studies to demonstrate utility of the system, including activity identification in six able-bodied subjects with an accuracy of 98%, and monitoring motion/muscle changes in a subject with cerebral palsy and of a single leg amputee over extended periods (~5 hours). We believe these results provide a foundation for mapping human muscle activity and corresponding motion changes over time, providing a basis for a range of novel rehabilitation therapies.

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Telehealth, Wearable Sensors, and the Internet: Will They Improve Stroke Outcomes Through Increased Intensity of Therapy, Motivation, and Adherence to Rehabilitation Programs?
Burridge JH, Lee ACW, Turk R, Stokes M, Whitall J, Vaidyanathan R, Clatworthy P, Hughes AM, Meagher C, Franco E, Yardley L
Journal of Neurologic Physical Therapy
DOI: 10.1097/NPT.0000000000000183
Publication Year: 2017 , Page(s): S32-S38 vol.41
Tags: Rehabilitation, Wearable Sensors, Muscle Myography, Stroke, Telehealth
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BACKGROUND AND PURPOSE:

Stroke, predominantly a condition of older age, is a major cause of acquired disability in the global population and puts an increasing burden on health care resources. Clear evidence for the importance of intensity of therapy in optimizing functional outcomes is found in animal models, supported by neuroimaging and behavioral research, and strengthened by recent meta-analyses from multiple clinical trials. However, providing intensive therapy using conventional treatment paradigms is expensive and sometimes not feasible because of social and environmental factors. This article addresses the need for cost-effective increased intensity of practice and suggests potential benefits of telehealth (TH) as an innovative model of care in physical therapy.

SUMMARY OF KEY POINTS:

We provide an overview of TH and present evidence that a web-supported program, used in conjunction with constraint-induced therapy (CIT), can increase intensity and adherence to a rehabilitation regimen. The design and feasibility testing of this web-based program, "LifeCIT," is presented. We describe how wearable sensors can monitor activity and provide feedback to patients and therapists. The methodology for the development of a wearable device with embedded inertial and mechanomyographic sensors, algorithms to classify functional movement, and a graphical user interface to present meaningful data to patients to support a home exercise program is explained.

RECOMMENDATIONS FOR CLINICAL PRACTICE:

We propose that wearable sensor technologies and TH programs have the potential to provide most-effective, intensive, home-based stroke rehabilitation.

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