Showing papers in "Journal of Medical Engineering & Technology in 2007"

Online fingerprint verification.

Abstract: As organizations search for more secure authentication methods for user access, e-commerce, and other security applications, biometrics is gaining increasing attention. With an increasing emphasis on the emerging automatic personal identification applications, fingerprint based identification is becoming more popular. The most widely used fingerprint representation is the minutiae based representation. The main drawback with this representation is that it does not utilize a significant component of the rich discriminatory information available in the fingerprints. Local ridge structures cannot be completely characterized by minutiae. Also, it is difficult quickly to match two fingerprint images containing different number of unregistered minutiae points. In this study filter bank based representation, which eliminates these weakness, is implemented and the overall performance of the developed system is tested. The results have shown that this system can be used effectively for secure online verification applications.

The false premise in measuring body-support interface pressures for preventing serious pressure ulcers.

Abstract: Presently, commercial cushioning products for pressure ulcer prevention are being evaluated for their protective effect exclusively based on interfacial pressures between the cushion/mattress and the patient. However, interface pressures cannot predict elevated mechanical stresses in deep tissues adjacent to bony prominences. Such deep tissue stress concentrations are associated with local ischaemia and hypoxia, which over time result in deep tissue necrosis, particularly of muscle tissue. In order to demonstrate this phenomenon, a physical phantom of the mechanical interaction between the ischial tuberosities (IT) and gluteus muscles of the buttocks was built, incorporating geometric replica of the human IT and real (bovine) muscle tissue. Internal muscle stresses directly under the IT were five to 11-fold greater than stresses at more distal locations, and a Pearson correlation test showed that they could not have been predicted from the interface pressures in the phantom. Accordingly, though pressure u...

DWT-DCT hybrid scheme for medical image compression.

Abstract: With the development of communication technology the applications and services of health telemetics are growing. In view of the increasingly important role played by digital medical imaging in modern health care, it is necessary for large amount of image data to be economically stored and/or transmitted. There is a need for the development of image compression systems that combine high compression ratio with preservation of critical information. During the past decade wavelets have been a significant development in the field of image compression. In this paper, a hybrid scheme using both discrete wavelet transform (DWT) and discrete cosine transform (DCT) for medical image compression is presented. DCT is applied to the DWT details, which generally have zero mean and small variance, thereby achieving better compression than obtained from either technique alone. The results of the hybrid scheme are compared with JPEG and set partitioning in hierarchical trees (SPIHT) coder and it is found that the performa...

An investigation into the feasibility of locating portable medical devices using radio frequency identification devices and technology.

Abstract: Background and purpose: Portable medical devices represent an important resource for assisting healthcare delivery. The movement of portable devices often results in them being unavailable when needed. Tracking equipment using radiofrequency identification technology/devices (RFID) may provide a promising solution to the problems encountered in locating portable equipment.Methods: An RFID technology trial was undertaken at Royal Alexandra Hospital, Paisley. This involved the temporary installation of three active readers and attaching actively transmitting radio frequency tags to different portable medical devices. The active readers and computer system were linked using a bespoke data network. Tags and readers from two separate manufacturers were tested.Results: Reliability difficulties were encountered when testing the technology from the first manufacturer, probably due to the casing of the medical device interfering with the signal from the tag. Improved results were obtained when using equipment from...

Micro robot prototype for colonoscopy and in vitro experiments.

Abstract: For actively diagnosing the colon's pathologies micro-invasively or non-invasively, an autonomous prototype of the earthworm-like robot for colonoscopy was designed according to the principle of bionics, and manufactured using precision process technology. In vitro experiments in pig colon were carried out. The micro robot was driven directly by an electromagnetic linear driver. The mobile cells were joined with joints of two degrees of freedom, and the whole body was flexible. The direction of movement and the angle of imaging can be controlled by the shape memory alloy (SMA). In experiments, locomotion efficient and locomotion ability was analysed carefully. Locomotion force and velocity were tested. In vitro experiments in pig colon demonstrated that the micro robot can navigate though the colon by itself reliably and freely, which will be useful for the application of the robot to colonoscopy in the clinic.

Effect of coating thickness and its material on the stress distribution for dental implants.

Abstract: Dental implants have been increasingly used to recover the masticatory function of lost teeth. It has been well known that the success of a dental implant is heavily dependent on initial stability and long-term osseointegration due to optimal stress distribution in the surrounding bones by the concept implant surface coating. Hydroxyapatite (HAP), as a coating material, has been widely used in dentistry due to its biocompatibility. Some investigations show a benefit of coating dental implants with HAP, and others concluded that HAP coating reduces the long-term implant survival. Therefore, the aim of this investigation is to design a new functionally graded dental implant coating, as well as studying the effect of coating thickness on the maximum von Mises stresses in bone adjacent to the coating layer. The gradation of the elastic modulus is changed along the longitudinal direction. Stress analysis using a finite element method showed that using a coating thickness of 150 µm, functionally graded from tit...

Development of a fibre optic goniometer system to measure lumbar and hip movement to detect activities and their lumbar postures

Abstract: If sitting postures influence the risk of developing low back pain then it is important that quantification of sedentary work activities and simultaneous measurement of lumbar postural characteristics takes place. The objective of this study was to develop a system for identifying activities and their associated lumbar postures using fibre optic goniometers (FOGs). Five student subjects wore two FOGs attached to the lumbar spine and hip for 8 min while being recorded using a video camera when sitting, standing and walking. Observer Software was used to code the video recording, enabling the sagittal movement characteristics of each FOG to be described for individual activities. Results indicated that each activity produced unique data, and could be independently identified from their motion profiles by three raters (k = 1). The data will be used to develop algorithms to automate the process of activity detection. This system has the potential to measure behaviour in non-clinical settings.

A hybrid ECG compression algorithm based on singular value decomposition and discrete wavelet transform.

Abstract: Increasing use of computerized ECG processing systems requires effective electrocardiogram (ECG) data compression techniques which aim to enlarge storage capacity and improve data transmission over phone and internet lines. This paper presents a compression technique for ECG signals using the singular value decomposition (SVD) combined with discrete wavelet transform (DWT). The central idea is to transform the ECG signal to a rectangular matrix, compute the SVD, and then discard small singular values of the matrix. The resulting compressed matrix is wavelet transformed, thresholded and coded to increase the compression ratio. The number of singular values and the threshold level adopted are based on the percentage root mean square difference (PRD) and the compression ratio required. The technique has been tested on ECG signals obtained from MIT-BIH arrhythmia database. The results showed that data reduction with high signal fidelity can thus be achieved with average data compression ratio of 25.2:1 and av...

Strategies to identify changes in SEMG due to muscle fatigue during cycling

Abstract: Detection, quantification and analysis of muscle fatigue are crucial in occupational/rehabilitation and sporting settings. Sports organizations such as the Australian Institute of Sports (AIS) currently monitor fatigue by a battery of tests including invasive techniques that require taking blood samples and/or muscle biopsies, the latter of which is highly invasive, painful, time consuming and expensive. SEMG is non-invasive monitoring of muscle activation and is an indication of localized muscle fatigue based on the observed shift of the power spectral density of the SEMG. But the success of SEMG based techniques is currently limited to isometric contraction and is not acceptable to the human movement community. This paper proposes and tests the use of spectral analysis of narrow windows of SEMG near the peak of a cyclic activity to identify the onset of muscle fatigue during cyclic activities. The results demonstrate a highly significant relationship of reduction of the median frequency with the onset of muscle fatigue. The paper also reports the validation of the SEMG study using biochemical analysis of muscle biopsy and blood tests and further verified using power output of the cycle and speed of pedalling.

Performance of glucose dehydrogenase (GDH) based and glucose oxidase (GOX) based blood glucose meter systems at moderately high altitude.

Abstract: Objective: Self-monitoring of blood glucose (SMBG) is a fairly efficient method of preventing hypoglycaemia in diabetic patients. Blood glucose meters (BGMs) are influenced by factors such as altitude, temperature, blood oxygen concentration, low atmospheric pressure or humidity. In this study we aimed at evaluating the performance of glucose dehydrogenase (GDH) or glucose oxidase (GOX) based glucometers at moderately high altitude.Method: A total of 286 female or male patients, most of whom had type 2 diabetes, were included in this study. The simultaneous readings made by two different glucometers were compared with the readings made at the reference laboratory.Results: Blood glucose levels measured by a GDH based glucometer at moderately high altitude were significantly (p = 0.007) higher compared to those measured at the reference laboratory. Although blood glucose levels measured by a GOX based glucometer were lower compared to those measured at the reference laboratory, the difference was not signif...

Extraction and reconstruction of retinal vasculature.

Abstract: Information about retinal vasculature morphology is used in grading the severity and progression of diabetic retinopathy. An image analysis system can help ophthalmologists make accurate and efficient diagnoses. This paper presents the development of an image processing algorithm for detecting and reconstructing retinal vasculature. The detection of the vascular structure is achieved by image enhancement using contrast limited adaptive histogram equalization followed by the extraction of the vessels using bottom-hat morphological transformation. For reconstruction of the complete retinal vasculature, a region growing technique based on first-order Gaussian derivative is developed. The technique incorporates both gradient magnitude change and average intensity as the homogeneity criteria that enable the process to adapt to intensity changes and intensity spread over the vasculature region. The reconstruction technique reduces the required number of seeds to near optimal for the region growing process. It a...

Computer aided analysis of phonocardiogram

Abstract: In the present paper analysis of phonocardiogram (PCG) records are presented. The analysis has been carried out in both time and frequency domains with the aim of detecting certain correlations between the time and frequency domain representations of PCG. The analysis is limited to first and second heart sounds (S1 and S2) only. In the time domain analysis the moving window averaging technique is used to determine the occurrence of S1 and S2, which helps in determination of cardiac interval and absolute and relative time duration of individual S1 and S2, as well as absolute and relative duration between them. In the frequency domain, fast Fourier transform (FFT) of the complete PCG record, and short time Fourier transform (STFT) and wavelet transform of individual heart sounds have been carried out. The frequency domain analysis gives an idea about the dominant frequency components in individual records and frequency spectrum of individual heart sounds. A comparative observation on both the analyses gives...

The DETECT™ System: portable, reduced-length neuropsychological testing for mild traumatic brain injury via a novel immersive environment

Abstract: Undiagnosed mild traumatic brain injury (mTBI) often leads to poor patient management and significant morbidity. The lack of an efficient screening tool is especially apparent in the athletic setti...

Time-frequency characterization of atrial fibrillation from surface ECG based on Hilbert-Huang transform

Abstract: In this paper, based on Hilbert-Huang transform (HHT), we develop a new non-invasive time-frequency analysis method to characterize the dynamic behaviour of atrial fibrillation (AF) from surface ECG. We first extract f waves from single-lead ECG records of AF patients using PCA analysis. To capture the non-stationary behaviours of AF signals at different time scales, we use HHT to find the Hilbert spectrum and instantaneous frequency (IF) distribution of residual signals from principal component analysis. Two important feature variables, namely mean IF (mIF) and index of frequency stability over time (IS), are derived from the IF distribution, and in combination will be able to effectively discriminate two different AF types: self-terminating and non-terminating termination. The proposed AF signal decomposition and analysis method will help us efficiently differentiate individual AF patients, advance our understanding of AF mechanisms, and provide useful guidelines for improving administration of AF patients, especially paroxysmal AF.

Computer-aided oral implantology: methods and applications

Abstract: Aiming at transferring the preoperative planning information to the patient in oral implantology, this study presents an image guided oral implant system (IGOIS), which integrates 3D medical modelling, preoperative surgical planning and intraoperative tracking into a dental navigation system With the fabrication of a tooth-supported polymer resin template, a non-invasive point-based registration method through ICP algorithm is explicitly discussed The experimental test shows that deviation between planned and achieved position of the implant is 12 mm at the tip and 13 mm at the head, which thereby demonstrates that IGOIS can reach a level of accuracy where further clinical developments are feasible

Speckle reduction in ultrasound medical images using adaptive filter based on second order statistics.

Abstract: This article discusses an adaptive filtering technique for reducing speckle using second order statistics of the speckle pattern in ultrasound medical images. Several region-based adaptive filter techniques have been developed for speckle noise suppression, but there are no specific criteria for selecting the region growing size in the post processing of the filter. The size appropriate for one local region may not be appropriate for other regions. Selection of the correct region size involves a trade-off between speckle reduction and edge preservation. Generally, a large region size is used to smooth speckle and a small size to preserve the edges into an image. In this paper, a smoothing procedure combines the first order statistics of speckle for the homogeneity test and second order statistics for selection of filters and desired region growth. Grey level co-occurrence matrix (GLCM) is calculated for every region during the region contraction and region growing for second order statistics. Further, these GLCM features determine the appropriate filter for the region smoothing. The performance of this approach is compared with the aggressive region-growing filter (ARGF) using edge preservation and speckle reduction tests. The processed image results show that the proposed method effectively reduces speckle noise and preserves edge details.

A new method for selective measurement of joint movement in hand tremor in Parkinson's disease patients

Abstract: Parkinson's disease (PD) is a progressive degenerative disorder of the central nervous system with tremor being one of its four main clinical features. Currently used methods can directly evaluate tremor amplitude and frequency but not joint movement in the affected limb. Measurement of joint movement facilitates the location of muscle groups that participate in PD tremor and this is important for treatment with local botulinum toxin injections. We developed and tested a method that measured tremor amplitude and frequency in a specific joint of the hand in PD patients. The tremor analysis method was based on force transducers adapted to record rest tremor of the wrist and metacarpophalangeal joints in two degrees of freedom for each joint. Direct measurements of joint movement in the hand can evaluate tremor amplitude and frequency and also locate the muscle groups that are most active in tremor movement, thus enabling their local treatment.

Assessment and classification of normal and restrictive respiratory conditions through pulmonary function test and neural network

Abstract: In this work, an attempt to classify respiratory abnormality using a pulmonary function test and neural networks is reported. The flow – volume curves generated by spirometric pulmonary function tests were recorded from subjects under study. The pressure and resistance parameters were derived using theoretical approximation of the activation function representing the pressure – volume relationship of the lung. The pressure – time and resistance – expiration volume curves were obtained during maximum expiration. The derived values together with spirometric data were used for classification of normal and restrictive abnormality using feed forward network. Results demonstrate the ability of the proposed method in identifying and classifying pulmonary function data into normal and restrictive cases. The validity of the results was confirmed by measuring accuracy (92%), sensitivity (92.3%), specificity (91.6%) and adjusted accuracy (91.95%). As spirometric evaluation of human respiratory functions are essentia...

Electrical impedance plethysmography technique in estimating pulmonary function status.

Abstract: An attempt has been made to study the appropriateness of electrical impedance plethysmography (EIP) in detecting pulmonary health status. A feasibility study was conducted on normal, obstructive and restrictive subjects aged between 20 and 60 years. Quantitative assessment of pulmonary function was made by way of both EIP and pulmonary function tests (PFT). Amongst the various EIP parameters, a statistically significant difference was observed for the respiratory band power, between normal (129.7) and obstructive (35.8) subjects, indicating that this EIP variable can be used to distinguish between the two pulmonary function states. A significant positive correlation was observed between a spirometry parameter, peak expiratory flow rate (PEFR), and an EIP parameter, respiratory amplitude (r = 0.372, p < 0.05), thereby indicating that EIP information by way of respiratory amplitude is comparable to that provided by PEFR. Hence, both respiratory amplitude and respiratory band power were seen to provide usefu...

PIC microcontroller-based RF wireless ECG monitoring system.

Abstract: This paper presents a radio-telemetry system that provides the possibility of ECG signal transmission from a patient detection circuit via an RF data link. A PC then receives the signal through the National Instrument data acquisition card (NIDAQ). The PC is equipped with software allowing the received ECG signals to be saved, analysed, and sent by email to another part of the world. The proposed telemetry system consists of a patient unit and a PC unit. The amplified and filtered ECG signal is sampled 360 times per second, and the A/D conversion is performed by a PIC16f877 microcontroller. The major contribution of the final proposed system is that it detects, processes and sends patients ECG data over a wireless RF link to a maximum distance of 200 m. Transmitted ECG data with different numbers of samples were received, decoded by means of another PIC microcontroller, and displayed using MATLAB program. The designed software is presented in a graphical user interface utility.

A four-generation Ehlers-Danlos syndrome with vascular dissections. Skin ultrastructure and biomechanical properties.

Abstract: Ehlers-Danlos syndrome (EDS) is heterogenous with regard to genetic traits, clinical manifestation, the biomechanical and microscopic properties of connective tissues, and basic molecular defects. We report on nine relatives of four generations who suffered from large vessel dissections and cutaneous microscopic changes consistent with EDS. Measurements of the mechanical properties of skin were performed using a computerized suction device (Cutometer®). Morphological and biomechanical alterations suggestive of EDS were present in all examined subjects. A loose network of collagen bundles was admixed with clumsy elastic fibres. Factor XIIIa-positive dermal dendrocytes looked almost normal but were slim and rarefied in four subjects. The severity in ultrastructural alterations of the collagen network differed among the subjects. The group with the most prominent changes showed the most striking biomechanical alterations characterized by increased biologic elasticity without any excess in skin extensibility....

Electrical impedance signal analysis in assessing the possibility of non-invasive diagnosis of knee osteoarthritis

Abstract: Knee osteoarthritis (OA) is a degenerating disorder that leads to pain, disability and dependence. Although significant numbers of elderly people are affected by this irreversible damage, not many non-invasive methods have been found that can detect onset of OA. The traditional x-ray has the disadvantage of detecting a problem only after many changes have taken place. Others, such as MRI and ultrasound, are either expensive or unsuitable for mass screening and repeated use. In this paper, an attempt has been made to study the usefulness of electrical impedance plethysmography (EIP) in non-invasive diagnosis of knee OA. In two experiments on 10 OA knees and eight control knees in groups aged 45 - 65 years (OA group: 62.40 +/- 3.47 years, controls: 53.38 +/- 8.55 years), knee swing (active flexion and extension of leg in sitting position, KS) and normal walking (WN) electrical impedance changes (DeltaZ) around the knee were analysed. The results indicate that there is significant difference in amplitudes of signals. Difference in mean of variances of two groups was significant (p < 0.05) for KS and WN. The difference in the mean rms values was also significant (p < 0.05) for KS and WN. Impedance changes suggest that EIP signal around the knee have the potential for non-invasive diagnosis of knee OA.

A re-evaluation of modelling of the current flow between electrodes: consideration of blood flow and wounds.

Abstract: Electrical stimulation has been used for exercise, healing wounds, relieving pain, and strengthening muscle. The assumption is that current will flow predictably between electrodes and, therefore, there will be predictability in the clinical response to electrical stimulation. This may not be the case. The present investigation shows that considerable channelling of current occurs when the skin is heated or when there is a wound between the electrodes. By studying current movement in nutrient agar (a homogenous medium), blood agar and layered blood and nutrient agar to simulate areas of increased blood flow, it was found that areas of high or low resistance, especially in the surface layer, caused significant current movement toward (low resistance area) or away (high resistance area) from those areas. When a resister model was used to measure dispersion characteristics of current in a three-dimensional array, it was shown that if even a single resister value was lowered by 20% in the upper layer, current...

Knowledge based system with embedded intelligent heart sound analyser for diagnosing cardiovascular disorders.

Abstract: Cardiovascular disease (CVD) is the leading cause of death worldwide, and due to the lack of early detection techniques, the incidence of CVD is increasing day by day. In order to address this limitation, a knowledge based system with embedded intelligent heart sound analyser (KBHSA) has been developed to diagnose cardiovascular disorders at early stages. The system analyses digitized heart sounds that are recorded from an electronic stethoscope using advanced digital signal processing and artificial intelligence techniques. KBHSA takes into account data including the patient's personal and past medical history, clinical examination, auscultation findings, chest x-ray and echocardiogram, and provides a list of diseases that it has diagnosed. The system can assist the general physician in making more accurate and reliable diagnosis under emergency conditions where expert cardiologists and advanced equipment are not readily available. To test the validity of the system, abnormal heart sound samples and medical data from 40 patients were recorded and analysed. The diagnoses made by the system were counter checked by four senior cardiologists in Malaysia. The results show that the findings of KBHSA coincide with those of cardiologists.

Optimization of block size for DCT-based medical image compression.

Abstract: In view of the increasing importance of medical imaging in healthcare and the large amount of image data to be transmitted/stored, the need for development of an efficient medical image compression method, which would preserve the critical diagnostic information at higher compression, is growing. Discrete cosine transform (DCT) is a popular transform used in many practical image/video compression systems because of its high compression performance and good computational efficiency. As the computational burden of full frame DCT would be heavy, the image is usually divided into non-overlapping sub-images, or blocks, for processing. This paper aims to identify the optimum size of the block, in reference to compression of CT, ultrasound and X-ray images. Three conflicting requirements are considered, namely processing time, compression ratio and the quality of the reconstructed image. The quantitative comparison of various block sizes has been carried out on the basis of benefit-to-cost ratio (BCR) and reconstruction quality score (RQS). Experimental results are presented that verify the optimality of the 16 x 16 block size.

A review of high frequency oscillation ventilation in the neonate.

Abstract: In this study the use of high frequency oscillation (HFO) to treat neonates with respiratory failure is analysed. The theories behind gas exchange during HFO are reviewed and its specific application to neonatal care discussed. The mechanical performance of three HFO ventilators currently in use is compared with the views of medical staff operating them on a regular basis. The complex interactions between initial ventilator settings have led to difficulties in accurately comparing performance characteristics and ventilation strategies; each ventilator is seen to have its own strengths and weaknesses that contribute to the ventilator selection made. These interactions together with the specific HFO modes available on each ventilator should be taken into account when using a HFO for the first time or when switching from an alternative ventilation method. Medical staff who care for neonates suggest staff education and training into the variations of HFO will greatly improve its use in neonatal medicine.

Three-part passive constitutive laws for the aorta in simple elongation

Abstract: A variety of uniaxial constitutive laws have been proposed for the characterization of the aorta's nonlinear passive response, but a detailed comparison of them appears to be lacking. In this study, a systematic presentation of all available phenomenological formulations is undertaken and explicit formulae of constitutive laws are provided for simple elongation tests performed on healthy aortic strips. Common to all derived laws is the use of three analytical functions to approximate the low, physiologic, and high-stress parts of the aortic response, and the very close and essentially equally accurate fits that they give to the experimental data over the full range of stresses. Another feature of the three-part laws is their compatibility with the biphasic nature of the aortic tissue under passive conditions, allowing direct microstructural interpretation of their parameters. Importantly, although it is found that the aorta displays strain softening, i.e. its passive response is dependent on the highest previously experienced stress, the three-part character of the laws seems to be unaffected by the preconditioning procedure.

Novel diamond-coated tools for dental drilling applications.

Abstract: The application of diamond coatings on cemented tungsten carbide (WC-Co) tools has been the subject of much attention in recent years in order to improve cutting performance and tool life in orthodontic applications. WC-Co tools containing 6% Co metal and 94% WC substrate with an average grain size of 1 – 3 μm were used in this study. In order to improve the adhesion between diamond and WC substrates it is necessary to etch cobalt from the surface and prepare it for subsequent diamond growth. Alternatively, a titanium nitride (TiN) interlayer can be used prior to diamond deposition. Hot filament chemical vapour deposition (HFCVD) with a modified vertical filament arrangement has been employed for the deposition of diamond films to TiN and etched WC substrates. Diamond film quality and purity has been characterized using scanning electron microscopy (SEM) and micro Raman spectroscopy. The performances of diamond-coated WC-Co tools, uncoated WC-Co tools, and diamond embedded (sintered) tools have been compa...

Modified adaptive resonance theory based control strategy for EMG operated prosthesis for below-elbow amputee.

Abstract: This paper presents a modified adaptive resonance theory (ART1)-based control strategy for a below-elbow (BE) prosthesis. The statistical parameters and histogram from two channels of an electromyogram (EMG) signal have been used as the feature space for the classification of four limb functions. The ART1 neural network (NN) has been used for the classification. ART1 has been modified to learn the patterns in supervised manner to suit the application. Further, the criteria for the modification of the stored pattern have been made bi-directional and the matching criteria have been designed for bit-by-bit matching. The major challenge of using ART1 is to decide on the value of the vigilance parameter, as the classification success is drastically affected by this parameter. The criteria have been evolved to get the optimal value of the vigilance parameter. It is concluded that the best value of vigilance parameter is that which provides the same tolerance in matching as the minimum bit distance between the stored patterns. This scheme has also been implemented on an 8031 microcontroller.

A new algorithm developed based on a mixture of spectral and nonlinear techniques for the analysis of heart rate variability

Abstract: In this paper, an algorithm based on a joint use of spectral and nonlinear techniques for heart rate variability (HRV) analysis is proposed. First, the measured RR data are passed into a trimmed moving average (TMA)-based filtering system to generate a lower frequency (LF) time series and a higher frequency (HF) one that approximately reflect the sympathetic and vagal activities, respectively. Since the Lyapunov exponent can be used to characterize the level of chaos in complex physiological systems, the largest Lyapunov exponents corresponding to the complex sympathetic and vagal systems are then estimated from the LF and HF time series, respectively, using an existing algorithm. Numerical results of a postural maneuver experiment indicate that both characteristic exponents or their combinations might serve as a set of innovative and robust indicators for HRV analysis, even under the contamination of sparse impulses due to aberrant beats in the RR data.