Search

The curvelet transform, which represents images in terms of their geometric and textural characteristics, was investigated toward revealing differences between moderate (50%–69%, n = 11) and severe (70%–100%, n = 14) stenosis asymptomatic plaque from B-mode ultrasound. Texture features were estimated in original and curvelet transformed images of atheromatous plaque (PL), the adjacent arterial wall (intima-media [IM]) and the plaque shoulder (SH) (i.e., the boundary between plaque and wall), separately at end systole and end diastole. Seventeen features derived from the original images were significantly different between the two groups (4 for IM, 3 for PL and 10 for SH; 9 for end diastole and 8 for end systole); 19 of 234 features (2 for IM and 17 for SH; 8 for end systole and 11 for end diastole) derived from curvelet transformed images were significantly higher in the patients with severe stenosis, indicating higher magnitude, variation and randomness of image gray levels. In these patients, lower body height and higher serum creatinine concentration were observed. Our findings suggest that (a) moderate and severe plaque have similar curvelet-based texture properties, and (b) IM and SH provide useful information about arterial wall pathophysiology, complementary to PL itself. The curvelet transform is promising for identifying novel indices of cardiovascular risk and warrants further investigation in larger cohorts. © 2021 World Federation for Ultrasound in Medicine & Biology

This paper reviews state-of-the-art research solutions across the spectrum of medical imaging informatics, discusses clinical translation, and provides future directions for advancing clinical practice. More specifically, it summarizes advances in medical imaging acquisition technologies for different modalities, highlighting the necessity for efficient medical data management strategies in the context of AI in big healthcare data analytics. It then provides a synopsis of contemporary and emerging algorithmic methods for disease classification and organ/ tissue segmentation, focusing on AI and deep learning architectures that have already become the de facto approach. The clinical benefits of in-silico modelling advances linked with evolving 3D reconstruction and visualization applications are further documented. Concluding, integrative analytics approaches driven by associate research branches highlighted in this study promise to revolutionize imaging informatics as known today across the healthcare continuum for both radiology and digital pathology applications. The latter, is projected to enable informed, more accurate diagnosis, timely prognosis, and effective treatment planning, underpinning precision medicine. © 2013 IEEE.

Motion extracted from the carotid artery wall provides unique information for vascular health evaluation. Carotid artery longitudinal wall motion corresponds to the multiphasic arterial wall excursion in the direction parallel to blood flow during the cardiac cycle. While this motion phenomenon has been well characterized, there is a general lack of awareness regarding its implications for vascular health assessment or even basic vascular physiology. In the last decade, novel estimation strategies and clinical investigations have greatly advanced our understanding of the bi-axial behavior of the carotid artery, necessitating an up-to-date review to summarize and classify the published literature in collaboration with technical and clinical experts in the field. Within this review, the state-of-the-art methodologies for carotid wall motion estimation are described, and the observed relationships between longitudinal motion-derived indices and vascular health are reported. The vast number of studies describing the longitudinal motion pattern in plaque-free arteries, with its putative application to cardiovascular disease prediction, point to the need for characterizing the added value and applicability of longitudinal motion beyond established biomarkers. To this aim, the main purpose of this review was to provide a strong base of theoretical knowledge, together with a curated set of practical guidelines and recommendations for longitudinal motion estimation in patients, to foster future discoveries in the field, toward the integration of longitudinal motion in basic science as well as clinical practice. © 2020 World Federation for Ultrasound in Medicine & Biology

Asynchronous movement of the carotid atheromatous plaque from B-mode ultrasound has been previously reported, and associated with higher risk of stroke, but not quantitatively estimated. Based on the hypothesis that asynchronous plaque motion is associated with vulnerable plaque, in this study, synchronisation patterns of different tissue areas were estimated using cross-correlations of displacement waveforms. In 135 plaques (77 subjects), plaque radial deformation was synchronised by approximately 50% with the arterial diameter, and the mean phase shift was 0.4 s. Within the plaque, the mean phase shifts between the displacements of the top and bottom surfaces were 0.2 s and 0.3 s, in the radial and longitudinal directions, respectively, and the synchronisation about 80% in both directions. Classification of phase-shift-based features using Random Forests yielded Area-Under-the-Curve scores of 0.81, 0.79, 0.89 and 0.90 for echogenicity, symptomaticity, stenosis degree and plaque risk, respectively. Statistical analysis showed that echolucent, high-stenosis and high-risk plaques exhibited higher phase shifts between the radial displacements of their top and bottom surfaces. These findings are useful in the study of plaque kinematics. © 2020, The Author(s).

The estimation of cardiovascular tissue motion from ultrasound images is a task of considerable importance but has remained difficult in clinical practice, mainly due to the limitations of ultrasound imaging and the complexity of tissue motion. This paper presents a survey of methodologies, along with physiologically relevant findings, regarding the estimation of motion of the myocardium and of central and peripheral arteries. Speckle tracking and modeling, and registration are the dominant methods used to calculate tissue displacements from sequences of images. Kinematic and mechanical indices are extracted from these displacements, which can provide valuable functional information about the cardiovascular system in normal and diseased conditions. An important application of motion-based strain indices involves the estimation of elastograms of the cardiovascular tissue. Motion analysis methods can be used to estimate a number of regional mechanical phenomena representing functional tissue properties, which are more sensitive to early changes due to ageing or disease. The importance of these methods lies in their potential to quantify in vivo tissue properties and to identify novel noninvasive personalized disease markers, toward early detection and optimal management of disease, along with increased patient safety. Their clinical usefulness remains to be demonstrated in large trials. © 2008-2011 IEEE.

Stroke is a leading cause of morbidity and mortality worldwide, and characterization of vulnerable carotid plaque remains the spearhead of scientific research. Plaque destabilization, the key factor that induces the series of events leading to the clinical symptoms of carotid artery disease, is a consequence of complex mechanical, structural and biochemical processes. Novel imaging and molecular markers have been studied as predictors of disease outcome with promising results. The aim of this review is to present the current state of research on the association between ultrasound-derived echogenicity indices and blood parameters indicative of carotid plaque stability and activity. Bibliographic research revealed that there are limited available data. Among the biomarkers studied, those related to oxidative stress, lipoproteins and diabetes/insulin resistance are associated with echolucent plaques, whereas adipokines are associated with echogenic plaques. Biomarkers of inflammation and coagulation have not exhibited any conclusive relationship with plaque echogenicity, and it is not possible to come to any conclusion regarding calcification-, apoptosis- and neo-angiogenesis-related parameters because of the extremely limited bibliographic data. © 2016

Valid characterization of carotid atherosclerosis (CA) is a crucial public health issue, which would limit the major risks held by CA for both patient safety and state economies. This paper investigated the unexplored potential of kinematic features in assisting the diagnostic decision for CA in the framework of a computer-aided diagnosis (CAD) tool. Tothis end, 15CAD schemes were designed and were fed with a wide variety of kinematic features of the atherosclerotic plaque and the arterial wall adjacent to the plaque for 56 patients from two different hospitals. The CAD schemes were benchmarked in terms of their ability to discriminate between symptomatic and asymptomatic patients and the combination of the Fisher discriminant ratio, as a feature-selection strategy, and support vector machines, in the classification module, was revealedas the optimal motion-based CAD tool. The particular CAD tool was evaluated with severalcross-validationstrategies and yielded higher than 88% classification accuracy; the texture-based CAD performance in the same dataset was 80%. The incorporation of kinematic features of the arterial wall in CAD seems to have a particularly favorable impact on the performance of image-datadriven diagnosis for CA, which remains to be further elucidated in future prospective studies on large datasets. 2168-2194 © 2014 IEEE. Translations and content mining are permitted for academic research only. Personal use is also permitted, but republication/redistribution.

Automatic segmentation of the arterial lumen from ultrasound images is an important task in clinical diagnosis. Carotid artery recognition, the first task in lumen segmentation, should be performed in a fully automated, fast, and reliable way to further facilitate the low-level task of arterial delineation. In this paper, a user-independent, real-time algorithm is introduced for carotid artery localization in longitudinal B-mode ultrasound images. The proposed technique acts directly on the raw image, and exploits basic statistics along with anatomical knowledge. The method's evaluation and parameter value optimization were performed on a threefold cross validation basis. In addition, the introduced algorithm was systematically compared with another algorithm for common carotid artery recognition in B-mode scans, separately for multi-frame and single-frame data. The data sets used included 2,149 images from 100 subjects taken from three different institutions and covering a wide range of possible lumen and surrounding tissue representations. Using the optimized values, the carotid artery was recognized in all the processed images in both multi-frame and single-frame data. Thus, the introduced technique will further reinforce automatic segmentation in longitudinal B-mode ultrasound images. © 1992-2012 IEEE.

Efficient management of the asymptomatic carotid disease remains a crucial challenge in clinical practice, because the ultrasonographically estimated degree of stenosis, which is currently used to determine treatment decisions, has been shown to be inadequate. In this study, texture (morphological) characteristics were investigated in a sample of asymptomatic male subjects, at the atheromatous plaque, the adjacent arterial wall and the plaque shoulder, i.e. the boundary between plaque and adjacent wall. A total of 25 arteries were interrogated, 11 with low (50-69%) and 14 with high (70-100%) degrees of stenosis. The two groups had similar ages. Texture characteristics were estimated from systolic and diastolic B-mode ultrasound images, and included four second-order statistical parameters (contrast, correlation, energy and homogeneity), each calculated at four different image directions (0 degrees, 45 degrees, 90 degrees, 135 degrees), yielding a total of 16 characteristics. Between high and low stenosis groups, 8 out of 16 characteristics were statistically different at the plaque shoulder at systole and 6 at diastole. No differences were observed between the two groups for any of the texture characteristics at the plaque nor at the adjacent wall. Differences in morphology along the arterial wall (wall - shoulder - plaque) were more pronounced in cases of high stenosis. The findings indicated that (a) the plaque shoulder is a particular area, requiring additional investigation so as to better understand the pathophysiology of atherosclerosis, (b) the phase of the cardiac cycle (systole or diastole) is important in texture analysis, and (c) the variability of morphology along the arterial wall, which is indicative of areas of tissue discontinuities, and therefore more vulnerable to rupture, can be characterized quantitatively with texture indices, toward an improved assessment of cardiovascular risk. It can be concluded that ultrasound-based texture indices may reveal novel markers for early detection and monitoring of subjects at high risk of cerebrovascular events, in the context of individualized, noninvasive and affordable diagnosis.

Efficient management of asymptomatic carotid atherosclerosis remains a crucial issue in clinical practice, because the currently used determinant for deciding surgical or medical treatment, namely the stenosis degree, has proven inadequate. Various features derived from ultrasound image analysis have shown promise for enhancing the effectiveness of decision making. Among these, multiresolution, i.e. wavelet-transform-based, texture analysis has been shown to adequately characterise atheromatous tissue, especially in terms of horizontally oriented texture in longitudinal B-mode sections. We sought to investigate the horizontally-oriented multiresolution textural properties of arterial wall and plaque in a carefully selected sample of asymptomatic male subjects. Of the 19 carotid arteries that were interrogated, 7 had low stenosis degrees (50-69%) and 12 had high stenosis degrees (70-100%); the two groups had similar ages. Multiresolution analysis was performed using wavelet packets and the coiflet 1 wavelet, for three levels of decomposition. Seven features were derived from the resulting approximation (A) and horizontal detail (Dh) images, for two segments in each artery, namely plaque and the adjacent intima-media complex (IM). All features were statistically similar between low and high stenosis cases, suggesting that stenosis degree may not be sufficient to characterise the two case types. Differences between IM and plaque were observed for most multiresolution features. The differences were more prominent for higher decomposition levels. The feature Dh(3)A(2)A(1) was different between plaque and IM in the low stenosis cases but was not different in the high stenosis cases. The opposite was observed for Dh(2)Dh(1). Such differences suggest discontinuities in tissue properties and therefore increased vulnerability. In conclusion, multiresolution texture analysis may provide valuable information about normal and atheromatous tissue, because certain tissue properties are revealed at high decomposition levels.

Valid risk stratification for carotid atherosclerotic plaques represents a crucial public health issue toward preventing fatal cerebrovascular events. Although motion analysis (MA) provides useful information about arterial wall dynamics, the identification of motion-based risk markers remains a significant challenge. Considering that the ability of a motion estimator (ME) to handle changes in the appearance of motion targets has a major effect on accuracy in MA, we investigated the potential of adaptive block matching (ABM) MEs, which consider changes in image intensities over time. To assure the validity in MA, we optimized and evaluated the ABM MEs in the context of a specially designed in silico framework. ABMFIRF2, which takes advantage of the periodicity characterizing the arterial wall motion, was the most effective ABM algorithm, yielding a 47% accuracy increase with respect to the conventional block matching. The in vivo application of ABMFIRF2 revealed five potential risk markers: low movement amplitude of the normal part of the wall adjacent to the plaques in the radial (RMAPWL) and longitudinal (LMA PWL) directions, high radial motion amplitude of the plaque top surface (RMAPTS), and high relative movement, expressed in terms of radial strain (RSIPL) and longitudinal shear strain (LSSI PL), between plaque top and bottom surfaces. The in vivo results were reproduced by OFLK(WLS) and ABMKF-K2, MEs previously proposed by the authors and with remarkable in silico performances, thereby reinforcing the clinical values of the markers and the potential of those MEs. Future in vivo studies will elucidate with confidence the full potential of the markers. © 2013 Institute of Physics and Engineering in Medicine.

Stroke is a serious and frequent cerebrovascular disease with an enormous socioeconomic burden worldwide. Stroke prevention includes treatment of carotid atherosclerosis, the most common underlying cause of stroke, according to a specific diagnostic algorithm. However, this diagnostic algorithm has proved insufficient for a large number of mostly asymptomatic subjects, which poses a significant research challenge of identifying novel personalized risk markers for the disease. This paper illustrates the potential of carotid ultrasound image analysis toward this direction, with ultrasound imaging being a low-cost and noninvasive imaging modality and ultrasound-image-based features revealing valuable information on plaque composition and stability. A concise report of state-of-the-art studies in the field is provided and a perspective for clinical scenario for optimal management of atherosclerotic patients is described. Challenges and necessary future steps toward the realization of this scenario are discussed in an attempt to urge and orient future research, and mainly include systematic applications to sufficiently large patient samples, appropriately designed longitudinal studies, confirmation with histological results, and clinical trials. © 2013 IEEE.

Motion of the carotid artery wall is important for the quantification of arterial elasticity and contractility and can be estimated with a number of techniques. In this paper, a framework for quantitative evaluation of motion analysis techniques from B-mode ultrasound images is introduced. Six synthetic sequences were produced using 1) a real image corrupted by Gaussian and speckle noise of 25 and 15 dB, and 2) the ultrasound simulation package Field II. In both cases, a mathematical model was used, which simulated the motion of the arterial wall layers and the surrounding tissue, in the radial and longitudinal directions. The performance of four techniques, namely optical flow (OF HS), weighted least-squares optical flow (OF LK(WLS)), block matching (BM), and affine block motion model (ABMM), was investigated in the context of this framework. The average warping indices were lowest for OF LK(WLS) (1.75 pixels), slightly higher for ABMM (2.01 pixels), and highest for BM (6.57 pixels) and OF HS (11.57 pixels). Due to its superior performance, OF LK(WLS) was used to quantify motion of selected regions of the arterial wall in real ultrasound image sequences of the carotid artery. Preliminary results indicate that OF LK(WLS) is promising, because it efficiently quantified radial, longitudinal, and shear strains in healthy adults and diseased subjects. © 2012 IEEE.

In this paper, three multiscale transforms with directional character, namely the dual-tree complex wavelet (DTCWT), the finite ridgelet (FRIT) and the fast discrete curvelet (FDCT) transforms, were comparatively assessed with respect to their ability to characterize carotid atherosclerotic plaque from B-mode ultrasound and discriminate between symptomatic and asymptomatic cases. The standard deviation and entropy of the detail subimages produced for each decomposition scheme were used as texture features. Feature selection included ranking the features according to their highest separability value and the minimum correlation among them. Due to the rather limited size of the sample population, the selected features were resampled 100times by the bootstrap technique and divided into training and test sets. For each pair of sets, a support vector machine classifier was trained on the training set and evaluated on the test set. The average overall classification performance for systole (diastole) was 70% (65.2%), 72.6% (70.4%) and 84.9% (73.6%) for the DTCWT, FRIT and FDCT, respectively. These preliminary results showed the superiority of the curvelet transform, in terms of classification accuracy, being of great importance for the diagnosis and management of plaque instability in carotid atheromatous stenosis. © 2012 IOP Publishing Ltd.

In this paper, a multiresolution approach is suggested for texture classification of atherosclerotic tissue from B-mode ultrasound. Four decomposition schemes, namely, the discrete wavelet transform, the stationary wavelet transform, wavelet packets (WP), and Gabor transform (GT), as well as several basis functions, were investigated in terms of their ability to discriminate between symptomatic and asymptomatic cases. The mean and standard deviation of the detail subimages produced for each decomposition scheme were used as texture features. Feature selection included 1) ranking the features in terms of their divergence values and 2) appropriately thresholding by a nonlinear correlation coefficient. The selected features were subsequently input into two classifiers using support vector machines (SVM) and probabilistic neural networks. WP analysis and the coiflet 1 produced the highest overall classification performance (90% for diastole and 75% for systole) using SVM. This might reflect WP's ability to reveal differences in different frequency bands, and therefore, characterize efficiently the atheromatous tissue. An interesting finding was that the dominant texture features exhibited horizontal directionality, suggesting that texture analysis may be affected by biomechanical factors (plaque strains). © 2006 IEEE.

Block matching (BM) has been previously used to estimate motion of the carotid artery from B-mode ultrasound image sequences. In this paper, Kalman filtering (KF) was incorporated in this conventional method in two distinct scenarios: (a) as an adaptive strategy, by renewing the reference block and (b) by renewing the displacements estimated by BM or adaptive BM. All methods resulting from combinations of BM and KF with the two scenarios were evaluated on synthetic image sequences by computing the warping index, defined as the mean squared error between the real and estimated displacements. Adaptive BM, followed by an update through the second scenario at the end of tracking, ABM-KF-K2, minimized the warping index and yielded average displacement error reductions of 24% with respect to BM. The same method decreased estimation bias and jitter over varying center frequencies by 30% and 64%, respectively, with respect to BM. These results demonstrated the increased accuracy and robustness of ABM-KF-K2 in motion tracking of the arterial wall from B-mode ultrasound images, which is crucial in the study of mechanical properties of normal and diseased arterial segments. © 2011 IOP Publishing Ltd.

The motion of the carotid artery wall can quantitatively be estimated from sequences of B-mode ultrasound images. In this paper, the effects of dynamic range (DR) and persistence, along with that of image normalization, were studied, in an attempt to suggest optimal values for reliable motion analysis. Image sequences were recorded using four different values for DR, i.e., 0, 48, 66, and 90 dB, and three different values for persistence, i.e., 0, 5.6, and 50. Radial and axial displacements, as well as the correlation coefficients (CCs), were estimated using block matching from recordings with durations of about 3 s. The variances of radial and axial displacements were not significantly affected by changes in DR and persistence. The mean value of the CC, which is an index of the reliability of motion analysis, was also not significantly affected by these settings. However, an increase in persistence increased the delays between peak radial displacements and cardiac systole. Image normalization did not affect the results of motion analysis. It is suggested that high values of DR (66 or 90 dB) and low values of persistence (0 or 5.6) are used for motion analysis based on block matching. © 2009 IEEE.

The present study investigated how end-expiratory ribcage and abdominal volume regulation during exercise is related to the degree of dynamic chest wall hyperinflation in patients with different spirometric severity of chronic obstructive pulmonary disease (COPD) based on the Global Initiative for Chronic Obstructive Lung Disease (GOLD) classification. In total, 42 COPD patients and 11 age-matched healthy subjects were studied during a ramp-incremental cycling test to the limit of tolerance (Wpeak). Volume variations of the chest wall (at end expiration (EEVcw) and end inspiration) and its compartments (ribcage (Vrc) and abdominal (Vab)) were computed by optoelectronic plethysmography. At Wpeak, only patients in GOLD stages III and IV exhibited a significant increase in EEVcw (increase of 454±509 and 562±363 mL, respectively). These patients did not significantly reduce end-expiratory Vab, whereas patients in GOLD stage II resembled healthy subjects with significantly reduced end-expiratory Vab (decrease of 287±350 mL). In patients, the greater the increase in EEVcw at Wpeak, the smaller the reductions in end-expiratory Vab and the greater the increase in end-expiratory Vrc. In chronic obstructive pulmonary disease patients with different spirometric disease severity, greater degrees of exercise-induced dynamic chest wall hyperinflation were accompanied by lower degrees of end-expiratory abdominal volume displacement and larger increases in end-expiratory ribcage volume. Copyright©ERS Journals Ltd 2008.

Measurement of respiratory muscle blood flow (RMBF) in humans has important implications for understanding patterns of blood flow distribution during exercise in healthy individuals and those with chronic disease. Previous studies examining RMBF in humans have required invasive methods on anesthetized subjects. To assess RMBF in awake subjects, we applied an indicator-dilution method using near-infrared spectroscopy (NIRS) and the light-absorbing tracer indocyanine green dye (ICG). NIRS optodes were placed on the left seventh intercostal space at the apposition of the costal diaphragm and on an inactive control muscle (vastus lateralis). The primary respiratory muscles within view of the NIRS optodes include the internal and external intercostals. Intravenous bolus injection of ICG allowed for cardiac output (by the conventional dye-dilution method with arterial sampling), RMBF, and vastus lateralis blood flow to be quantified simultaneously. Esophageal and gastric pressures were also measured to calculate the work of breathing and transdiaphragmatic pressure. Measurements were obtained in five conscious humans during both resting breathing and three separate 5-min bouts of constant isocapnic hyperpnea at 27.1 ± 3.2, 56.0 ± 6.1, and 75.9 ± 5.7% of maximum minute ventilation as determined on a previous maximal exercise test. RMBF progressively increased (9.9 ± 0.6, 14.8 ± 2.7, 29.9 ± 5.8, and 50.1 ± 12.5 ml·100 ml·-1·min -1, respectively) with increasing levels of ventilation while blood flow to the inactive control muscle remained constant (10.4 ± 1.4, 8.7 ± 0.7, 12.9 ± 1.7, and 12.2 ± 1.8 ml·100 ml -1·min-1, respectively). As ventilation rose, RMBF was closely and significantly correlated with 1) cardiac output (r = 0.994, P = 0.006), 2) the work of breathing (r = 0.995, P = 0.005), and 3) transdiaphragmatic pressure (r = 0.998, P = 0.002). These data suggest that the NIRS-ICG technique provides a feasible and sensitive index of RMBF at different levels of ventilation in humans. Copyright © 2008 the American Physiological Society.

Proceedings of the 29th Annual International Conference of the IEEE EMBS Cité Internationale, Lyon, France August 23-26, 2007 The time-varying microstructure of sleep EEG spindles may have clinical significance in dementia studies. In this work, the sleep spindle is modeled as an AM-FM signal and parameterized in terms of six parameters, three quantifying the instantaneous envelope (IE) and three quantifying the instantaneous frequency (IF) of the spindle model. The IE and IF waveforms of sleep spindles from patients with dementia and normal controls were estimated using the time-frequency technique of Complex Demodulation (CD). Sinusoidal curve-fitting using a matching pursuit (MP) approach was applied to the IE and IF waveforms for the estimation of the six model parameters. Specific differences were found in sleep spindle instantaneous frequency dynamics between spindles from dementia subjects and spindles from controls.

Previous work suggests that exercise-induced arterial hypoxaemia (EIAH), causing only moderate arterial oxygen desaturation (SaO2 92 ± 1%), does not exaggerate diaphragmatic fatigue exhibited by highly trained endurance athletes. Since changes in arterial O2 tension have a significant effect on the rate of development of locomotor muscle fatigue during strenuous exercise, the present study investigated whether hypoxia superimposed on EIAH exacerbates the exercise-induced diaphragmatic fatigue in these athletes. Eight trained cyclists (V̇O2max 67.0 ± 2.6 ml kg-1 min-1; mean ± s.e.m.) completed in balanced order four 5 min exercise tests leading to different levels of end-exercise SaO2 (64 ± 2, 83 ± 1, 91 ± 1 and 96 ± 1%) via variations in inspired O2 fraction (FIO2 0.13, 0.17, 0.21 and 0.26, respectively). Measurements were made at corresponding intensities (65 ± 3, 80 ± 3, 85 ± 3 and 90 ± 3% of normoxic maximal work rate, respectively) in order to produce the same tidal volume, breathing frequency and respiratory muscle load at each FIO2. The mean pressure time product of the diaphragm did not differ across the four exercise tests and ranged between 312 ± 28 and 382 ± 22 cmH2O s min-1. Ten minutes into recovery, twitch transdiaphragmatic pressure (Pdi,tw) determined by bilateral phrenic nerve stimulation, was significantly (P=0.0001) reduced after all tests. After both hypoxic tests (FIO2: 0.13, 0.17) the degree of fall in Pdi,tw (by 26.9 ± 2.7 and 27.4 ± 2.6%, respectively) was significantly greater (P

The time-varying microstructure of sleep EEG spindles may have clinical significance in dementia studies. In this work, the sleep spindle is modeled as an AM-FM signal and parameterized in terms of six parameters, three quantifying the instantaneous envelope (IE) and three quantifying the instantaneous frequency (IF) of the spindle model. The IE and IF waveforms of sleep spindles from patients with dementia and normal controls were estimated using the time-frequency technique of Complex Demodulation (CD). Sinnsoidal curve-fitting using a matching pursuit (MP) approach was applied to the IE and IF waveforms for the estimation of the six model parameters. Specific differences were found in sleep spindle instantaneous frequency dynamics between spindles from dementia subjects and spindles from controls.

In healthy subjects expiratory flow limitation (EFL) during exercise can lower O2 delivery to the working muscles. We hypothesized that if this affects exercise performance it should influence O2 kinetics at the end of exercise when the O2 debt is repaid. We performed an incremental exercise test on six healthy males with a Starling resistor in the expiratory line limiting expiratory flow to ∼ 1 l s-1 to determine maximal EFL exercise workload (Wmax). In two more square-wave exercise runs subjects exercised with and without EFL at Wmax for 6 min, while measuring arterial O2 saturation (% SaO2), end-tidal pressure of CO2 (PET CO2) and breath-by-breath O2 consumption (V̇O2 taking into account changes in O2 stored in the lungs. Over the last minute of EFL exercise, mean PET CO2 (54.7 ± 9.9 mmHg) was significantly higher (P < 0.05) compared to control (41.4 ± 3.9 mmHg). At the end of EFL exercise %SaO2 fell significantly by 4 ± 3%. When exercise stopped, EFL was removed, and we continued to measure V̇O2 During recovery, there was an immediate step increase in V̇O2 so that repayment of EFL O2 debt started at a higher V̇O2 than control. Recovery VO2 kinetics after EFL exercise was best characterized by a double-exponential function with fundamental and slow time constants of 27 ± 11 and 1,020 ± 305 s, compared to control values of 41 ± 10 and 1,358 ± 320 s, respectively. EFL O2 debt was 52 ± 22% greater than control (2.19 ± 0.58 vs. 1.49 ± 0.38 l). We conclude that EFL exercise increases the O2 debt and leads to hypoxemia in part due to hypercapnia. © Springer-Verlag 2006.

In order to investigate underlying mechanisms, the present authors studied the effect of pulmonary rehabilitation on the regulation of total chest wall and compartmental (ribcage, abdominal) volumes during exercise in patients with chronic obstructive pulmonary disease. In total, 20 patients (forced expiratory volume in one second, mean ± SEM 39 ± 3% predicted) undertook high-intensity exercise 3 days·week-1 for 12 weeks. Before and after rehabilitation, the changes in chest wall (cw) volumes at the end of expiration (EEV) and inspiration (EIV) were computed by optoelectronic plethysmography during incremental exercise to the limit of tolerance (Wpeak). Rehabilitation significantly improved Wpeak (57±7 versus 47±5 W). In the post-rehabilitation period and at identical work rates, significant reductions were observed in minute ventilation (35.1 ±2.7 versus 38.4±2.7 L.min-1), breathing frequency (26±1 versus 29±1 breaths.min-1) and EEVcw and EIVcw (by 182±79 and 136±37 mL, respectively). Inspiratory reserve volume was significantly increased (by 148 ± 70 mL). Volume reductions were attributed to significant changes in abdominal EEV and EIV (by 163 ± 59 and 125 ± 27 mL, respectively). The improvement in Wpeak was similar in patients who progressively hyperinflated during exercise and those who did not (24 and 26%, respectively). In conclusion, pulmonary rehabilitation lowers chest wall volumes during exercise by decreasing the abdominal volumes. The improvement in exercise capacity following rehabilitation is independent of the pattern of exercise-induced dynamic hyperinflation. Copyright © ERS Journals Ltd 2007.

Proceedings of the Information Technology Applications in Biomedicine, Ioannina - Epirus, Greece, October 26-28, 2006 Parameter estimation for an assumed sleep EEG spindle model (AM-FM signal) is performed by using four time-frequency analysis methods. Results from simulated as well as from real data are presented. In simulated data, the Hilbert Transform-based method has the lowest average percentage error but produces considerable signal distortion. The Complex Demodulation and the Matching Pursuit-based methods have error rates below 10%, but the Matching Pursuit-based method produces considerable signal distortion as well. The Wavelet Transform-based method has the poorest performance. In real data, all methods produce reasonable parameter values. However, the Hilbert Transform and the Matching Pursuitbased methods may not be applicable for sleep spindles shorter than about 0.8 sec. Matching Pursuit-based curve fitting is utilized as part of the parameter estimation process.

Gender differences in resting pulmonary function are attributable to the smaller lung volumes in women relative to men. We sought to investigate whether the pattern of response in operational lung volumes during exercise is different between men and women of similar fitness levels. Breath-by-breath volume changes of the entire chest wall ((V) over dot(cw)) and its rib cage ((V) over dot(Rc)) and abdominal ((V) over dot(Ab)) compartments were studied by optoelectronic plethysmography in 15 healthy subjects (10 men) who underwent a symptom-limited (W-peak) incremental bicycle test. The pattern of change in end-inspiratory and end-expiratory (V) over dot(cw) ((V) over dot(CW,EI) and (V) over dot(CW,EE), respectively) did not differ between the sexes. With increasing workload the decrease in (V) over dot(CW,EE) was almost entirely attributable to a reduction in end-expiratory (V) over dot(Ab), whereas the increase in (V) over dot(CW,El) was due to the increase in end-inspiratory (V) over dot(Rc) in both sexes. In men, at W-peak tidal volume [(V) over dot(T), 2.7 (0.2) 1] and inspiratory capacity [IC, 3.4 (0.2) 1] were significantly greater than in women [1.8 (0.2) and 2.6 (0.2) 1, respectively]. However, after controlling for lung size using forced vital capacity (FVC) as a surrogate, the differences between men and women were eliminated [(V) over dot(T) /FVC 49 (3) and 45 (3) respectively, and IC/FVC 63 (2) and 65 (3) respectively]. All data are presented as mean (SE). In both men and women the contribution of the rib cage compartment to (V) over dot(T) expansion was significantly greater than that of the abdominal compartment. We conclude that gender differences in operational lung volumes in response to progressive exercise are principally attributable to differences related to lung size, whereas compartmental chest wall kinematics do not differ among sexes.

In this paper, a pilot study regarding carotid atherosclerotic plaque instability using B-mode ultrasound (US) images was carried out. The fractal dimension of plaques obtained from ten symptomatic subjects (i.e., subjects having experienced neurological symptoms) as well as from nine asymptomatic subjects, was estimated using a novel method, called the kth nearest neighbour (KNN) method. The results indicated a significant difference, as per the fractal dimension, between the two groups, providing a significantly lower value for the asymptomatic group. Moreover, the phase of the cardiac cycle (systole/diastole) during which the fractal dimension was estimated had no systematic effect on the calculations. The fractal dimension of the plaques was also estimated using a well-known method, namely the box-counting (BC) method. No significant differences between the two groups, as per the fractal dimension, were observed using the BC method. The presented pilot study suggests that the fractal dimension, estimated by the proposed method, could be used as a single determinant for the discrimination of symptomatic and asymptomatic subjects. Copyright © 2002 World Federation for Ultrasound in Medicine & Biology.