Compliant support surfaces affect sensory reweighting during balance control.

To maintain upright posture and prevent falling, balance control involves the complex interaction between nervous, muscular and sensory systems, such as sensory reweighting. When balance is impaired, compliant foam mats are used in training methods to improve balance control. However, the effect of the compliance of these foam mats on sensory reweighting remains unclear. In this study, eleven healthy subjects maintained standing balance with their eyes open while continuous support surface (SS) rotations disturbed the proprioception of the ankles. Multisine disturbance torques were applied in 9 trials; three levels of SS compliance, combined with three levels of desired SS rotation amplitude. Two trials were repeated with eyes closed. The corrective ankle torques, in response to the SS rotations, were assessed in frequency response functions (FRF). Lower frequency magnitudes (LFM) were calculated by averaging the FRF magnitudes in a lower frequency window, representative for sensory reweighting. Results showed that increasing the SS rotation amplitude leads to a decrease in LFM. In addition there was an interaction effect; the decrease in LFM by increasing the SS rotation amplitude was less when the SS was more compliant. Trials with eyes closed had a larger LFM compared to trials with eyes open. We can conclude that when balance control is trained using foam mats, two different effects should be kept in mind. An increase in SS compliance has a known effect causing larger SS rotations and therefore greater down weighting of proprioceptive information. However, SS compliance itself influences the sensitivity of sensory reweighting to changes in SS rotation amplitude with relatively less reweighting occurring on more compliant surfaces as SS amplitude changes.

Systolic blood pressure estimation using PPG and ECG during physical exercise.

In this work, a model to estimate systolic blood pressure (SBP) using photoplethysmography (PPG) and electrocardiography (ECG) is proposed. Data from 19 subjects doing a 40 min exercise was analyzed. Reference SBP was measured at the finger based on the volume-clamp principle. PPG signals were measured at the finger and forehead. After an initialization process for each subject at rest, the model estimated SBP every 30 s for the whole period of exercise. In order to build this model, 18 features were extracted from PPG signals by means of its waveform, first derivative, second derivative, and frequency spectrum. In addition, pulse arrival time (PAT) was derived as a feature from the combination of PPG and ECG. After evaluating four regression models, we chose multiple linear regression (MLR) to combine all derived features to estimate SBP. The contribution of each feature was quantified using its normalized weight in the MLR. To evaluate the performance of the model, we used a leave-one-subject-out cross validation. With the aim of exploring the potential of the model, we investigated the influences of the inclusion of PAT, regression models, measurement sites (finger and forehead), and posture change (lying, sitting, and standing). The results show that the inclusion of PAT reduced the standard deviation (SD) of the difference from 14.07 to 13.52 mmHg. There was no significant difference in the estimation performance between the model using finger- and forehead-derived PPG signals. Separate models are necessary for different postures. The optimized model using finger-derived PPG signals during physical exercise had a performance with a mean difference of 0.43 mmHg, an SD of difference of 13.52 mmHg, and median correlation coefficients of 0.86. Furthermore, we identified two groups of features that contributed more to SBP estimation compared to other features. One group consists of our proposed features depicting beat morphology. The other comprises existing features depicting the dicrotic notch. The present work demonstrates promising results of the SBP estimation model during physical exercise.

Adaptation of multijoint coordination during standing balance in healthy young and healthy old individuals.

Standing balance requires multijoint coordination between the ankles and hips. We investigated how humans adapt their multijoint coordination to adjust to various conditions and whether the adaptation differed between healthy young participants and healthy elderly. Balance was disturbed by push/pull rods, applying two continuous and independent force disturbances at the level of the hip and between the shoulder blades. In addition, external force fields were applied, represented by an external stiffness at the hip, either stabilizing or destabilizing the participants' balance. Multivariate closed-loop system-identification techniques were used to describe the neuromuscular control mechanisms by quantifying the corrective joint torques as a response to body sway, represented by frequency response functions (FRFs). Model fits on the FRFs resulted in an estimation of time delays, intrinsic stiffness, reflexive stiffness, and reflexive damping of both the ankle and hip joint. The elderly generated similar corrective joint torques but had reduced body sway compared with the young participants, corresponding to the increased FRF magnitude with age. When a stabilizing or destabilizing external force field was applied at the hip, both young and elderly participants adapted their multijoint coordination by lowering or respectively increasing their neuromuscular control actions around the ankles, expressed in a change of FRF magnitude. However, the elderly adapted less compared with the young participants. Model fits on the FRFs showed that elderly had higher intrinsic and reflexive stiffness of the ankle, together with higher time delays of the hip. Furthermore, the elderly adapted their reflexive stiffness around the ankle joint less compared with young participants. These results imply that elderly were stiffer and were less able to adapt to external force fields.

Low-complexity intrauterine pressure monitoring by Teager energy estimation.

Monitoring the progression of maternal uterine activity provides important prognostic information during pregnancy and parturition. Currently used methods, however, are unsuitable for long-term observation of uterine activity. The abdominally measured electrohysterogram (EHG) provides a non-invasive alternative to the existing methods for long-term ambulatory uterine contraction monitoring. A new EHG signal analysis method for intrauterine pressure (IUP) estimation based on the Teager energy estimate is proposed. The new method is compared to existing methods from the literature in terms of estimation accuracy and computational complexity. An accurate IUP estimate, with a complexity up to 40 times lower than that of algorithms from the literature is obtained. Therefore, the proposed method offers a valuable new option for long-term uterine monitoring.

Improving pulse oximetry accuracy by removing motion artifacts from photoplethysmograms using relative sensor motion: a preliminary study.

To expand applicability of pulse oximetry in low-acuity ambulatory settings, the impact of motion on extracted parameters as saturation (SpO2) and pulse rate (PR) needs to be reduced. We hypothesized that sensor motion relative to the skin can be used as an artifact reference in a correlation canceller to reduce motion artifacts in photoplethysmograms (PPGs), in order to improve SpO2 and PR measurements. This has been proven true in in vivo measurements, where forehead PPGs have been obtained while subjects are walking on a treadmill and relative sensor motion has been measured via self-mixing interferometry. By using relative motion in a normalized least mean square algorithm, the standard deviation of SpO2 and PR errors is on average reduced by 31 % and 13 %, respectively.

Assessment of ventricular mechanical dyssynchrony by short-axis MRI.

Nowadays, patients with symptomatic heart failure and intraventricular conduction delay can be treated with a cardiac resynchronization therapy. Electrical dyssynchrony is typically adopted to represent myocardial dyssynchrony, to be compensated by cardiac resynchronization therapy. One third of the patients, however, does not respond to the therapy. Therefore, imaging modalities aimed at the mechanical dyssynchrony estimation have been recently proposed to improve patient selection criteria. This paper presents a novel fully-automated method for regional mechanical left-ventricular dyssynchrony quantification in short-axis magnetic resonance imaging. The endocardial movement is described by time-displacement curves with respect to an automatically-determined reference point. These curves are analyzed for the estimation of the regional contraction timings. Four methods are proposed and tested for the contraction timing estimation. They were evaluated in two groups of subjects with and without left bundle branch block. The standard deviation of the contraction timings showed a significant increase for left bundle branch block patients with all the methods. However, a novel method based on phase spectrum analysis shows a better specificity and sensitivity. This method may therefore provide a valuable prognostic indicator for heart failure patients with dyssynchronous ventricular contraction, adding new possibilities for regional timing analysis.

Severe gastrointestinal tract bleeding in a two-month-old infant due to congenital intrahepatic arterioportal fistula.

A 2-month-old boy was referred for assessment of severe upper gastrointestinal tract bleeding and melena. On physical examination, a continuous murmur was heard over the right upper quadrant of the abdomen. A splenomegaly and dilated veins were also noted on the abdominal wall. Liver functions were normal. There was no history of trauma or jaundice. Doppler ultrasonography, magnetic resonance arteriography and angiography suggested the presence of an intrahepatic arteriovenous fistula between the phrenic artery and the portal vein. Management consisted of successful embolization by coiling of the phrenic artery. To our knowledge this is the first documented case report of a congenital fistula between the phrenic artery and the portal vein.

Self-help strategies among patients with substance use disorders.

The objective of this study was to determine (1) the type and extent of self-help efforts among patients presenting for treatment of substance use disorders, and (2) the association of self-help with demographic and clinical characteristics. A retrospective report of life self-help methods, current demographic characteristics, and current and lifetime clinical characteristics was used. Six hundred and forty-two patients in treatment for substance use disorder were interviewed at one of two university medical centers with Alcohol-Drug Programs located within departments of psychiatry. A research associate (RA) interviewed patients regarding seven types of self-help involving specific, mutually exclusive behaviors and rated the patient's lifetime self-help methods. The patient, RA, and addiction psychiatrists provided demographic, familial, and clinical information. Most patients (78%) had tried one or more types of self-help, with a mean of 2.7 methods per patient. They more frequently chose methods related to the substance (decreasing amounts or frequency, or changing substance type) or joining a self-help group than methods that involved changing friends, residence, or occupation/job/school. Certain patterns of self-help tended to occur together (e.g., changing substance frequency and dose), whereas others appeared more independent (e.g., joining a self-help group). Some self-help approaches occurred mostly in association with other methods rather than alone (e.g., changing occupation/job/school). More self-help was associated with higher socioeconomic class, more relatives with substance use disorder, greater severity of substance use disorder, and more treatment for substance use disorder. Self-help tends to occur more often after exposure to addicted relatives or addiction treatment. Clinicians and public adult education should promulgate self-help methods in the general population.

Influences of lung parenchyma density and thoracic fluid on ventilatory EIT measurements.

Ventilatory impedance changes can be measured by electrical impedance tomography (EIT). Several studies have pointed out that the ventilatory-induced impedance change measured over the lungs shows a linear relationship with tidal volume. However, EIT measures the ventilatory impedance changes relative to a reference. Therefore, changes in the reference due to lung parenchyma destruction (increase of thoracic impedance) or lung water (decrease of thoracic impedance) might influence ventilatory EIT measurements. A study was designed to evaluate the influence of the density of lung parenchyma and the thoracic fluid content on ventilatory EIT measurements. Eleven emphysema patients with a variable degree of lung parenchyma destruction, nine haemodialysis patients with general fluid overload and ten healthy subjects were measured. The impedance changes were measured with the subject in the supine position breathing a constant tidal volume of 1 litre starting at the maximum end-expiratory level. In the emphysema group a significantly lower impedance change between ins- and expiration was found in comparison with the healthy subjects (11.6 +/- 6.4 AU l-1 versus 18.6 +/- 4.2 AU l-1, p < 0.05), whereas the haemodialysis group showed a significantly larger impedance change between ins- and expiration before haemodialysis (30.5 +/- 13.1 AU l-1, p < 0.05). A significant decrease in ventilation-induced impedance change during dialysis was found (30.5 +/- 13.1 AU l-1 versus 21.4 +/- 8.6 AU l-1, p < 0.01). Furthermore, a significant correlation between lung function parameters, which indicate the severity of lung parenchyma destruction, and the measured impedance change was found in emphysema patients. From these results it can be concluded that the density of lung parenchyma and the thoracic fluid content have a serious impact on the ventilation-induced impedance change.

Flexible protocols improve parallel experimentation throughput.

Advanced chemical workstations offer the potential to substantially improve the productivity of experimental research. To fully exploit such technologies, effective scheduling of experiments is crucial. Chemists tend to define experimental protocols with rigid time constraints, although often the scientific objectives can be achieved without adhering to such constraints. Investigation of a scheduling algorithm that allows flexible time constraints shows that improvements in workstation throughput as great as 50% can be reached by modest flexibility in the timing of operations in the experiments. Several heuristics that might be used with the scheduling algorithm were tested; a heuristic that schedules long experiments while first keeping the workstation busy was shown to be a good general choice.

Tandem multipass Fabry-Perot interferometer for Brillouin scattering.

A new design of a plane mirror Fabry-Perot interferometer with the mirror blanks freely supported by horizontal rings is described. Special attention is paid to the surface flatness and dielectric coatings of the mirrors. It is shown that any two piezoelectrically scanned Fabry-Perot interferometers can be synchronized in tandem operation using simple optics and standard electronic driving and stabilization equipment. Applications of the tandem system to Brillouin scattering are given. The observation of Brillouin spectra of supported thin plastic films and of a clamped metal surface is reported.