Juan C. Alvarez

Real-time gait event detection for normal subjects from lower trunk accelerations

In this paper we report on a novel algorithm for the real-time detection and timing of initial (IC) and final contact (FC) gait events. We process the vertical and antero-posterior accelerations registered at the lower trunk (L3 vertebra). The algorithm is based on a set of heuristic rules extracted from a set of 1719 steps. An independent experiment was conducted to compare the results of our algorithms with those obtained from a Digimax force platform. The results show small deviations from times of occurrence of events recorded from the platform (13+/-35 ms for IC and 9+/-54 ms for FC). Results for the FC timing are especially relevant in this field, as no previous work has addressed its temporal location through the processing of lower trunk accelerations. The delay in the real-time detection of the IC is 117+/-39 ms and 34+/-72 ms for the FC, improving previously reported results for real-time detection of events from lower trunk accelerations.

Comparison of Step Length Estimators from Weareable Accelerometer Devices

Wearable accelerometry provides easily portable systems that supply real-time data adequate for gait analysis. When they do not provide direct measurement of a spatio-temporal parameter of interest, such as step length, it has to be estimated with a mathematical model from indirect sensor measurements. In this work we are concerned with the accelerometry-based estimation of the step length in straight line human walking. We compare five step length estimators. Measurements were taken from a group of four adult men, adding up a total of 800 m per individual of walking data. Also modifications to these estimators are proposed, based on biomechanical considerations. Results show that this modifications lead to improvements of interest over previous methods

Comparison of three prophylactic antibiotic regimens in clean-contaminated head and neck surgery

Although appropriate perioperative antibiotic prophylaxis has significantly reduced wound infection rates in clean‐contaminated head and neck surgical procedures, controversy still remains regarding the optimal antibiotic regimen.

Multisensor Approach to Walking Distance Estimation with Foot Inertial Sensing

Walking distance estimation is an important issue in areas such as gait analysis, sport training or pedestrian localization. A natural location for portable inertial sensors for gait monitoring is to attach them to the user shoes. Step length can be computed by means of a biaxial accelerometer and a gyroscope on the sagital plane. But estimations based on the direct signal integration are prone to error. This paper shows the results achieved by using a multisensor model approach to reduce uncertainty. Unbounded growth of error is reduced by means of sensor fusion techniques. The method has been tested, and early experimental results show that it provides an estimation of the walking distance with a standard deviation smaller than with single IMU similar systems.

Pedestrian navigation based on a waist-worn inertial sensor.

We present a waist-worn personal navigation system based on inertial measurement units. The device makes use of the human bipedal pattern to reduce position errors. We describe improved algorithms, based on detailed description of the heel strike biomechanics and its translation to accelerations of the body waist to estimate the periods of zero velocity, the step length, and the heading estimation. The experimental results show that we are able to support pedestrian navigation with the high-resolution positioning required for most applications.

Neuronal loss in human medial vestibular nucleus

The data concerning the effects of age on the brainstem are inconsistent, and few works are devoted to the human vestibular nuclear complex. The medial vestibular nucleus (MVN) is the largest nucleus of the vestibular nuclear complex, and it seems to be related mainly to vestibular compensation and vestibulo‐ocular reflexes.

Aging and the human vestibular nuclei: morphometric analysis

The data concerning the effects of age on the brainstem are scarce and few works are devoted to the human vestibular nuclear complex. The study of the effects of aging in the vestibular nuclei could have clinical interest due to the high prevalence of balance control and gait problems in the elderly. We have used in this work eight human brainstems of different ages sectioned and stained by the formaldehyde-thionin technique. The neurons profiles were drawn with a camera lucida and Abercrombies method was used to estimate the total number of neurons. The test of Kolmogorov-Smirnov with the correction of Lilliefors was used to evaluate the fit of our data to a normal distribution and a regression analysis was done to determine if the variation of our data with age was statistically significant. Aging does not affect the volume or length of the vestibular nuclear complex. Our results clearly show that neuronal loss occurs with aging in the descending (DVN), medial (MVN), and lateral (LVN) vestibular nuclei, but not in the superior (SVN). There are changes in the proportions of neurons of different sizes but they are not statistically significant. The neuronal loss could be related with the problems that elderly people have to compensate unilateral vestibular lesions and the alterations of the vestibulospinal reflexes. The preservation of SVN neurons can explain why vestibulo-ocular reflexes are compensated after unilateral vestibular injuries.

Modified Pendulum Model for Mean Step Length Estimation

Step length estimation is an important issue in areas such as gait analysis, sport training or pedestrian localization. It has been shown that the mean step length can be computed by means of a triaxial accelerometer placed near the center of gravity of the human body. Estimations based on the inverted pendulum model are prone to underestimate the step length, and must be corrected by calibration. In this paper we present a modified pendulum model in which all the parameters correspond to anthropometric data of the individual. The method has been tested with a set of volunteers, both males and females. Experimental results show that this method provides an unbiased estimation of the actual displacement with a standard deviation lower than 2.1%.

Expression of the AMPA-selective receptor subunits in the vestibular nuclei of the chinchilla.

The distribution of the AMPA type glutamate receptor has been investigated throughout the central nervous system; however, no detailed description of its distribution is available in the vestibular nuclei. In the present study, in situ hybridization histochemistry and immunohistochemistry were used to localize the messenger RNAs and proteins of the AMPA-selective receptor subunits GluR1, GluR2, GluR3 and GluR4 in the vestibular nuclei of the chinchilla. Immunohistochemistry with subunits specific antisera showed differential distribution of the subunits in the vestibular nuclei. GluR2/3 antiserum labeled the most neurons, suggesting that many if not all vestibular neurons receive glutamatergic input. GluR1-positive neurons were fewer than GluR2/3 immunoreactive neurons and GluR4 immunoreactivity was found in the fewest number of neurons. GluR1 and GluR4 immunoreactivity was also found in astrocyte-like structures. In situ hybridization with 35S-labeled complementary RNA probes confirmed the distribution of the AMPA receptor subunits obtained by immunohistochemistry. Quantitative analysis of the levels of hybridization showed a high degree of diversity in the levels of expression of the GluR2 subunit mRNA, with the highest levels of expression in the giant Deiters cells of the lateral vestibular nuclei and the lowest levels in the small neurons throughout the vestibular nuclei. The subunit compositions of the AMPA receptors determine their physiological properties. Differential distribution and levels of expression of the receptor subunits in the vestibular nuclei may be related to the characteristics of information processing through the vestibular system.

Online motion planning using Laplace potential fields

Robot Navigation is an especially challenging problem when only online sensor information is available. The main problem is to guarantee global properties, such as algorithm convergence or trajectory optimality, based on local information. In this paper we present a new non-heuristic sensor-based planning algorithm, characterized by: 1) it is based in potential functions, allowing to introduce optimality criteria, 2) it is computed incrementally to introduce last sensor readings, and 3) it accounts for robot dynamics. The result is a method suitable for real-time navigation, it is intuitive and easy to understand, and produces smooth and safe trajectories.