Enhancing Walking Performance With a Bilateral Hip Exoskeleton Assistance in Individuals With Above-Knee Amputation.

Transfemoral amputation is a debilitating condition that leads to long-term mobility restriction and secondary disorders that negatively affect the quality of life of millions of individuals worldwide. Currently available prostheses are not able to restore energetically efficient and functional gait, thus, recently, the alternative strategy to inject energy at the residual hip has been proposed to compensate for the lack of energy of the missing leg. Here, we show that a portable and powered hip exoskeleton assisting both the residual and intact limb induced a reduction of walking energy expenditure in four individuals with above-knee amputation. The reduction of the energy expenditure, quantified using the Physiological Cost Index, was in the range [-10, -17]% for all study participants compared to walking without assistance, and between [-2, -24]% in three out of four study participants compared to walking without the device. Additionally, all study participants were able to walk comfortably and confidently with the hip exoskeleton overground at both their self-selected comfortable and fast speed without any observable alterations in gait stability. The study findings confirm that injecting energy at the hip level is a promising approach for individuals with above-knee amputation. By reducing the energy expenditure of walking and facilitating gait, a hip exoskeleton may extend mobility and improve locomotor training of individuals with above-knee amputation, with several positive implications for their quality of life.

Nonlinearity of EHG signals used to distinguish active labor from normal pregnancy contractions.

Labor prediction using the electrohysterogram has immediate clinical applications and has been the aim of several studies in recent years. Studies using various linear methods such as classic spectral analysis do not give clinically useful results. In this paper we present the use of two methods that investigate nonlinearity to predict normal labor. We show the comparison between a linear method that is known from the literature (mean power frequency) and two nonlinear methods (approximate entropy and time reversibility) using ROC analysis. The comparison indicates that the best method for pretreatment to classify pregnancy and labor signals is time reversibility. The results indicate that time reversibility is a very promising tool for distinguishing between labor and physiological contractions during pregnancy. This could be the first step in developing a clinical application method to predict preterm labor.

Evolution of phase synchronization of the two frequency components of the electrohysterogram (EHG): application to the detection of human labor.

The analysis of the electrical activity of the uterus recorded externally, the electrohysterogram (EHG), may find an application in the prediction of labor. In the literature parameters that are supposed to be related to the excitability of the uterine cells have almost exclusively been used for this purpose. In the present paper we evaluate the possible use of synchronization parameters for EHG measured in several places on the uterus for this prediction. The EHG is mainly composed of two frequency components called FWL and FWH. These components may be related to the synchronization and the excitability phenomenon respectively. In order to study independently these frequency components, we extracted the corresponding ridges of the wavelet transform of the EHG using the GVF-snake method. For each frequency component we computed parameters that are related to the frequency content of the signals and parameters that consider the synchronization relationship between signals. The synchronization parameters used were the mean phase coherence and the phase entropy. The values of the different parameters were compared during pregnancy and labor by statistical analysis. The detection quality of each parameter was evaluated using ROC curves. Our results suggest that synchronization parameters could be used for the detection of labor in addition to the classical previously published parameters. Another important result of our study is that both FWH and FWL seem related to excitability but only FWL seems to be related to the synchronization of the uterus at term.

Improving the classification rate of labor vs. normal pregnancy contractions by using EHG multichannel recordings.

Most of the studies on the synchronization between EHG signals, recorded during the same contractions at different locations, are limited to the use of only two channels. Multichannel techniques have however been widely applied to EEG signals but rarely to EHG. In this paper, we investigate the use of multichannel uterine EMG signals for classifying contractions. We compare the performance of phase synchronization in distinguishing between labor and normal pregnancy contractions by using either only two channels or a 4x4 matrix positioned on the woman's abdomen. We used two indexes to measure the phase synchronization: mean phase coherence and phase entropy. ROC curves indicate that the use of multichannel signals can significantly improve the classification rate of pregnancy and labor contractions.

In vivo characterization of the novel neuropeptide Y Y1 receptor antagonist H 409/22.

We studied the effects of the novel neuropeptide Y (NPY) Y1 receptor antagonist H 409/22, and its inactive enantiomer H 510/45, on vascular responses evoked by endogenous and exogenous NPY in the pig in vivo. H 409/22 and H 510/45 were given as 30-min infusions, and the antagonistic effects and circulating plasma concentrations were measured. The initial and terminal half-lives of H 409/22 in plasma were approximately 3 and 30 min, respectively. In pigs pretreated with reserpine and transection of sympathetic nerves (depletion of noradrenaline), sympathetic nerve stimulation evoked nonadrenergic vasoconstrictor responses in kidney and hindlimb, mediated by neuronally released NPY. Significant inhibition of these vasoconstrictor responses, as well as of vascular responses to injections of exogenous NPY, were seen during a low-dose infusion of H 409/22 (1.8 nmol/kg/min), when plasma levels of the antagonist reached 77 +/- 8 nM. Greatest inhibitory effects were seen at the highest dose of H 409/22 (180 nmol/kg/min, giving plasma levels of 7.4 +/- 0.6 microM) when all vascular responses evoked by NPY were strongly attenuated or largely abolished. H 510/45 did not affect any of the vascular responses studied. It is concluded that H 409/22 potently and dose-dependently antagonizes vascular responses to exogenous and endogenous NPY in the pig, and thus represents an interesting tool for studies on NPY Y1 receptor-mediated effects in vivo.