M.A. Mananas

Apathy in Parkinson's Disease: Neurophysiological Evidence of Impaired Incentive Processing

Apathy is one of the most common and debilitating nonmotor manifestations of Parkinsons disease (PD) and is characterized by diminished motivation, decreased goal-directed behavior, and flattened affect. Despite its high prevalence, its underlying mechanisms are still poorly understood, having been associated with executive dysfunction, and impaired emotional processing and decision making. Apathy, as a syndrome, has recently been associated with reduced activation in the ventral striatum, suggesting that early- to middle-stage Parkinsons disease patients with this manifestation may have a compromised mesocorticolimbic dopaminergic pathway and impaired incentive processing. To test this hypothesis, we measured the amplitude of the feedback-related negativity, an event-related brain potential associated with performance outcome valence, following monetary gains and losses in human PD patients (12 women) and healthy controls (6 women) performing a gambling task. Early- to middle-stage PD patients presenting clinically meaningful symptoms of apathy were compared with nonapathetic PD patients and healthy controls. Patients with cognitive impairment, depression, and other psychiatric disturbances were excluded. Results showed that the amplitude of the feedback-related negativity, measured as the difference wave in the event-related brain potential between gains and losses, was significantly reduced in PD patients with apathy compared with nonapathetic patients and healthy controls. These findings indicate impaired incentive processing and suggest a compromised mesocorticolimbic pathway in cognitively intact PD patients with apathy.

Evaluation of muscle activity and fatigue in extensor forearm muscles during isometric contractions

Work-related upper extremity disorders as epycondylitis and tendonitis are closely related to localized muscle fatigue of extensor forearm muscles. The aim of this work is to evaluate levels of activity, fatigue and interactions between the main extensor muscles of the wrist. Surface EMG signals were acquired from extensor carpi radialis (ECR), extensor digitorum comunis (EDC) and extensor carpi ulnaris (ECU) muscles during isometric contractions using linear electrode array technique. Parameters such as muscle fiber conduction velocity (CV), EMG average rectified value (ARV) and frequency parameters were estimated to study muscle activity during selective contractions, during a non specific task at different percentage of the maximum voluntary contraction (MVC) level and during a fatiguing exercise at 50% MVC. Results show that it is possible to enhance significantly ECR and ECU muscle ARV during their selective activation. Moreover, in the non selective task, ECU muscle ARV significantly decreases with respect to the other muscles with the increase of the MVC level. The activity of ECR muscle in a non specific task is predominant with respect to the other muscles at 80% MVC. EMG spectral parameters and CV show fatigue in all muscles during a sustained contraction at 50% MVC

Activation of Forearm Muscles for Wrist Extension in Patients Affected by Lateral Epicondylitis

Work related upper extremity disorders are associated with cumulative trauma resulting from the continuous use of forearm muscles rather than from a specific incident. The aim of this work is to compare wrist extensor muscles activation between patients with lateral epicondylitis and healthy subjects. Differences can be used in the design of rehabilitation or injury prevention programs according to biomechanical deficits. Surface EMG signals from three forearm extensor muscles (Carpi Radialis-ECR, Digitorum Communis-EDC and Carpi Ulnaris-ECU) were recorded by linear electrode arrays in wrist extension as well as during selective contractions.Average Rectified Values(ARV) were calculated in order to identify the contribution of each muscle to different tasks. On the other hand, Muscle Fiber Conduction Velocity, Mean and Median Frequencies and also ARV were studied to obtain fatigue indexes related to metabolic changes in the muscles during a high force sustained contraction. Results showed muscular imbalance with lower ECR activity compensated by higher ECU activation, and higher fatigue indexes in patients with lateral epicondylitis.

Influence of estimators of spectral density on the analysis of electromyographic and vibromyographic signals.

Electromyographic (EMG) and vibromyographic (VMG) signals are related to electrical and mechanical muscle activity, respectively. It is known that variations in their frequency components are related to changes in muscle activity and fatigue. The aims of this study were: (1) to analyse the resolution, variance and bias of different estimations of power spectral density function (PSD); and (2) to evaluate the influence of the spectral estimation method on three indices calculated from the PSD of EMG and VMG signals: mean (fm) and median (fc) frequencies and the ratio of high and low frequency components (H/L ratio) to select the most suitable estimator. Myographic signals were recorded from the sternomastoid muscle, an accessory respiratory muscle, during breathing. For non-parametric methods, Welch periodograms and correlograms were analysed with different windows. Autoregressive (AR) moving average (MA) and ARMA models with different orders were evaluated in the parametric methods. The reproducibility of the results was also studied. Frequency indices, particularly the H/L ratio and fc, changed considerably when varying the following parameters of the estimators: periodogram with segment durations longer than 150 ms in EMG and with any duration in VMG signals; correlogram with window length shorter than 10% of the total number of samples; and AR models with an order lower than 10, 20 and 40 in fc, fm and H/L ratio, respectively, in both myographic signals.

Analysis of stationarity and statistical changes in myographic signals from respiratory muscles

Spectral analysis of myographic signals from respiratory muscles is a promising non-invasive technique to study respiratory diseases. However, it requires that the signal be at least weakly stationary. Electromyographic (EMG) and vibromyographic (VMG) signals are related to electrical and mechanical activity, respectively. Local stationarity of the signals from an accessory respiratory muscle is evaluated by means of the reverse arrangement test. A methodology for change detection and to analyze the evolution of the stationarity during the respiratory cycle in myographic signals is also presented. These studies are performed in healthy subjects and patients with chronic obstructive pulmonary disease. Local stationarity decreases with the increase of the level of ventilation and when a maintained exercise goes forward. High levels of ventilation and respiratory muscle fatigue produce statistical changes in myographic signals.

Analysis of vibromyographic and electromyographic signals from sternomastoid muscle in COPD patients

Analysis of the respiratory muscles activity is a promising technique for diagnosis of respiratory diseases, such as chronic obstructive pulmonary disease (COPD). The sternomastoid muscle was selected to study the activity of respiratory muscles, due to its accessibility. This work proposes the analysis of vibromyographic and electromyographic signals from the sternomastoid muscle, in order to evaluate the muscle function in a ventilatory test. Spectral analysis was performed. The Welch periodogram and autoregressive models were used. Results from a group of 5 patients with COPD are shown at different levels of inspiratory loads. Activity of sternomastoid muscle was measured by means of root-mean-square (rms) values and mean and median frequencies, and they were related to level of severity of COPD patients.<<ETX>>

A comparative study of respiratory models in control of ventilation

The aim of this work is to evaluate responses and characteristics of three respiratory models (RS1, RS2 and RS13) in the presence of the following stimuli: exercise, hypercapnia and hypoxia. A comparative study among the three closed-loop systems is performed in simulation: RS1 has a controller to minimize the mechanical and chemical work rate of breathing. RS2 and RS3 fit better to physiological systems with peripheral and central components. The steady state response is evaluated at different levels of stimulus by means of the variables: ventilation, PaCO/sub 2/ and PaO/sub 2/. In general, the stimulus and variable that produces more differences among models are exercise and ventilation, respectively. The best model to indicate the homeostasis during the exercise is RS1 but it is not possible to analyze hypoxia because there is no feedback of PaO/sub 2/. In the transient response, a settling time of several seconds is found in RS1 and a more realistic value around some minutes is obtained in the other models. Besides, whereas there are no overshoots in the responses of RS1, they appear in PaO/sub 2/ with RS2 and RS3 models because an exponential feedback of PaO/sub 2/ is considered. The influence of these time constants and gains on the transient response is analyzed to obtain the maximum values to keep the system stable. Finally, the sensitivity of the system response with the dead space is studied during exercise.

Time and frequency analysis of signals from sternomastoid muscle in COPD patients and control group

Analysis of sternomastoid muscle (SMM) could become a non-invasive method for diagnosis of chronic obstructive pulmonary disease (COPD). This work studies electromyographic (EMG) and vibromyographic (VMG) signals from SMM during respiratory load tests, in six COPD patients and six normal subjects. These signals are related to electrical and mechanical activity of this muscle that could be different in patients and normal subjects. Time and frequency analysis are performed by means of root-mean-square (RMS) values, cross-correlation of EMG and VMG (EVC), mean and median frequency, and ratio of high and low frequency components (H/L). RMS values and H/L ratio show different behaviour at the end of respiratory tests between groups. Parameters calculated from EVC during tests are different in patient and control group.

Evaluation of vibromyographic signals from sternomastoid muscle in COPD patients during respiratory load tests

Analysis of the sternomastoid muscle activity in respiration can be a new non-invasive tool to assess the significance of chronic obstructive pulmonary disease (COPD). The aim of this work is the evaluation of vibromyographic (VMG) signals from the sternomastoid muscle, in order to study the muscle function in a ventilatory test. Simultaneous electromyographic (EMG) signals were recorded and a comparative analysis with VMG was done. Results from a group of 6 patients with COPD are shown, following two respiratory tests. The root-mean-square (RMS) showed the same behaviour of VMG and EMG signals in both tests. H/L ratios of power spectral density pointed out muscle fatigue in the last steps of the respiratory test. Cross-correlation of EMG and VMG found different patterns of relationship between the electrical and mechanical activity of muscle and allow the study of EMG-VMG time delay, during execution of respiratory load tests.

Changes of HD-sEMG maps of the upper limb during isometric endurance contractions

Recent research in the field of surface EMG recorded with 2D electrode arrays have shown muscle adaptations as reflected on the spatial activation of motor units in response to pain, direction of movement or fatigue. The purpose of this study was to evaluate time- changes in the activation maps of upper limb muscles during endurance tasks associated with the degrees of freedom at the elbow joint. Preliminary results show time-variations in the distribution of intensity, that is, in the spatial recruitment of motor units, and that such changes may be dependent on the type of task.