Quantification of motor impairment in Parkinson's disease using an instrumented timed up and go test.

The Timed Up and Go (TUG) test is a clinical test to assess mobility in Parkinson's disease (PD). It consists of rising from a chair, walking, turning, and sitting. Its total duration is the traditional clinical outcome. In this study an instrumented TUG (iTUG) was used to supplement the quantitative information about the TUG performance of PD subjects: a single accelerometer, worn at the lower back, was used to record the acceleration signals during the test and acceleration-derived measures were extracted from the recorded signals. The aim was to select reliable measures to identify and quantify the differences between the motor patterns of healthy and PD subjects; in order to do so, besides comparing each measure individually to find significant group differences, feature selection and classification were used to identify the distinctive motor pattern of PD subjects. A subset of three features (two from Turning, one from the Sit-to-Walk component), combined with an easily-interpretable classifier (Linear Discriminant Analysis), was found to have the best accuracy in discriminating between healthy and early-mild PD subjects. These results suggest that the proposed iTUG can characterize PD motor impairment and, hence, may be used for evaluation, and, prospectively, follow-up, and monitoring of disease progression.

Estimation of expiratory resistance: a simulation study.

It is of particular importance to detect and quantify obstructive pathological conditions in mechanically ventilated patients, especially in the presence of expiratory flow limitation (EFL), in order to help the clinicians in the choice of the most appropriate ventilation and pharmacological strategies. Aim of this work is to test by simulation a non invasive procedure for estimating the total apparent expiratory resistance of the respiratory system (Rtae). The proposed procedure is based on a time-varying two-element viscoelastic model characterized by the variable resistance Rtae and by a constant compliance estimated by the end-inspiratory occlusion technique. A non linear, dynamic, morphometric model of respiratory mechanics, based on Weibel's representation of the tracheobronchial tree, was used to simulate normal and obstructive respiratory conditions, leading to EFL, during artificial ventilation. The proposed resistance was computed in all simulated cases when the 50% and the 75% of tidal volume has been exhaled during a normal expiration. Rtae appeared to be dependent on the degree of airway obstruction and could provide useful information on how the airway compression varies during expiration.

Mathematical modeling of arterial pressure response to hemodialysis-induced hypovolemia.

A computer model of pressure response to hemodialysis-induced hypovolemia is reported. Heart rate and hematocrit, measured in the course of hemodialysis, are imposed as computer model inputs and the model computes the arterial pressure response after tuning model parameters representative of patient's cardiovascular reactivity. Computer model reproduced with good accuracy experimental data (arterial pressure, cardiac output and total peripherical resistance). Parameter identification over successive sessions of the same patients revealed satisfactory reliability, providing a physiological interpretative key to patient's hemodynamic behavior during hemodialysis.

A simulation model of the oxygen alveolo-capillary exchange in normal and pathological conditions.

This paper presents a mathematical model of the oxygen alveolo-capillary exchange to provide the capillary oxygen partial pressure profile in normal and pathological conditions. In fact, a thickening of the blood-gas barrier, heavy exercise or a low oxygen partial pressure (PO2) in the alveolar space can reduce the O2 alveolo-capillary exchange. Since the reversible binding between haemoglobin and oxygen makes it impossible to determine the closed form for the mathematical description of the PO2 profile along the pulmonary capillaries, an approximate analytical solution of the capillary PO2 profile is proposed. Simulation results are compared with the capillary PO2 profile obtained by numerical integration and by a piecewise linear interpolation of the oxyhaemoglobin dissociation curve. Finally, the proposed model is evaluated in a large range of physiopathological diffusive conditions. The good fit to numerical solutions in all experimental conditions seems to represent a substantial improvement with respect to the approach based on a linear approximation of the oxyhaemoglobin dissociation curve, and makes this model a candidate to be incorporated into the integrated descriptions of the entire respiratory system, where the datum of primary interest is the value of end capillary PO2.