A medical information system for monitoring respiratory function and related nonlinear dynamics

In this paper the nonlinear effects in the respiratory systems at low frequencies are measured and evaluated in healthy children and healthy adults. To this aim forced oscillations technique (FOT) has been used to non-invasively measure the lung tissue mechanics. FOT does not require any special effort from the patient in contrast with standardized tests where maneuvers are necessary. Hence, FOT is an ideal lung function test for extreme ages, more specifically children and elderly, given the simpleness of measurement technique. Hitherto, measurements at low frequencies (i.e. close to the breathing frequency similar to 0.3 Hz) have been invasively performed in sacrificed animals and on anesthetized humans. Here we measure in the frequency interval 0.1-2 Hz a total number of 94 volunteers (37 adults with ages between 25-35 years and 57 children with ages between 8-11 years). To evaluate the nonlinear contributions of the respiratory tissue, a novel T-index has been introduced. We have tested the hypothesis whether the nonlinear distortions are changing with growth/development of the respiratory tree and aim to quantify its dependence to biometric values. The results obtained indicate that the proposed index can differentiate between the two analyzed groups and that there is a dependence to age, height and weight. A medical information system may use this information to update predictions of respiratory function and provide aid in decision-making process of drug therapy

Measurements, Models, Systems and Design

531 s.

Investigation of the Hammerstein hypothesis in the modeling of electrically stimulated muscle

To restore functional use of paralyzed muscles by automatically controlled stimulation, an accurate quantitative model of the stimulated muscles is desirable. The most commonly used model for isometric muscle has had a Hammerstein structure, in which a linear dynamic block is preceded by a static nonlinear function, To investigate the accuracy of the Hammerstein model, the responses to a pseudo-random binary sequence (PRBS) excitation of normal human plantarflexors, stimulated with surface electrodes, were used to identify a Hammerstein model but also four local models which describe the responses to small signals at different mean levels of activation. Comparison of the local models with the Linearized Hammerstein model showed that the Hammerstein model concealed a fivefold variation in the speed of response. Also, the small-signal gain of the Hammerstein model was in error by factors up to three. We conclude that, despite the past widespread use of the Hammerstein model, it is not an accurate representation of isometric muscle. On the other hand, local models, which are more accurate predictors, can be identified from the responses to short PRBS sequences. The utility of local models for controller design is discussed