Improving regulation of mean arterial blood pressure during anesthesia through estimates of surgery effects.

In this paper, a scheme for improvement of the regulation of mean arterial blood pressure (MAP) during anesthesia based on model predictive control (MPC) and estimates of the effects of disturbances (surgical events) is proposed. A linear model for the combined effects of surgical stimulations and volatile anesthetics on MAP is derived from experimental data. Based on it the potential improvement in blood pressure regulation is evaluated via a simulation study. The simulation study shows that when information about the effect of the surgical events on MAP is utilized by the controller maximum MAP deviations can be reduced by as much as 50% even when this information is inaccurate. At worst, (highly inaccurate information) no improvement is obtained.

Identification and targeting policies for computer-controlled infusion pumps.

In this article a series of useful techniques is presented to improve the adaptation capabilities of computer-controlled infusion pumps: an identification algorithm for the time constant of the effect compartment, a smoothing technique for estimation based on noisy data, and an infusion policy to target any effect site concentration with no overshoot.

Artifact-tolerant controllers for automatic drug delivery in anesthesia.

This article presents a method for treating measurement artifacts in model-based control systems. A nonlinear modification to the usual observer structure is introduced to prevent the measurement artifacts from winding up the controller states. It is shown how stability of the closed loop system can be analyzed and an example of a successful application in a clinical study is provided.

Analysis of double-joint movements in controls and in parkinsonian patients.

The motor performance of seven patients with Parkinson's disease and seven control subjects was tested in a choice reaction aiming task. The subjects were instructed to aim as fast and as accurately as possible to a light stimulus, which defined one of eight possible target positions. In order to reach the targets, elbow flexions had to be combined with forearm supinations or with forearm pronations. For single-joint movements, forearm supinations or pronations were executed faster than the long elbow flexions in both groups. In the double-joint movements of the control group, the flexion movement times (flex.MTs) and the supination movement times (sup.MTs) or pronation movement times (pron.MTs) were similar to the MTs of the corresponding single-joint movements. MTs of parkinsonian patients were significantly longer than those of control subjects. MTs were most increased in the forearm supination and forearm pronation of double-joint movements. In contrast to the controls, sup.MT and pron.MT were significantly increased in double-joint movements as compared to single-joint movements. The variations in the flex.MT and sup.MT of the double-joint movements neither correlated for a control subject nor for a parkinsonian patient. For controls, the independent MTs in double-joint movements cannot be explained by minimal principles (minimum energy, minimal torque change), but suggest that two separate motor programs are superimposed. In Parkinson's disease, there seems to be a deficit in superimposing two separate motor programs.

A model of human aiming movements applied to Parkinson's disease.

Healthy control subjects and Parkinsonian patients with and without l-DOPA medication were tested in a motor paradigm. The subjects were instructed to aim with the forearm as fast and as accurately as possible to the illuminated target. A quantitative dynamic model for planning and execution of voluntary aiming movements is developed. The proposed 'motor model' reproduces Parkinsonian symptoms and the therapeutic effects of the drug. The proposed model implies that the basal ganglia store movement and limb specific parameters which are necessary for the control of voluntary aiming movements. The model is contrasted against analytic concepts of motor control. Analytic concepts assume that movements are planned in space coordinates and then transformed to neural activities corresponding to the muscle force. In contrast, the neuronal activities simulated in the proposed 'motor model' can not be described by the terms 'planned trajectory', 'muscle force' or similar terms but suggest a more abstract dynamic concept.

A dynamic model of motor basal ganglia functions.

Fast aiming movements were measured in a choice reaction paradigm in a healthy control group and in Parkinsonian patients. The patients were tested without ('off') and with 3,4-dihydroxyphenylalanine ('on') (L-dopa) medication. The movement trajectories were used to estimate the parameters of a dynamic linear model. The model is based on the functional structure of the basal ganglia-thalamocortical circuit with direct and indirect pathways linking the putamen to the basal ganglia output nuclei (Albin et al. 1989). The output of the circuit is connected to a model for the motor neuron-musculo-skeletal system. The gain kd for the direct pathway and the gain ki for the indirect pathway were estimated. They were found to be significantly decreased for Parkinsonian patients in 'off' compared with the control group. L-dopa therapy in Parkinsonian patients increased the gains of the direct and the indirect pathway almost to normal values which implies that the long-term dopamine level in the striatum was excitatory for the direct and for the indirect pathway. This result is restricted to movements of correct size. For movements of diminished size, which are typical for Parkinsonian patients, the model predicts that the dopamine level in the striatum is excitatory for the direct pathway but inhibitory for the indirect pathway. The simulated values for neuronal activities are in agreement with expected values according to the experimental data. The proposed model of the 'motor' basal ganglia thalamocortical circuit implies that information about biomechanical properties of the musculo-skeletal system is stored in the 'motor' basal ganglia-thalamocortical circuit, and that the basal ganglia are involved in computation of the desired movement amplitude.