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Biomedical subjects

A J Mulder

Publications and source records attributed to A J Mulder.

7 recordsLinked to original sources
PubMed1993

Fatigue during functional neuromuscular stimulation.

Discontinuous activation of muscle compartments is used to postpone the occurrence of fatigue during both normal activation and artificial stimulation. Periods of force development are interrupted by passive periods during which the muscle can recover. Since it is not known how fatigue parameters depend on intermittent stimulation, we compared fatigue generated by continuous electrical stimulation with fatigue resulting from intermittent stimulation schemes. T5-T6 paraplegics participated in the experiments. Continuous stimulation generated a torque time course that can be described by a rising and a falling exponential time constant. The falling time constant ranged from 100 to 200 sec in all four patients and did not depend on the amplitude of the stimulation pulses. The torque developed at times greater than 250 sec was asymptotically constant and proportional to the maximal torque developed by each patient. Intermittent stimulation appears to postpone fatigue markedly. The torque time course developed in each on/off cycle again was a double exponential. In intermittent stimulation schemes average torque determines the muscle's performance. Therefore, average torque versus time was calculated from the intermittent stimulation data. These relations also follow a double exponential, accurately providing confident estimates of fatigue parameters. Fatigue caused average muscle torque to decline to a constant level which, for each patient, was uncorrelated with the duty cycle of the stimulation pattern. Between patients these levels varied from 18.3 +/- 7.1 to 9.9 +/- 4.3 (% of maximal torque +/- standard error). These findings result in a model that could be of use in controllers for functional neuromuscular stimulation (FNS) that take into account non-stationarity caused by fatigue.

Electric Stimulation Therapy↗
PubMed1992

On/off control in FES-induced standing up: a model study and experiments.

Control of paraplegic standing up was studied with respect to the limitation of the end-velocity of the knee joint when the patient reaches the upright position. Closed-loop on/off control of knee extensor muscle was compared with open-loop controlled standing up both in a model study and in paraplegic patients in a controlled model situation. Criteria were knee-end-velocity and knee extensor muscle activation time. Sensitivity of the system to additional arm support and (in the model study) to the dynamics of knee extensor muscle was studied. It is concluded that the control scheme may reduce knee-end velocity to about 40 per cent and knee extensor activation time to near 70 per cent of the respective open-loop values.

Biomechanical Phenomena↗
PubMed1992

Low-level finite state control of knee joint in paraplegic standing.

Low-level finite state (locked-unlocked) control is compared with open-loop stimulation of the knee extensor muscles in functional electrical stimulation (FES) induced paraplegic standing. The parameters were: duration of standing, relative torque loss in knee extensor muscles, knee angle stability, average stimulus output and average arm effort during standing. To investigate the impact of external mechanical conditions on controller performance, experiments were performed both under the condition of a freely moving ankle joint and of a mechanically stabilized ankle joint. Finite state control resulted in a 2.5 to 12 times increase of standing duration or in a 1.5 to 5 times decrease of relative torque loss in comparison with open-loop stimulation. Finite state control induced a limit cycle oscillation in the knee joint. Average maximum knee flexion was 6.2 degrees without ankle bracing, and half that value with ankle bracing. Average arm support was 13.9 and 7.5% of the body weight without and with ankle bracing respectively.

Adult↗
PubMed1990

Artificial-reflex stimulation for FES-induced standing with minimum quadriceps force.

A control strategy is proposed to decrease quadriceps activity during standing. Modified on/off (or artificial reflex) control is used: a non-numerical or finite-state control scheme based on feedback of knee angle and angular velocity. The control strategy is evaluated in paraplegic patients in an experimental setup using transcutaneous stimulation. The stability of the system and its sensitivity to various control parameters are determined. It is concluded that the control scheme will enable reduction of muscle force independent of additional mechanical bracing or specific posture, and may result in continuous dynamic activation of muscle.

Electric Stimulation Therapy↗
PubMed1988

Antagonism of midazolam sedation by flumazenil: a placebo-controlled study in patients recovering from intravenous anaesthesia with high doses of midazolam.

Twenty adult surgical patients were anaesthetized with high-dose midazolam and alfentanil by infusion, vecuronium, and intubated and ventilated with 50% N2O in O2. The midazolam and alfentanil infusions were stopped at the end of surgery. Residual neuromuscular blockade and ventilatory depression were antagonized and the patients extubated. In the recovery room, patients were randomly allocated to receive either flumazenil 1 mg of placebo i.v. Before, and until 2 h after injection, patients were asked to perform psychomotor tests. In addition, sedation, comprehension and orientation were scored. The flumazenil (n = 10) and the placebo (n = 10) groups were comparable. Prior to injection all patients were heavily sedated. After flumazenil all were awake within 2-3 min, but fell asleep again 15-60 min later. The improvement in test scores was sustained for a longer time. After placebo, patients awoke in 1-2 h. At 60 and 120 min, test scores in the two groups were similar. Heart rate, blood pressure and respiration rate did not change. No side-effects were observed or reported. It is concluded that flumazenil is an effective and safe antagonist of high dose midazolam, with a rapid onset but a short duration of action.

Adult↗
PubMedDate not supplied

A low-cost FES exercise bicycle for training paraplegics at home.

The success of FES exercise programmes for training paraplegic muscles at home depends highly upon the availability of reliable, easy-to-use and inexpensive training equipment. For endurance training, FES bicycle exercisers are well accepted. However, they are not suited for home use due to the high expense of commercially available equipment. This paper describes the development of a FES exercise bicycle for use at home. It consists of a standard bicycle ergometer with minimum modifications. The exerciser can be used by the patient sitting in the wheelchair, and may be used with any two-channel muscle stimulator.

Bicycling↗