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Biomedical subjects

J A van Alsté

Publications and source records attributed to J A van Alsté.

15 recordsLinked to original sources
PubMed1994

Dynamic pumping characteristics of the Hemopump.

While pumping blood with the Hemopump in sheep, the ability of predicting the instantaneous pump flow from the pressure difference over the pump system and pump parameters was investigated. For rotational speed n between 300 and 475 revolutions per second (rps), maximum pump flow QO(n) at zero pressure difference, internal pump resistance R(n), and inertia parameter Lc were found to be suitable parameters for Hemopump characterization. The instantaneous pump flow could be estimated with an accuracy of approximately 1.0 [ml/s]. The values of the pump source parameters (+/- sd) were: (the figures in parentheses represent earlier reported values found while pumping water) Lc was a constant of 21.4 +/- 6.4 [Pa.s2/ml] (in water: 10.8). QO(n) is linearly related to rotational speed n according to: QO(n) = QO(ncen) + CQ(n-ncen), with QO(ncen) = 49.4 +/- 4.5 [ml/s] (in water: 60.3), CQ = 142 +/- 22.4 [10(-3) ml] (in water: 146), and ncen = 387.5 [rps]. R(n) is linearly related to rotational speed n according to: R(n) = R(ncen) + CR(n-ncen), with R(ncen) = 556 +/- 124 [Pa.s/ml] (in water: 502) and CR = 1.47 +/- 0.83 [Pa.s2/ml] (in water: 1.67).

Animals↗
PubMed1992

Dynamic pumping performance of the Hemopump--a small intraventricular blood pump.

We studied the pumping characteristics of the Hemopump, a commercially available miniature intraventricular blood pump for temporary support of failing hearts. The Hemopump is an axial flow pump of which the characteristics can be described by turbomachine theory. Experiments with water and a mock circulation verified that the pumping characteristics of the Hemopump in terms of both pressure head and flow as a function of rotational speed, very well can be described by a first order differential equation. The influence of blood with its non-Newtonian character is being investigated.

Heart-Assist Devices↗
PubMed1990

Real-time gait assessment utilizing a new way of accelerometry.

Real-time registration of body segment angles is essential in artificial body position control. A new method is presented for the real-time calculation of the lower extremity angles using data obtained from pairs of two one-dimensional accelerometers. It is shown that, assuming rigid-body dynamics and simple hinge joints, relative angles (i.e. angles between segments) can be calculated without integration, thereby solving the problem of integration drift normally associated with accelerometry. During the stance phase of walking, the relative angles can be transformed to absolute angles (i.e. relative to the gravitational field direction) for the different leg segments. The feasibility of relative angle calculation is demonstrated by calculation of the knee angle of a healthy subject. Stability and resolution were demonstrated with measurements during standing. Measurements during standing up, sitting down and walking showed that shock (heel-strike) and skin movements, due to movements of the underlying muscle tissue, are the main error sources. Additional signal processing, e.g. low-pass filtering, can be used to diminish this error. The accuracy of the knee angle found is shown to be high enough to be used in a feedback controller for functional electrostimulation of the lower extremities.

Biomechanical Phenomena↗
PubMed1989

Multielectrode intrafascicular and extraneural stimulation.

The relationship between nerve stimulation, pulse amplitude and isometric muscle force was measured to investigate recruitment of motor units. Force addition experiments were performed to obtain insight in the intersection of motor unit groups recruited by different electrodes. Intrafascicular and extraneural multielectrode configurations were used for nerve stimulation. Experiments were performed on rats. The common peroneal nerve was stimulated and the forces of the tibial anterior and extensor digitorum longus muscles were measured isometrically. Recruitment was more stable for intrafascicular electrodes than for extraneural electrodes. Especially for intrafascicular electrodes no strict inverse recruitment was observed. Force addition experiments indicated that small overlap of recruited motor unit groups occurred more often for intrafascicular than for extraneural electrodes.

Animals↗
PubMed1987

Lower extremity amputees with peripheral vascular disease: graded exercise testing and results of prosthetic training.

Thirty-nine subjects, mean age 72 (range 52 to 89), with a leg amputation because of peripheral vascular disease performed graded exercise testing at the start of their prosthetic training program. Their walking performance at the end of the program was assessed and compared with the test findings. They had a history and rest electrocardiogram (ECG) examination which revealed cardiac problems in 75% of the patients. The exercise test was performed on a specially designed arm ergometer permitting coordinated exercise of arm and trunk muscles. Cardiac condition was judged by the achieved peak heart rate (mean 125 +/- 3.8 beats per minute) and observed ECG abnormalities. In only three patients exercise-induced ECG abnormalities were found at peak workload. The mean peak workload was 52 +/- 1.9W. It was concluded from these results that the average physical and cardiac condition is poor in vascular leg amputees. In 34 patients (87%) the prosthetic training was successful. Fourteen patients needed a walking frame and twenty could walk without a walking frame. The probability of achieving walking without a walking frame was 70% in patients with peak workload above 45W and 30% in those with peak workload lower than 45W.

Aged↗
PubMed1986

ECG baseline wander reduction using linear phase filters.

The continuous real time reduction of baseline wander is a considerable problem in electrocardiography during exercises. Our solution consists of spectral filtering. The legitimacy of high-pass filtering of the ECG by means of digital linear phase filters with a low cut-off frequency as high as the heart rate is shown. The specifications of these filters are derived from experimental results. Special hardware is presented that simultaneously performs the desired real-time filter operation in four ECG leads.

Analog-Digital Conversion↗
PubMed1985

Exercise electrocardiography using rowing ergometry suitable for leg amputees.

Patients unable to perform heavy leg exercises cannot perform standard exercise ECG tests using bicycle or treadmill ergometry. A rowing ergometer was developed to enable an electrocardiographic stress test. Sixteen ambulatory patients with documented coronary insufficiency performed graded exercises. Comparison revealed no significant differences in several areas. Eleven patients with above-knee amputations, inevitable because of peripheral vascular disease, were able to perform rowing exercise only. This can result in cardiac loads adequate for diagnosis of coronary heart disease. No patient experienced difficulties with rowing. Rowing exercise can be a suitable alternative to bicycle exercise for the evaluation of coronary artery disease.

Adult↗
PubMed1985

Exercise testing of leg amputees and the result of prosthetic training.

Thirty-nine patients undergoing rehabilitation following leg amputation were examined to determine cardiac status, which included clinical examination and a graded exercise ECG test, using an arm ergometer. Results were compared to final walking ability. It was found that the cardiac status of these patients was generally poor and that the exercise ECG results did co-relate to walking ability.

Adult↗
PubMedDate not supplied

Interactive control of physiological experiments.

Physiological and biological experiments often require the imposition of repeated influences on an organ or organic system. Then the experimental protocol requires many repetitive functions with adjustable interval times and magnitudes, which are prepared or dictated by experimental results. To control such an experimental set-up interactively with a small computer we chose a more or less general approach. A special language syntax has been developed for: experiment definition; experiment composition in advance; real-time control during the actual experiment; and registration of the actual protocol parameters. The interactive control was realized using the special language and an interpreter as one of the parallel processes for the experimental control.

Animals↗
PubMedDate not supplied

Multi-tasking control system for real-time processing of biomedical signals.

A general multi-tasking control system has been developed for real-time signal processing. This control system, written in the language PASCAL, enables tasks (expressed as PASCAL procedures) to be performed as separate, concurrent processes, with adjustable priority levels. Modifications of this system such as the addition of new processes and a change of the number of priority levels can be realised easily. The system has been used for the implementation of the real-time algorithms involved in monitoring exercise electrocardiograms. For this application an LSI 11/23 is used with the support of a slave processor for the calculation of inner products. The control system is also suitable for other real-time applications when process requirements are not too heavy.

Algorithms↗