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Biomedical subjects

J A Malmivuo

Publications and source records attributed to J A Malmivuo.

9 recordsLinked to original sources
PubMed1990

The influence of electromagnetic interference and ionizing radiation on cardiac pacemakers.

Adverse effects of the ionizing and non-ionizing electromagnetic fields on five pacemaker models have been tested. The study consisted of three parts: 1. measurement of magnetic fields in a radiotherapy room (microtron MM14), 2. the application of non-ionizing electromagnetic fields on pacemakers in a test laboratory (1...1000 microT, 10...10000 Hz), and 3. the application of ionizing radiation of different types of radiotherapy devices on the pacemakers. The magnetic field strength in the microtron treatment room was found to be under 7.5 microT, which is one order of magnitude lower than the tolerance level obtained for the pacemakers in the test laboratory. All the tested pacemakers tolerated the ionizing radiation dose levels (less than 60 Gy) which are used in the radiotherapy.

Electromagnetic Fields↗
PubMed1986

Comparative study of the normal vector magnetocardiogram and vector electrocardiogram.

The normal vector magnetocardiogram and its statistical variation are described in detail. The magnetic heart vector of 18 healthy subjects is detected with the corrected unipositional lead system and analysed together with the simultaneously recorded Frank vector electrocardiogram. The mean values and standard errors for the magnitudes and directions of the magnetic QRS and T waves are calculated with a digital computer. The interindividual variability of the normal magnetic and electric heart vectors was found to be about the same. The inaccuracy in the detector placement at the fourth intercostal space gives rise to only a small error in the direction of the detected magnetic heart vector. This is due to the self-centering effect of the lead fields in the heart's region, which arises from the difference in conductivity between the well-conducting heart and the intracardiac blood mass and the low-conducting lungs. The shape of the magnetic heart vector remains unchanged when it is measured at various distances from the chest surface on the line which is perpendicular to the frontal plane and joins with the beginning of the fourth intercostal space. The relationship between the normal magnetic and electrical heart vectors was also studied. The angle between the maximum magnetic and electrical heart vectors was shown to differ slightly from the theoretically predicted value of 90 degrees. Our results support the theoretically known difference in the relative sensitivities of the magnetocardiographic and electrocardiographic leads: the magnetic heart vector is more sensitive than the electrical vector to the terminal phase of the ventricular depolarization, when the activation in the heart appears in a more tangential direction than at the initial phase.

Adult↗
PubMed1983

A pressure curve monitor for intratracheal jet ventilation.

Most of the complications during intratracheal jet ventilation for laryngomicroscopy are due to the unnoticed wearing off of laryngeal muscle relaxation. Recovering laryngeal muscle function will, by slightly narrowing the size of the glottis, influence the slope of the quickly rising part of the pressure curve, when influences on maximum airway pressure are still not detectable. An electronic device incorporating the window comparator technique monitors the pressure curve and sets off an alarm before changes in maximum airway pressure or recovery of muscle strength in the forearm are detectable. The pressure curve monitor could be useful also with intratracheal jet ventilation for treating adult respiratory deficiency and with conventional ventilators during anaesthesia to detect the wearing off of muscle relaxation.

Humans↗
PubMed1977

Measurement of the human magnetic heart vector.

A unipositional lead system has been developed to record the human magnetic heart vector and to permit comparison with the electric heart vector recorded with a conventional Frank lead system. Recordings made in five normal subjects showed a remarkably consistent relation between the electric and magnetic heart vectors. However, the angle between electric heart vector R and T waves was markedly different from the magnetic heart vector R-T angle. In addition, recordings made in two patients with bundle branch block showed a different relation between the electric and magnetic heart vectors compared to normal subjects. These data support the hypothesis that magnetic measurements have a different sensitivity to some components of cardiac activation compared with body surface potential measurements.

Electrocardiography↗
PubMedDate not supplied

Sensitivity distributions of impedance cardiography using band and spot electrodes analyzed by a three-dimensional computer model.

Impedance cardiography (ICG) offers a safe, noninvasive, and inexpensive method to track stroke volume estimates over long periods of time. Several modified ICG measurement configurations have been suggested where for convenience or improved performance the standard band electrodes are replaced with electrocardiogram electrodes. This report assesses the sensitivity of the conventional and three modified ICG methods in detecting regional conductivity changes in the simulated human thorax. The theoretical analyses of the measurement sensitivity employ the reciprocity theorem and the lead field theory with a highly detailed, anatomically accurate, three-dimensional computer thorax model. This model is based on the finite-difference element method and the U.S. National Library of Medicine's Visible Human Man anatomy data. The results obtained indicate that the conventional four-band ICG is not specifically sensitive to detect conductivity changes in the region of the heart, aortas, and lungs. Analyzed modified electrode configurations do not reproduce exactly the measurement sensitivity distribution of the conventional four-band ICG. Thus, although the signals measured with modified spot arrangements may appear similar to the four-band configuration, the distribution of the signal origin may not be the same. Changing from band to spot electrodes does not overcome the methodological problems associated with ICG.

Biomedical Engineering↗