PubMed · 1070233
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H Elmqvist. 1976. Pacemakers and external interference.. https://doi.org/10.1111/j.0954-6820.1976.tb08386.x
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STUDY DESIGN: A direct method for three-dimensional in vivo spine kinematic studies was developed and used to measure segmental motion patterns in healthy subjects. OBJECTIVES: To validate the new method, and to study the L3-L4 segmental motion patterns for complex dynamic movements. SUMMARY OF BACKGROUND DATA: Conventional two-dimensional and three-dimensional radiographic methods have been used in the past to study spine kinematics. Few studies provided a direct approach to study segmental kinematics. No dynamic recordings of three-dimensional segmental motion patterns have been reported previously. METHODS: In 16 healthy men, Kirschner wires were inserted in the spinous processes of L3 and L4. Electromagnetic tracking sensors were attached to the pins. Motion data recorded during ranging exercises were used with biplanar radiographs to calculate L3-L4 segmental motion patterns. Errors resulting from pin deformation and the dynamic accuracy of the tracking system were investigated thoroughly. RESULTS: The average range of motion for flexion-extension was 16.9 degrees, for one side lateral bending 6.3 degrees and for one side axial rotation 1.1 degrees. Large intersubject variation was found in flexion-extension with values ranging from 7.1 to 29.9 degrees. Coupled motion patterns were found to be consistent among subjects in active lateral bending and inconsistent for active axial rotation. CONCLUSIONS: This new method offers dynamic recording capabilities and a measurement error comparable with stereo radiographic methods. Repetitive ranging experiments are highly reproducible. The range of motion for axial rotation seems overestimated in previous cadaveric studies. Coupling patterns show large variations between individuals.
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The article contains analysis of national standards determining maximal allowable levels of electromagnetic exposure in some developed countries. The point of specific interest is the levels in frequency range of 300 MHz-30 GHz, as this range is widely used in most apparatus for mobile communication. Different in various countries, values of the maximal allowable levels appear to be the most strict in Russia. Incomplete knowledge of long-standing exposure to mild electromagnetic fields requires through medical and technical research to determine limits of safe application of mobile communication devices.