| 1. |
- Magnusson, Mats, 1968, et al.
(författare)
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Intervertebral motion during vibration.
- 1991
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Ingår i: Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine. - 0954-4119 .- 2041-3033. ; 205:1, s. 39-44
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Tidskriftsartikel (refereegranskat)abstract
- Vibration exposure is widely recognized as a risk factor for low back pain. An experimental protocol was designed to quantify the intervertebral motion response in human subjects to sinusoidal vertical vibration at 5 and 8 Hz, and at a variety of acceleration levels. Intervertebral motion in the mid-sagittal plane was measured using a transducer linkage system attached to pins placed directly into the spinous processes of adjacent vertebrae. The postures of the subjects were carefully controlled. The effects of forward flexion, arm support, gravitational load, and sitting on a cushion were evaluated. The rigid body motion of the superior vertebra with respect to the inferior vertebra was expressed in terms of relative sagittal plane rotation, axial translation, and anterior-posterior shear translation. It was found that the lumbar motion segments exhibited coupled periodic behaviour in response to sinusoidal vertical vibration, with up to 1 mm peak-to-peak displacement in the axial direction. The greatest intervertebral motion occurred when the subject was exposed to 5 Hz vibration as compared to 8 Hz. For a constant frequency of 5 Hz excitation, the peak-to-peak amplitudes of the computed motions tended to increase as the acceleration level increased. In the flexed posture, with no arm support, the active trunk musculature helped reduce the intervertebral motion. Additional gravitational load on the shoulders caused increased relative axial displacement. A polyethylene foam cushion placed on the seat reduced vibration transmission at 5 Hz excitation and consequently decreased the intervertebral motion.
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| 2. |
- Naredi, Peter, 1955, et al.
(författare)
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Aggregation of microspheres in blood flow measurements.
- 1991
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Ingår i: International journal of microcirculation, clinical and experimental / sponsored by the European Society for Microcirculation. - 0167-6865. ; 10:2, s. 169-80
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Tidskriftsartikel (refereegranskat)abstract
- The aggregation of NEN-TRAC radionuclide-labeled 15 microns resin microspheres was studied in vitro and in vivo. In vitro, the control group not agitated at all was compared with groups subjected to agitation with a Vortex Shaker or agitation with first a Vortex shaker and then a sonification bath. Loading the microspheres in a catheter made agitation unnecessary (5.6 +/- 1.7 aggregates/100 spheres and 2.3 +/- 0.5 microspheres/aggregate). Sonification increased aggregation when the solution was drawn into 1 cc syringes (13.7 +/- 2.6 aggregates/100 spheres and 2.8 +/- 1.2 microspheres/aggregate). In vivo less aggregates were observed. Loading the microspheres into PK 50 catheters and then injecting them into the left ventricle of the heart after agitation in a Vortex shaker for 1 min minimized aggregation (1.6 +/- 1.0 aggregates/100 spheres and 2.2 +/- 0.4 spheres/aggregate). Sonification increased both the number of aggregates and the number of spheres in each aggregate significantly (10.0 +/- 3.1 aggreates/100 spheres and 2.8 +/- 1.3 spheres/aggregate). Aggregates of 10 to 40 microspheres were occasionally observed. When the microspheres were injected into the aorta at the level of the diaphragm, one large aggregate (approximately 50 spheres) was seen. The handling of the microsphere solution is important to prevent aggregation and the treatment recommended by the manufacturer does not seem to be the optimal. Large aggregates, which are rare, might embolize the precapillary arteries. Small aggregates are more common and they might result in disproportionately fewer microspheres in vessels than their actual blood flow. This would make the microsphere method less reliable in blood flow measurements.
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