Temporomandibular joint injury potential imposed by the low-velocity extension-flexion maneuver.

PURPOSE: It has been proposed that significant temporomandibular joint injury can occur as a result of rapid extension-flexion motion of the neck (whip-lash). This motion, which is experienced by passengers in vehicles that undergo rear-end collisions, has been described as causing rapid protrusion and opening of the mandible. It has been speculated that this relative motion between the mandible and the cranium produces forces at the temporomandibular joint (TMJ) that injure the articular elements. The objective of this study was to measure these forces by an experimental method. MATERIALS AND METHODS: Accelerometer sensor and high-speed cinematographic data were obtained from the kinematic responses of live human test subjects positioned as occupants in motor vehicles that underwent staged low-velocity rear-end collisions. Linear and moment forces generated at the TMJs were obtained from the resultant acceleration pulse at the craniomandibular complex, estimation of the mass properties of the mandible and its appended soft tissues, and the application of Newton's Second Law of motion. RESULTS: The maximum linear forces generated at the TMJ in a rear-end collision resulting in a velocity change of the test subject of 8 km/h (5 mph) were in the 7 to 10 N (1.6 to 2.2 lb) range. Moment forces at the joint peaked briefly at 0.55 N.m (4.81 lb-in). CONCLUSIONS: These force magnitudes generated at the TMJ constitute a minor fraction of the forces experienced at the joint during normal physiologic function. It is a conclusion of this study that injuries to the TMJ attributed to low-velocity "whiplash" cannot be accounted for by the joint forces produced by this maneuver.

Cardiac cycle phase uncertainty: another source of error in indirect blood pressure measurement.

Cardiac cycle phase uncertainty causes a small error in indirect estimation of arterial blood pressure by sphygmomanometry. A simple analysis yields a statistical description of the error and a rule for its reduction: correct bias by adding to the systolic estimate and subtracting from the diastolic estimate one-half of the per-cardiac-cycle cuff deflation decrement. If several measurements are taken, the least-square estimate is approximately the arithmetic mean of the greatest and least of the bias corrected estimates.

A quasi-power theorem for bulk conductors: comments on rheoencephalography.

A special case of Tellegen's theorem, the quasi-power theorem, can be readily developed for bulk conductors, and a bulk conductor analog of Cohn's theorem follows which allows prediction of sensitivity of impedance plethysmographic measurements to tissue impedance changes in a system of bulk conductors. An example addressing the effects of scalp and cranium on the inference of regional blood flow in brain tissue begs additional questions about the origins of the rheoencephalogram.

Mean-square error due to gradiometer field measuring devices.

Gradiometers use spatial common mode magnetic field rejection to reduce interference from distant sources. They also introduce distortion that can be severe, rendering experimental data difficult to interpret. Attempts to recover the measured magnetic field from the gradiometer output will be plagued by the nonexistence of a spatial function for deconvolution (except for first-order gradiometers), and by the high-pass nature of the spatial transform that emphasizes high spatial frequency noise. Goals of a design for a facility for measuring biomagnetic fields should be an effective shielded room and a field detector employing a first-order gradiometer.