This paper investigates the performance of a modified conventional solenoid valve as a low-cost controllable reciprocating force actuator. The applied modifications include adding a spring for plunger return mechanism, applying a bias current for pre-compression of the spring, and minor machining of the plunger rod. Potentially, this actuator can be employed in many applications, e.g. active noise and vibration control systems. A mathematical model of the actuator is given using the fundamental electromagnetic relationships. This model identifies the transfer function between the applied current and the output force. An experimental analysis in the frequency domain is conducted to obtain the current/force transfer function and validate the mathematical model. It is shown that in the stroke range of interest, the nonlinear analytical model of this actuator can be well estimated by a linear model. To investigate the performance of the actuator in a real application, this actuator is installed and tested in an active engine mount prototype. The analytical model of this engine mount is modified to include the actuator. The simulation result indicates that the stiffness and damping of this mount is tunable by controlling the input current to the actuator. The experimental results are also in close agreement with the simulations.

Study design: Prospective observational study of acute spinal cord-injured (SCI) patients. Objectives: To determine how effectively mean arterial blood pressure (MAP) and spinal cord perfusion pressure (SCPP) are maintained at target levels in acute SCI patients. Setting: Single-institution study at a Canadian level-one trauma center. Methods: Twenty-one individuals with cervical or thoracic SCI were enrolled within 48 h of injury. A lumbar intrathecal drain was inserted for monitoring intrathecal cerebrospinal fluid pressure (ITP). The MAP was monitored concurrently with ITP, and the SCPP was calculated. Data was recorded hourly from the time of first assessment until at least the end of the 5th day post injury. Results: All subjects had at least one recorded episode with a MAP below 80 mm Hg, and 81% had at least one episode with a MAP below 70 mm Hg. On average, subjects with cervical injuries had 18.4% of their pressure recordings below 80 mm Hg. Subjects with thoracic cord injuries had on average 35.9% of their MAP recordings o80 mm Hg. Conclusion: It is common practice to establish MAP targets for optimizing cord perfusion in acute SCI. This study suggests that even in an acute SCI referral center, when prospectively scrutinized, the actual MAP may frequently fall below the intended targets. Such results raise awareness of the vigilance that must be kept in the hemodynamic management of these patients, and the potential discrepancy between routinely setting target MAP according to 'practice guidelines' and actually achieving them.

No abstract