Ambulance Stretcher Suspensions

Existing methods for vibration isolation of patients transported by ambulance are discussed. Some alternative suspensions are outlined and a relatively simple mechanism analysed. This can give virtually constant vertical natural frequency over a wide range of patient load. Variation in pitch natural frequency can also be minimized at the expense of some variation in vertical natural frequency. The elements used are a coil spring, load arm and an electric actuator. Initial testing of the mechanism has been made to confirm the feasibility of the concept.

The Development and Performance of an Ambulance Stretcher Suspension

The deterioration of the medical condition of stretchered patients during ambulance transport is discussed. The dominant vibration is generally low frequency (below 10 Hz) and in the vertical direction. Assessment of the sensitivity of supine patients to front-to-back vibration is referred to.

Methods of alleviating the vibration experienced by stretchered patients are discussed and particular types of stretcher suspension described.

This suspension has a constant natural frequency of vertical oscillations over a wide range of patient mass. A stretcher ride height (above the ambulance floor) independent of patient mass is achieved.

The stretcher suspension was tested over four types o surface (one ofl-highway), using a commercial vehicle having a chassis similar to that of a commonly used ambulance. Vibration of the vehicle floor and of the stretcher in both the vertical and the pitch senses was measured using accelerometers.

Transmissibility of the stretcher suspension, the stretcher frame and the stretcher mattress was obtained. The vertical vibration level (averaged over the four types of surface) experienced by the patient is compared with vibration tolerance levels for supine patients. Vibration inputs are closest in magnitude to the vibration exposure limit in the range 1.5–4 Hz. The transmissibility of the suspension in this range is between −7 and −9 dB.

Subjective evaluation of the suspension has been favourable.

Clinical experience in rehabilitation robotics

A robotic workstation system for the disabled, based on a commercially available arm, was tested with six patients at the Spinal Injuries Unit, Odstock Hospital, Salisbury. A questionnaire was administered to those who used the system. Users evaluated the usefulness and performance of the system and commented on their reactions to the use of robots in rehabilitation. The users were generally favourable as regards the ease of use of the system using a two-switch input, operating a scanning menu. All users wanted the robot to be able to replay previously created routines, and the majority also wanted to be able to directly control the robot as well. The users were unsure about the potential usefulness of the system. Because a robot is by definition a flexible device, the context in which it is introduced will effect the way it is received by potential users. Tests in a hospital environment are useful because there is a high concentration of users in their own home situations will give a better idea of the usefulness of such devices. The system was not ideal from the point of visibility and layout, and was too large for use in a domestic environment. The layout was largely dictated by the geometry of the manipulator. Therefore a new workstation system has been constructed using a purpose built manipulator. This new system particularly aims to overcome the poor layout of the earlier workstation and benefits from feedback from users.

Development of a robot arm and workstation for the disabled

A robotic workstation for the severely physically disabled is being developed. The prototype system consists of a commercially available arm mounted in a workstation set up for various manipulative tasks. This system has been tested with eight disabled users in a hospital situation and is to undergo evaluation in the homes of disabled users. Based on experience with this system, a new arm has been designed and will be built into a redesigned workstation.

Mechanical feeding aids for patients with ataxia: design considerations

A mechanism has been designed which transforms steady, vertical hand motion into the scooping motion of a spoon. The mechanism incorporates vibration isolation through a spring-damper system to attenuate the transmission of low frequency (2-8 Hz) hand tremor to the spoon. A series arrangement of spring and damper has produced spoon amplitudes of between 5 and 12% of the hand amplitude at the lowest ataxic tremor frequencies. A prototype has been tested by four ataxic patients. The degree of vibration isolation and the ability to pick up food were adequate but the mechanism was felt to be unacceptable as a feeder for social reasons. Two other mechanisms have also been considered.

A feeding mechanism for Parkinson's disease patients

A pivotted four-bar chain mechanism has been studied and built as a feeding aid for Parkinson's patients. This system provides a good feeding path. Guidance is by means of a spring restrained sliding handle. The tremor exhibited by three patients was established in constant force tests. Shake tests using simulated inputs spanning the frequency range indicated (2.5 Hz-6 Hz) established the vibration isolation properties of the system.