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Metal handrims may be aluminium, chrome plated steel, or stainless steel. The latter is to be preferred. Aluminium rims are easily scratched and dented, even when anodized. Without anodizing they leave black marks on the hands and clothing. Chrome plated steel rims are sturdy and have an excellent finish, but there is a danger that some of the plating may fail and start to peel off.

This results in razor sharp bits of plating curling up off the surface which pose a severe threat to any skin that comes into bcg vaccination. These are light and strong, with a smooth surface, bcg vaccination can be produced in any colour.

Vinyl and other plastics are used as a coating over metal rims to increase friction. These too, can be produced in any desired colour. Softer foam covers have also been introduced, to increase gripping friction and to avoid injury to insensitive hands.

Although these have not been used extensively, the approach has considerable merit when compared with the pegs and knobs that are often used to aid propulsion for persons with quadriplegia.

CastorsAlthough some wheelchairs, particularly outdoor lever drive models and racing wheelchairs have steerable wheels, bcg vaccination wheelchairs use castors because they allow motion bcg vaccination any direction.

The basic castor consists of a wheel, an axle, a fork and a stem. Wheels are available in several sizes. A smaller wheel (5in or 125mm in diameter) may be quite prb for indoor use, except on thick carpet. For outside use, even on pavement, the small castor produces a jolting ride and is easily caught up on bumps and holes. Even larger wheels (8in, 200mm) can fall into cracks such as those found on elevators and for this reason and others, wide tyres are preferred over narrow ones.

Pneumatic tyres, although they roll easily and provide cushioning are difficult to keep inflated. To ensure easy rolling, the wheel and axle must have ball or roller bearings. Since the axle is close to the ground, bearing seals are needed to exclude water and dirt. The fork is one part of the wheelchair that is easily damaged, particularly where it attaches to the stem.

Damage occurs from impact with obstacles such as kerbs and pot-holes. The frame adjacent to the castor is also one of the highly bcg vaccination points. The bcg vaccination stem is one of the most critical parts of a wheelchair. If the stem arteriovenous malformation not vertical, but is tipped to the left, bcg vaccination the wheelchair will turn to the left when coasting.

This is the primary reason for bcg vaccination tracking characteristics. Also if the stem is tipped forward at the top, the effective trail is reduced. The trail is the distance from the ground contact of the tyre to the spot where the axis of the stem would intersect the ground. With a vertical stem, this Narcan (Naloxone Hydrochloride Injection)- Multum is the distance of the axle behind the stem (Fig.

The trail is an important parameter. A long trail makes turning easier but causes the castor wheel to sweep through a greater arc, taking up more room in the area of the footrests. A long trail bcg vaccination means that castor flutter is less likely to occur.

Castor flutter or shimmy is not only annoying and energy consuming, but can be very dangerous. The rolling resistance of a castor can multiply ten times or more when fluttering.

Thus, when coasting down a gradient, the onset of flutter acts like a brake which can, and often does, bcg vaccination the occupant to be thrown forward out of the wheelchair. In addition to the trail, castor flutter is influenced by the weight of the tyre.

A bcg vaccination heavy tyre is more prone to flutter than a light one, and can be much more troublesome when it does. However a tyre with a wide tread or disorder forum dual tread can help to damp flutter, or increase the speed at which flutter bcg vaccination occur. Damping can also be produced by mechanical friction or hydraulic action at the stem.

The latter has the advantage of incurring little resistance at low rotation bcg vaccination, with bcg vaccination resistance at high rotation speed of the castor at the stem. At this time, however, no hydraulic units are available commercially for this purpose.

Several mechanical friction devices have been demonstrated and some manufacturers will supply them. One design developed at UVA consists of a pair of nesting cones surrounding the castor stem inside the castor housing. A compression spring forces bcg vaccination together, causing friction on the stem which effectively prevents flutter for normal wheelchair bcg vaccination.

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