Life on Wheels (58 page)

Gel cushion designs attempt, in effect, to replace the consistency and support of atrophied muscle tissue. Highly engineered gel fluids are placed in pouches and usually attached to a foam base so that the cushion conforms to the pressures placed on it. As a result, gel cushions provide excellent pressure distribution and are very comfortable. Many gel products also offer supplemental inserts to stabilize your legs. Your knees might tend to fall together (adduction) or apart (abduction), so such an accessory can help keep your legs straight, which also aids your overall posture.

Gel cushions are much heavier than other types, which can cancel out some of the benefits of your lightweight wheelchair. If you will be taking the cushion in and out of the chair often—transferring into a theater seat, getting in and out of the car, etc.—then weight becomes a consideration for ease of this much handling.

If you jump up and down curbs using wheelie techniques, or commonly experience similar impact in your chair, a gel cushion might not be ideal. When you sit in a gel cushion, there is no further “cushiness” to absorb impact, a concept known as impact loading. Other cushion types are better able to absorb impact.

Another drawback to gel cushions is the possibility of them “bottoming out” as the gel is pushed aside by your weight. You can help prevent this distribution problem by kneading your gel cushion once a day, keeping the fluids loose and spread evenly. Look for a design that divides the gel portion into several sections so that all of the gel cannot push entirely to the sides.

There is also the chance of the gel leaking. Although cushions arrive with patching kits, patches are ineffective when the breach is at a seam, which is often the case. A leak might be very minor, or it could be an extremely messy affair.

Air floatation cushions support the body entirely on air. A typical example is the ROHO® cushion, designed with a group of small, interconnected rubber balloons arranged in rows. Pressure is balanced by air shifting out to surrounding balloons, spreading pressure evenly against your skin. The whole system is closed, so air floatation cushions can’t bottom out the way gel cushions can.

If you have a pressure sore, you can tie off individual balloons to reduce contact under that area, allowing you to spend more time sitting as the sore heals. Air cushions are relatively lightweight and are waterproof, allowing for double duty in the bathtub or on a boat.

Air cushions can be less stable for those who move around a lot in their chair, but recent designs offer either low-or high-profile options that minimize this problem. Some allow halves or quadrants of the cushion to be inflated separately, which also helps ensure optimal posture if there is some asymmetry in your body. The balloons used in air cushions can be punctured, of course, and leaks do occur, although a fairly heavy-duty rubber is used, similar to the rubber used for tire tubes. Patching them is easier than with the gel design. The hard part is submerging the cushion under water to find the leak (look for escaping air bubbles).

The biggest drawback to air cushions is that they require more maintenance. It is necessary to check the pressure frequently, especially if you have pressure sores.

Thermoplastic urethane honeycomb cushions, such as those from Supracor®, are the most recent development in the world of cushions. Because there are many individual cells—like a beehive—these cushions are able to distribute weight evenly, but there is no risk of leaking gel or of an air bladder being punctured. The many open spaces in the beehive structure of the cushion allow air to travel more effectively. This design helps to protect against skin breakdown because your skin is kept cooler and moisture is prevented from collecting.

Urethane honeycomb cushions are very light and absorb shock, and a low-profile cushion can provide significant support. These cushions can even be thrown into your washing machine and dryer, making them attractive for people with incontinence problems, during which the cushion will be soiled from time to time despite best efforts at bowel and bladder management. Urethane cushions are available in standard or in contoured shapes and can also be purchased for use with a bed mattress.

In this design, an air pump creates alternating pressure in various chambers of the cushion, of particular interest to those with more significant disabilities who are unable to perform their own weight shifts to relieve pressure. Sitting for extensive periods of time without pressure relief causes the muscle and fatty tissues to separate, putting the delicate skin layer in closer contact with the bone. This creates even more pressure on the skin. Lack of air circulation increases the temperature between you and the cushion. Moisture collects and is trapped against the skin. All of this further increases the risk of a sore.

One alternating pressure solution is the ErgoDynamic™ Therapeutic Seating System from ErgoAir in New Hampshire. This system pumps air into and out of alternating portions of the cushion. The product is contoured for pelvic stability. Special vent holes serve to allow the flow of air and moisture. In a five-minute cycle, compartments are inflated and deflated to shift support alternately between the ischial (sit) bones and the hips. Both areas get regular periods of complete pressure relief. The manufacturer likens it to a massage while you sit, with the resulting promotion of blood flow. In some cases, the makers suggest that a pressure sore can even heal while you sit. This cushion system can be plugged into some power chair batteries or charged in a cigarette lighter in your car.

Alternating pressure products are of course heavier—given their use of batteries and air pumps—and, like air floatation cushions, are prone to puncture. However, the technology for these innovative systems is likely to evolve further in the future as new materials and batteries are developed.

Although we usually think of a seat as a single unit—such as a couch or recliner—seats, backs, cushions, and armrests are distinct when you are choosing your wheelchair. Seats, backs, and cushions have a number of interrelationships, so, to some degree, you will need to think about them all at the same time. For instance, how high you will sit on the chair and where your feet are in space will be determined by the seat-to-floor height of the seat pan plus the thickness of the cushion.

Your chair should be as narrow as possible for your body size without creating contact points that can cause pressure sores. A seat that is too wide limits mobility. Even an additional fraction of an inch in the width of the chair can make the difference between being able to get down an aisle in a store or past a couch at the home of a friend. You don’t want to squeeze yourself into the seat—if you wear a heavy coat in the winter, or typically work in a business suit with a jacket, the width of the seat should take this into account—but you also don’t need the wasted space or mobility limitations of a chair that is too wide. A wider chair is also heavier, given the extra metal in the frame.

A seat that is too wide will promote poor posture. If you have extra space, you are more likely to slump to one side or the other. You might think that because you would have more room to shift your position, extra seat width would be helpful in the prevention of pressure sores, but this is not a good strategy for skin management. You don’t want to protect your skin by risking damage to your spine with twisted sitting postures. Rather, your skin management program should consist of proper cushioning and diet, as well as pushups while you are in the chair. Put a high priority on good postural habits.

A wider chair also means that the wheels will be wider apart, making it necessary for a manual-chair wheeler to reach farther, extending the arms out to the side. Wheeling with the arms extended is a less efficient way to wheel, will be more fatiguing, and puts your shoulders at a great risk of overstraining. If the chair has armrests, they might further interfere with the process of wheeling if the chair is too wide for you, or the armrests may rub against your arms as you wheel.

A wider chair does provide better lateral stability, which will help prevent a manual chair from tipping over sideways, but, frankly, unless you are reckless or wheel on rough terrain, tipping sideways is highly unlikely. Stability can be similarly achieved by proper adjustment of camber (discussed above), determined by the axles and plates that are typical on most chairs today.

If weight management is difficult for you, you will want to take the possibility of weight gain into consideration when determining the seat width. You don’t want to find yourself ultimately squeezed into a chair purchased when you were lighter. Your risk of pressure sores—particularly at your hip bones—will increase considerably. If you become heavier and truly need a new chair, you might have to fight with your funding source for approval or be forced to dip into your own savings or credit limit to buy new wheels. But do you want to purchase a wider chair on the assumption that you will gain weight? Is that risking a self-fulfilling prophesy, inviting weight gain? The best solution is to reach a stable weight, whatever is normal for you, and then specify a chair that will remain appropriate to your needs while you practice the best weight-control habits you can.

It is critical to get the depth of the seat pan right when you specify the dimensions of your chair. The seat pan should be deep enough so that the seat is in contact with as much of the bottom of your thighs as possible without making contact behind your knees.

When the seat pan is too shallow, your upper legs extend beyond the front edge and more pressure is placed on your ischial “sitting” bones. This additional pressure increases the risk of skin breakdown. You are also giving up greater stability. The chair can’t “carry” you if it can’t make full contact with your body. Without full seat support, your body might be prevented from being in its neutral position, risking spinal curvature or muscle and tendon strain. A too-shallow seat pan also means that your feet will not rest properly in the footrests, which will be located further back underneath your legs instead of under or just ahead of your knees where they belong.

On the other hand, when the seat pan is too deep, you will be unable to sit properly against the chair back. You will be kept from sliding back fully in the seat, stopped behind the knees. When the seat is too deep, the only way to make contact with the back of the chair is to rotate the pelvis backward and round the spine. In other words, you will have to slump. Slumping is potentially dangerous for the spine, as it can cause degeneration, and is also a source of chronic back pain. This posture also makes it difficult for you to wheel efficiently in a manual chair and, so, contributes to the risk of chronic shoulder strain as well.

A seat pan that is too deep can interfere with the position of your legs if you use calf supports with your footrests. Calf supports keep the legs in a more-forward position. The seat pan might need to be shallower to compensate.

A deeper seat means a heavier chair due to the added metal in the frame. When more of the chair is ahead of the axle, you will feel as though you are pushing even more weight. If you require extra depth in the seat pan, you will need to adjust the forward position of the main wheel axles so the chair is not too front heavy, particularly if you rely on doing wheelies in your wheeling style.

A crucial element that must be taken into consideration before you can determine the appropriate depth of the seat pan is the type of seat back you will use. A fabric-upholstered back requires you to sit a little farther back in the chair and tends to loosen with time unless it is equipped with adjustable tension straps. A rigid back will not change much over time, but some are quite thick and cause you to sit more forward on the seat.

The minimum height you can sit off the ground will be determined by physical factors. The main considerations are the length of your legs and the clearance needed for footrests. Whether you’ll choose to sit higher than the minimum—and how much higher—will depend on environment, such as the height of standard tables or other surfaces that your knees must go under, and on personal preferences.

The seat-to-floor height of a chair (typically specified separately for the front and back of the seat) will be part of the frame dimensions ordered from the factory. It can also be adjusted in a manual chair in which the axles are installed relative to the frame. By lowering the axles, you essentially raise the frame and, so, the higher the seat. On a modular power chair, the seat structure is installed on top of an independent drive unit and so does not depend on the wheel position. The seat will often be adjustable within a range of a certain number of inches. The manufacturer will offer either a specific set of height choices or a variety of height ranges if adjustability is a feature of the chair.

The minimum seat height for your wheelchair is determined by how much space your footrests need to clear the floor. How high you sit, how long your legs are, and the angle of the seat will determine where the bottom of your feet will be in space. To decide minimum footrest ground clearance, you’ll want to account for bumps in sidewalks, table-leg bases, or any other kinds of changes in the surface you might encounter. Two inches of clearance for footrests is recommended as an absolute minimum, but, depending on where you will be riding, you might need more.