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Differential Walking Assist: an inflatable walking support
Charles G Burgar, MD; Douglas Schwandt, MS; James Anderson, JEM; Robert Whalen, PhD; Gregory Breit, PhD; NASA-ARC
Need - An improved walking assist device, which comfortably reduces lower limb muscle and joint forces, is needed for patients recovering from neurologic diseases and orthopedic procedures.
A variety of techniques have been used to help suspend a patient's weight during walking rehabilitation. Most of these techniques have disadvantages associated with them, in addition to interfering with normal gait:
- Water immersion - inconvenience, possible infection of open wounds or incisions, viscous drag, and difficulty in modulating forces
- Parallel bars and walker - strength required of the patient's upper body
- Hand-held waist belts - physically stressful for the therapist supporting a patient's weight; possible patient falls
- Overhead suspension harness - locally high interface contact pressures.
Concept - Lower body differential pressure chambers have been developed at the Life Science Division of NASA Ames Research Center to investigate the application of differential pressure to exercise in space, and to simulate hypo- and hyper-gravity locomotion.
Lower body positive pressure may be used to partially lift a patient, reducing the loads on the lower body during standing and walking. The patient's lower body is enclosed in an inflatable chamber isolated from the upper body at the waist by a flexible, air-tight seal.
The lifting force is equal to the product of the pressure difference and the waist cross-sectional area. Since the upper and lower body air pressures are uniformly distributed over the body surface, the subject simply feels lighter, similar to being buoyed up by waist-deep water. The lifting force can easily be controlled by adjusting chamber pressure to adapt to an individual patient's needs as he or she progresses through rehabilitation.
Design - The first prototype of a differential pressure walking assist device has been constructed to investigate cardiovascular effects on able- bodied subjects during standing. The device consists of an inflatable conical reinforced vinyl skirt attached to a circular plywood base holding a force plate (Figure 1). A computer controls a servo-valve connected to a blower which regulates the pressure in the chamber, while simultaneously recording and displaying pressure and ground reaction force.
Figure
1. Components of the lower body differential pressure (LBDP) chamber.
Results - A pilot study of eight healthy male subjects between the ages
of 29 to 52 established the relationship between ground reaction force and
pressure, and evaluated the cardiovascular responses for chamber pressures to
45 mmHg (equivalent to the hydrostatic pressure under two feet of water).
Changes in heart rate and blood pressure were within the range of values
observed between the supine resting baseline and standing. A 75% mean reduction
in vertical ground reaction force was found at a chamber pressure of 45 mmHg.
Discussion - The use of lower body positive pressure is a comfortable way to reduce the effects of gravitational forces. Since the upward resultant air pressure force acts at or near the center of mass of the body, we anticipate walking in the device will resemble normal gait but with proportionally reduced musculoskeletal forces. There is contact with the patient only at the waist seal. The arms are free to move as the pressure does all of the lifting. The waist seal provides front, back and lateral support to prevent falling.
Future Plans - Prototype development is continuing by enclosure of a treadmill to provide for walking. If results of ongoing work continue to be encouraging, a commercial version of the device will be developed in collaboration with an industrial partner.
Acknowledgments - This work is an application of a patented invention by Robert Whalen, PhD, and Alan Hargens, PhD, entitled Exercise method and apparatus utilizing differential pressure (US Patent No. 5,133,339). Jeff Emery and Josh Beach contributed to the development of the pressure control and data acquisition systems at NASA-ARC. The neoprene waist seal was constructed by Mark Stugen at Stan's Skin Diving Shop in San Jose, California.
Republished from the 1994 Rehabilitation R&D Center Progress Report. For
current information about this project, contact Douglas F. Schwandt, MS.
