UCSD Orthopaedics Surgery professor Alan Hargens, co-inventor of the chamber during his days at NASA, believes the unique pressure chamber will allow patients who have lower-extremity orthopaedic surgery to begin upright, normal gait rehabilitation very early post-surgically, something not usually possible in standard rehabilitation protocols using swimming pools, parallel bars, or walking devices.
Dr. Cutuk described the pressure chamber and a study determining its safety Sunday, April 3, at Experimental Biology 2005 in San Diego. His presentation was part of the scientific sessions of The American Physiological Society and the International Union of Physiological Sciences 2005 Congress.
Patients step into a see-through Plexiglas box, tighten a Neoprene sleeve around their waists to create an airtight seal, much as a kayaker adjusts the waterproof sleeve at the top of the kayak, and wait while researchers adjust the air pressure precisely according to how much lower body weight they want the patient to experience. Air pressure is changed by adding air in (positive air pressure) or releasing it out (negative air pressure), using the exhaust port of a common vacuum cleaner. It's possible to adjust the positive air pressure to provide so much buoyancy that weight-bearing on the treadmill is only 5 or 10 percent of the patient's actual weight or, in the case of the lightest patients, the sensation that they are actually floating over the treadmill.
As a patient's strength and flexibility return and the surgical wounds heal, the chamber can be adjusted appropriately, adding a few more "pounds" each week. (If the researchers wanted to make the exercise especially hard, of course, the chamber could be adjusted to negative air pressure, making each step heavier, just as athletes sometimes train by wearing ankle weights.)
The study presented by Dr. Cutuk at Experimental Biology 2005 found that standing, walking, and exercising on the treadmill while the lower body is at high positive pressure is safe. When nine healthy male and female participants ages 20 to 55 ran upright at a speed of 5 plus kilometers an hour in the chamber, their heart rate actually decreased as the positive pressure on their lower body increased, making their steps lighter and the work of walking and running easier.
More importantly for the researchers, who wanted to make certain the positive air pressure on the lower body would not result in too much blood being pushed to the upper body or head, risking stroke, no such risks appeared, nor did the high positive pressure significantly change blood pressure. This is good news, says Dr. Cutuk, making the device useful among older or higher risk patients who make up a sizeable proportion of people undergoing hip or other lower body surgeries.
Having tested the chamber for safety, the UCSD researchers now are beginning a study with patients who have hip fracture surgery at the University of California San Diego Medical Center. The goal is to compare their outcomes with those of patients in the hospital's traditional rehabilitation program.
Other researchers have worked with positive air pressure devices, but Dr. Hargens believes this is the first chamber built around a treadmill, which allows patients to reacclimatize more rapidly to the normal process of walking. The researchers believe the positive air chamber has three important advantages over swimming pool exercises.
First, the patient's gait can be normal, not a struggle against the drag of the water.
Second, the impact on the treadmill, the patient's weight coming down on each step, or "off-loading" in physiological terms, can be precisely adjusted based on the amount of air pressure placed in the chamber, first allowing for almost no impact after surgery, then offering more weight-bearing as the patient's coordination and strength increase.
Third, patients can begin rehabilitation almost immediately after surgery when risk of infection in their surgical wounds prevents them from getting in a pool. In fact, the air pressure squeezes out excess swelling from the surgery site with the promise of faster healing.
Funding for the study was supported by the Toby Freedman Endowment Fund, University of California, San Diego Chancellor's Associates, the Orthopaedic Research and Education Foundation Center of Excellent Grant and by a National Institutes of Health grant to the University of California San Diego General Clinical Research Center.