New Technologic Approach to Minimizing Immobilization Effects

By: Friedemann Müller MD,MSc; Head Physician Neurology, Neurological Clinic Bad Aibling, Germany

Some of the most valued technological advances in medicine either reduce fatiguing or repetitive tasks, or enable healthcare professionals to perform procedures that would otherwise have been difficult or impossible to accomplish. Mechanical systems, harnessed to increasingly sophisticated computers, are demonstrating their ability to assist in the neurorehabilitation of severely brain injured patients, a challenge that is both physically demanding for their care providers and – with standard instrumentation – minimally productive for patients.

One of the new systems with potential to accelerate early rehabilitation of traumatic brain injury patients is the Erigo®,1 which combines a tilt table with a computer controlled stepping mechanism. Experience at our institution suggests this system may alter the way in which patients are treated in intensive care units, as well as enhance early and intensive rehabilitation protocols that ideally would begin as soon as the patient is stabilized.

Prolonged bed rest inevitably results in reduction of exercise capacity,2 a condition that was first reported in the medical literature more than 50 years ago, and most recently, has been aggressively studied by space programs worldwide. Underlying physiological mechanisms include dramatic reductions in cardiac output with reduced stroke volume, and reduced oxygen uptake. Immobilization for more than a few days is associated with reduced muscle blood flow, even altered blood physiology. The resultant deconditioning can be independent of the primary disease, and can be physically debilitating for patients who, having recovered from a traumatic injury or disease, attempt to resume normal ambulation. Once they do so, the consequences of muscle atrophy and skeletal demineralization can put them at increased risk of injury to bones and joints.

Therefore, reduction of immobilisation is a major goal in the management of patients recovering from traumatic brain injury, cerebrovascular accident, and similar insults and diseases.  A challenge to clinicians and health care specialists has been the identification of appropriate and effective methods to reduce losses, and even to restore the exercise capacity of patients during prolonged bed rest.

Examination of physiological responses of healthy subjects to bed-rest deconditioning and exercise training has provided valuable guidance for development of the principles and techniques that might be applied to rehabilitation of immobilised patients. Most important may be assumption of the upright position, because it is associated with a reduction in venous return and increase in cardiac output. In the upright position, the cerebral arteries are positioned well above the heart. Consequently, perfusion pressure is reduced and cerebral blood flow is appropriately challenged. Even in healthy subjects, orthostatic intolerance after prolonged bed rest is not uncommon. Blood pressure is ordinarily maintained by a sympathetically mediated increase in vascular resistance. This maintenance is compromised after long periods of supine inactivity. In comatose patients, vegetative functions may be especially insufficient to deal with systemic organ and muscle demands. Absence of leg muscle tone compromises the physiological muscle pump responsible for normal venous return.

This systemic deterioration is most unfortunate, since clinical experience has proven that, besides motor function, various other functions improve as soon as the patient assumes an upright position. Even the duration of unconsciousness might be shortened if the patient could be raised to some degree of vertical position. Such a normal orientation provides strong vestibular input and sensory information from joint and position sensors, augmenting sensory information processing that may contribute to accelerated recovery of consciousness.

Erigo Setup

Therefore, in many institutions, tilt-table training has become standard therapy during early rehabilitation of severely affected patients with neurological disorders such as vegetative or minimally conscious state, or even paralysis. The goal is to slowly adapt the patient again to a vertical position, and to slowly rechallenge the legs to support the body. A different and more common approach is to repetitively move the legs to prevent contractures, atrophies or even deep venous thrombosis.

The development of the Erigo tilt table with an integrated stepping system provides physicians and therapists with the ability to combine intensive movement therapy of legs with verticalisation. It facilitates the simultaneous application of these two accepted forms of therapy. This combination promises to facilitate rehabilitation of bed-ridden patients, and thus, enable them to resist many of the adverse effects of prolonged immobilisation.

The Erigo has been engineered by Hocoma3 -, the Swiss company that entered the rehabilitation market with a computer-controlled gait orthosis called Lokomat®. Its technology of controlling leg movements was developed in collaboration with physiologists and rehabilitation experts, and is founded on well-established principles. In the Erigo, a computer controls the motion profiles of the linear drives so as to encourage physiological hip kinematics comparable to normal walking.

In use, the upper body of the patient is secured to the table with a chest and shoulder harness. Each thigh is fastened by a cuff to a linear drive mechanism. The patient’s feet are fixed in two variable foot plates with integrated springs, allowing individual adjustment to the patient’s anatomy and neuromuscular condition. While hip and knee are extended during the stance phase, a spring underneath the foot plate applies load to the sole. When hip and knee are flexed, the spring applies no load to the plate. This design assures the most physiologic challenge to hip, knee and ankle joint movements. A touch-screen computer allows adjustment of the speed (cadence) and the range of motion of each leg to each individual patient. The training data and settings for each patient are saved in the computer.

Figure from Czell et al. 
Figure from Czell et al.

The Erigo is adjustable to different angles, up to a vertical position, to accommodate various patient conditions, and to intensify the therapy. This range of positioning enables the patient to acclimate to the upright position. It has been known for more than 50 years that a tilt angle above approximately 55 degrees will cause patients to develop syncope if they are prone to orthostatic hypotension.4 In our experience this response can be observed on a tilt table. 
However, the venous pump effect induced by the Erigo should allow mobilizing most, if not all patients above that critical angle.  We are awaiting imminent results of randomized controlled Erigo studies that may define just how significant the combination of verticalisation and leg movements may be in immobilized patients.

 

1 Hohenstein K, Heydari B, Greif R, Prager C; Pilotstudie ERIGO; Frühvertikalisation von Intensivpatienten mittels Kipptisch mit automatischen Beinantrieb. Phys Rehab Kur Med 2006; 16

2 Graf C Functional decline in hospitalized older adults Am J Nurs. 2006 Jan;106(1):58-67

3 Hocoma AG, Industriestrasse 4b, 8604 Volketswil, Switzerland

4 Brigden W, Howarth S, Sharpey-Shaefer EP. Postural changes in the peripheral blood-flow of normal subjects with observations on vasovagal fainting reactions as a result of tilting, the lordotic posture, pregnancy and spinal anesthesia. Clin Sci Lond, 1950; 9: 79-90.