Sympathetic-Somatomotor Coupling in Human Spinal Cord Injury

The regulation of cardiovascular systems during muscle activity is poorly understood in
people with incomplete spinal cord injury (SCI). In the past, disruptions in somatomotor and
sympathetic control have been investigated separately in SCI. We propose to investigate the
coupling of sympathetic and somatomotor control because it is relevant to exercise training
paradigms that are designed to improve somatomotor function or enhance physical fitness. Our
approach will be to measure tendon tap reflexes, voluntary muscle activation, and blood flow
of the knee (below injury) and elbow (above injury) before and after sympathetic stimuli
consisting of cold pressor tests, mental math and an acute bout of exercise. These data will
provide information about sympathetic control of blood flow during muscle activity.
Plasticity of the sympatheticsomatomotor coupling will also be investigated by making
measurements before and after a treadmill training exercise program. These experiments will
enable us to address three aims. Aim 1 will be to characterize coupling of sympathetic and
somatomotor systems below the level of spinal injury. This aim will examine spinal
sympathetic and motor reflexes and their interactions. It will also examine how descending
somatomotor coupling is disrupted by the spinal injury. In Aim 2, we will identify changes
in the interactions of sympathetic and somatomotor systems above a spinal injury. Because of
the injury and the changes that occur below the injury, the sympathetic-somatomotor coupling
is also likely to be disrupted in the arm. Aim 3 will then demonstrate plasticity of
sympathetic-somatomotor coupling after exercise training. Three different eight week
exercise training programs will be tested including 1) treadmill training with exertion
level matched to 70-80% of HRR 2)treadmill training with 30-40% HRR. The exercise training
will be tested in a randomized crossover study design with one month between exercise
training paradigms. We anticipate that there will be plasticity of sympathetic-somatomotor
coupling and that the exercise training effects will normalize control of these systems.
However, because of the injury, we anticipate that adaptations will differ from non-injured
controls.

This study has implications for exercise training in human SCI. The coupling of sympathetic
and somatomotor systems is expected to depend on whether exercise targets the upper or lower
body. The recovery of function requires both the improvement in the control of movement as
well as in the regulation of blood flow to active muscle groups. In addition, this study is
important for understanding the potential impact of treadmill exercise training on
cardiovascular fitness, a topic of increasing interest in people with limitations to
physical activity.

Inclusion Criteria:

- incomplete SCI

- subjects will be over age 18

- to fit in the apparatus and to assure a mature gait pattern

- at least 6 months post injury, and medically stable with an incomplete lesion between
levels T1-T10

- lower extremity motor score of 10 or greater

- presence of intact stretch reflexes, detected clinically

- no previous history or evidence of peripheral nerve damage in the lower extremities

- Subjects must be able to step on a treadmill with no more than 40% body weight
support.

Healthy controls will be age and sex matched to the subjects with spinal cord injury.

Exclusion Criteria:

- unhealed decubiti,

- bladder or other infection

- severe contracture or osteoporosis

- heterotopic ossification

- cardiac arrhythmia

- inability to give informed consent

- an episode of autonomic dysreflexia in the past year

- use of spasticity or cardiovascular medications (e.g. baclofen)