Ischemic Nerve Block to Improve Hand Function in Stroke Patients

This study will determine whether impaired hand function due to stroke can be improved by blocking nerve impulses to the unaffected arm. Following a stroke, the unaffected side of the brain might negatively influence the affected side. Studies in healthy volunteers show that function in one hand improves when ischemic nerve block (inflating a pressure cuff to block nerve impulses) is applied to the forearm of the other hand. This study will examine whether similar improvement also occurs in the affected hand of patients with chronic impairment after stroke. Stroke patients with sensory (numbness) or motor impairment (weakness) in the hand that has persisted at least 12 months after the stroke may be eligible for this study. Patients who have had more than one stroke, whose stroke affected both sides of the body, who have a history of deep vein thrombosis (blood clotting), or who are receiving anticoagulant (blood-thinning) treatment at the time of the study will not be enrolled. Participants will have physical and neurological examinations and will undergo the following procedures: Session 1

• Magnetic resonance imaging (if one has not been done within the previous 6 months): MRI uses a magnetic field and radio waves to produce images of body tissues and organs. For this procedure, the patient lies on a table that is moved into the scanner (a narrow cylinder) and wears earplugs to muffle loud knocking and thumping sounds that occur during the scanning process. The procedure lasts about 45 to 90 minutes, during which the patient lies still up to a few minutes at a time.
• Mini Mental State Examination - Patients will take a short test to assess cognitive function. Sessions 2 (and possibly 3 and 4)
• Motor task practice: Patients practice a motor task several times to achieve optimal performance. The task is a rhythmic, repetitive pinch grip at maximal strength at a frequency of one grip every 10 seconds. If technical difficulties arise during the session, the procedure will be repeated in sessions 3 and 4. Sessions 5 (and possibly 6)
• Pinch grip and ischemic nerve block (INB): Patients perform the pinch grip task several times and then INB is applied. For INB, a blood pressure cuff is inflated around the arm at the level of the elbow for 35 to 50 minutes. The procedure causes temporary numbness, tingling, loss of muscle strength, and discoloration or the forearm and hand. Patients repeat the pinch grip task during the INB and again 20 minutes after the INB is released. If technical difficulties arise during the session, the procedure will be repeated in session 6. Session 7 This session is identical to session 5, except the INB is applied immediately above the ankle instead of on the forearm.