Mechanisms of Muscle Blood Flow Dysregulation and Exercise Intolerance in Chronic Kidney Disease

Progressive muscle weakness and premature fatigue are characterize the condition of chronic kidney disease (CKD) which can be very debilitating. Mechanisms underlying exercise intolerance in CKD is not completely understood. Previous studies have demonstrated impaired skeletal muscle vasodilation during exercise in CKD patients, which may contribute to exercise intolerance. Normally, there is blunting of sympathetic mediated vasoconstriction in exercising muscle to allow for steady blood supply to exercising muscles. This phenomenon is called functional sympatholysis. Functional sympatholysis is impaired by increases in reactive oxygen specie and may be impaired in CKD.

Experiments will be performed on 2 groups of subjects 1) Normal kidney function (eGFR>90) 2) Stage 2-3 CKD (eGFR 30-89). VAsoactive medications will be held for 72 hours before study. All participants will attend a baseline study visit, which will include a physical examination, a medical history review, vital sign measurements, and blood collection. Muscle nerve activity and muscle oxygenation will be measured while the subjects perform hand grip exercise at 30% maximum voluntary contraction with and without lower body negative pressure (- 20 mmHg). Muscle blood flow will be measured before and after hand grip exercises. CKD subjects will then be randomized to exercise training (to squeeze a tennis ball repeatedly for at least 30 min/day) or no exercise training for 28 days. Procedures in baseline visit will be repeated followed by cross over to alternate group for 28 days followed by repeat of baseline procedures. Blood flow, muscle oxygenation and muscle nerve activity will be compared between CKD and normal subjects as well as before and after exercise training for CKD subjects.