Exaggerated Reductions In Muscle Interstitial Ph During Exercise In Patients With Chronic Kidney Disease

PURPOSE: Chronic kidney disease (CKD) patients have exaggerated increases in blood pressure (BP) during exercise due to an augmented exercise pressor reflex. CKD is characterized by acid retention and decreased HCO3- bioavailability. Since HCO3- is the major buffer of exercise-induced increases in muscle H+, one of the activators of the exercise pressor reflex, CKD patients are at risk for exaggerated reductions in muscle interstitial pH (pHMI) during exercise that could lead to sensitization of the exercise pressor reflex. Therefore, in the present study we tested the hypothesis that CKD patients have a greater reduction in pHMI compared to controls (CON) during low-levels of rhythmic handgrip (RHG) exercise with concomitant exaggerated increases in BP. METHODS: Ten CKD patients (eGFR, 40 ± 10 ml/min/1.73m2) and eight CON (86 ± 20 ml/min/1.73m2) performed 3-min of RHG exercise at 20% of maximal voluntary contraction (MVC). BP, heart rate, and estimated pHMI by near-infrared spectroscopy were measured continuously. Rate of perceived exertion (RPE) was collected at the end of RHG. Delta pHMI and BP were calculated as the absolute difference between the resting and the nadir pHMI, and between resting and mean BP response during the last 20s of RHG, respectively. The area under the curve (AUC) was calculated to quantify the total pHMI and BP response to RHG. Independent t-tests were used to compare groups for all outcomes. Pearson correlation assessed the association between pHMI and RPE. RESULTS: No differences in MVC were observed between groups. Low-levels of RHG exercise led to a greater reduction in pHMI in CKD (ΔpH CKD: -0.2 ± 0.1 vs. CON: -0.1 ± 0.1 units; P = 0.01) followed by an augmented BP reactivity (ΔBP CKD: 18 ± 7 vs. CON: 9 ± 5 mmHg; P = 0.01). The RPE was higher in CKD (CKD: 4 ± 1 vs. CON: 2 ± 1 a.u.; P = 0.03). The AUC for pHMI (CKD: 26 ± 4 vs. CON:12 ± 4 units.s−1; P = 0.01) and BP (CKD: 2417 ± 313 vs. CON: 1160 ± 410 mmHg.s−1; P = 0.01) was higher during the low-intensity RHG in CKD patients compared to CON. The pHMI decrease was negatively correlated with the RPE (R = -0.71, P = 0.01) in CKD patients. CONCLUSIONS: These preliminary findings suggest that exaggerated reductions in pHMI during exercise that might modulate the perceived exertion and may play a role in the augmented BP reactivity to low-intensity exercise in patients with CKD. Supported by: Supported by NIH R01HL135183; NIH R61AT10457; NIH R33AT010457-03.