Exaggerated muscle mechanoreflex control of reflex renal vasoconstriction in heart failure

In heart failure (HF) patients, reflex renal vasoconstriction during exercise is exaggerated. We hypothesized that muscle mechanoreceptor control of renal vasoconstriction is exaggerated in HF. Nineteen HF patients and nineteen controls were enrolled in two exercise protocols: 1) low-level rhythmic handgrip (mechanoreceptors and central command) and 2) involuntary biceps contractions (mechanoreceptors). Renal cortical blood flow was measured by positron emission tomography, and renal cortical vascular resistance (RCVR) was calculated. During rhythmic handgrip, peak RCVR was greater in HF patients compared with controls (37 +/- 1 vs. 27 +/- 1 units; P < 0.01). Change in (Delta) RCVR tended to be greater as well but did not reach statistical significance (10 +/- 1 vs. 7 +/- 0.9 units; P = 0.13). RCVR was returned to baseline at 2-3 min postexercise in controls but remained significantly elevated in HF patients. During involuntary muscle contractions, peak RCVR was greater in HF patients compared with controls (36 +/- 0.7 vs. 24 +/- 0.5 units; P < 0.0001). The Delta RCVR was also significantly greater in HF patients compared with controls (6 +/- 1 vs. 4 +/- 0.6 units; P = 0.05). The data suggest that reflex renal vasoconstriction is exaggerated in both magnitude and duration during dynamic exercise in HF patients. Given that the exaggerated response was elicited in both the presence and absence of central command, it is clear that intact muscle mechanoreceptor sensitivity contributes to this augmented reflex renal vasoconstriction.