Dissociation of muscle sympathetic nerve activity and leg vascular resistance in humans

We examined the hypothesis that the increase in inactive leg vascular resis tance during forearm metaboreflex activation is dissociated from muscle sym pathetic nerve activity (MSNA). MSNA (microneurography), femoral artery mea n blood velocity (FAMBV, Doppler), mean arterial pressure (MAP), and heart rate (HR) were assessed during fatiguing static handgrip exercise (SHG, 2 m in) followed by posthandgrip ischemia (PHI, 2 min). Whereas both MAP and MS NA increase during SHG, the transition from SHG to PHI is characterized by a transient reduction in MAP but sustained elevation in MSNA, facilitating separation of these factors in vivo. Femoral artery vascular resistance (FA VR) was calculated (MAP/MBV). MSNA increased by 59 +/- 20% above baseline d uring SHG (P < 0.05) and was 58 +/- 18 and 78 +/- 18% above baseline at 10 and 20 s of PHI, respectively (P < 0.05 vs. baseline). Compared with baseli ne, FAVR increased 51 +/- 22% during SHG (P < 0.0001) but returned to basel ine levels during the first 30 s of PHI, reflecting the changes in MAP (P < 0.005) and not MSNA. It was concluded that control of leg muscle vascular resistance is sensitive to changes in arterial pressure and can be dissocia ted from sympathetic factors.