Frequency of slow oscillations in arterial pressure and R–R intervals during muscle metaboreflex activation

Altered frequency of slow (0.04–0.15 Hz) arterial pressure and R–R interval oscillations has been observed in various diseases but the mechanisms for this frequency shift are unclear. The median (Med) frequencies of slow R–R interval and blood pressure (BP) oscillations were recorded in 11 healthy subjects with paced breathing (0.25 Hz) during muscle metaboreflex and baroreflex mediated sympathetic stimuli: 1) handgrip exercise (HG) followed by post-exercise circulatory occlusion (PECO), 2) handgrip exercise during ischemia by circulatory occlusion (IHG) and 3) passive head-up tilt (TILT). MedBP shifted to the higher frequency during HG, PECO and IHG (from 0.070 ± 0.009 Hz to 0.088 ± 0.013, 0.085 ± 0.015 and 0.099 ± 0.013 Hz, respectively, p < 0.01 for all) but not during TILT (0.078 ± 0.012 Hz). Similarly, MedR–R shifted to the higher frequency during HG, PECO and IHG (from 0.072 ± 0.009 Hz to 0.085 ± 0.014, 0.085 ± 0.016 and 0.095 ± 0.015 Hz, respectively, p < 0.01 for all) but not during TILT (0.075 ± 0.012 Hz). MedBP and MedR–R were higher during IHG compared to HG and lower during TILT compared to both HG and IHG (p < 0.01 for all). We conclude that the sympathetic stimulus induced by muscle metaboreflex is an important mechanism increasing the frequency of slow oscillations in arterial pressure and R–R intervals. The present results give new insight to understand the physiology underlying the frequency of slow arterial pressure and R–R interval oscillations.