Submitted on October 31, 2006
Accepted on March 12, 2007
Modulation of the spontaneous beat-to-beat fluctuations in peripheral vascular resistance during activation of muscle metaboreflex
Masashi Ichinose1, Shunsaku Koga2, Naoto Fujii3, Narihiko Kondo1, and Takeshi Nishiyasu3*
1 Faculty of Human Development, Kobe University, Kobe, Hyogo, Japan
2 Applied Physiology Laboratory, Kobe Design University, Kobe, Hyogo, Japan
3 Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan
* To whom correspondence should be addressed. E-mail: nisiyasu{at}taiiku.tsukuba.ac.jp.
Continuous measurement of leg blood flow (LBF) using Doppler ultrasound with simultaneous noninvasive mean arterial blood pressure (MAP) measurement permits beat-to-beat estimates of leg vascular resistance (LVR) in humans. We tested the hypothesis that the beat-to-beat fluctuations in LVR and the dynamic relationship between MAP and LVR are modulated by the activation of muscle metaboreflex. Twelve healthy subjects performed a 1-min isometric handgrip exercise at 50% maximal voluntary contraction, which was followed by a period of imposed post-exercise muscle ischemia (PEMI). We then employed transfer function analysis to examine the dynamic relationships between MAP and LBF, and MAP and LVR, both at rest (control) and during PEMI. (a) The spectral power for LBF and LVR in low-frequency (LF: 0.03~0.15Hz) range significantly increased from control during PEMI without a significant change in the high-frequency (HF: 0.15~0.35Hz) power. (b) During PEMI, the transfer function gains for MAP-LBF and MAP-LVR relationships in the LF (0.05~0.15Hz) range were significantly increased during PEMI (vs. control), but were unchanged in the HF (0.2~0.3Hz) range. (c) The phase for MAP-LBF, and MAP-LVR relationships did not different during the control and PEMI. The phase for MAP-LVR relationship revealed that changes in MAP were followed by directionally similar changes in LVR, which is consistent with the characteristics of intrinsic vascular regulatory mechanisms such as the myogenic response of the resistance arteries. We suggest that, in humans, modulation of the dynamic MAP-LVR relationship during activation of the muscle metaboreflex reflects complex interactions between intrinsic vascular regulatory mechanisms and sympathetic vascular regulation.
