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1 University of Tsukuba, Institute of Health and Sport Sciences, Tsukuba, Ibaraki, Japan
* To whom correspondence should be addressed. E-mail: nisiyasu{at}taiiku.tsukuba.ac.jp.
We aimed to investigate the interaction between the arterial baroreflex and muscle metaboreflex [as reflected by alterations in the dynamic responses shown by leg blood flow (LBF: by the ultrasound Doppler method), leg vascular conductance (LVC), mean arterial blood pressure (MAP), and heart rate (HR)] in humans. In twelve healthy subjects (ten male, two female), who performed sustained 1-min handgrip exercise at 50% maximal voluntary contraction followed immediately by an imposed post-exercise muscle ischemia (PEMI), 5-s periods of neck pressure (NP) (50mmHg) or neck suction (NS) (-60mmHg) were used to evaluate carotid baroreflex function both at rest (CON) and during PEMI. (a) The decreases in LVC and LBF and the augmentation of MAP elicited by NP were all greater during PEMI than in CON (
LVC, -1.2 ± 0.2 vs. -1.9 ± 0.2 ml min-1 mmHg-1;
LBF, -97.3 ± 11.2 vs. -177.0 ± 21.8 ml min-1;
MAP, 6.7 ± 1.2 vs. 11.5 ± 1.4 mmHg, CON vs. PEMI; each, P < 0.05). (b) In CON, NS significantly increased both LVC and LBF (
LVC, 0.9 ± 0.2 ml min-1 mmHg-1;
LBF, 46.6 ± 9.8 ml min-1; significant change from baseline: each, P < 0.05), and whereas during PEMI no significant increases in LVC and LBF occurred during NS itself (
LVC, 0.2± 0.1 ml min-1 mmHg-1;
LBF, 10.8 ± 9.6 ml min-1; each, P > 0.05), a decrease was evident in each parameters at 5s after the cessation of NS. (c) During PEMI, the decrease in MAP elicited by NS was smaller (
MAP, -8.4 ± 1.0 vs. -5.8 ± 0.4 mmHg, CON vs. PEMI; P < 0.05) and it recovered to its initial level more quickly after NS (vs. CON). (d) However, the HR responses to NS and
NP were not different between PEMI and CON. These results suggest that during muscle-metaboreflex activation in humans, the arterial baroreflex dynamic effect on peripheral vascular conductance is modulated, as exemplified by (i) an augmentation of the NP-induced LVC decrease, and (ii) a loss of the NS-induced LVC increase.
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