Open AccessEnhanced muscle pump during mild dynamic leg exercise inhibits sympathetic vasomotor outflow
Author(s) -
Katayama Keisho,
Ishida Koji,
Saito Mitsuru,
Koike Teruhiko,
Hirasawa Ai,
Ogoh Shigehiko
Publication year - 2014
Publication title -
physiological reports
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.918
H-Index - 39
ISSN - 2051-817X
DOI - 10.14814/phy2.12070
Subject(s) - microneurography , medicine , impedance cardiography , baroreceptor , heart rate , vasomotor , cardiology , cardiac output , reflex , stroke volume , isometric exercise , blood volume , anesthesia , hemodynamics , baroreflex , blood pressure
Muscle sympathetic nerve activity ( MSNA ) is not increased during leg cycling at light and mild intensities, despite activation of central command and the exercise pressor reflex. We determined whether increasing central blood volume and loading the cardiopulmonary baroreceptors modulate sympathetic vasomotor outflow during leg cycling. To this end, we changed the pedaling frequency to enhance skeletal muscle pump. Subjects performed two leg cycle exercises at differential pedal rates of 60 and 80 rpm (60 EX and 80 EX trials) for two conditions (with and without MSNA measurement). In each trial, subjects completed leg cycling with a differential workload to maintain constant oxygen consumption ( VO 2 ). MSNA was recorded via microneurography at the right median nerve of the elbow. Without MSNA measurement, thoracic impedance, stroke volume ( SV ), and cardiac output ( CO ) were measured non‐invasively using impedance cardiography. Heart rate and VO 2 during exercise did not differ between the 60 EX and 80 EX trials. Changes in thoracic impedance, SV , and CO during the 80 EX trial were greater than during the 60 EX trial. MSNA during the 60 EX trial was unchanged compared with that at rest (25.8 ± 3.1 [rest] to 28.3 ± 3.4 [exercise] bursts/min), whereas a significant decrease in MSNA was observed during the 80 EX trial (25.8 ± 2.8 [rest] to 19.7 ± 2.0 [exercise] bursts/min). These results suggest that a muscle pump‐induced increase in central blood volume, and thereby loading of cardiopulmonary baroreceptors, could inhibit sympathetic vasomotor outflow during mild dynamic leg exercise, despite activation of central command and the exercise pressor reflex.