Altered firing pattern of single-unit muscle sympathetic nerve activity during handgrip exercise in chronic heart failure.
Sympathetic activation in chronic heart failure (CHF) is greatly augmented at rest but the response to exercise remains controversial. We previously demonstrated that single-unit muscle sympathetic nerve activity (MSNA) provides a more detailed description of the sympathetic response to physiological stress than multi-unit nerve recordings. The purpose of this study was to determine whether the reflex response and discharge properties of single-unit MSNA are altered during handgrip exercise (HG, 30% of maximum voluntary contraction for 3 min) in CHF patients (New York Heart Association functional class II or III, n = 16) compared with age-matched healthy control subjects (n = 13). At rest, both single-unit and multi-unit indices of sympathetic outflow were augmented in CHF compared with controls (P < 0.05). However, the percentage of cardiac intervals that contained one, two, three or four single-unit spikes were not different between the groups. Compared to the control group, HG elicited a larger increase in multi-unit total MSNA (Delta1002 +/- 50 compared with Delta636 +/- 76 units min(-1), P < 0.05) and single-unit MSNA spike incidence (Delta27 +/- 5 compared with Delta8 +/- 2 spikes (100 heart beats)(-1)), P < 0.01) in the CHF patients. More importantly, the percentage of cardiac intervals that contained two or three single-unit spikes was increased (P < 0.05) during exercise in the CHF group only (Delta8 +/- 2% and Delta5 +/- 1% for two and three spikes, respectively). These results suggest that the larger multi-unit total MSNA response observed during HG in CHF is brought about in part by an increase in the probability of multiple firing of single-unit sympathetic neurones.
Murai
Hisayoshi
H
Disease Control and Homeostasis, Graduate School of Medical Science, Kanazawa University, Kanazawa, Japan. sakurasoma1209@yahoo.co.jp
Takamura
Masayuki
M
Maruyama
Michirou
M
Nakano
Manabu
M
Ikeda
Tatsunori
T
Kobayashi
Daisuke
D
Otowa
Kan-ichi
K
Ootsuji
Hiroshi
H
Okajima
Masaki
M
Furusho
Hiroshi
H
Takata
Shigeo
S
Kaneko
Shuichi
S
D000200:Action Potentials; D000368:Aged; D001794:Blood Pressure; D016022:Case-Control Studies; D002908:Chronic Disease; D015444:Exercise; D017079:Exercise Tolerance; D005260:Female; D018737:Hand Strength; D006333:Heart Failure / Q000503:physiopathology*; D006339:Heart Rate; D006801:Humans; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000098:blood supply / Q000294:innervation*; D010543:Peroneal Nerve / Q000503:physiopathology; D011999:Recruitment, Neurophysiological; D012018:Reflex; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D014661:Vasoconstriction