Sdr. Galloway et al., Effects of sympathetic inhibition on exertional dyspnoea, ventilatory and metabolic responses to exercise in normotensive humans, CLIN SCI, 99(3), 2000, pp. 223-230
Augmentation of circulating noradrenaline concentration stimulates ventilat
ion during the initial stages of exercise and this is accompanied by an inc
reased sensation of dyspnoea and exertion. This previous study [Clark, Gall
oway, MacFarlane, Henderson, Aitchison and McMurray (1997) fur. Heart J. 18
, 1829-1833] suggested a link between dyspnoea, which commonly limits exerc
ise tolerance in heart failure patients, and high circulating noradrenaline
concentration in these patients. The present study investigated this relat
ionship further using sympathetic inhibition. Ten healthy normotensive male
s performed 10 min of submaximal cycling exercise at approx, 70% of maximal
oxygen uptake per min ((V) over dot O-2max) On three occasions one week ap
art. The first of these sessions was a familiarization session and the othe
r two were experimental study days. On each of the study days, subjects att
ended the laboratory in the morning after an overnight fast and, following
a resting blood sample, were administered placebo or moxonidine (0.4 mg) in
a double blind cross-over design. After a 90-min absorption period, subjec
ts undertook the exercise task. Blood was drawn, expired gas was analysed b
reath by breath, blood pressure, heart rate and ratings of perceived dyspno
ea and exertion were obtained. Moxonidine treatment significantly reduced p
lasma noradrenaline concentration (P < 0.01), mean arterial pressure (P < 0
.01), and blood glycerol concentration (P < 0.05), but no differences were
observed in heart rate, the ventilatory response to exercise or subjective
ratings of dyspnoea and exertion. This study indicates that reducing sympat
hetic activity does not affect ventilation, perceived dyspnoea or perceived
exertion in normotensive males. Therefore it can be concluded that reducin
g sympathetic activity may not be an appropriate strategy to help reduce pe
rceived dyspnoea.