C. Dodt et al., CENTRAL BLOOD-VOLUME INFLUENCES SYMPATHETIC SUDOMOTOR NERVE TRAFFIC IN WARM HUMANS, Acta Physiologica Scandinavica, 155(1), 1995, pp. 41-51
The objective of this study was to test whether changes in central blo
od volume can induce reflex effects on sweating. Multi-unit skin sympa
thetic nerve activity (SSA) was recorded from the posterior cutaneous
nerve of the forearm or radial nerve branches in 11 healthy volunteers
. Skin electrical resistance and skin blood flow were recorded in the
area innervated by the impaled nerve fascicle. Sudomotor nerve traffic
and sweating was induced by whole body heating. Lower body negative p
ressure (LBNP) and tilting (30 degrees head up) was used for blood vol
ume displacement from the chest to the lower body. Low levels of LBNP
(5 and 10 mmHg) had no effect on blood pressure, heart rate or skin bl
ood flow but induced a prompt inhibition of SSA and a reduced number o
f transient skin resistance changes (n = 9), both rapidly returning to
control levels after cessation of LBNP. Quantitatively, the effect wa
s similar at, both levels of LBNP. Head up tilting also reduced SSA (1
1 = 3, 19 tilt manoeuvres). A capacity for mental stress-induced SSA i
ncrease remained during LBNP. Spontaneous fluctuations in blood pressu
re did not affect SSA, arguing against arterial (high-pressure) barore
ceptors modulating SSA. Consequently, the present results indicate tha
t unloading of cardiopulmonary (low-pressure) volume receptors reduces
sympathetic sudomotor nerve traffic and sweating in warm subjects. It
is suggested that the reflex contributes to counteracting hypovolaemi
a.