Jm. Legramante et al., Positive and negative feedback mechanisms in the neural regulation of cardiovascular function in healthy and spinal cord-injured humans, CIRCULATION, 103(9), 2001, pp. 1250-1255
Citations number
26
Categorie Soggetti
Cardiovascular & Respiratory Systems","Cardiovascular & Hematology Research
Background-We tested the hypothesis that in humans, hypertension/tachycardi
a and hypotension/bradycardia nonbaroreflex sequences that occur within spo
ntaneous arterial pressure (AP) and R-R interval fluctuations are an expres
sion of positive feedback mechanisms neurally regulating the cardiovascular
system.
Methods and Results-We studied 15 spinal cord-injured (SCI) subjects (8 tet
raplegics and 7 paraplegics) and 8 healthy subjects. The occurrence of nonb
aroreflex (NBseq) and baroreflex (Bseq) sequences, ie, hypertension-bradyca
rdia and hypotension-tachycardia sequences, was assessed during rest and he
ad-up tilt (HUT). The ratio between Bseq and NBseq (B/NB ratio) was also ca
lculated. In resting conditions, the occurrence of NBseq was significantly
lower (P < 0.05) in tetraplegics (7.9 +/- 1.5) than in paraplegics (16.2 +/
- 3.2) and normal subjects (19.0 +/- 3.5), whereas the occurrence of Bseq w
as not significantly different between the 3 groups (38.6 +/- 11.9 versus 4
5.4 +/- 6.0 versus 47.0 +/- 11.9). In tetraplegics, the B/NB ratio showed a
marked, significant decrease (from 8.4 +/- 4.2 to 1.9 +/- 0,8, P < 0.05) i
n response to HUT, whereas in normal subjects, it showed a significant incr
ease (from 3.5 +/- 0.7 to 9.4 +/- 2.7, P<0.05). In paraplegics, the B/NB ra
tio did not change significantly in response to HUT (from 4.5 +/- 1.6 to 4.
8 +/- 1.1).
Conclusions-Our data suggest that nonbaroreflex sequences occur in humans a
nd might represent the expression of an integrated, neurally mediated, feed
-forward type of short-term cardiovascular regulation that is able to inter
act dynamically with feedback mechanisms of baroreflex origin.