Central hypervolemia in the conscious rat: a model of
cardiovascular deconditioning.
Martel, Eric, Pascal Champeroux, Patrick Lacolley, Serge Richard,
Michel Safar, Jean-Louis Cuche.
Department of Internal Medicine, H[circumflex]opital Broussais, 75
014 Paris, Centre de Recherches Biologiques, 18 800 Baugy, Department
of Pharmacology, INSERM U-337, Broussais H-D Faculty of Medicine, 75
270 Paris
APStracts 3:0031A, 1996.
The aim of the present study was to investigate whether increased
central hypervolemia induced by tail suspension (TS) in the rat is an
appropriate model of cardiovascular deconditioning (CVD). -A- Study
of the physiological relationship between central venous pressure
(CVP) and extracellular fluid volume (ECFV). 20 tail suspension
increased CVP (5.8+/-0.7 vs 2.8+/-0.8 mmHg, p<0.01). After 24
hour TS, CVP had return to control range while ECFV was reduced by
19%. CVP kinetics during 24hour TS was not affected by either
reduction (-20%) or augmentation (+35%) of the ECFV. The
normalisation of CVP is likely to be a consequence of ECFV reduction,
itself reduced by increased urinary excretion of water and sodium.
-B- Recovery from tail-suspension. Resuming the horizontal position
was shown to be associated with a significant increase of heart rate
(HR) and a slight reduction of blood pressure (BP); there was an
apparent delay between increased HR and reduced BP. This dysbalance
between HR and BP is compatible with CVD. A model of simulated
orthostatism (SO) was developed to further investigate the responses
of HR and BP. Interestingly, SO (90 rotation) in the normal rat was
associated with significant tachycardia and a slight increase of BP.
This pattern remained stable for at least 3 hours. In rats, that were
tail suspended for 48 hours, episodes of hypotension-bradycardia ( 5
+/-1 in 3 hours) suggested a defect in adaptation to increased
hydrostatic pressure. In conclusion, tail-suspension appears to be an
appropriate model of CVD. Reduction of ECFV is likely to play a major
role in the deconditioning process. Return to horizontal position in
tail-suspended rats induced a tachycardia with minimal effects on BP;
this pattern is close to that observed in humans assuming upright
posture. SO in previously tail-suspended rats disclosed episodes of
hypotension-bradycradia that deserve further investigation.
Received 5 February 1995; accepted in final form 28 November
1995.
APS Manuscript Number A133-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 January 96