L. Cheng et Aj. Rankin, PROBLEMS ASSOCIATED WITH THE MEASUREMENT OF MEAN CIRCULATORY FILLING PRESSURE BY THE ATRIAL BALLOON TECHNIQUE IN ANESTHETIZED RATS, Canadian journal of physiology and pharmacology, 70(2), 1992, pp. 233-239
To examine the existence of pressure equilibrium between tributary vei
ns and the central vena cava during the mean circulatory filling press
ure manoeuvre, pressures in the hepatic portal vein, renal vein, and i
nferior vena cava were determined at 4-s intervals over a 20-s period
of circulatory arrest induced by inflating a right atrial balloon in n
ormal blood volume, 10% volume depletion, and 10% volume expansion sta
tes in urethane-anaesthetized rats. Portal vein pressure determined 8
s after arrest during volume depletion and expansion was significantly
higher than vena caval pressure (6.2 +/- 0.8 vs. 3.4 +/- 0.2 and 7.7
+/- 0.5 vs. 6.2 +/- 0.4 mmHg (1 mmHg = 133.32 Pa), respectively; p < 0
.01); this pressure disequilibrium continued for 16 s during volume ex
pansion and for the entire 20 s during volume depletion. Renal vein pr
essure was equal to vena caval pressure during this manoeuvre. Portal
vein pressure at normal blood volume was significantly different from
vena caval pressure following circulatory arrest (4.6 +/- 0.3 vs. 3.8
+/- 0.4 mmHg, respectively). Following ganglionic blockade, portal vei
n pressure was still significantly higher than vena caval pressure for
12 s during volume alterations. At the 8th s of the arrest the portal
pressure determined in volume depletion was 3.6 +/- 0.3 mmHg and the
inferior vena caval pressure was 2.6 +/- 0.4 mmHg (p < 0.05). Under th
e volume expansion condition, the respective values were 6.5 +/- 0.3 a
nd 5.3 +/- 0.4 mmHg (p < 0.05). We conclude that, under conditions of
blood volume alterations, there is no pressure equilibrium between the
portal vein and the inferior vena cava when mean circulatory filling
pressure is measured by this technique; a transhepatic barrier indepen
dent of reflex control during the measurement of mean circulatory fill
ing pressure appears to play a role in obstructing the establishment o
f pressure equilibrium within the venous system.