Ea. Denhartog et al., SYSTEMIC FILLING PRESSURE IN INTACT CIRCULATION DETERMINED ON BASIS OF AORTIC VS CENTRAL VENOUS-PRESSURE RELATIONSHIPS, American journal of physiology. Heart and circulatory physiology, 36(6), 1994, pp. 80002255-80002258
In the intact circulation, mean systemic filling pressure (P-sf) is de
termined by applying a series of inspiratory pause procedures (IPPs) a
nd using Guyton's equation of venous return (Q(v)) and central venous
pressure (P-cv): Q(v) = a - b x P-cv. During an IPP series, different
tidal volumes are applied to set P-cv at different values. From the li
near regression between Q(v) and P-cv, P-sf can be calculated as P-sf
= a/b. Guyton's equation can also be written as Q(v) = (P-sf - P-cv/R(
sd), where R(sd) is the flow resistance downstream of the places where
blood pressure is equal to P-sf. During an IPP, a steady state is obs
erved. Therefore, we can also formulate the following equation for flo
w: Q(s) = (P-ao - P-sf)/R(su), where Q(s) is systemic flow, R(su) is t
he systemic flow resistance upstream to P-sf, and P-ao is aortic press
ure. Because both flows (Q(s) and Q(v)) are equal, it follows that P-a
o = P-sf(1 + R(su)/R(sd)) - R(su)/R(sd) x P-cv. This equation implies
a method to determine mean systemic filling pressure on the basis of P
-ao measurements instead of flow determinations. Using 22 IPPs in 10 p
iglets, we determined the mean systemic filling pressure, and we compa
red the values obtained from the flow curves with those obtained from
the aortic pressure curves. The mean difference between the two method
s was 0.03 +/- 1.16 mmHg. With the use of P-ao measurements, the P-sf
can be estimated as accurately as in using flow determinations. The ad
vantage of the new method is that estimation of cardiac output is not
required.