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CARDIAC, RENAL, AND RESPIRATORY INTEGRATION
1Department of Chemical Engineering, University of Notre Dame and2South Bend Center for Medical Education, Indiana University School of Medicine, Notre Dame, Indiana 46556
Submitted 28 April 2003 ; accepted in final form 4 June 2003
Measurement of venous function in vivo is inherently difficult. In this
study, we used the Hilbert transform to examine the dynamic relationships
between venous pressure and cardiac output (CO) in rainbow trout whose blood
volume was continuously increased and decreased by ramp infusion and
withdrawal (I/W). The dorsal aorta and ductus Cuvier were cannulated
percutaneously and connected to pressure transducers; a flow probe was placed
around the ventral aorta. Whole blood from a donor was then I/W via the dorsal
aortic cannula at a rate of 10% of the estimated blood volume per minute, and
the duration of I/W was varied from 40, 60, 80, 90, 120, 230, 240, 260, 300,
and 340 s. Compliance [change in (
) blood vol/
venous pressure]
was 2.8 ± 0.2 ml · mmHg-1 · g-1
(N = 25 measurements; 6 fish with closed pericardium) and 2.8
± 0.3 ml · mmHg-1 · kg-1
(N = 19 measurements, 4 fish with open pericardium). Compliance was
positively correlated with the duration of I/W, indicative of cardiovascular
reflex responses at longer I/W durations. In trout with closed pericardium, CO
followed venous pressure oscillations with an average time lag of 4.2 ±
1.0 s (N = 9); heart rate (HR) was inversely correlated with CO.
These studies show that CO is entrained by modulation of venous pressure, not
by HR. Thus, although trout have a rigid pericardium, venous pressure
(vis-a-tergo), not cardiac suction (vis-a-fronte), appears to be the primary
determinant of CO. Estimation of venous compliance by ramp-modulation of
venous pressure is faster and less traumatic than classical capacitance
measurements and appears applicable to a variety of vertebrate species, as
does the Hilbert transform, which permits analysis of signals with disparate
frequencies.
fish cardiovascular system; blood transit time; cardiovascular time series; vascular compliance; Hilbert transform
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