Dynamic synchronization analysis of venous pressure-driven cardiac output in rainbow trout. Am J Physiol Regul Integr Comp Physiol 285: R889-R896, 2003. First published June 12, 2003 10.1152/ajpregu.00228.2003.-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

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... nd 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 Ϯ 0.2 ml ⅐ mmHg Ϫ1 ⅐ g Ϫ1 (N ϭ 25 measurements; 6 fish with closed pericardium) and 2.8 Ϯ 0.3 ml ⅐ mmHg Ϫ1 ⅐ kg Ϫ1 (N ϭ 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 Ϯ 1.0 s (N ϭ 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 EURYHALINE TELEOST FISH, such as the rainbow trout, are potentially useful models for integrative cardiovascular studies. First, trout have a permeable integument yet thrive in environments that are potentially volumeloading and salt-depleting (freshwater), or volume-depleting and salt-loading (saltwater). This enables inde-