The relevance of right atrial pressure (RAP) as the backpressure for venous return (Q) and mean systemic filling pressure as upstream pressure is controversial during dynamic changes of circulation. To examine the immediate response of Q (sum of caval vein flows) to changes in RAP and pump function, we used a closed-chest, central cannulation, heart bypass porcine preparation ( = 10) with venoarterial extracorporeal membrane oxygenation. Mean systemic filling pressure was determined by clamping extracorporeal membrane oxygenation tubing with open or closed arteriovenous shunt at euvolemia, volume expansion (9.75 ml/kg hydroxyethyl starch), and hypovolemia (bleeding 19.5 ml/kg after volume expansion). The responses of RAP and Q were studied using variable pump speed at constant airway pressure (P) and constant pump speed at variable P Within each volume state, the immediate changes in Q and RAP could be described with a single linear regression, regardless of whether RAP was altered by pump speed or P ( = 0.586-0.984). RAP was inversely proportional to pump speed from zero to maximum flow ( = 0.859-0.999). Changing P caused immediate, transient, directionally opposite changes in RAP and Q (RAP: ≤ 0.002 and Q: ≤ 0.001), where the initial response was proportional to the change in Q driving pressure. Changes in P generated volume shifts into and out of the right atrium, but their effect on upstream pressure was negligible. Our findings support the concept that RAP acts as backpressure to Q and that Guyton's model of circulatory equilibrium qualitatively predicts the dynamic response from changing RAP. Venous return responds immediately to changes in right atrial pressure. Concomitant volume shifts within the systemic circulation due to an imbalance between cardiac output and venous return have negligible effects on mean systemic filling pressure. Guyton's model of circulatory equilibrium can qualitatively predict the resulting changes in dynamic conditions with right atrial pressure as backpressure to venous return.
Frequency potentiation and postextrasystolic potentiation of myocardial contractility were induced in 17 patientsfound not to have cardiac disease (group i) and in Io patients with coronary arterial disease (group 2). Atrial stimulation was performed starting at a rate of IoI/min and going up to 200/nin (frequency potentiation). Single, premature ventricular beats with decreasing coupling intervals were induced everyfifteenth beat during basal atrial stimulation at 2s/min, after which compensatory pauses were provided (postextrasystolic potentiation). The time derivative of left ventricular pressure (dp/dt) was used as an index of contractility. With increasing heart rate dp/dt max was augmented equally, in bothgroups ofpatients, byfrequency increases and premature beats (the coupling interval of the extrasystole being expressed as heart rate). dp/dt min and left ventricular systolic pressure remained unchanged while left ventricular end-diastolic pressure decreased in bothgroups ofpatients with the twoforms ofpotentiation. It was concluded that both theseforms ofpotentiation have the same augmenting effect on myocardial contractility. Shortening the coupling intervals of premature beats caused a decrease in left ventricular end-diastolic pressure, suggesting that the Frank-Starling mechanism was not involved in postextrasystolic potentiation. Patients with coronary arterial disease had lower values of dp/dt max, dp/dt min, and higher values of left ventricular end-diastolic pressure during rest and stimulation procedures, while the systolic pressures equalled those in the control group. Though individual case values from the healthy and diseased hearts might be similar, it was only under the stress ofpotentiation that the true state of contractility was made apparent. Impairment of dp/dt min was not found without an impairment of dp/dt max in the presence of myocardial ischaemia.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.