Balancing the circulation: theoretic optimization of pulmonary/systemic flow ratio in hypoplastic left heart syndrome.

Abstract

OBJECTIVES:

This study examined the effects of the pulmonary (QP)/systemic (QS) blood flow ratio (QP/QS) on systemic oxygen availability in neonates with hypoplastic left heart syndrome.

BACKGROUND:

The management of neonates with hypoplastic left heart syndrome is complex and controversial. Both before and after surgical palliation and before heart transplantation, a univentricle with parallel pulmonary and systemic circulations exists. It is generally assumed that balancing pulmonary and systemic blood flow is best to stabilize the circulation.

METHODS:

We developed a mathematical model that was based on the simple flow of oxygen uptake in the lungs and whole-body oxygen consumption to study the effect of varying the QP/QS ratio. An equation was derived that related the key variables of cardiac output, pulmonary venous oxygen saturation and the QP/QS ratio to systemic oxygen availability.

RESULTS:

The key findings are 1) as the QP/QS ratio increases, systemic oxygen availability increases initially, reaches a maximum and then decreases; 2) for maximal systemic oxygen availability, the optimal QP/QS ratio is < or = 1; 3) the optimal QP/QS ratio decreases as cardiac output or percent pulmonary venous oxygen saturation, or both, increase; 4) the critical range of QP/QS, where oxygen supply exceeds basal oxygen consumption, decreases as cardiac output and percent pulmonary venous oxygen saturation decrease; 5) the relation between oxygen availability and QP/QS is very steep when QP/QS approaches this critical value; and 6) the percent oxygen saturation of systemic venous blood is very low outside the critical range of QP/QS and high within the critical range.

CONCLUSIONS:

This analysis provides a theoretic basis for balancing both the pulmonary and systemic circulation and suggests that evaluating both systemic arterial and venous oxygen saturation may be a useful way to determine the relative pulmonary and systemic flows. When high systemic arterial and low systemic venous oxygen saturation are present, pulmonary blood flow should be decreased; conversely, when both low systemic arterial and venous oxygen saturation are present, more flow should be directed to the pulmonary circulation.

• Authors: O Barnea, E H Austin, B Richman, W P Santamore
• Journal: Journal of the American College of Cardiology (J Am Coll Cardiol) Vol. 24 Issue 5 Pg. 1376-81 (Nov 01 1994) ISSN: 0735-1097 [Print] United States
• PMID: 7523473 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Oxygen

Topics

• Cardiac Output (physiology)
• Humans
• Hypoplastic Left Heart Syndrome (blood, physiopathology, therapy)
• Infant, Newborn
• Models, Cardiovascular
• Models, Theoretical
• Oxygen (blood)
• Palliative Care
• Pulmonary Circulation (physiology)