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[Coronary and renal circulation in patients with cardiac failure after converting enzyme inhibitors]
Insights
In heart failure, angiotensin converting enzyme inhibitors improve cardiac output and redistribute blood flow, increasing renal flow while maintaining coronary flow, aligning with physiological needs.
Area of Science:
- Cardiovascular Physiology
- Renal Physiology
- Pharmacology
Context:
- Cardiac output and organ blood flow are critical for metabolic demands.
- Coronary and renal circulations differ in regulation, flow rates, and oxygen extraction.
- Heart failure involves complex circulatory adjustments, including vasoconstriction mediated by the renin-angiotensin system.
Purpose:
- To investigate the impact of angiotensin converting enzyme inhibitors on cardiac output distribution in heart failure.
- To compare the effects of these inhibitors on coronary and renal blood flow.
- To assess whether observed flow redistribution aligns with physiological requirements.
Summary:
- In heart failure, cardiac output is often maintained by vasoconstriction, leading to reduced renal blood flow (less than 15% of cardiac output) but preserved coronary blood flow (more than 15%).
- Treatment with angiotensin converting enzyme inhibitors increases cardiac output and favorably redistributes blood flow.
- Coronary blood flow remains stable or decreases proportionally to reduced myocardial oxygen demand, with preserved metabolic regulation and no coronary steal phenomenon.
- Renal blood flow typically increases by a percentage greater than the increase in cardiac output.
Impact:
- Angiotensin converting enzyme inhibitors promote a physiological redistribution of blood flow in heart failure patients.
- This redistribution supports the distinct functional roles of the coronary and renal circulations.
- Findings provide insights into the therapeutic mechanisms of angiotensin converting enzyme inhibitors in managing heart failure.
Abstract:
The cardiac output and its peripheral distribution must fulfill the metabolic and/or functional requirements of the different organs. The various techniques used to measure blood flow rates in the coronary and renal arteries provide much information on this point, but they do not tell us all we would like to know about the distribution and "utilization" of these flows in tissues. In normal subjects the myocardial oxygen consumption is not markedly different from the renal oxygen consumption, but the mechanisms that regulate the coronary and renal circulations are not the same. The flow rate in the coronary vessels is about 10% of the cardiac output, the arteriovenous oxygen gradient is superior to 10 vol % and regulation is metabolic. In the renal vessels, which are primarily "functional", the flow rate is about 25% of the cardiac output and the arteriovenous oxygen gradient is inferior to 2 vol %. In heart failure patients, despite reduced cardiac output the blood pressure is kept normal for a long time by vasoconstriction of the arterioles, a process which involves, at least partly, the renin-angiotensin system. The vasoconstriction predominates in some circuits (the renal flow rate is less than 15% of the cardiac output) and spares the "privileged" circuits (the coronary flow rate is more than 15% of the cardiac output). Under the influence of angiotensin converting enzyme inhibitors, the cardiac output increases and its distribution is modified. The coronary flow rate remains stable or is reduced in proportion to the decrease in myocardial oxygen consumption, the metabolic regulation is preserved and there is no "coronary steal". The percent increase in renal flow rate is usually superior to that of the cardiac output. This peripheral redistribution of coronary and renal blood flow rates in heart failure patients after treatment with converting enzyme inhibitors seems to correspond to the physiological purposes of the two regional blood flows.