Regional blood flow supply and demand in heart failure.

Heart failure results not only in a fall in cardiac output but also in a redistribution of blood flow favoring some regional beds (the brain and the heart) at the expense of others (the kidney and working skeletal muscle). The chronic resting hypoperfusion of striated muscle is further compromised with exercise. Maladaptive vasoconstrictor control mechanisms prevent the redirection of blood flow from nonworking muscle and liver to working muscle. This inappropriate preservation of nonworking organ perfusion further compromises the functional capacity of working muscle and is associated with evidence for metabolic deconditioning with reduced oxygen extraction and impaired oxidative phosphorylation. It is becoming increasingly clear that the clinical response to the inotropic and vasodilator therapy used in heart failure is in part dependent on the differing regional blood flow profiles of the various agents studied. The ability of the angiotensin-converting enzyme inhibitors to redirect blood flow away from nonworking regional beds to exercising muscle, and thereby to reestablish an appropriate physiologic response to changing metabolic needs, may be the overriding reason for their long-term efficacy. Certainly in the future the comprehensive therapy of heart failure will have to take into consideration not only central hemodynamic but also regional blood flow/supply and demand issues.