Heart failure: role of cardiovascular reflexes

The cardiovascular reflexes have the key role in the rapid adjustments of the circulatory system in response to daily stresses such as standing and muscular exercise. Arterial and cardiopulmonary mechanoreceptors continuously signal to the cardiovascular centers in the brain the moment to moment pressure changes in the larger arteries, atria and ventricles and exert a tonic restraint on the sympathetic noradrenergic outflow. Depending on the stress, the vasomotor centers adjust this outflow, both qualitatively and quantitatively, to the heart and to the different vascular beds to maintain an appropriate arterial blood pressure. In addition, the sympathetic nerves modulate renin release from the juxtaglomerular cells and receptors at the veno-atrial junctions regulate vasopressin release from the posterior pituitary. Congestive heart failure is characterized by excessive neuro-humoral excitation as evidenced by direct recordings of sympathetic activity and by increased plasma levels of catecholamines, renin, angiotensin II and arginine vasopressin. The evidence indicates that this is a consequence of the reduced ability of the arterial and cardiopulmonary mechanoreceptors to inhibit the vasomotor centers. The cause(s) of this diminished circulatory control requires further studies. The cardiac glycosides, which normally cause vasoconstriction, cause vasodilatation in patients with heart failure. This is attributed to sensitization of the mechanoreceptors. The term atrial natriuretic factor refers to a family of peptide hormones released when the atrial myocytes are stimulated by an increase in transmural pressure. They cause diuresis, natriuresis and vasorelaxation. In severe congestive heart failure, the plasma levels are increased and this helps to compensate for the increased neurohumoral activation by inhibiting the renin-angiotensin system and enhancing sodium and water excretion.(ABSTRACT TRUNCATED AT 250 WORDS)