Grant: Travel Awards - Institute Community Support

Patients with heart failure have increased activity of the sympathetic nervous system, which causes blood vessels to constrict, heart rate to increase, retention of salt and water, and early death. The cause of high sympathetic activity is unknown. One reflex mechanism that helps to control sympathetic activity in healthy people is from stretch or pressure receptors in the heart. Normally, increased pressure decreases sympathetic activity. In heart failure this reflex is blunted. Experiments show the heart has two types of receptors, one that increases and one that decreases sympathetic activity to increasing pressure. We think that in heart failure the activity of receptors which increase sympathetic activity may predominate. Our study measured sympathetic activity by placing an electrode in a nerve below the knee during periods with increased and decreased pressure in the heart. We found that increased pressure in the heart caused the majority of sympathetic fibres to paradoxically increase firing in heart failure patients. This is a never before demonstrated reflex that could help explain why sympathetic activity is elevated. It can also explain why decreasing pressure in the heart improves survival in patients with heart failure.