OCCURRENCE OF PRESYNCOPE IN SUBJECTS WITHOUT VENTRICULAR INNERVATION

1. To determine whether activation of the left ventricular C-fibre mec hanoreceptors initiates the vasodepressor reflex that often causes syn cope, we exposed six orthotopic cardiac transplant patients and six ma tched, healthy control subjects to progressively increasing lower body negative pressure until the onset of vasodepressor responses. 2. Ther e was no significant difference (P=0.78) between the central hypovolae mia tolerances of the cardiac transplant and the control groups. 3. Th e decrease in systolic blood pressure before the onset of vasodepresso r reflexes was greater in the cardiac transplant group. The cardiac tr ansplant group did not maintain diastolic blood pressure during centra l hypovolaemia. From baseline to the onset of vasodepression, there we re no differences in leg circumference, forearm blood flow and forearm vascular resistance responses between the two groups. 4. We conclude that the left ventricular mechanoreceptors may not be the primary affe rent trigger for syncope.