Cerebrovascular and Cardiovascular Measurements During Neurally Mediated Syncope Induced by Head-Up Tilt

Abstract

The decrease in cerebrovascular resistance during NMS indicates that the integrity of cerebrovascular autoregulation is maintained even when syncope is imminent. The selective loss of diastolic flow during syncope and the increase in pulsatility index are likely caused by collapse of downstream vessels as diastolic blood pressure decreases below the critical closing pressure of cerebral vessels.