P1.13 The pathologic relevance of the initial reaction during head-up tilt

An intermittent, short lasting fall in blood pressure during start of head-up tilt is called “initial reaction”. However clear criteria defining the initial reaction are missing. It was systematically investigated in physiologic studies in small numbers of subjects [1;2]. Initial reactions were mainly observed during active standing, but to a much lesser degree during head-up tilt (HUT). Adaptations of the peripheral resistance and baroreceptor mechanisms were discussed as underlying mechanisms.