Hormonal and plasma volume changes after presyncope

12 healthy male adults

Passive 4-min 70° head-up tilt followed by 4-min sequences of additional lower body negative pressure of increasing intensity (15 mmHg steps) to induce presyncope

Supine rest (baseline)

Plasma volume changes and hormone levels (plasma renin activity, aldosterone, ACTH, adrenomedullin, and vasopressin) at presyncope and 20-min post-presyncopesurrogate