ORTHOCAP - Use of Plasma Galanin and Adrenomedullin Responses to Quantify Orthostatic Capacity

The aim of the project is to test the hypothesis that the release of hormones during orthostatic stress follows patterns that indicate particular cardiovascular regulatory states. This is based on recent observations published by the project team: They showed that plasma adrenomedullin concentration rises proportionally with the degree of orthostatic stimulation, whereas plasma galanin does not change until a presyncopal situation is reached, upon which its plasma level increases.

A progressive orthostatic stress until presyncope (POSUP) stimulation paradigm is used (Fig. top). It consists of 4 minutes head-up tilt (HUT), plus additional 4 minutes 15-mmHg lower body negative pressure increments to provoke a presyncopal situation, that is the state preceding imminent loss of consciousness, which is avoided by bringing the test subject back to supine when presyncope is reached. This way, maximum orthostatic competence can be quantified as standing time until reaching presyncope, before and after simulated weightlessness.

In addition to measuring hormone concentration changes (including catecholamines, the renin-aldosterone system, and vasopressin), we monitor heart rate, arterial blood pressure, autonomic nervous indices, baroreflex sensitivity and effectiveness, and markers of blood volume change (plasma mass density, hematocrit) before, during, and after application of POSUP. By these data, orthostatic competence can be explained in depth.

Preliminary results are the following: Among 24 healthy test persons, typical hemodynamic POSUP patterns emerged as expected (Fig. bottom). Parameters of autonomic nervous activity changed according to the degree of cardiovascular challenge. There were big, well reproducible interindividual differences in terms of orthostatic resilience. We found a significant effect of time on plasma vasopressin, renin activity, aldosterone, but not galanin. Other hormones are still to be determined. The bed rest campaign that we will participate in is designed for 2011.

Coordinator

Institute of Adaptive and Spaceflight Physiology

Institute of Adaptive and Spaceflight Physiology
Wormgasse 9
A-8010 Graz
Tel.: +43 (316) 380 4490
Fax: +43 (316) 380 9632
E-Mail: helmut.hinghofer@medunigraz.at