Benefit of repeated receptor stimulation as a spaceflight medical tool to promote cardiovascular fitness: different orthostatic paradigms compared.
We used various orthostatic stimulus combinations to better understand the physiology and countermeasure potential of repeated change of body position in humans. The purpose of the investigations reported was threefold: To investigate cardiovascular and hormonal effects of repeated transition between partially antiorthostatic (-30 degrees HDT) and partially head-up passive body tilt (+30 degrees HUT). Protocol Y denotes the repeated transition between these two body positions; To apply, in the same test persons, repeated transition between supine and passive upright (Protocol X), and to compare the effect of the two protocols; To find out which stimulus pattern provides the largest physiological effects and, hence, presumably the largest countermeasure potential. We chose our tilt protocol according to tilt angle sine ranges: The sine difference is 1.0 both in Protocol X (sine=0 vs. sine=1.0) and Y (sine= -0.5 vs. sine= +0.5) since this difference, and not the angle change per se, determines hydrostatic effect intensities. Due to longer-lasting neurohormonal effects elicited by tilting procedures, they all should be a useful countermeasure against post-immobilization orthostatic instability, a conjecture not yet been tested in this specific form. Therefore, one of the questions asked in this study were if movement between the two defined body positions produces similar changes when employing Protocol X vs. Protocol Y.
Hinghofer-Szalkay
Helmut
H
Institute of Physiology, Medical University, Harrachgasse 21, A-8010 Graz, Austria. helmut.hinghofer@meduni-graz.at
Rössler
Andreas
A
D000324:Adrenocorticotropic Hormone / Q000378:metabolism; D000328:Adult; D000450:Aldosterone / Q000097:blood; D009320:Atrial Natriuretic Factor / Q000097:blood; D001794:Blood Pressure; D002320:Cardiovascular Physiological Phenomena; D017097:Electric Impedance; D005260:Female; D006339:Heart Rate; D006400:Hematocrit; D006801:Humans; D008150:Lower Body Negative Pressure; D008297:Male; D010953:Plasma Volume; D011187:Posture / Q000502:physiology*; D012083:Renin / Q000097:blood; D013026:Space Flight; D016683:Supine Position; D018667:Tilt-Table Test; D013997:Time Factors
D000450:Aldosterone; D009320:Atrial Natriuretic Factor; D000324:Adrenocorticotropic Hormone; D012083:Renin