Orthostatic response
The orthostasis reaction describes reactions in human as well as animal organisms to changes in position. The name refers to the orthostasis , the standing posture.
physiology
During the transition from lying down to standing, an increase in hydrostatic pressure leads to an expansion of the leg veins . As a result, the venous return flow to the heart is reduced. The lowering of the preload of the heart is compensated for in healthy individuals by activating the sympathetic nervous system . The drop in cardiac output is limited to a maximum of 30%, since vasoconstriction occurs primarily in the supply area of the major splanchnic nerve and the heart rate increases by 30%. The mean arterial pressure , although there is a decrease in stroke volume, is maintained by a constriction of the resistance vessels. The blood pressure amplitude decreases as the cardiac output decreases. The systolic blood pressure decreases by about 10 to 15 mm Hg , while the diastolic blood pressure increases by a few mm Hg.
Clinical review
The decrease in blood volume during the orthostatic reaction is also responsible for ADH secretion in syncope (fainting). The orthostatic reaction can therefore be used to check the intactness of the RAAS , as it reacts directly to the degrees of erection during a tilt table examination .
In extreme cases, patients with hypotension can develop orthostatic syncope.
literature
- E. Buddecke, M. Fischer: Pathophysiology, Pathobiochemistry, Clinical Chemistry . de Gruyter, ISBN 3-11-012844-6 .
Individual evidence
- ↑ Melin et al. Comparison of passive heat orexercise-induced dehydration on renal water and electrolyte excretion: the hormonal involvement. Eur J Appl Physiol 85 (2001) 250-258 PMID 11560078
- ↑ Laszlo et al. Cardiovascular and hormonal changes with different angles of head-up tilt in men. Physiol Res 50 (2001) 71-82. PMID 11373890