The term orthostasis response (orthostatic adaptation) is used to define the ability of the organism to equalize blood pressure when moving to the upright position. This effect can occur, for example, when a person suddenly moves from a lying to a sitting or standing position.
What is the orthostasis response?
When the body undergoes an extreme change of position, the circulatory system faces an extraordinary challenge because the return flow of venous blood to the heart decreases sharply. Prior to this, the increase in hydrostatic pressure causes the leg veins to expand noticeably. About half a liter of blood can accumulate there due to the abrupt change in pressure. The orthostasis response can compensate for this.
Function and task
The term orthostasis response (orthostatic adaptation) is used to define the organism’s ability to equalize blood pressure during a change to the upright position. To keep the circulation stable in almost any body position and to balance it after a change in position, many body processes occur simultaneously. For example, the stroke volume of the heart decreases significantly, in drastic cases by 40 percent. This in turn leads to an increase in heart rate of about 30 percent. A state of collapse is thus reached. Even in less severe cases, there is a very rapid drop in blood pressure. It drops directly due to the sudden change in position from lying to sitting or standing and also indirectly due to the reduction in cardiac output. This situation is compensated for by the so-called pressoreceptor reflex (also baroreceptor reflex). This stimulates the sympathetic nervous system of the autonomic nervous system. The receptors in the leg veins cause an increase in sympathetic tone, which is why the venous return flow to the heart increases again. This also helps to quickly compensate for the drop in blood pressure. This is supported by the temporary slight decrease in renal blood flow.
Diseases and complaints
If the orthostasis response does not function, the condition is referred to as orthostatic dysregulation. People affected by this may even become briefly unconscious in severe cases during a rapid change to the upright posture from a lying position. This condition results from an undersupply of blood and thus oxygen to the brain. The result can be orthostatic collapse – the immediate falling over. However, this also solves the problem, because in a recumbent state, the circulatory conditions will quickly stabilize again on their own. Minor consequences of the disturbed orthostasis mechanism can be ringing in the ears and dizziness. The complete absence of the orthostasis reaction often affects people with chronically low blood pressure. These include predominantly young slim women and adolescents who are in special growth phases. One cause of this deficiency may be the venous pump not working properly, possibly causing larger volumes of blood to drop into the legs. Those who have such a tendency to orthostasis deficiency can initially help themselves with very simple means. First and foremost, the slow, not hasty raising to a vertical position leads to improvement. Often, a stronger cup of coffee and an abundant supply of fresh, cold air can also help. Insufficient orthostatic adaptation can also be caused by too long sunbathing, latent overtiredness, prolonged bed rest or, for example, the consumption of a cigarette after a longer period of abstinence. Then it is often accompanied by a feeling of emptiness in the head, strong palpitations, ‘stars’ before the eyes and slight trembling. These more or less harmless symptoms can occasionally occur even in completely healthy people. If the false reaction in question appears very often or even constantly, then it is orthostatic hypotension, the chronic drop in blood pressure when the body is upright. This condition often presents itself with increasing age. In people over 65, it occurs in nearly 30 percent of cases. However, only one in nine of those affected reports the typical symptoms. According to concrete measurements, orthostatic hypotension can be assumed if the systolic blood pressure drops by at least 20 mmHg and the diastolic blood pressure by at least 10 mmHg within one minute.However, such a drop in blood pressure could lead to a considerable risk of death, for example in patients with cardiovascular disease who may already have had a heart attack. Elderly people suffering from hypotension (drop in blood pressure) are also extremely susceptible to stroke. In addition, the risk of dementia increases for them. Elderly people are also susceptible to the related condition of postprandial hypotension. In these cases, the dysfunctions occur against a background of elevated blood pressure. In this case, it is not necessarily the sinking of the blood into the legs that causes the complaints, but they often occur in the course of digestion after a large meal. This special form is no less dangerous for older people. The sharp drop in blood pressure about two hours after eating often affects patients with Parkinson’s disease or diabetes mellitus. The medications they take often greatly exacerbate the unpleasant effects of postprandial hypotension. Slow elevation and great caution when moving too quickly are particularly advisable for these patients. This is particularly important when getting up in the morning. It is advisable to sit on the edge of the bed for a while and only rise later. It is also better to get up slowly from the toilet, especially at night. Small training units are also helpful, such as repeatedly lifting the feet alternately before raising the whole body. If possible, long periods of standing motionless should be avoided, as should prolonged exposure to intense heat. It is important to drink enough every day, especially with meals. At least one hour before bedtime, fluid intake should then be reduced or discontinued to avoid frequent trips to the toilet at night.
