Perfusion

When blood flow or perfusion (exact hemoperfusion ) the supply of organs or parts of organs is called with blood. The supplied via arteries, which drain through veins ( and lymphatic vessels ). This is used to supply tissues with oxygen, nutrients and other essential blood components and the removal of metabolic waste products and carbon dioxide. The organ perfusion can be artificially maintained. As the re- flow reperfusion of an organ (eg, after an embolism ) called after temporary interruption of blood supply.

Disturbances different causes are referred to as the blood flow and can cause both acute and chronic impairments of various organ and tissue function and lead in extreme cases to the destruction of the less perfused organ districts.

Quantification

Also referred to as perfusion ( in terms of a quantifiable size) the volume of blood flowing per unit time through an organ or more generally by biological tissue mass. Depending on the reference, the physical unit of perfusion is either (based on an organ such as the kidney ):

Or (based on the regional blood flow, also referred to as specific perfusion )

The (total) in renal blood flow, for example, an adult is about 1200 ml / min; the specific perfusion is about 4 ml / (g · min). The total circulation of an organ can also be as a quotient of the pressure drop between arterial () and venous pressure () and the vascular resistance of the organ, so as describe.

Measurable is the (specific ) perfusion with various imaging techniques such as perfusion MRI, perfusion CT or nuclear medicine methods.

Variability of the blood flow

A distinction is a resting blood flow of a maximum possible blood flow ( or perfusion reserve). The individual organs are very different extents supplied with blood: At rest, the kidneys receive ( in proportion to their weight) the largest relative percentage of blood, with maximum blood flow, these are the muscles ( skeletal and cardiac muscle) and skin. The demand adjustment of blood flow is ensured by complex control mechanisms.

Factors

Under physiological conditions play next to the systemic blood pressure numerous systemic and local factors play a role:

Neurovascular

The effect of the sympathetic nervous system via the release of noradrenaline to a narrowing of arterial resistance vessels and thus to a reduced blood flow from downstream Gewebsbezirken. The function of the parasympathetic nervous system is limited by its vasodilator function to its effect on sweat and salivary glands and the genital organs.

Autoregulation of blood flow

The blood flow to important organs such as the brain ( see blood supply to the brain ), the kidneys ( see autoregulation of renal blood flow ) and the gastrointestinal tract ( as an organ system ) is secured by mechanisms that a constant blood flow independent of the over wide ranges systemic blood pressure seek to ensure. An important component of this is the so-called auto-regulation Bayliss effect, which is also referred to as myogenic response ( the afferent blood vessel ).

Pregnancy

In pregnancy, the blood flow to the uterus which ultimately a share of 10-15 per cent of the maternal ( maternal ) cardiac output (CO ) increases (via the Aa. Uterinae ) of 50 at the beginning of 500-750 ml / min at the end of pregnancy, corresponds to ( uterine or maternoplazentare blood flow). The driving force here is the mother's blood pressure while the fetal blood pressure allows the so-called fetoplacental circulation. Of the more than 250-400 ml / min of fetal HMV flow to the 50-60 per cent in the umbilical artery ( umbilical aa. ).