Vascular tone

The vascular tone is the active tension that is developed in a vascular segment by the smooth vascular muscles . It is a crucial actuator for the organ blood flow and significantly influences the physics of the blood circulation .

function

See also : tone  and pulse

Organ blood flow

The vascular tone of the individual vascular segments can be regulated differently from organ to organ and determines the resistance that the individual organ opposes to the blood flow. This then influences the blood flow to the individual organ.

blood circulation

In total, the respective vascular tone in the body periphery generates the total peripheral or pulmonary resistance ( total peripheral resistance TPR or systemic vascular resistance SVR ), which, together with the cardiac output (CO), influences the blood pressure , analogous to Ohm's law .

Circuit: ${\displaystyle R={\frac {U}{I}}}$

corresponds to the resistance of a single vessel segment

${\displaystyle R={\frac {\Delta p}{\dot {V}}}}$

${\displaystyle {\text{TPR}}={\frac {{\text{MAP}}-{\text{ZVD}}}{\text{HZV}}}}$

${\displaystyle \Delta p}$(arteriovenous pressure difference) is the pressure difference between the venous ( central venous pressure CVP ) and arterial ( mean arterial pressure MAD or English MAP ) leg and corresponds to the electrical voltage U in the electrical circuit . The CO or Q (blood flow) corresponds to the current  I and the electrical resistance   R (resistance) to the TPR.

regulation

→ Main article : "Regulation" in the article blood circulation

Regulation takes place via central ( blood pressure ) and local mechanisms. There are different distributions of receptors in the body, and the vessels also have different properties.

• Vascular nerves ( vasomotors ): release of norepinephrine acts
  • low doses of alpha1 receptors ⇒ vascular constriction (constriction) especially of small arteries.
  • (high doses of presynaptic alpha2 receptors ⇒ inhibition of noradrenaline release as counter-regulation)
• Circulating hormones: adrenaline reaches the beta ₂ receptors via the bloodstream ⇒ widening of the coronary vessels
• myogenic smooth muscle response to stretch
• local factors:
  • Metabolic end products such as ADP , AMP , adenosine , potassium , hydrogen ions ("acid"), CO ₂ and O ₂ deficiency signal the small arteries to have an increased need for blood flow and have a vasodilating effect.
  • Prostacyclin I 2 (PGI2)
  • Nitric oxide NO (synonym EDRF ( endothelium-derived relaxing factor ))
  • Endotheline
• flow-dependent vasodilation (vasodilation)

further vascular dilators:

• histamine
• various inflammation mediators

literature

• Erland Erdmann : Vasoconstriction and vasodilation. In: Clinical Cardiology. Diseases of the heart, the circulatory system and the vessels near the heart. Springer, Heidelberg 2009, ISBN 978-3-540-79011-2 , p. 292, books.google.de

Individual evidence

1. ↑ ^{a b} Entry on vascular tone in Flexikon , a Wiki of the DocCheck company , accessed on May 20, 2014.
2. ↑ CO monitoring - calculation formulas ( Memento of December 24, 2004 in the Internet Archive ), accessed on May 20, 2014. (PDF, p. 8/9.)
3. ↑ Important laws of blood flow regulation (PDF) on diss.fu-berlin.de, accessed on May 20, 2014.
4. ↑ Standard formula for calculating the TPR p. 14 on d-nb.info, accessed on May 20, 2014.
5. ↑ Hans Walter Striebel: normal values, calculation formulas, conversions. In: Operative Intensive Care Medicine. Safety in clinical practice. Schattauer, Stuttgart 2008, ISBN 978-3-7945-2480-8 , p. 736.

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