Vascular resistance

As vascular resistance refers to the resistance to flow that a blood vessel the blood stream opposes. The vessel resistance is defined analogously to the ohmic resistance as the quotient of the pressure difference between the ends of the vessel and the volume flow rate:

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

If you replace a vessel with a rigid tube with the radius r and the length l , the vessel resistance results according to the Hagen-Poiseuille law :

${\displaystyle R={\frac {8\cdot \eta \cdot l}{\pi \cdot r^{4}}}}$

It shows that the vascular resistance depends not only on the properties of the vessel, but also on the viscosity η of the blood (which, however, is not a constant, but depends on the vessel diameter and the flow rate). Nonetheless, it can be stated that the vascular resistance increases with the length of the vessel and reacts very sensitively to changes in the vascular radius (halving the radius sixteen times the resistance in the model). Stenoses (e.g. of the coronary arteries in coronary artery disease ) increase the vascular resistance and thus reduce the blood flow; however, they often only affect short vessel sections, which is why only high-grade stenoses become symptomatic.

By analogously applying the rules for adding electrical resistances in series and parallel connection , resistances for entire circulatory sections can be calculated from individual vessel resistances. A basic distinction is the total vascular resistance (TPR, of English resistance total peripheral , equivalent resistance of the systemic circulation ) and the pulmonary vascular resistance (PVR, from English resistance pulmonary vascular , equivalent resistance of the pulmonary circulation ). In addition, the vascular resistance of individual organs (e.g. the cerebral vascular resistance in the brain ) can also be specified.

literature

• Reinhard Larsen, Thomas Ziegenfuß : Ventilation: Basics and Practice . Springer-Verlag, 2nd edition Berlin Heidelberg 2013, et al. P. 66 ff. ( Online )
• Dee Unglaub Silverthorn: Physiology . Pearson Deutschland GmbH, Munich 2009, et al p. 718 ff. ( Online )
• Franz-Josef Kretz, Frank Teufel: Anesthesia and intensive care medicine . Springer Medizin Verlag, Berlin Heidelberg 2006, p. 72 ff. ( Online )
• Richard Rost: Sports and exercise therapy for internal diseases: textbook for sports teachers, trainers, physiotherapists and sports medicine specialists . Deutscher Ärzteverlag, Cologne 2005, p. 55 ff. ( Online )
• Alexander and Konstantin Bob (eds.): Internal medicine . Special edition from the Dual Series , Georg Thieme Verlag, Stuttgart 2001, p. 251 ff. ( Online )
• Wolfgang Oczenski, Harald Andel, Alois Werba: Breathing - breathing aids: breathing physiology and ventilation technology . Georg Thieme Verlag, Stuttgart 2012, p. 98 ( online )
• Dieter Vaitl: Essential hypertension: Psychological-medical aspects . Springer-Verlag, Berlin Heidelberg 1982, p. 29 ( online )

Web links

• Vascular resistance - explanation on criticalcare.at

Individual evidence

1. ↑ Entry on pulmonary vascular resistance in Flexikon , a wiki from DocCheck , accessed on November 26, 2015.