Arterial resistivity index

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The arterial resistivity index (also called as Resistance index, abbreviated as RI), developed by Leandre Pourcelot, is a measure of pulsatile blood flow that reflects the resistance to blood flow caused by microvascular bed distal to the site of measurement.


The formula used to calculate resistance index is:[1]

RI = \frac{v_{systole} - v_{diastole}}{v_{systole}}


Resistance index Description
0 Continuous flow
1 Systolic flow, but no diastolic flow
>1 Reversed diastolic flow

The RI is altered not by vascular resistance alone but by the combination of vascular resistance and vascular compliance.[2][3]


See also[edit]


  1. ^ Sistrom, Theodore E. Keats, Christopher (2002). Atlas de medidas radiológicas. Madrid: Harcourt. p. 481. ISBN 978-84-8174-612-9. 
  2. ^ Bude, RO; Rubin, JM (May 1999). "Relationship between the resistive index and vascular compliance and resistance.". Radiology 211 (2): 411–7. doi:10.1148/radiology.211.2.r99ma48411. PMID 10228522. 
  3. ^ Boas FE, Desser TS, and Kamaya A (2011). "Does separating the resistive index into pre- and post-glomerular resistance and vascular compliance improve the diagnostic accuracy of renal transplant doppler ultrasound?". American Journal of Roentgenology 196 (5): A87. 
  4. ^ Hobbins, John C. (2007). Obstetric ultrasound : artistry in practice. Oxford: Blackwell. p. 37. ISBN 978-1-4051-5815-2. 

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