Arterial resistivity index

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.

Calculation

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

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

Description

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]

Uses

• It is used in ultrasound testing of umbilical artery for placental insufficiency. RI should not exceed 0.60 at 30 weeks of gestation.^[4]

See also

• Pulsatility index
• Leandre Pourcelot (French)

References

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. doi:10.2214/ajr.196.5_supplement.0a84.
4. Hobbins, John C. (2007). Obstetric ultrasound : artistry in practice. Oxford: Blackwell. p. 37. ISBN 978-1-4051-5815-2.

External links

• Resistivity index (English/Spanish)
• Pulsatility index (Spanish)