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.

Arterial resistivity index
Medical diagnostics
Purposemeasure of pulsatile blood flow

Calculation

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

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

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

Normal mean renal artery RI for an adult is 0.6 with 0.7 the upper limit of normal. In children, RI commonly exceeds 0.7 through 12 months of age and can remain above 0.7 through 4 years of age.[4]

Uses

It is used in ultrasound testing of umbilical artery for placental insufficiency. RI should not exceed 0.60 at 30 weeks of gestation.[5] RI is also commonly used to monitor kidney status, especially following kidney transplant.

Following kidney transplantation, patients with an RI > 0.8 have an increased mortality.[4][6]

See also

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, 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): A84–A87. doi:10.2214/ajr.196.5_supplement.0a84.
  4. American Journal of Roentgenology. 2003;180: 885-892. 10.2214/ajr.180.4.1800885
  5. Hobbins, John C. (2007). Obstetric ultrasound : artistry in practice. Oxford: Blackwell. p. 37. ISBN 978-1-4051-5815-2.
  6. N Engl J Med. 2013 Nov 7;369(19):1797-806. doi: 10.1056/NEJMoa1301064.
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