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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.

Calculation

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

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]

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 renal status, especially following renal transplant. Following renal transplant 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.{{cite book}}: CS1 maint: multiple names: authors list (link)
  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): A87. doi:10.2214/ajr.196.5_supplement.0a84.
  4. ^ a b 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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