Arterial resistivity index
Template:Infobox diagnostic 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 kidney status, especially following kidney transplant.
Following kidney transplantation, patients with an RI > 0.8 have an increased mortality.[4][6]
See also
- Pulsatility index
- Leandre Pourcelot (French)
References
External links
- Resistivity index (English/Spanish)
- Pulsatility index (Spanish)
- ↑ Template:Cite book
- ↑ Template:Cite journal
- ↑ Template:Cite journal
- ↑ 4.0 4.1 American Journal of Roentgenology. 2003;180: 885-892. 10.2214/ajr.180.4.1800885
- ↑ Template:Cite book
- ↑ N Engl J Med. 2013 Nov 7;369(19):1797-806. doi: 10.1056/NEJMoa1301064.