Resistance index in mediastinal lymph nodes: a feasibility study.

Objective: The purpose of this study was to determine the range of Doppler ultrasonographic measurements of the resistance index in presumed normal mediastinal lymph node arteries.

Methods: Consecutive patients referred for bronchoscopy for various indications and normal CT findings in the mediastinum were included. The resistance index (RI) in mediastinal lymph node arteries was examined with Color Doppler ultrasonography. The peak systolic velocity (PSV) and the end-diastolic velocity were measured, which allowed for calculation of the resistance indices in different lymph node stations and in each lymph node artery.

Results: Eighty-nine patients (32 female; 57 male; mean age, 42.2 years) were examined, and of these, 50 patients (24 female; 36 male; mean age, 44.7 years) had measurable RIs. PSV and ESV were measured in all visible nodes (n = 196) and an interpretable value was obtained in 127 nodes (2.5 nodes per patient.). The median PSV was 15.6 cm/s (range, 8.9-23.2 cm/s, SD +/- 2.6, 25-75% percentile 13.8-17.5), and the median end-diastolic velocity was 5.8 cm/s (range, 3.6-11.4 cm/s, SD 1.15 cm/s, 25-75% percentile 5.1-6.3). The median RI values for arteries were 0.63 (range, 0.52-0.75, SD 0.04, 25-75% percentile 0.6-0.64) respectively. The Doppler measurements lasted on average 4.3 minutes and no complications were seen.

Conclusion: Color Doppler ultrasonography allows for quantification of velocities like PSV and ESV in mediastinal lymph node arteries, which in turn allow calculation of a resistance index. Knowledge of the resistance index's normal range (which describes the resistance of the blood flow within the lumen of the lymph node artery) may be a useful adjunct to the ultrasonic assessment of the mediastinum.