Influence of resting before sonographic examination on Doppler measurements of renal blood flow

Renal artery stenosis (RAS) is the most common cause of secondary hypertension, via increases in plasma renin-angiotensin-aldosterone levels. Renal artery stenosis is diagnosed from blood examinations such as renin activity and from imaging examinations such as sonography. Patients are required to lie on the bed for 30 min before and during phlebotomy, since plasma renin activity is easily altered by posture. However, no such pre-examination rest is required for sonography. The present study therefore investigated the possible influence of resting before examination on Doppler parameters used for the diagnosis of RAS. Subjects comprised 55 healthy young adults (24 males, 31 females; mean age, 22 +/- 1 years). Sonographic measurements were made shortly after subjects entered the examination room and again after 30 min of rest lying on a bed. Median peak systolic velocity in the renal artery was significantly decreased after rest (106 cm/s, interquartile range (IQR) 96-121 cm/s) compared with before rest (120 cm/s, IQR 107-135 cm/s; p < .001). Median acceleration time in the intra-renal segmental artery was also significantly shorter after rest (49 ms, IQR 38-54 ms) compared to before rest (50 ms, IQR 38-59 ms; p = .039). The present results suggest that serious consideration should be given regarding whether pre-examination resting is needed to accurately interpret Doppler measurements of renal blood flow when diagnosing RAS from sonography.