Renal ultrasonography as a tool for detecting dynamic changes in blood pressure

Renal ultrasonography has been used to assess renal blood flow under pathological conditions. We attempted to determine if sonographically derived renal resistive index measurements would be affected by subtle changes in flow as a consequence of transiently induced mild increases in blood pressure in persons with normal renal functioning. Nine subjects free of structural renal disease were studied with duplex Doppler ultrasonography. Main renal artery resistive indices were determined under resting baseline conditions and in response to graded infusions of phenylephrine sufficient to increase blood pressure by approximately 13/5 mm Hg. Change in blood pressure correlated with the change in main renal artery resistive index (r = 0.254, P < 0.05). Thus, the resistive index varies in association with transient increases in blood pressure and may reflect concurrent alterations in distal resistance under physiologic conditions.