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Correlation between Renal Vascular Resistance, Pulse Pressure, and the Resistive Index in Isolated Perfused Rabbit Kidneys¹

¹ From the Departments of Radiology (M.E.T., F.N.T.) and Pharmacology (M.E.M.), Albany Medical College, 43 New Scotland Ave, Albany, NY 12208. From the 1998 RSNA scientific assembly. Received October 1, 1998; revision requested November 10; revision received December 17; accepted February 17, 1999. M.E.T. supported in part by a 1996 RSNA Seed Grant. M.E.M. supported in part by a grant-in-aid from the American Heart Association. Address reprint requests to M.E.T. (e-mail: tublin@rad.amc.edu).

View larger version (32K): [in a new window]   Figure 1. Diagram of the adjustable perfusion system.

View larger version (62K): [in a new window]   Figure 2a. (a) Arterial spectral Doppler US waveform from a rabbit kidney shows a normal RI of 0.45. (b) Graph shows a plot of instantaneous perfusate pressure versus fraction of time through the pulse cycle. Data were obtained at the same time as the US image.

View larger version (18K): [in a new window]   Figure 2b. (a) Arterial spectral Doppler US waveform from a rabbit kidney shows a normal RI of 0.45. (b) Graph shows a plot of instantaneous perfusate pressure versus fraction of time through the pulse cycle. Data were obtained at the same time as the US image.

View larger version (16K): [in a new window]   Figure 3a. Graphs show correlation between RVR and RI. (a) Plot of the mean RI versus RVR from five experiments, each denoted by a different symbol (error bars omitted for clarity). RVR was adjusted by using phenylephrine hydrochloride and sodium nitroprusside, as described in b. The relationship of RI versus RVR in each experiment was analyzed by using linear regression with all RI values recorded under each condition (n = 7-13 for each point, n = 25-42 for each line). The regression lines appear curved because RVR is plotted on a logarithmic scale. The slope of each line was significantly greater than zero (P < .05). (b) By using the data from a, the change in RI versus the mean control RI value from each experiment is plotted against the change in logarithm of the RVR versus the mean logarithm of the control RVR values from each experiment. In each experiment, the RVR was adjusted by adding 3 x 10-7 mol/L phenylephrine hydrochloride (open symbols), 1 x 10-6 mol/L phenylephrine hydrochloride (black symbols) plus 10-4 mol/L sodium nitroprusside (gray symbols) to the perfusion solution. For clarity, control values are not shown but were analyzed by using linear regression together with the depicted values. The regression had an R2 value of 0.18 (n = 187). The slope of the regression line was 0.063 ± 0.010 (SEM), which is significantly greater than zero (P < .001). The figure depicts the regression line and the 95% confidence interval of the slope.

View larger version (19K): [in a new window]   Figure 3b. Graphs show correlation between RVR and RI. (a) Plot of the mean RI versus RVR from five experiments, each denoted by a different symbol (error bars omitted for clarity). RVR was adjusted by using phenylephrine hydrochloride and sodium nitroprusside, as described in b. The relationship of RI versus RVR in each experiment was analyzed by using linear regression with all RI values recorded under each condition (n = 7-13 for each point, n = 25-42 for each line). The regression lines appear curved because RVR is plotted on a logarithmic scale. The slope of each line was significantly greater than zero (P < .05). (b) By using the data from a, the change in RI versus the mean control RI value from each experiment is plotted against the change in logarithm of the RVR versus the mean logarithm of the control RVR values from each experiment. In each experiment, the RVR was adjusted by adding 3 x 10-7 mol/L phenylephrine hydrochloride (open symbols), 1 x 10-6 mol/L phenylephrine hydrochloride (black symbols) plus 10-4 mol/L sodium nitroprusside (gray symbols) to the perfusion solution. For clarity, control values are not shown but were analyzed by using linear regression together with the depicted values. The regression had an R2 value of 0.18 (n = 187). The slope of the regression line was 0.063 ± 0.010 (SEM), which is significantly greater than zero (P < .001). The figure depicts the regression line and the 95% confidence interval of the slope.

View larger version (18K): [in a new window]   Figure 4. Graph shows the results of five experiments (each denoted by a different symbol) in which the elevated bottles were adjusted in steps to generate various combinations of pulse pressures. The mean RI values (error bars omitted for clarity) were plotted against the pulse pressure index, which was calculated as described in Materials and Methods. The relationship of RI to pulse pressure index in each experiment was analyzed with linear regression by using all RI values (n = 7-11 for each point, n = 15-53 for each line). The slopes of these lines ranged from 0.77 to 1.15, and none differed significantly from a slope of 1.00 (P > .05). The mean of the five slopes (0.91 ± 0.07) was not significantly different from 1.00 (P > .05). When all data were analyzed together, R2 was 0.89, which indicates a significant correlation (P < .001). The slope of the regression line was 0.90 ± 0.06, which is not significantly different from 1.00 (P > .05).

View larger version (12K): [in a new window]   Figure 5a. Graphs show correlation between pulse rate and pulse profile and RI. (a) In two separate experiments ( vs ), the length of the pulse cycle was adjusted from 1 to 3 seconds. Linear regression analysis was used to generate best-fit lines for each experiment, the slopes of which were not significantly different from zero. (b) The cycle pattern of the solenoid valve was adjusted to apply the higher pressure to the perfusion system for 10%-50% of the overall cycle period (1.589 seconds in this experiment). Linear regression analysis was used to generate a best-fit line, the slope of which was not significantly different from zero.

View larger version (14K): [in a new window]   Figure 5b. Graphs show correlation between pulse rate and pulse profile and RI. (a) In two separate experiments ( vs ), the length of the pulse cycle was adjusted from 1 to 3 seconds. Linear regression analysis was used to generate best-fit lines for each experiment, the slopes of which were not significantly different from zero. (b) The cycle pattern of the solenoid valve was adjusted to apply the higher pressure to the perfusion system for 10%-50% of the overall cycle period (1.589 seconds in this experiment). Linear regression analysis was used to generate a best-fit line, the slope of which was not significantly different from zero.

View larger version (16K): [in a new window]   Figure 6. Graph represents measurement of vascular resistance. indicates the pressure versus flow rate for the kidney, with the solenoid outlet closed off. indicates the pressure versus flow rate for the cannula alone. Resistance is determined by the slope of the best-fit line obtained with regression analysis.