Comparison of two methods of determining renal perfusion with and without captopril pretreatment in groups of patients with left ventricular dysfunction

Methods of effective renal plasma flow measurement by 125I-orthoiodohippurate elimination and para-aminohippurate clearance were compared with and without captopril pretreatment in 10 chronic heart failure patients and in 20 patients after transmural myocardial infarction. In the chronic heart failure group measurements of effective renal plasma flow by the two techniques were strongly correlated (r = 0.92, P <0.00001), as was the captopril-mediated change in effective renal plasma flow by the two methods (r = 0.85, P = 0.002). However, in absolute terms para-aminohippurate clearance significantly exceeded 125I-orthoiodohippurate clearance by a mean (+/- SD) of 24.8 +/- 43.7 ml.min-1 (P <0.05) so that only using the former technique was a significant increment in renal perfusion observed in response to converting enzyme inhibition. In the post-myocardial infarction group, correlations between the two methods were variable and much poorer than in the chronic heart failure group (r = 0.54, P = 0.01 and r = 0.74, P = 0.002 on consecutive days). Furthermore, captopril-mediated increments in effective renal plasma flow by the two techniques were unrelated (r = -0.19, P = 0.59). In this group 125I-orthoiodohippurate elimination significantly exceeded para-aminohippurate clearance (P <0.05). This reversed association and the weaker relationships between methods in post-infarction as compared to chronic heart failure patients may be related to interference by thrombolytic or aspirin treatments.