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-orthoiodohippurateelimination and para-aminohippurate clearance were comparedwith and without captopril pretreatment in 10 chronic heartfailure patients and in 20 patients after transmural myocardialinfarction. In the chronic heart failure group measurements of effectiverenal plasma flow by the two techniques were strongly correlated(r=0·92, P<0·00001), as was the captopril-mediatedchange in effective renal plasma flow by the two methods (r=0·85,P=0·002). However, in absolute terms para-aminohippurateclearance significantly exceeded ¹²⁵I-orthoiodohippurate clearanceby a mean (± SD) of 24·8 ± 43·7ml. min^–1 (P<0·05) so that only using the formertechnique was a signifincant in renal perfusion observed inresponse to converting enzyme inhibition. In the post-myocardial infarction group, correlations betweenthe two methods were variable and much poorer than in the chronicheart failure group (r=0·54, P=0·01 and r=0·74,P=0·002 on consecutive days). Furthermore, captoprilmediatedincrements in effective renal plasma flow by the two techniqueswere unrelated (r= – 0·19, P=0·59). In thisgroup ¹²⁵I-orthoiodohippurate elimination significantly exceededpara-aminohippurate clearance (P<0·05). This reversedassociation and the weaker relationships between methods inpost-infarction as compared to chronic heart failure patientsmay be related to interference by thrombolytic or aspirin treatments.