Specifically , the levosimendan and placebo group exhibited significantly different changes over time in GFR ( P = 0.037 ) , renal blood flow ( P = 0.037 ) , and renal artery diameter ( P = 0.033 ) , with ensuing improvements in serum levels of BUN ( P = 0.014 ) , creatinine ( P = 0.042 ) , and cystatin C ( P = 0.05 ) .